IJSBA · Hull and handling

Aftermarket seat assembly / seat base, IJSBA

Runabout and Sport only in practice.

This page is IJSBA only, and the bodies do not agree. The same part under IHRA and UIM. Which one applies to you is decided by whoever sanctions the race you enter.

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This is one body's answer, not the sport's. You are bound by whichever body sanctions the event you enter. If you race more than one series, build to the stricter answer. The differences are set out in the rulebook comparison.

The Seat Appendix adds hard limits wherever aftermarket seats are legal: front may not protrude more than 1 in over the top deck vs OEM, knee/leg cradles must be entirely soft flexible material cradling no more than 50%, no hard material over the leg or knee, no velcro or adhesive binding the rider, and a rear height cap of riding-height x 0.30.

Where it stands, class by class

11 classes, grouped where the same rule gives the same answer rather than listed one by one, because an answer that holds for a class usually holds for every class that borrows its rules.

What each answer below means

OEM part required

This comes off. Only the part the manufacturer fitted is allowed here.

Legal, with conditions

Keep it, but measure it: the rules permit this part only inside stated limits.

Legal

Keep it. The rules permit this part in this class.

OEM part required 1 class

OEM SEAT BASE MUST BE USED. Cover change allowed; height +/-12.7mm (0.5 in); cover adds no more than 0.5 in thickness.

• Runabout Rec Lites · RRL

OEM part required 1 class

OEM seat base required. · RAS.2.10

• Runabout Stock

OEM part required 1 class

OEM stock seat base required. Height may be changed and/or covered.

• Sport Spec · section headings, no numbered rules

Legal, with conditions 1 class

Two-stroke: OEM base required. Four-stroke: aftermarket seat assembly per the Appendix.

• Runabout Naturally Aspirated · RNA

Legal, with conditions 1 class

Seat covers and assemblies modified or aftermarket, with seat height no more than 3 in above original.

• Vintage SC · VSC

Legal, with conditions 1 class

Seat covers and assemblies modified or aftermarket, with seat height no more than 10 in above original.

• Vintage X2 · VX2

Legal 3 classes

Aftermarket seat assembly, height may be modified.

• Runabout Superstock · RSS.2.10
• Sport GP · SPGP.3.10
• Runabout Open / GP · ROP.3.10

Legal 1 class

Aftermarket seat per the Appendix provisions. The Stock OEM-base requirement is lifted. · RAL.2.10

• Runabout Limited

Legal 1 class

Sport and Runabout seat assembly modified or aftermarket. Presence of a seat classifies the craft as Sport or Runabout by dimension.

• Freestyle · FREST

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What we corrected here, and when

• Vintage Ski. Corrected 2026-10-10: this row refused an aftermarket seat because the Vintage Ski rules name none. The class runs a stand-up Kawasaki 550 with no seat to replace, which is how Vintage Ski Limited records the same hull.

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Aftermarket seat assembly / seat base: if the rule your class applies reads differently to you, or the rulebook has changed since this was read, ask. We answer with the section we read it from, or that we have not read it. Ask a rules question.

Every IJSBA class · where the rulebooks differ · checks on parts the shop sells · how this site reads a rulebook.