Biggest front sprocket that will fit?

[Blown 331]

I've got an 85 ATC250R and I want to gear it up so I was wanting to put a larger front sprocket on it. It has stock sprockets on it now, I think a 13 in front? I have 18" tires on it and I'm used to the high first gear of the 450R so it is geared way to low for me. And what do you guys thing switching to a 14 or 15 tooth (if it fits) will do for my acceleration. The bike is pretty stock.

[ESR350r]

If you put a 15 tooth front on a stock motor even with the 18 inch tires unless you have a really tall rear sprocket you will not have any power at all in 6th gear, alot of you question has to do with the size of your rear sprocket. I would say a 14 tooth on a stock motor would be about all you can get.

[Blown 331]

I wouldn't be surprised if my rear sprocket is the same one that it rolled out of the factory with. I'll try going up to a 14 and see what happens. So I take it up to a 15 will fit? It still has the stock piston, boyseen reeds, and a ESR ATC-5 on they way. I'm thinking of putting a CR head gasket on it or maybe a 12 to 1 piston.

[Roostin250R]

I couldnt get a 14 tooth to fit on my 89R with a 39 tooth rear. Unless your chain is really stretched. I'm sure a 15 would be near impossible without a longer chain. Be sure you have enough case clearance if you do fit a 15 on it. A better choice would be to change the rear sprocket instead.

[skidaddyjr]

12-15t front and 36-44t rear are the options 15front 36rear being the tallest but it wont fall out of a tree with a stock cylinder. I'm thinking those came with like a 40 something tooth sprocket stock ,trying a 36-39tooth rear would be closer to usable.

[Blown 331]

Everyone has to make fun of my stock cylinder. ha ha kidding. What is a good cylinder to go with, not power valve, I don't want to spend that kinda of money. Just like a 330 ESR or something like that?

u can fit a 14 on with a case saver, if you use a 15 the case saver wont fit


you really dont need a 15 though

i doubt the motor would turn a 14 37 so dont even try a 15

I run 14 38 with 20's with a worked stock cylinder but its worked

[deathman53]

I'm using 14/38 on my 86 atc-r with a esr 330, carb, reeds, esr pipe, cr iginiton and a ton of other stuff. Don't get the 330 kit, for one you need a 87-89 rod(mine has one), it revs slow, runs hot, but it makes alot of power, its a real good motor for dunes and such, but for mx its not real good. I like a revving motor more, I'm getting a 265 pv. Do you have a wider axle? your gonna need one with the 310 kit or so, also you are gonna have a big problem keeping the front wheel on the ground(if you don't already). I could run taller gearing, but I ride mx, 4th gear is the highest I get to. I was using 14/39 with the stock cylinder(ported) and for a time I used a 14/38(thats when I did fire roads -ILLEGAL STUFF in New Jermany) before you get a big bore get a 38 a/s, set of good reeds, maybe get your cylinder ported, cr head gasket and you will have a real fast bike. that stuff will cost less than the big bore alone, which only works good with the good stuff.