sprocket and gearing Question

[John250X]

I have a 87 honda 250x with a RCM exaustand a jetted 400ex carb with no choke. I can beat my buddies 300ex on the top end (I have been clocked at 60mph) but I get beat off the line. I am running a f/r 12/38 sprocket set up. Is this a good set up or should I change it and if so what too?

[John250X]

Also I am running a 20 inch tire. But thinking of going to an 18

[John250X]

anyone?

[Bajakawi]

Easiest fastest mod would be to try an 11t front...see if that makes any difference at all...that is equal to about 3.5t on the rear sprocket. If that is too much then try upper your rear sprocket to a 39t or 40t...On your tires...every inch of tire height is worth about 1.5 teeth on your rear sprocket..so you can take your gearing you have now..12t-38t...and work it about any way you like by changing tires or front or rear sprockets. I would say that is you need tires anyways, try that ...but check the ACTUAL height first..some 18" tires are closer to 17".. I know that RAZR 2's that are said to ne 22" actually measure 21"..... so do your homework.... Watch out though, all these mods I spoke of will slow your top end down a little bit..... Bajapred

[John250X]

If I wanted to change my bottom what should I go to as far as the rear sprocket. Like I said I am running a 38 tooth now.

[Bajakawi]

Okay, to "change your bottom end" I am assuming you want "more" bottom end..you need to go bigger in rear sprocket size. This will give you more bottom end power, but will also slow you down on top end speed. Read my other thread carefully, I explained how your gearing changes with each mod. If you are 38t now on the rear then I would try 39t. Or if you are planning on new tires and changing the size to a smaller diameter, then that would do about the same thing, 1" at a time...rmember 1" of tire height is equal to about 1.5 teeth on rear sprocket. good luck..Bajapred