I have a 1985 Honda ATC 350x three-wheeler that in stock configuration runs a 13 tooth front sprocket, and a 40-tooth rear sprocket, with 22-inch tires. What number of teeth front and rear sprocket would I need to keep the gearing the same as stock if I install smaller 20-inch tires instead of the stock 22-inch tires?
Would I need to go up one tooth on the front sprocket, (up to 14 tooth) and down one tooth on the rear sprocket (down to 39 tooth) with the 20-inch tires to keep the gearing the same as stock? Or could I just go down three or four teeth on the rear sprocket with the 20-inch tires and still have the same gearing as stock? Is this the right formula, or am I way off base? Also, do you always have to change the front and rear sprocket number of teeth, or can you just change the rear, and still come up with the right gear ratio, and not cause any negative effects to the engine?

 

Area 51,

It's simple math. Your 350X has a gear ratio of 3.08 for the final drive. The 22" tires have a circumference(sp)of 108.46" (pi squared x radius). The 20" tires would have one of 98.60. That leaves a difference of 9.86" or 10%. To gear your quad the same way it was, you'd need to put a smaller sprocket on the rear or a bigger one on the front. You need a 2.77 gear ratio to equal the same gearing you have with the 22" tires. You'd need a 36 tooth rear sprocket and a 13 tooth front to come close.

 

Thanks Mike. It currently has a 13 tooth front sprocket and a 40-tooth rear sprocket. Will it hurt anything to only change the size of the rear sprocket with out changing the size of the front sprocket? I had read a post on this forum suggesting that someone in a similar situation go up one tooth on the front, and down one tooth on the rear. Is this necessary, or can you get the exact same effect by just changing the rear sprocket? I could go with a 14 tooth on the front (if it will fit) and a 39 tooth on the rear, or like you said, go with a 13 tooth on the front, and a 36 tooth on the rear with basically the same effect. If I leave a 13 tooth on the front, and just go with a 36 tooth on the rear will it be harder on the engine, than if I went with a 14 tooth up front and a 39 tooth in the rear? Or is gearing just gearing, and as long as I come up with the same ratio, it won't matter? I’m just afraid that I will order a 14 tooth for the front, then it wont fit and I will have to order a 13 tooth anyway. I would like to get it right the first time.

Thanks so much for your quick response.

 

Area 51,

The 14-39 gearing would work out to about the same gear ratio as the 13-36. It should be no harder to pull one as the other. However, most companies only make the rear sprockets in an even number of teeth (i.E. 36, 38, 40 42). I've heard that chains can bind if you have too small of a front sprocket, but the 13 tooth you have should be fine.

 

Area 51 don't put a 14tooth frt sprocket on,there is no room for a case saver if you do.Do all your gear changing on the rear sprocket.That engine has alot of low end power so don't worry about mooning out the gears too much.

 

Thanks a bunch Truck. I ordered a 13 tooth for the front, and went with a 36 tooth for the rear. That should get my gearing back to about stock with the new 20" Holeshots. I ordered the sprockets and chain from SideWinder. I hope there as good as people say! I ordered the Tool Steel front 13 tooth, and a Billet Alloy 36 tooth rear sprocket. I also ordered there Ti series chain. For what it all cost, it better last as long as they say, and some performance increase would be nice as well :-)

Hey Truck, what are your opinions on the stock carb with your big bore kit? Powroll told me to get a 300Ex carb for my 368cc big bore kit since I need to replace my carb. Honda says that it is a 32mm Keihin, but Powroll said that it measures 29mm, they said that it is the same size as the stock carb, but a better design. Do you think that the small stock type carb is enough for the big bore and cam?

Thanks,

Brian