UIM · ski
UIM2026, 501.01. A closed-list class. The craft must stay stock except where the rules allow otherwise, so anything unlisted is not permitted.
Places where the rulebook contradicts itself, or where a figure could not be settled. Nothing in this list is decided, and it sits here rather than in a footnote because it is what you would want before spending money.
22 permitted outright, 16 answered by our reading of the class rather than by a quoted rule, 0 the rules do not settle. Grouped by the answer, because an open class gives one answer to most questions and printing it once per part would say the same sentence forty times.
Not permitted, not listed in the rulesOur reading, not a rule we can quote at you. This class requires the craft to stay stock except where the rules allow otherwise, and this part is not on the list.
Not legal4 parts
Explicitly prohibited by this class.
Not legal1 part
ECU must be original. Aftermarket ECU prohibited. 501.01.05
Not legal1 part
No internal engine modifications of any kind; ports may not be cleaned with abrasive material. 501.01.03.01
Not legal1 part
Not a listed configuration; barred by the closed list.
Not legal1 part
ANY internal modification - grinding, surfacing, polishing, machining, shot blasting - of any transmission component, including the stator and exit cone, is prohibited. 501.01.06.02
Not legal1 part
Moot - no transmission modification at all.
Not legal1 part
Homologated production craft only - 50 specimens, marketed, conformity certificate.
OEM part required1 part
Crankshaft must remain stock; replacement bearings or bearing shells only, of original type and dimensions. 501.01.03.02
OEM part required1 part
Camshaft(s) must remain stock; replacement bearings of original type and dimensions only. 501.01.03.03
Not permitted, not listed in the rules7 parts
Not listed in this class. Illegal under the class's own stock clause.
Not permitted, not listed in the rules1 part
No exhaust article exists in 501.01.
Not permitted, not listed in the rules1 part
Only the flame-arrester-to-throttle-body ducting allowance.
Not permitted, not listed in the rules1 part
No fuel-system hardware article.
Not permitted, not listed in the rules1 part
No fuel-system hardware article; treat as stock under the closed list.
Not permitted, not listed in the rules1 part
Only the ducting allowance.
Not permitted, not listed in the rules1 part
Not addressed in 501.01.
Not permitted, not listed in the rules1 part
No trim article.
Not permitted, not listed in the rules1 part
No hood article.
Not permitted, not listed in the rules1 part
No ballast article.
Legal, within limits1 part
Equivalent aftermarket air filters available on the market. 501.01.04.01
Legal, within limits1 part
Excess oil or fuel leaving it must be caught and must not spill into the engine compartment. 501.01.04.03
Legal, within limits1 part
Must fit the OEM battery box and be securely fastened. GP2 additionally allows relocation of the battery, box or housing limited to the strict minimum needed to fit an aftermarket exhaust.
Legal, within limits1 part
The FRONT ENGINE SUPPORT may be reinforced or replaced. 501.01.02.13
Legal, within limits1 part
Modified or aftermarket impeller provided THE ORIGINAL DIAMETER IS MAINTAINED. 501.01.06.01
Legal, within limits1 part
Replacement wear rings within OEM internal diameter specification.
Legal, within limits1 part
Max 100 mm beyond the end of the OEM plate; extension no wider than OEM; sides connected to the radiused portion; no fins, rudders or skegs.
Legal, within limits1 part
Full-length type with at least one bar parallel to the drive shaft, all leading edges radiused, extending no more than 12.00 mm below the flat plane of the pump intake area. GP1 adds that the projecting member must be filed so as not to create a hazard.
Legal, within limits1 part
Max 2 per side. Max 126 cm each, 153 cm total with two sets. Max 100 mm lateral protrusion, 52 mm vertical channel, 50 mm below the hull side/bottom intersection, 50 mm below the lower bond flange. Minimum 6 mm thick if aftermarket.
Legal, within limits1 part
The handlebar must be padded at the mounting bracket, or the crossbar padded if fitted. Original switches required.
Legal, within limits1 part
Switch HOUSINGS may be modified or aftermarket and the switch position may be changed, but ORIGINAL SWITCHES are required.
Legal, within limits1 part
Replacement bumpers allowed. A soft flexible water-spray deflector may attach to the hull sides or bond flange, not exceeding the perimeter of the original bumpers or the external hull edge measured with a plumb line. SAFETY BUMPERS ARE COMPULSORY in both GP1 classes.
Legal, within limits1 part
Allowed. NO WATER EXIT may be added to the cylinder head, cylinder or casing. Bypass fittings must be directed downward and/or rearward. 501.01.03
Legal, within limits1 part
All cooling system valves must be of FIXED OR AUTOMATIC type - thermostats, pressure regulators, solenoids. Manually controlled devices that alter cooling water flow while under way are prohibited in every class, as are electronic water injection systems unless of origin.
Legal1 part
501.01.04.02
Legal1 part
ECU must be original; SOFTWARE may be reprogrammed. 501.01.05
Legal1 part
Aftermarket spark plugs of a different heat rating are allowed in every class that addresses them.
Legal1 part
Handle pole and mounting bracket may be modified or aftermarket provided they function as originally designed. The attaching point may be reinforced. The spring may be modified or aftermarket. 501.01.02.09/.10
Legal1 part
Plus quick-turn steering modifications. 501.01.02.09
Legal1 part
Padding and mat kits may be added and custom painting is allowed. Metal components above the bond flange may be polished, shot peened or painted.
Legal1 part
The original bilge pump may be modified, disconnected or removed and aftermarket bilge draining systems are allowed if no hazard is created. 501.01.02.12
Legal1 part
Cooling system flush kits are allowed in every class that addresses them.
UIM 2026, 501.01, read from the rulebook on 2026-09-08, not verified by a racer. Read the rule yourself, Ski Division GP4. Every UIM class · where the rulebooks differ.
This is one class. Every part below also has a page of its own showing where it stands across every class this body runs, and legality by part is the index of them.
50 parts read · 22 permitted outright · 2026 rulebook