If you are currently running at a sprint track, in Yamaha KT100S Heavy (2004 IKF National Class #11), the most likely road race crossover classes are...
 
 

IKF National Class #2 - Yamaha Limited Light Sprint

 
Rule Differences...
 

Weight:
 

330 lbs
 

Brakes:
 

Front brakes are optional.
 

Tires:
 

No compound or manufacturer restrictions.  5" or 6" rim diameter.
 

Intake:
 

Air filter may be used, in place of an air box, unless local authority mandates differently.
 

Exhaust:
 

Open pipe.
 

Race / Heats:
 

30 minute race.
 

IKF National Class #3 - Yamaha Limited Heavy Sprint

 
Rule Differences...
 

Weight:
 

360 lbs
 

Brakes:
 

Front brakes are optional.
 

Tires:
 

No compound or manufacturer restrictions.  5" or 6" rim diameter.
 

Intake:
 

Air filter may be used, in place of an air box, unless local authority mandates differently.
 

Exhaust:
 

Open pipe.
 

Race / Heats:
 

30 minute race.