90 MX gearing

[Cowan39]

I just rebuilt engine from stock. Changed to a 53 piston with 45 crank. Engine has been ported and case matched. Question is on stock engine I was running 19/33 for gears seem to be best for MX. With added power should i go up in rear or stay same. Thanks for any suggestions.

[nordic quad]

We run a similar gearing on our 100cc 20-30,try out the gearing you have first,without using a tacometer and knowing the peak peformance numbers its going to be an trial and error,you may need to play with your clutching first.IMO
Stein A

[Cowan39]

Thanks, I need to stay with 19 up front got slipper locked in and dont want to touch. I dont want to go any more high end was thinking trying 19/35 it may be to much but most of are tracks are bottom and mid range. Looking for something smooth all the way through.

[dericsdad]

bigger rear sprocket=quicker acceleration and more torque.

smaller rear sprocket=faster top speed

[bulldogfallon]

Originally posted by nordic quad
without using a tacometer and knowing the peak peformance numbers its going to be an trial and error,.IMO
Stein A


Right on the money.....Nice to see a reply like this!!

[Cowan39]

Gents, Thanks for the answers. I know what gears do. My question was when adding power do you need to change gearing or is it consistant regardless of power. I was just trying to get idea of what others run and what works best for MX.

[bulldogfallon]

I think your best bet would be to call the engine builder

They can either tell what they recomend or tell you where this setup makes power.

There is not set way to gear when you build an engine.

It all depends on where the quad makes power....


If you have a torque engine you may need to reduce the rear sprocket to get speed and if you have one that needs rpms to make power you may add teeth to get it into the power faster and more often.


Your CVT would also need to be tuned and then select the sprocketing that fits the engine setup and track style best....along with tire selection.

We change our mod 70 gearing when we change tire size...

(I am sure you know some of this already,but I listed it for the others that will read the post that may not)

[JIM GRACE]

Originally posted by Cowan39
Thanks, I need to stay with 19 up front got slipper locked in and dont want to touch. I dont want to go any more high end was thinking trying 19/35 it may be to much but most of are tracks are bottom and mid range. Looking for something smooth all the way through.

our 90 has the bigger maxxis tires with a mallossi
cyl and 19/30 has been great all around. If you are running sno hogs and a 35 sproket I would imagine a lot of tire spin leaving the gate. A good friend who runs the nat's uses a 27 tooth .

Every set up is diff or it would be too easy. Lol

[EthansDad]

do you have a tach? if not, I'd lay down the $100 and get one. We did some testing once we worked over one of our motors and it was quite the opposite of what I would have expected.

We started with 19/35, and after the increase in power, I dropped to a 19/32. I did testing with a tach and GPS unit (to measure speed). what I found is that with the 19/35, the motor turned more RPMs, had a harder bottom hit, AND had a higher top speed than the 19/32. go figure. on a built 90 like yours, I'd guess that you should drop down a bit to reduce wheel spin, maybe 19/32, but to know for sure, try a similar test with tach and GPS or some sort of top speed measurement.

[Cowan39]

Thanks, #22 that was some interesting info. I quess I will start with the 19/33 that is on there now. I hope to start testing next weekend. I will post results.

[greenmachine70]

Our best holeshot and top end mix is with a 20/30.
I know some guys who are beating us with a 20/28 and they are also running the big quad cross tires too......