HELP! Gear ratio's?

[2000 stomper]

Can someone clarify this for me? I was told that gear ratios are only true if your running a 26" tall tire. So if this is true, what ratio would i be running with 3.42's and a 27" tall tire, also 3.42's with a 31" tall tire? Any help would be appreciated.:confused:

[Tink]

Your actual gear ratio won't change... since your drive ratio stays the same - 3.42 in 3rd (1:1) and 2.39 in OD... asssuming you have an automatic. This would only change with a change in gear.

What changes is your rpms at certain speeds... with 26" tires, you are turning about 2 grand at 65mph. With 27" tires it will drop to around 1950rpms and with 31" tires it will drop to about 1700rpm. So, you'll need to have your speedo re-calibrated, or just need to know how far 'off' it is.... if you have a tach, then you can drive using the tach. So, it is like running 3.23s by upsizing tires, but in actuality your drive ratio stays the same.

This is a great site for checking out how gears and tire sizes affect things:
http://www.grimmjeeper.com/gears.html

[Mikz86TA]

X2

[bespurcell]

X3

[2000 stomper]

Thanks for the link, but it diden't help, not sure i asked this question right, lol. Ok, in a racing application, would a 4.11 ratio only be effective as a 4.11 ratio with a 26" tall tire? May be this will help shed some light on things, I'm runnung a 4spd OD man. trans, (RPO MY6), 3.42 gears in the rear and a 27" tall tire. Lol, Can you tell me what gears i should change to in order to get the true performance of at least a 3.42 or better? I appoligize in advance for sounding like a dumb a$%!

[Mikz86TA]

Not a dumb question, just maybe tha way youre asking is a bit unclear.
Most of the time in racing, people will change tire size and gearing to get a certain trap speed.
Say if Im running the 1/8 mile, I have 3.42s and a 26" tall tire. And I notice that my speed is OK but Im only at 5500RPM when I cross the line in top gear. But my car peaks power at 6500RPM. Then I would want to make a swap either in tire size or gearing to change that. I could use an online calculator to figure it out.
Youll need to have a known tranny gear (say if your in 3rd through the traps or 4th or 5th you wil need that perticular ratio to put in the formula), and you need the final drive (rear gear) ratio and your tire size.
Is that more along thre lines of what you are looking for?

[T Man]

Gear ratio refers to the number of teeth on the ring gear divided by the number of teeth on the pinion gear. There is no difference no matter how much you change tire size. Gear ratio will stay the same without a gear change (taking apart the rear end and physicaly changing the gears)

[2000 stomper]

Yep, thanks for the LIGHT, lol. Next time i know to put certian info in to get the answer im looking for. Thanks to everyone who replyed!