Gears... once and for all!

[HoodStrype]

Okay, I've been having a 2 year long debate with two of my friends... I've heard (and they believe) a lot of people here and elsewhere say that the taller the tire, the smaller the Gear Ratio gets... hmmmm I didn't think so.

Here is the equation I pulled from the net:

(New Tire Diameter / Old Tire Diameter) * Old Axle Ratio = New Axle Ratio

Soooo... that would mean that I had 23.5" on the back, I now have 26" on the back, I had a 3.73:1 gear ratio, and now I have 4.13:1 ratio because I went to a taller tire.

This would make sense to me because for every turn that Tire makes, the gear has to make 3.73 turns to keep up. Now that I have a Taller tire, it has to turn more often (4.13) for every turn.

Am I correct here?

26" / 23.5" = 1.11
1.11 * 3.73 = 4.13

[fiveohpatrol]

the taller the tire, the lower (numerically) the gear ratio. Think about it, it's all about getting your engine RPMs up. If you had a small tire before, then went and put a taller one on, the taller one will be spinning slower than a small tire at the speed. A tire with half the circumference than another will need to spin half as much to cover the same distance.

A general rule of thumb is to subtract 0.1 from your numerical rear gear ratio for every 1" increase in tire diameter. So if you have 3.73's with a 23.5" tire, thats roughly equivalent to having a 3.48 gear with your 26's.

The real question is, what the heck are you doing with 23.5" tires on the rear of a mustang?
If you're concerned about it, just put in some 4.10's or 4.30's

[fiveohpatrol]

if you wanted a quick equation, you would have to divide your old tire size by the new one, so 23.5/26 =.90 then multiply by your gear .9*3.73=3.37.

either way, get rid of those puny tires

[HoodStrype]

I never actually had 23.5's on the back, but we were using that as an example- I have 26" on the back and the puny ones are on the front. Okay so my equation is wrong- it is right the opposite... cool!

I guess this means I eat my hat... *&^%!

[HoodStrype]

Ah hah! That ratio I used was the equivilant ratio... I would need 4.13 gears to return to a 3.73 ratio... can anyone see the light bulb that just broke over my head?

[~The Jester~]

Just keep this in mind. The gear ratio's on the gears themselves (ie 3.55 3.73 4.10 4.30 etc etc) are mechanical ratios determined by PHYSICS. It's ASSUMED (and we all know about that) that if you run a 26" tire, you're right on the money with your mechanical gear ratio.

LOWER numerical gear ratio is actually a HIGHER ratio. This is where most guys get confused. Physically speaking, a 3.55 is a higher gear than a 4.10 With me?

[HoodStrype]

...I got it now, thanks guys. I've gotten alot of "I told you so" this weekend. That's okay, my Mustangs faster than anything they own- HAHAHA!