Does anybody have a formula (in English!) that can help me determine how to get near to stock gearing when running 20" tires instead of stock 22"? Thanks.

 

On a what?

 

I think he's talking about his truck. Am I right?

 

This should be the correct way:

Take stock tire size and divide it by the new tire size which in your case is 1.1. Than take that number and divide it into your stock gearing that should give the correct size.
Hope this helps

------------------
Ramit

 

quad_man,
Someone posted a formula a few months ago.I can't remember who it was. Maybe he'll see your post here and reply. I've always used the seat- of- the- pants formula


------------------
THE AZ HARD PACKER, calmiller@kachina.net

save the public land FOR you, not FROM you..join the Blue Ribbon Coalition online @ www.sharetrails.org



[This message has been edited by hot_shoe_cv (edited 01-05-2000).]

 

I think seat of the pants might be the best way now. I am going to try going up 2 teeth on the front sprocket I guess. That will be more than stock, but I could use it anyway.

I don't see many trucks that run 20-22" tires.

 

Now I understand the question.
On my ex 20 inch tires, gearing stock 15/38.
With 22 inch tires, Very near stock gearing 14/39. Just a hair lower.

In other words.
add 1 to the front.
minus 1 to the rear.
That should get you where you want to be.

Adding two to the front will make you taller geared than stock.

[This message has been edited by trx430ex (edited 01-05-2000).]

 

So on my Mojave, I should run:
12/43 W/22" rear tires (stock)&
14/39 W/20" rear tires?

 

Adam-

What you wish to maintain as you change tire sizes is the ratio of countershaft rotation to vehicle displacement. Simply put, this is how far your ATV travels with each revolution of the countersprocket. The formula for determining this ratio is given as: d = (Tcs/Ts)*(PI*Dw)
Where: d = the amount of displacement per countersprocket rotation, Tcs = number of teeth on countersprocket, Ts = number of teeth on sprocket, Dw = diameter of wheel, PI = ratio of the circumference of a circle to its diameter

If d1 is the ratio with the stock or present components installed, and d2 is the ratio with the proposed new components installed, then equating d1 to d2 (to maintain a constant ratio) yields the following equation: (Tcs1/Ts1)*(PI*Dw1) = (Tcs2/Ts2)*(PI*Dw2) where the variables are as previously defined but with the “1” indicating stock or old setup and the “2” indicating the new setup.

Once the tires have been selected, there remains two other components that effect this ratio – the countersprocket and the sprocket. You must select one or the other, then plug it into the equation above and solve for the unknown.

If you choose a new countersprocket size and want to know what size sprocket you need to maintain your countersprocket rotation to displacement ratio with the new tires you selected, solve the above equation for Ts2 to get: Ts2 = (Ts1*Tcs2*Dw2)/(Tcs1*Dw1)

If you choose a new sprocket size and want to know what size countersprocket you need to maintain your countersprocket rotation to displacement ratio with the new tires you selected, solve the above equation for Tcs2 to get: Tcs2 = (Tcs1*Ts2*Dw1)/(Ts1*Dw2)

Hope this is clear enough and you find it useful.

 

That post was really funny. I never knew that you could take something as simple as adding a tooth or two on the countershaft to make up for smaller tires so impossible for most of the people in this forum to understand.

Good job - Unfortunately, the fact that the question was even asked, shows that the person asking wouldn't know what the heck you are talking about.

No one bothered to say these simple things. a) it's not necessary to exactly duplicate stock gearing when changing tires, getting close is all that's necessary. b) one post above said it best - had 20" and now have 22" tires, so 22/20 = about 1.1 so multiply the number of teeth on your existing front sprocket by this number (ex: 14 x 1.1 = 15.4) 15's close enough so use it. If you want to get closer to stock gearing, then drop a tooth or two off the rear sprocket.

It's just a ratio. If you can mix two stroke oil, then you can calculate gearing.

[This message has been edited by SandmanBlue (edited 01-12-2000).]