I had the chance to run my MP7.5 on a onroad track in August on holiday.
Basically they go bloody fast!
I was running an old set of kit Kyosho mini spike tyres which wore to slicks after 3 tanks. As slicks they have not grip & probably are the wrong rubber type. The biggest problem was my engine was over revving & would sieze after 2 mins (a RB WS7 II) not good for the engine. I richened by a turn & 1/2 to try to cure the problem & got to the point where if I came of the gas a bit on the long straights it would keep running. Good fun.
Anyway for next year (or sooner if I can find a track) I plan to make the following mods:-
Slick tyres, either solid rubber slicks, or foam inserts slicks.
Try
http://www.grpgandini.com
Clutch bell, on road tyres are smaller diameter. This has the effect of increasing the cars gear ratio which is the opposite of what you want!
I worked out that a 15T clutch bell gives the same ratio as a 13T on off road tyres. Plus you want the car to go faster, so look at something around 17T (this would depend on the size of track). If you go for solid tyres, they do not balloon at all, where as foam filled ones will. This helps to lower the gear ratio.
Other than that run as low ride height as you can & set your wing to its lowest angle!
Tim.