RM85 Advice needed from racing Dad's


My kid races arenacross, supercross and motocross. Should I change the

front sprocket on the RM85 for the different tracks. If so what do you recommend. New to racing.:busted:



well if u want to be quicker and have more top end on different tracks then yea.

When I raced 85s, we changed the back sprocket over the front.

Reason for that is by changing one tooth on front, you can change the ratio severely.

Ex., my 98 RM250 runs a 14/51 combo for 3.64:1

If I was to drop to a 13, that would be 3.92:1

15? 3.4

Now, a 14/52 would be 3.71:1

14/50 3.57:1

it doesn't seem like much, but it also saves your chain from having to wrap around a 12 tooth sprocket on an arenacross track.

And don't forget! Rear sprocket and chain get replaced as a set!

I would be swapping the rear sprocket 1 or 2 teeth more depending on the track. Tighter more technical tracks (SX and arena cross tracks)require quicker acceleration for the tight turns and shorter runs. On MX tracks the acceleration and top speed need to be balanced out, which would leave you at your stock front and rear sprockets.

Thanks guys,

I will keep it stock 14/48 for motocross and go 14/46 for supercross and arenacross. Does this sound right? Thanks for the input.:thinking:


Go up one or two teeth on the rear sprocket. 14/49 or 14/50. When you change your sprocket change your chain like someone stated. What we do is get ziplock one gallon bags and put the chain and sprocket in it and mark the size down on the bag. Hope it helps.

14/48 for MX and 14/50 for SX

I'd take the settings everyone else seems to have suggested (14/48 outdoors, 14/50 indoors) and use that as a baseline.

My old YZ80 (I know, it's a Yamaha, but bear with me!) was supposed to run 14/49 outdoors, but I normally ran 14/50 at my local track, with some of the longer tracks being changed to a 14/46 or a 15/50, depending on what I remembered to bring with me. Those changes were mostly for comfort, and to adapt my rather old school riding style to the modern bike.

Getting your son comfortable on the bike is more important than fast laps in the beginning, because the more comfortable he is on the bike, the faster he'll feel safe going.

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