Reference
You are bound by whichever body sanctions the event you enter, not by whichever answer suits the part. These are the places two rulebooks disagree enough to change what you would buy.
Each block below opens with how many of a body's classes publish component rules of their own. Every class short of that number borrows another class's rules, so an answer about one takes a step through its parent before it can be given at all.
UIM publishes a second rulebook, and it is not in this comparison. The same body sanctions motorised surfboard racing under a separate document with its own article numbering, and this site reads it on a site of its own, class by class, each one citing the article behind it. It is kept out of the tables above deliberately. The two books share a publisher and nothing else, so a number carried across from one would be cited at a scrutineering bay that has never heard of it. Read it as its own thing at motorised surfboard racing.
Each comparison below ends with what that pair agrees on. Nothing in those lists is a difference, which is why none of it has a row in the table above it. It is there because a table of disagreements cannot show a match, and a figure both bodies state is worth as much as one only a single body states.
20 differences that change an answer, out of two rulebooks read on 2026-09-07 and 2026-09-08.
The first comparison this site held, and the one a rider entering both series needs. IJSBA runs North America and its affiliate network on twenty-five class documents; UIM runs the European and Gulf championships on one. They disagree hardest at the gate, where IJSBA wants ten times the production units UIM does, and again on the rider, where UIM names a certificate for almost everything worn and IJSBA names almost none.
| IJSBA | UIM | |
|---|---|---|
| Rulebook read | 2025, 25 separate PDFs, rule years 2021-2025 | 2026, one 189-page PDF, published 22 December 2025 |
| Same season throughout | No, the class documents carry different rule years | Yes |
| Classes | 20, 20 with their own technical rules | 24, 8 with their own technical rules |
| Homologation threshold | 500 units | 50 units |
| Sound measured at | 22.86 m | 24 m |
IJSBA publishes 20 of its 20 classes with component rules of their own. UIM publishes 8 of 24.
IJSBA
500 units, or 100 through a limited-production route that carries a top-up obligation
Homologation rules, HOM
UIM
50 specimens
UIM 2026 homologation article
A small-builder hull can clear UIM homologation at 50 units and fail IJSBA's outright. This is the single largest divergence between the two and it decides whether a machine can enter at all, before any part on it is considered.
IJSBA
Parts may only be updated or backdated within the same listed model
HOM.5.8
UIM
No equivalent rule was found
No rule found on this point
The rule that a JS750SXi Pro may not run a 1995 JS750SXi cylinder is IJSBA's alone. It is also the rule that makes "fits" and "is legal" different questions, so do not carry it across to a UIM racer, and do not assume its absence means UIM has thought about the question.
IJSBA
86 dB(A) at 22.86 m, which is 75 feet
general rules
UIM
86 dB(A) at 24 m, and 90 dB(A) for both GP1 classes
UIM 500
The two 86 dB figures are not comparable, because they are measured at different distances. A craft measured under one standard has not been measured under the other, and a pipe sold as "86 dB legal" is answering only one of the two questions.
IJSBA
A picture with no dimensions
general rules
UIM
Background at least 30 cm by 30 cm, digits at least 22 cm, spacing at least 13 mm, black Arial Black on white for every category
UIM 206
If this site ever sells number plates or graphics, UIM's is the only specification in either rulebook that can actually be built to.
IJSBA
Four vintage classes, Kawasaki only, a real division
VSK, VSKL, VX2, VSC
UIM
No vintage division of any kind
No rule found on this point
Anything from the 550, 650, X2 or SC era is an IJSBA question only. There is no UIM answer to give, and a page that showed one would be inventing it.
IJSBA
Competition Membership is issued at Novice, Expert or Pro, with Beginner below and the combined Amateur and Pro-Am tiers beside them. The grade gates entry: Novices may not enter Open, Modified or GP classes where supercharged or turbocharged runabouts are allowed. IJSBA states in the same document that it does not test skill and cannot guarantee competency, so the grade is assigned rather than examined.
MEM.1.1, MEM.2.1, MEM.3.1, MEM.6.1, MEM.7.1
UIM
An International licence issued by the rider's National Authority, and Rule 107 defines no grades or tiers at all and maps no licence to any class. Class access is gated by age and by the separate Superlicence.
UIM 107, 203.01.01, 203.02
A rider's IJSBA grade does not travel. There is no UIM equivalent to be recognised, and no IJSBA equivalent of the Superlicence, so a rider moving between the two series qualifies from scratch in the other. The Veterans threshold differs too: 35 years or older at IJSBA (MEM.8.1) against over 40 at UIM (203.01.01), which is five seasons of a rider's life and decides which class they can enter.
IJSBA
Permitted from Runabout Limited upward
Runabout Limited class document
UIM
Stock in all six production classes, with replacement bearings of the original type and dimensions only. The GP1 classes are disputed inside this site's own data. This row said stock in every class including GP1 when it was written, and the part matrix records no engine article in either GP1 class and answers them from the open-list reading instead. Both readings are kept here and neither is settled.
UIM 501.01, 501.03.04, 502.01.03-03, 502.03.04-03
A camshaft that is legal in IJSBA Limited is illegal in every UIM production class. That half of the row is not in doubt and it is the clearest case on the site of a part being sold to the wrong series. The GP1 half is unresolved, and no GP1 camshaft answer should be taken from this table until somebody reads 501.04 and 502.04 for an engine article. The contradiction was found on 2026-09-11 while the UIM against IHRA rows were being written, by reading this row against the part matrix.
IJSBA
Permitted from Superstock upward
Superstock class documents
UIM
Not permitted below GP1 in either division
UIM 501 and 502 technical rules
Porting work bought by a UIM racer below GP1 buys them an illegal ski. The work cannot be undone, which makes this the most expensive difference in the table to get wrong.
IJSBA
Ski Lites allows petals and bans cages
SKL
UIM
Ski GP3 has no reed article at all, so the whole assembly reads as prohibited by silence. GP2 allows the whole assembly
UIM 501.02 and 501.03
Do not carry the petal and cage split across. UIM does not make that distinction anywhere, so a part list that separates them is describing IJSBA's rulebook and calling it the sport's.
IJSBA
Permitted in Runabout Limited and Superstock, with no added inputs or outputs
Runabout Limited and Superstock class documents
UIM
Permitted in no class below GP1. Runabout GP2 says no aftermarket units are allowed, in terms
UIM 502.03
UIM is the stricter of the two here. A rider entering both series is bound by the stricter answer in every race, not by whichever body is running the event they are thinking about.
IJSBA
Required in Ski GP and Sport GP
SKGP and SPGP
UIM
Not required anywhere
No rule found on this point
Do not carry the IJSBA requirement across, and do not read its absence as UIM permitting unlimited boost. UIM publishes no boost limit at all for Ski GP1, Runabout GP2 or Runabout GP1.
IJSBA
Allowed broadly
class documents
UIM
Not permitted in Runabout GP4. The permission starts at GP3
UIM 502.01
Runabout GP4 is the only class in either rulebook where a quick-turn steering kit is illegal while the rest of the steering system is open.
IJSBA
91.45 cm each on both divisions. Ski vertical channel 63.5 mm, drop 38.00 mm or 63.5 mm by class
class documents
UIM
Ski 126 cm each in GP4 and GP3, 153 cm in GP2 and GP1. Runabout 92 cm each side. Ski channel 52 mm, drop 50 mm. Runabout channel and drop both 63.5 mm
UIM 501 and 502
One sponson listing cannot carry a single UIM dimension, let alone a single number for both bodies. Division matters more than class here, and this is the clearest case where an engine part carries across and a handling part does not.
IJSBA
2.00 mm
homologation rules
UIM
5 mm
UIM 500
A hull repaired to UIM's tolerance can fail IJSBA scrutineering while being entirely legal where it was repaired.
IJSBA
Required, and modifying it with tape or wire is prohibited
GEN.8.9
UIM
No equipment requirement anywhere in the rulebook
No rule found on this point
A lanyard is mandatory under IJSBA and merely conventional under UIM. The UIM rulebook mentions a lanyard only inside a false-start restart procedure, and mentions a kill switch only as a modification allowance.
IJSBA
Prohibited
GEN.7.2
UIM
No prohibition was found. The named standard is EN ISO 12402-5:2020
UIM 506
An absence is not a permission. UIM naming a standard that inflatables can meet is not the same as UIM having considered and allowed them.
IJSBA
DOT and Snell
General rules, personal safety equipment
UIM
National Authority, or Snell, or FIA, or ECE 2206. DOT is not mentioned
UIM 506
An ECE-only helmet is legal under UIM and illegal under IJSBA. The UIM document prints "ECE 2206" with no decimal point, which is almost certainly ECE 22.06 and is reported here as printed.
IJSBA
Neither is stated
No rule found on this point
UIM
Replace every 5 years from the manufacture date, and at least two thirds of the shell must be bright orange, red or yellow
UIM 506
A UIM-legal helmet carries a visual requirement and a service life that no IJSBA helmet needs. Anyone stocking helmets for European racing is stocking a different product, not the same one with a different sticker.
IJSBA
Not mentioned
No rule found on this point
UIM
Required for Runabout riders
UIM 506
One of two UIM personal equipment requirements with no IJSBA counterpart, alongside the certified back protector.
IJSBA
Required for Ski except Freestyle, with no certification named
General rules, personal safety equipment
UIM
Required always, to CE EN 1621-2:2014 level 1 or 2, with level 2 recommended
UIM 506
UIM names the certificate and IJSBA does not, so a UIM answer can be checked against a label and an IJSBA one cannot.
26 differences that change an answer, out of two rulebooks read on 2026-09-07 and 2026-09-11.
Two North American rulebooks that read alike and land differently. Both run a closed list, both measure sound at 86 dB and 75 feet, and both keep a real vintage division. The differences are mostly about where a rule lives rather than what it says: IHRA answers the parts every class shares once, in a general technical chapter, and IJSBA leaves them to each class document.
| IJSBA | IHRA | |
|---|---|---|
| Rulebook read | 2025, 25 separate PDFs, rule years 2021-2025 | 2026, one 95-page PDF, version V.20260603, sections A to EE |
| Same season throughout | No, the class documents carry different rule years | Yes |
| Classes | 20, 20 with their own technical rules | 29, 29 with their own technical rules |
| Homologation threshold | 500 units | 300 units |
| Sound measured at | 22.86 m | 22.86 m |
IJSBA publishes 20 of its 20 classes with component rules of their own. IHRA publishes 29 of 29.
IJSBA
500 units, of which 500 must exist inside the United States, or 100 through a limited-production route that obliges the builder to add 50 more by 2 September if the first hundred are gone before 1 July.
HOM.5.2, HOM.5.2.a
IHRA
300 identical units of a model, available for sale through an established distribution network that makes them accessible to the global market. No limited-production route and no territorial count.
B.7
A builder at 300 units clears IHRA and fails IJSBA outright, and a builder using IJSBA's 100-unit route has nothing to appeal to at IHRA, which publishes no small-series provision at all. This decides whether a machine can enter before any part on it is considered.
IJSBA
Publishes the homologation process and evaluates models from IJSBA OEM Manufacturer Members, so the set of homologated machines is a named thing a reader can be pointed at.
HOM
IHRA
Uses the word homologated for crankcases and fuel tanks and refers to hulls approved by the Race Committee and IHRA, and publishes neither list anywhere in the document.
CC.2.1, CC.3.4, K.8.1, V.9.1
No claim that a named aftermarket hull or a named replica crankcase is IHRA-approved can be sourced to the IHRA rulebook. The rule exists and the list it points at does not, so the only honest answer is to ask the series. That is an absence in the source and not a gap in what has been read.
IJSBA
Parts may be updated or backdated only within the same listed model, or to an IJSBA-recognised replacement model. A JS750SXi Pro may not run a 1995 JS750SXi cylinder, because those are two different listed models.
HOM.5.8
IHRA
OEM parts may be updated or backdated within the same make and model, provided the change produces no performance advantage and the part bolts on without modifying it or anything else. The drag section then permits backdating between models of the same family by name, FZR to FZR and RXP to RXP.
J.7.1, DD.1, DD.11
The two rules read alike and land differently. IJSBA's test is the listed model and it can be settled from a document. IHRA's is the make and model plus a no-advantage test a technical inspector applies on the day, so a catalogue can state IJSBA's answer and cannot state IHRA's.
IJSBA
A craft may enter classes of equal or greater designated displacement and never lower. A 580cc Sea-Doo may run 800cc classes and a 701 SuperJet may not enter 650cc classes.
HOM.5.8
IHRA
No equivalent rule was found. Each class states its own ceiling and the rulebook never addresses entering a class above the craft's own size.
No rule found on this point
IJSBA's rule is what stops a big-bore machine dropping into a small class, and IHRA has nothing in print doing that job. Do not carry it across, and do not read its absence as IHRA permitting the move.
IJSBA
The closed list is stated inside each class document and binds the Stock, Limited, Superstock, Spec and Vintage-Limited type classes. The others are framed as permitting a higher degree of modification.
SSK.1.1, SKL.1.1, FSSK.1.1
IHRA
The closed list is stated twice in the front matter and binds the whole rulebook. Freestyle is the single inversion and says so in terms, and the drag section restates the closed list harder than the front matter does.
A.2.2, J.1, CC.1, DD
The default flips between the two. Under IJSBA you establish which kind of class you are in before you read silence. Under IHRA silence means prohibited everywhere except one section. The same part, with no rule either way, is a different answer in each rulebook.
IJSBA
The general rules document is race-conduct procedure only. Fuel specification, sound testing procedure, minimum weight, ballast, racing numbers, scrutineering procedure and every blanket technology prohibition were each checked for and are absent from it. The technical baseline lives in each class document.
GEN.1 to GEN.15
IHRA
Section J is a technical chapter binding every class, covering the intake grate, ride plate, sponsons, impeller, wear ring, steering, handlebars, handle pole, ballast, bilge pump, battery, fasteners, fuel and repairs.
Section J
This changes how each rulebook is read before any single rule is looked up. Under IHRA a class section that never mentions the intake grate is not banning it, because section J already allows it. Under IJSBA there is no such chapter to fall back on, so the class document is the whole answer and its silence is the end of the matter.
IJSBA
Twenty-five separate PDFs carrying rule years from 2021 to 2025, so two class documents can disagree because they were written four seasons apart.
the published rule book set
IHRA
One 95-page PDF carrying one version string, V.20260603, revised four times between February and June 2026 with every change listed in the document itself.
A.1
A cross-class comparison is safe inside IHRA and is not safe inside IJSBA. It also changes what a citation has to carry. An IJSBA claim names a class document and its rule year; an IHRA claim names the version string or it names nothing, because the rulebook changed four times in five months.
IJSBA
Defines Original Equipment, Replacement Part and Aftermarket Part as three separate categories. A Replacement Part provides only the dimensions, performance and function of the OEM part, and is therefore legal wherever an OEM part is required.
glossary
IHRA
Defines Aftermarket and stops. Replacement Part, Stock, OEM, Original Equipment, Homologation, Hull and Deck are all used in the operative rules and none of them appears in the glossary.
EE
The three-way distinction that decides whether a part is legal in an IJSBA closed-list class has no IHRA counterpart. Do not carry IJSBA's definition across to fill the gap, because the word doing the work would not be IHRA's word.
IJSBA
86 dB(A) at 22.86 m as the general figure, with two classes raised to 100 dB, Runabout Open GP outright and Sport GP unless 14 days notice is given.
ROP.1.3, SPGP.1.3
IHRA
86 dB(a) at 75 feet, printed inside fifteen of the nineteen non-drag class sections. Ski GP, Runabout Endurance and Freestyle print none, Ski Limited publishes no class criteria at all so its figure arrives by inheritance, no drag class prints one, and no class anywhere is raised above 86.
class sections K to CC
The number agrees and the shape does not. IJSBA has two classes louder than 86 and IHRA has three with no stated ceiling at all, which is not the same as a ceiling of none. A pipe sold as 86 dB legal answers both bodies where both state a figure, and answers nothing where IHRA states none.
IJSBA
No drag division of any kind.
No rule found on this point
IHRA
Section DD, ten drag classes, added to the rulebook on 2 February 2026.
DD
Drag racing is an IHRA question only, and a page that showed an IJSBA answer would be inventing it. Section DD is also written unlike the rest of the IHRA rulebook, as bullet lists with no class criteria and no sound limit, which is recorded on each of those ten class records.
IJSBA
Four vintage classes, Kawasaki only, published as a real division with its own documents.
VSK, VSKL, VX2, VSC
IHRA
Two. Ski Vintage at 600cc with the Kawasaki 550 as the primary craft, and X2 Vintage for the Kawasaki X2 built 1986 to 1995. A Vintage 650 or a Vintage 701 exists only if the organiser chooses to offer one.
S.1, T.1
Both bodies run vintage and they do not run the same one. IHRA puts part of its eligible craft list in the organiser's hands rather than in the rulebook, so whether a 650 has a class is an event question there and a document question at IJSBA.
IJSBA
The general rules document carries no blanket technology prohibition. Traction control, telemetry, data logging, GPS and nitrous were each checked for and each is absent from it.
GEN.1 to GEN.15
IHRA
Bans electronic transmission to or from a moving craft in Runabout Endurance only, permitting official transponders, broadcast video, offline logging and rider-to-pit radio, and bans nitrous by name in seven of the ten drag classes.
W.1.3, DD.1 to DD.7
Neither body has a general position on data. IHRA has two specific ones and both sit in classes a stand-up racer never enters. A logger is an open question in most of both rulebooks, and in IHRA's closed-list classes an open question tends towards prohibited rather than towards permitted.
IJSBA
Competition Membership at Novice, Expert or Pro, with Beginner below and the combined Amateur and Pro-Am tiers beside them, and a Novice may not enter Open, Modified or GP classes where supercharged or turbocharged runabouts are allowed. Veterans from 35. IJSBA states in the same document that it does not test skill.
MEM.1.1, MEM.6.1, MEM.8.1
IHRA
Beginner, Novice, Expert, Amateur, Pro, Pro-Am and Veteran, with Veterans from 35 as well. Novices may not run Open or GP classes with a supercharged or turbocharged runabout. A rider must be 16 for Ski GP or any forced-induction runabout, with a written exception possible at 14 if it is requested at least five days before the event. Junior Ski starts at 8 and Junior Runabout at 12.
C.2, C.2.1, C.2.2, C.2.8
The tier names and the Veterans threshold match, which neither does against UIM. The age gates do not. IJSBA publishes no age threshold in its general rules at all, and IHRA gates its fastest classes at 16 with a named exception route, so a fourteen-year-old's eligibility is a documented question at one body and an unanswered one at the other.
IJSBA
Ski Lites permits modified or aftermarket petals and requires the cage assembly to remain original equipment. The whole assembly becomes legal at Ski Grand Prix.
SKL
IHRA
Ski Lites permits modified or aftermarket petals and requires the cage assembly to remain OE, in the same split and almost the same words. Ski Limited then permits the full assembly.
O.3.3, P.2.3
Both bodies make a distinction UIM does not make anywhere, so a petals- and-cage product split describes these two rulebooks and not the sport. The difference is only where the full assembly becomes legal, and it is the same step as the pipe.
IJSBA
Permits a titanium driveshaft, impeller housing or stator vane assembly in Vintage Ski, and nothing else anywhere in titanium.
VSK.6.1
IHRA
Prohibits substituting bolts, nuts and washers with titanium unless originally equipped, across the whole rulebook. Permits the same three components in Ski Vintage. Prohibits a titanium driveshaft by name in Sport Spec.
J.7, S.5.1, S.5.2, U.5.2
The vintage allowance is the same in both, down to the three named parts, and neither body extends it to fasteners. IHRA then adds one class that refuses the driveshaft outright, so under IHRA a titanium driveshaft is legal in one class, illegal by name in another and unmentioned in twenty-seven.
IJSBA
Prohibited in the stock and lites classes, permitted within limits in Runabout Limited and Runabout Superstock, and open in Ski Grand Prix, Sport GP and Freestyle. Three classes publish no ECU article at all, Ski Superstock, Ski Modified and Runabout Open GP, so they cannot be answered.
class documents
IHRA
Stated in every class. Open in fourteen, including Ski Lites, Ski GP3, Ski Vintage and every drag class. Restricted to reprogramming the OEM unit in nine, including Ski GP2, Four Stroke Ski Lites, both Ski Modified classes and Runabout Endurance.
K.6.1, L.4.1, O.4.1, AA.4.1
IHRA answers this question for every class and IJSBA leaves three unanswered, which is the reverse of the usual pattern between them. The practical split is the same shape though: an aftermarket box is a GP-and-above part under IJSBA and a reprogram-only part in most of IHRA's production classes.
IJSBA
Sport GP releases at 12.0 psi with a 1 psi tolerance and a 13.0 psi absolute test ceiling, and an IJSBA-approved boost pressure relief valve is required. Ski GP returned three mutually incompatible figures and no number from it is publishable.
SPGP.9.1, SKGP.9.3
IHRA
Sport GP requires a boost regulator and releases at 12 psi below 900cc and at 9 psi from 901cc to 1100cc, with forced induction capped at 1100cc and anything larger required to stay naturally aspirated. Ski GP permits forced induction under the same 1100cc cap and states no boost figure at all.
V.6.1, K.5.1
The Sport GP headline agrees at 12 psi and the rule underneath does not. IHRA splits by displacement and IJSBA does not, so a 1000cc craft released at 12 psi is inside one rulebook and over the limit in the other. Neither body publishes a usable Ski GP boost number.
IJSBA
91.45 cm per sponson and 100.0 mm lateral protrusion. The class documents give a 63.5 mm vertical channel and a 38.00 mm drop below the lower bond flange. The sponson appendix gives 50.8 mm as the Ski vertical channel, which the class documents contradict.
class documents and Appendix, Sponsons
IHRA
36 in, which is 91.45 cm, per sponson and 3.94 in, which is 100 mm, horizontal protrusion. Vertical channel 2 in, which is 51 mm, for Ski and 2.5 in, 63.5 mm, for Sport and Runabout. No more than 2.5 in below the point where the hull intersects its bottom surface, and at least 6 mm thick.
J.16
The lengths and the lateral figure agree to the millimetre. The Ski vertical channel does not. IHRA prints 51 mm, which sits with IJSBA's appendix figure of 50.8 mm and against IJSBA's own class documents at 63.5 mm. That is worth knowing and it settles nothing: the IJSBA disagreement is between two IJSBA documents and stays open on them.
IJSBA
The count varies class by class. Ski Stock allows up to four and Ski Lites allows two.
SSK.2.3, SKL.2.3
IHRA
Two as the rulebook-wide rule, with four-sponson configurations permitted in Ski and Sport classes only and the four capped at 90 in of total length.
J.16
IHRA states the exception once for two whole divisions and IJSBA states the count class by class. A four-sponson setup is a per-class question under one rulebook and a per-division one under the other, and in neither body is it legal on a runabout.
IJSBA
DOT and Snell motorised-vehicle standards, with no Snell revision year stated. Full coverage with chin and mouth protection. Bolt-on chin guards prohibited, and a face shield is allowed if it pivots with no locking mechanism.
GEN.7.3
IHRA
Snell M2015, M2020 or M2025, or DOT FMVSS 218, or ECE 22.05 or 22.06 in P, NP or J, or JIS T 8133:2007 Full. Full face required. Plastic and BMX-style helmets prohibited.
I.7
IHRA names the Snell generation and IJSBA does not, and IHRA accepts European and Japanese certificates IJSBA never mentions. A helmet carrying only ECE is legal at an IHRA event and has no IJSBA standard to point at, so a European rider's existing helmet is the thing to check first.
IJSBA
Not required for freestyle competitors during freestyle competition.
GEN.7.3
IHRA
Mandatory for all participants in both practice and competition, with no freestyle exemption anywhere. IHRA's freestyle carve-outs are the lanyard and eye protection instead.
I.7, I.10, J.6
A freestyle rider riding bare-headed under IJSBA rules is non-compliant at an IHRA event. Each body exempts freestyle from something and they do not exempt it from the same thing, so neither list can be read as the sport's position on freestyle safety.
IJSBA
Neither a colour requirement nor a service life is stated.
No rule found on this point
IHRA
A colour or reflectivity giving high visibility, with fluorescent highly recommended, and the event organiser stocks fluorescent tape to bring a helmet up to the requirement on the day. No service life is stated.
I.7
Neither body sets a helmet service life, which is one thing they are both silent on. Visibility is not: an IHRA technical director can send a dark helmet away to be taped and an IJSBA one has no rule to apply.
IJSBA
Eye protection and protective footwear are both recommended and neither is required.
GEN.7
IHRA
Eye protection is mandatory for every competitor except in Freestyle, and may be removed mid-race to improve visibility. Footwear is mandatory, with water shoes, wrestling shoes, surf shoes and tennis shoes named as acceptable.
I.10, I.13
Two items a rider can legally race without under IJSBA will stop them at an IHRA pre-race inspection. Both are cheap and neither is the sort of thing a rider thinks to check, which is what makes the difference worth printing.
IJSBA
Required for all Ski competitors except Freestyle. Rigid or soft, must not absorb water, and the coverage is specified geometrically, no more than 2 in below a line between the tops of the shoulders and no less than 3 in below a line between the hips. No thickness limit.
GEN.7.4
IHRA
Required in Ski and Endurance classes. Rigid or soft, shaped to the rider's body, must not absorb water, and no more than 45 mm thick at its thickest point. No coverage geometry.
I.14
Each body constrains a different dimension of the same product and neither names a certificate, so a label settles neither question. A protector sized to IJSBA's coverage rule can sit over IHRA's thickness cap, and IHRA's requirement also reaches Endurance riders where IJSBA's covers Ski alone.
IJSBA
Type I or Type III meeting local buoyancy requirements, worn at all times on the water. Inflatable devices are prohibited.
GEN.7.2
IHRA
A USCG-approved type I or III at all times on the water, and Jettribe competition race vests that are SGS buoyancy certified are approved by name. No prohibition on inflatables was found.
I.8
The type requirement matches. IHRA names a manufacturer, which no other rulebook on this site does anywhere, and states no inflatable ban. An absence is not a permission, so an inflatable is an IJSBA no and an IHRA unknown.
IJSBA
Ski Lites requires the stock exhaust, allowing only an insert in the stinger. For a two-stroke ski the next class that permits a pipe at all is Ski Grand Prix, because Ski Superstock and Ski Modified are four-stroke classes.
SKL.3.6, SKGP.3.7
IHRA
Ski Lites requires the stock exhaust, allowing only an insert in the stinger. Ski Limited then takes the same machine and permits an aftermarket manifold, head pipe and expansion chamber, provided the exit is not relocated and the original opening size is kept.
O.2.5, P.2.1
The two agree exactly in Ski Lites and diverge on where a rider goes next. Under IHRA the step is Ski Limited, a class built for stock-ish machines with a short list of additions. Under IJSBA the step is Grand Prix. The same SuperJet and the same pipe put a rider in two very different fields.
30 differences that change an answer, out of two rulebooks read on 2026-09-08 and 2026-09-11.
The two rulebooks with the least in common, and the last pair on this site to be read side by side. Nothing in either document is written with the other in mind. UIM gates its top classes with a national licence, a superlicence and a million euros of insurance; IHRA gates the same tier with a skill grade an official assigns and does not examine. Underneath that, UIM states its stock-conformity clause separately inside each production class and IHRA states one in its front matter for the whole book.
| UIM | IHRA | |
|---|---|---|
| Rulebook read | 2026, one 189-page PDF, published 22 December 2025 | 2026, one 95-page PDF, version V.20260603, sections A to EE |
| Same season throughout | Yes | Yes |
| Classes | 24, 8 with their own technical rules | 29, 29 with their own technical rules |
| Homologation threshold | 50 units | 300 units |
| Sound measured at | 24 m | 22.86 m |
UIM publishes 8 of its 24 classes with component rules of their own. IHRA publishes 29 of 29.
UIM
50 specimens manufactured, the craft marketed and available on the market, and a certificate of homologation confirming conformity with the manufacturer's chart, issued either by the official navigation services of the manufacturer's country or by an independent private expert. GP1 takes prototypes instead, under a UIM logbook valid four years.
500.02.01, 500.02.02
IHRA
300 identical units of a model, available for sale through an established distribution network that makes them accessible to the global market. No certificate, no logbook and no prototype route anywhere in the document.
B.7
UIM is the lower bar by unit count and the higher one by paperwork. Fifty units with a certificate is UIM-legal and six times short of IHRA's number, and 300 units with no certificate is the reverse. The sharper difference is the prototype: a one-off machine has a documented route into UIM GP1 and no route into IHRA at all.
UIM
There is no rulebook-wide principle. The stock-conformity clause is stated separately inside each production class, GP4, GP3 and GP2 in both divisions, and is absent from both GP1 classes.
501.01.01, 501.02.01, 501.03, 502.01-02, 502.02-02, 502.03-02
IHRA
Stated twice in the front matter and binding the whole rulebook, with the drag section restating it harder still. Freestyle is the single inversion.
A.2.2, J.1, CC.1, DD
Both bodies invert the default somewhere and they put the rule in opposite places. Under UIM you establish which class you are in before you can read silence at all. Under IHRA silence means prohibited everywhere except one section, which is the answer before you open the class.
UIM
Ski GP1 and Runabout GP1 carry no stock clause and no closed list, and are framed as promoting competition with a higher degree of modification. The rulebook never says that unlisted areas are free. That is the natural reading of the missing clause and it is an inference.
501.04, 502.04
IHRA
Freestyle says it outright, that any modification not explicitly restricted in the list is permitted. Three drag classes describe themselves as run what you brung while sitting under a section preamble saying anything unlisted is illegal.
CC.1, DD
UIM's open reading is an inference nobody can quote. IHRA's is a printed sentence in one class and a flat self-contradiction in three others. The two should never be rendered as the same kind of claim, because one is a rule and the other two are a reading and a defect.
UIM
Sixteen of the twenty-four classes publish no component rules and borrow a technical class. GP2 inherits GP3 by an explicit clause and the chain stops there, because GP3 does not inherit GP4.
501.03.02, 502.03-02
IHRA
All twenty-nine classes publish their own rules. Ski Limited is the only one that points elsewhere, sending four-stroke entries to Four Stroke Ski Lites and two-stroke entries to Ski Lites plus a list of its own.
P.1, P.2
A UIM answer usually takes two steps and an IHRA answer takes one. The one exception runs the other way. A question about IHRA Ski Limited resolves to two different parent sections depending on the engine, which is a shape neither body uses anywhere else.
UIM
No vintage division and no drag division of any kind.
No rule found on this point
IHRA
Two vintage classes, Ski Vintage for the Kawasaki 550 and X2 Vintage for the Kawasaki X2 built 1986 to 1995, and a drag section holding ten classes added on 2 February 2026.
S.1, T.1, DD
Anything from the 550 or X2 era, and anything about drag racing, is an IHRA question with no UIM answer to give. A page that showed one would be inventing it.
UIM
86 dB(A) at 24 m for the six production classes, and 90 dB(A) at 24 m for Ski GP1 and Runabout GP1.
501.03.04, 501.04.03, 502.03-04, 502.04-03
IHRA
86 dB(a) at 75 feet, which one section converts to 22.86 m. Printed inside fifteen of the nineteen non-drag class sections. Ski GP, Runabout Endurance and Freestyle print none, no drag class prints one, and nothing is raised above 86.
X.1, class sections K to CC
The two 86 figures are not comparable, because the meter stands more than a metre further back under UIM. UIM then raises its fastest classes to 90 where IHRA raises nothing and instead leaves three classes with no stated ceiling at all, which is not the same as having none.
UIM
Background at least 30 cm by 30 cm, digits at least 22 cm, spacing at least 13 mm, black Arial Black on white for every category. Number one is reserved for the reigning World Champion. Placement on the craft is not stated.
206
IHRA
Digits at least 7 in tall, standard block only, on both sides in a contrasting colour, and not in the footwell and not horizontal.
D.7
UIM specifies the graphic and not the placement, and IHRA specifies the placement and not the graphic. Between them they describe a number plate somebody could actually build and neither does alone. UIM's digits are also the taller, 22 cm against roughly 18.
UIM
General minimum 15, GP1 minimum 17, with an exception for a 16-year-old who has finished on a GP2 podium at a World or Continental Championship. Juniors 7 to 15, though the categories table gives Ski Future Electric as 5 to 7 and the rulebook is inconsistent on that. Veterans over 40. Age is taken as at 31 December of the year concerned.
203.01.01, 315.01
IHRA
Junior Ski from 8 and Junior Runabout from 12 to 15. A rider must be 16 for Ski GP or any supercharged or turbocharged runabout, with a written exception possible at 14 if it is requested at least five days before the event. Veterans from 35. Age is taken at the time of each event.
C.2.2, C.2.8
Every threshold differs and so does the clock. UIM reckons age at the end of the year and IHRA on the day, so one rider can be eligible under one body and not the other on the same weekend. The Veterans gap is five seasons of a rider's life.
UIM
An International licence from the rider's National Authority plus a signed risk disclaimer, with no grades, no tiers and no mapping from licence to class. A Superlicence gates the championships: four completed races, a sports CV, civil responsibility insurance of at least 1,000,000 EUR, and 150 EUR a year at World level.
107, 203.02
IHRA
An annual competition membership valid for the calendar year, and skill classes from Beginner to Pro which the rulebook says are assigned rather than examined. Ski GP and Runabout GP are restricted to Expert and Pro. No insurance requirement and no fee is published.
B.6.1.1, C.2
UIM gates its top classes with money and paperwork and IHRA gates them with an assigned grade. Neither credential is recognised by the other, so a rider crossing over qualifies from scratch. The million-euro insurance line is the largest single entry cost difference recorded on this site.
UIM
Authorised only by a UIM Technical Commissioner. The rider starts the next session from the last position on the grid, keeps the racing number, and may not change once the craft is on the starting grid. Changing a crankshaft, crankcase or cylinder block counts as an engine change. In Endurance the replacement must be the same category and the same make.
504.01, 318.12
IHRA
Barred outright in drag racing, in the rulebook's own words, you race what you register with, no exceptions. Outside drag the rulebook publishes no change-of-craft rule, though J.3.3 contemplates a backup boat by making both it and the final craft liable to inspection.
DD, J.3.3
UIM has a procedure with a named penalty and IHRA has a flat ban in one discipline and silence in the rest. A rider with a spare ski has a documented route under UIM and, in an IHRA closed-list class, an open question that tends towards prohibited.
UIM
Radio is expressly allowed, with radiomen registered at the time of registration. Telemetry, data logging and cameras are not mentioned anywhere in the document. GPS appears once, as a permitted timing method for record attempts.
505
IHRA
Electronic transmission to or from a moving craft is banned in Runabout Endurance only, with official transponders, broadcast video, offline logging and rider-to-pit radio carved out. Nothing anywhere else.
W.1.3
UIM permits radio by name and IHRA bans it in one class and never mentions it in the other twenty-eight. On a closed list that silence tends towards prohibited, so a pit radio is expressly fine at UIM and an open question at IHRA outside Endurance.
UIM
Three statements that are not reconciled anywhere. Rule 500 says the best five classified plus one randomly chosen craft, 306.01 says the first five must present at the closed pit, and 506.1 says the number is at the discretion of the O.O.D. and the Technical Inspector. Refuelling, mechanical intervention and hull work are prohibited in the closed pit.
500, 306.01, 506.1
IHRA
Typically the first three finishers in each class, with the final number set by the Race Director or Technical Director and announced at the riders' meeting. The rider or their mechanic performs the teardown, with their own tools, and refusing is disqualification from the event.
J.3.3
UIM impounds more craft and forbids anyone touching them. IHRA selects fewer and requires the rider to strip the engine on the spot. A rider who has only raced under UIM has probably never been asked to bring tools to the podium.
UIM
Regular unleaded pump gasoline in the production classes, printed as RON 95-98-100 and 95E10, and it must be available at petrol stations in the organiser's country. All other fuels prohibited there. GP1 is not bound by the pump-fuel restriction. Non-gasoline fuel is capped at 0.83 kg per cubic decimetre, tested against a sample from a nearby petrol station with a Digatron tester.
503.01, 503.02, 503.03
IHRA
Petroleum-based products meeting applicable national or regional standards, with ethers and alcohols the only permitted oxygenates and epoxides and nitrogen-bearing compounds prohibited. No octane figure, no density limit and no test method. Ski GP3 overrides all of it with a list capping alcohol at 15 per cent and banning E85 by name.
J.4.1, M.7
UIM ties its production classes to what a pump in the host country actually sells and publishes a method for checking. IHRA describes a chemistry and publishes neither a number nor a method. A fuel that passes IHRA's chemistry can fail UIM's availability rule without being different fuel.
UIM
0.8 mm maximum in GP3 and 1.52 mm in GP2, and the relaxation holds in both divisions.
501.02.03.06, 501.03.03.13, 502.02.03-06
IHRA
0.8 mm maximum in Ski GP2, in the two-stroke half of Ski GP3, in Four Stroke Ski Lites, in Ski Lites and in Runabout Lites. No class states a figure above it.
L.2.6, M.2.1, N.2.6, O.2.6, AA.2.5
The 0.8 mm figure is the same in both and reaches different classes. UIM then nearly doubles it at GP2 and IHRA never relaxes it anywhere, so the deck-height route UIM opens in its second tier has no IHRA equivalent.
UIM
Stock in all six production classes, with replacement bearings of the original type and dimensions only. Ski GP1 and Runabout GP1 publish no engine article, so the answer there rests on the open-list reading rather than on a stated rule.
501.01, 501.03.04, 502.01.03-03, 502.03.04-03
IHRA
Aftermarket in Ski GP, Runabout GP, Sport GP and several drag classes. Stock with timing adjustment permitted in the production classes.
K.2.3, X.2.8, V.4.7, AA.2.3
A camshaft has no UIM class that permits it outright and several IHRA ones. Both bodies keep it stock through the production tiers, and only IHRA puts a quotable permission at the top rather than an absence.
UIM
Prohibited below GP1 in both divisions, and stated as no internal modifications of any kind by grinding, surfacing, polishing, machining or shot peening. GP1 publishes no engine article.
501.02.03, 501.03.03.05, 502.02.03-02, 502.03.03-05
IHRA
Permitted in Sport GP, where two-stroke port height and width may be changed, and in two drag classes where cylinder head porting is allowed by name. Prohibited or unmentioned through the production classes.
V.2.7, DD.4, DD.5
Both bodies keep porting out of their production classes and admit it at the top. The difference is the drag section, which has no UIM counterpart and permits head porting in two classes that are otherwise close to stock. Porting cannot be undone, which makes this the most expensive row here to get wrong.
UIM
Permitted in no class below GP1. Runabout GP2 states in terms that no aftermarket units are allowed, and Ski GP4 requires the ECU to be original. Both GP1 classes publish no ignition article at all.
501.01.05, 502.03.08-02
IHRA
Permitted outright in fourteen classes, including Ski Lites, Ski GP3, Ski Vintage and every drag class. Restricted to reprogramming the OEM unit in nine others, among them Ski GP2, Four Stroke Ski Lites and Runabout Endurance.
O.4.1, K.6.1, L.4.1, AA.4.1
UIM is far the stricter. The same box sold to the same SuperJet owner is legal in IHRA's entry two-stroke ski class and illegal in every UIM production class, which makes this the sharpest single-part divergence between these two rulebooks.
UIM
Exactly one numeric boost figure exists in the whole rulebook, 10 to 14 psi for the HSR-Benelli S4 in Ski GP2. There is none for Ski GP1, Runabout GP2 or Runabout GP1, and the Overboost Control appendix that Runabout GP2 refers to is not in the document. The turbo housing and the exhaust manifold must both be of the full circulating water type.
501.03.04-09, 501.04.07, 502.04-07
IHRA
Sport GP requires a boost regulator releasing at 12 psi below 900cc and 9 psi from 901cc to 1100cc, with forced induction capped at 1100cc and anything larger required to stay naturally aspirated. Ski GP permits it under the same cap and states no figure. Only the turbo housing must be water-jacketed.
V.6.1, K.5.1
Neither body publishes a usable boost ceiling for its fastest classes, and UIM's single figure is tied to one named craft. The one requirement that clearly differs is the exhaust manifold: UIM wants it water-jacketed and IHRA does not ask.
UIM
5 mm. A repair may not alter the original configuration by more than that.
501.01.02.02, 502.01.02-02
IHRA
2 mm, which the rulebook also prints as 0.08 in. Ski division craft may reinforce hulls against course obstacles within the same limit.
J.13
UIM's tolerance is two and a half times IHRA's. A hull repaired to the limit where it was repaired can fail scrutineering at the other body, and the same sentence holds against IJSBA, which also says 2 mm.
UIM
Up to two per side. 126 cm each in Ski GP4 and GP3, and 153 cm in GP2 and GP1. Lateral protrusion 100 mm, vertical channel 52 mm, drop below the hull intersection 50 mm, minimum aftermarket thickness 6 mm.
501.01.02.04, 501.04.02.02
IHRA
36 in, which is 91.45 cm, each, and up to two except in four-sponson configurations, which Ski and Sport classes may run to a 90 in total. Horizontal protrusion 3.94 in, 100 mm. Vertical channel 2 in, 51 mm. Drop below the hull intersection 2.5 in, 63.5 mm. Minimum thickness 6 mm.
J.16
The lateral figure and the thickness agree exactly and the length does not. A UIM ski sponson may be 126 cm where IHRA caps it at 91.45 cm, so a UIM-legal sponson can be over a third longer than anything IHRA allows. The channels nearly agree at 52 mm and 51 mm and the drop does not.
UIM
Two rear sponsons are required. 92 cm each side, lateral protrusion 100 mm, vertical channel 63.5 mm, drop below the hull intersection 63.5 mm, identical across all four runabout classes.
502.01.02-05, 502.04.02-02
IHRA
The same envelope as every other division, 36 in or 91.45 cm each, channel and drop both 2.5 in or 63.5 mm, with four-sponson configurations not available to a runabout.
J.16
This is the closest the two come to agreeing on a handling part, 92 cm against 91.45 cm and both at 63.5 mm. The difference is not a dimension. UIM requires two rear sponsons and IHRA merely permits up to two, so a runabout running none is UIM-illegal and IHRA-legal.
UIM
A ballast article exists only for the GP1 classes. GP4, GP3 and GP2 in both divisions have no ballast rule, so under their own stock clause ballast is not permitted there, and those are the classes carrying the highest minimum weights. Water and any other fluid are prohibited.
501.04.05, 502.04.02-07
IHRA
Permitted in every class by the general technical regulations. Constant mass, and no other part may be modified to carry it.
J.19
Ballast is a general allowance at IHRA and a GP1-only one at UIM. A rider carrying a ballasted production-class setup from IHRA to UIM is carrying weight that no rule permits, in exactly the classes where minimum weight decides the most.
UIM
Current National Authority standards, or current Snell, or current FIA, or ECE 2206 as the document prints it. Mountain bike helmets prohibited. Full face is not required. At least two thirds of the shell bright orange, red or yellow. Replaced every five years from manufacture, after an accident, or on failing scrutineering. Freestyle competitors are exempt.
506.01
IHRA
Snell M2015, M2020 or M2025, or DOT FMVSS 218, or ECE 22.05 or 22.06 in P, NP or J, or JIS T 8133:2007 Full. Full face required, with plastic and BMX-style helmets prohibited. A colour or reflectivity giving high visibility, no service life stated, and no freestyle exemption.
I.7
Four separate differences in one item. IHRA requires full face and UIM does not. IHRA accepts DOT and UIM never mentions it. UIM retires a helmet at five years and IHRA never does. UIM lets a freestyle rider go bare-headed and IHRA does not.
UIM
A long wetsuit is required during all competitions, free practice, qualification, training and racing, with Freestyle exempt. Jeans, sweaters and shorts are prohibited as riding wear. No thickness is specified.
506.06
IHRA
Full-body waterproof clothing is required in Endurance and strongly recommended in closed course. Nothing is prohibited as riding wear.
I.9
A closed-course rider in shorts is UIM-illegal and IHRA-compliant. This is the widest gap in the personal equipment rules between the two, and the UIM rule covers every session rather than only the race.
UIM
Mandatory for every rider during tests, training and races, to a minimum of CE EN 1621-2:2014 level 1 or 2, with level 2 recommended. No thickness limit.
506.03
IHRA
Required in Ski and Endurance classes only. Rigid or soft, shaped to the rider's body, non-water-absorbing, and no more than 45 mm thick at its thickest point. No certification named.
I.14
UIM names a certificate and applies it to everybody. IHRA names a thickness and applies it to two class groups. A runabout rider needs a back protector at every UIM session and at no IHRA one outside Endurance, and a protector bought for UIM may sit over IHRA's thickness cap.
UIM
Required for runabout riders, with no standard named.
506.03
IHRA
Strongly recommended in Sport and Runabout classes, and not required.
I.15
The same item for the same riders, mandatory under one body and advisory under the other. A runabout rider crossing from IHRA to UIM has to buy something nobody has ever asked them for.
UIM
Gloves required, with no standard named, and closed footwear required for all participants, again with no standard named. A rider who loses a glove during a session may carry on racing.
506.03, 506.05
IHRA
Gloves strongly recommended and not required. Footwear mandatory, with water shoes, wrestling shoes, surf shoes and tennis shoes named as acceptable.
I.12, I.13
The two invert on gloves and agree on footwear while describing it differently. UIM says closed and names nothing. IHRA names four kinds of shoe and never says closed, so a pair of open surf shoes is explicitly acceptable at one body and explicitly not at the other.
UIM
Goggles should follow EN 1938:2010, stated as should rather than must, and a rider who loses goggles during a session may carry on racing.
506.03
IHRA
Shatterproof goggles or a face shield are mandatory for every competitor except in Freestyle, and may be removed mid-race to improve visibility.
I.10
IHRA makes eye protection compulsory and UIM recommends a standard for it. Both then let a rider carry on without it, UIM if it is lost and IHRA if visibility demands it, so the answer on the water is closer than the rules look on paper.
UIM
Freestyle competitors are exempt from the helmet requirement and from the wetsuit requirement.
506.01, 506.06
IHRA
Freestyle competitors are exempt from the lanyard kill switch and from eye protection. They are not exempt from the helmet.
J.6, I.10, I.7
Both bodies carve freestyle out of their equipment rules and neither carves out the same thing. Between them they exempt freestyle from four items and agree on none, which is why no page on this site presents a combined freestyle equipment list.
UIM
Ski GP3 and Runabout GP3 require the exhaust system to remain entirely of origin as delivered by the manufacturer. GP2 in both divisions then permits an aftermarket manifold, head pipe, expansion chamber and the chamber-to-waterbox hose, with the OEM waterbox mandatory.
501.02, 502.02.03-03, 502.03
IHRA
Ski Lites requires the stock exhaust with only a stinger insert, and Runabout GP3 says the same for two-stroke craft. Ski Limited and Runabout Limited then permit the aftermarket manifold, head pipe and expansion chamber, with the exit not relocated, the opening size unchanged and the OEM water box required.
O.2.5, Z.3.3, P.2.1, BB.3.4
This is the closest structural match between the two rulebooks. Both keep the pipe out of the entry two-stroke class, both open it at the second tier, and both hold the OEM waterbox while doing it. Only the class names differ, so a pipe listing can describe the shape of the rule once and must still name four different classes.
Where these two match at all, it is below the waterline. The pump, the grate and the crankshaft carry across almost unchanged. Everything the rider wears and everything that plugs into the engine does not, and those are the two areas a rider crossing between the series will be stopped on. No row says that on its own, because it is the shape of the whole set.
UIM for race numbers and graphics, which it specifies to a buildable dimension where IJSBA publishes a picture; for personal equipment, where it names a certificate for the helmet, life jacket, back protector and goggles; and for fuel testing, where it gives a method and a density limit.
IJSBA for anything vintage, because UIM has no vintage division at all; for part interchange between models, which UIM does not address; and for the difference between a replacement part and an aftermarket one, which UIM defines in a way that would read as excluding performance parts from the category entirely.
IHRA for drag racing, which is the only place any of these three publishes a drag rule at all; for the parts every class shares, which its section J answers once for the whole rulebook where IJSBA leaves them to each class document; and for reading two of its own classes against each other, because it publishes one document carrying one version string.
None of the three publishes a list of homologated models, or a procedure for homologating an aftermarket part. Each was checked for both.
Read from the rulebooks and not verified by a racer. Each is linked from its own page: IJSBA classes · UIM classes · IHRA classes · signed checks on parts the shop sells. Confirm anything that decides a purchase against the rulebook itself before a sanctioned event.
76 differences across 3 comparisons