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The following is a summary of snow drag racing rules typically used by events associated with the ISR. It is not intended to be a complete listing of the rules. For a complete and detailed list of rules please see the current ISR racing yearbook.

Stock: Stock is stock. Only changes allowed are clutching (weights, springs, no machining), jetting, gearing, track (if it is same length and width as OEM), and skis (as long as they are of same material as OEM and min. length 40 inches). Headlight can be removed (but not headlight console, and hole must be plugged). Instruments may be removed but holes must be plugged (console must remain in place). Airbox may not be modified but may be removed. Filter pods may be used. Windshield may be removed. Driver must weigh at least 180 lbs or ballast must be added. No other changes allowed that alter exterior appearance of sled.

Improved stock: Any change allowed in stock is allowed. No engine swaps allowed. No pressure charging or nitrous allowed. Aftermarket exhaust allowed. Reed changes allowed. Porting and headwork allowed. Head must maintain OEM exterior appearance. Overbore of OEM cylinder allowed up to class limit (IE 680 allowed to bore up to 700 to run in 700 but cannot be bored to 800 to run in 800). Pistons may be changed. Carbs must be OEM for model but may be bored. Lightweight hood may be used as long as it maintains OEM appearance. OEM seat, gas tank, suspension, and belly pan must be used. Long track kits may be used in 800 improved and 1000 improved only. Clutch cover required that covers top of clutches and faces down to center bolt.

1000 Improved only – aftermarket heads and cylinders may be used on OEM for the model crankcase. Carbs and ignition may be changed.

Minimum combined weights (sled and rider) are 440 & 500 cc – 600lbs, 600 cc – 700 lbs (675 for 2 cyl. Engine), 700 cc – 750 lbs (725 for 2 cyl. Engine), 800 cc & 1000 cc – 775 pounds (750 lbs for 2 cyl. Engine)

Pro Stock – Engine swaps within brand allowed as long as like chassis is used (trailing arm for trailing are, A-arm for a-arm). Over bores allowed but will change sled classification. (ie, a 600 cc sled can be bored to 800 cc’s but must now run in 800 cc class and not 600 or 700) OEM cylinders must be used. OEM fuel tank must be used and outer shell kept in tact but may be modified to accept fuel cell. Seat must maintain OEM contour and be stock appearing. Carbs may be changed. Cylinder heads may be changed. Suspension may be changed as long as OEM design concept maintained (a-arm, trailing arm, strut, etc.). Long track kits allowed. No pressure charging or nitrous allowed. Clutch cover required same as improved stock. Belly pan must remain in place and stock appearing.

1000 Pro Stock only – aftermarket cylinders are allowed.

Minimum combined weights (sled and rider) are 440 & 500 cc – 550lbs, 600 cc – 625 lbs (550 for 2 cyl. Engine), 700 cc – 625 lbs (550 for 2 cyl. Engine), 800 cc & 1000 cc – 625 pounds (550 lbs for 2 cyl. Engine)

ISR rules stipulate that for all classes above stock the rear of the tunnel must be enclosed down to 1 inch above the rear axle bolt with the driver on the sled. The enclosure must extend a minimum of 14 inches from the rear of the tunnel. In practice, this rule is typically only enforced for sleds using metal traction devices when they are allowed in the class by the rules of that race.

While there are more classes (heavy mod, factory mod, open mod, etc.) these are rarely used at smaller snow drag events. It is not uncommon to see three classes run per engine size (stock, improved stock, and open). These classes will most often result in fair competition at smaller races (less than 100 sleds).