Please help with gearing math
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Tuned
Joined: Sep 2002
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From: saline USA
Please help with gearing math
I have a V10 ford with 4.30 gears and 245/75/16E tires. I am thinking about putting 265/75/16E tires on it. That will be one inch of total height difference, and I know that for a fact. So with one inch difference will that effectively turn my rear gear ratio into a 4.10 or something close to that. That is my question, what will my overall gearing be with the larger tires. thanks.
I realize its only 1/2 and inch on the height of the vehicle.
I realize its only 1/2 and inch on the height of the vehicle.
Last edited by andrewzx92000; Feb 3, 2018 at 01:53 PM. Reason: left something out
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Your axle ratio remains the same, so don't get hung up on trying to figure out what the "exchange rate" is when you change tires.
Effective overall ratio changes a bit with taller tires.
Calculator here allows all variables to be changed.
https://www.novak-adapt.com/knowledge/gearing/
Their tire calculator shows 2" between the two, but TireRack shows 1.2" or so. So using a 1" difference and the above:
With the smaller tire at 30" diameter gets you 21 or 29 mph/1000 rpm in 4th/5th gear.
At 31", you get 21/30 per 1000. In other words, less than 1/2 mph per 1000 rpm in 4th.
A 4.10 puts you at 22/31 in 4th and 5th with a 30" tire, so you are correct with your initial estimate.
At 65 mph, in 5th/4th the 30" tire should run 2223/3130 rpm, the 31"er 2151/3030.
Effective overall ratio changes a bit with taller tires.
Calculator here allows all variables to be changed.
https://www.novak-adapt.com/knowledge/gearing/
Their tire calculator shows 2" between the two, but TireRack shows 1.2" or so. So using a 1" difference and the above:
With the smaller tire at 30" diameter gets you 21 or 29 mph/1000 rpm in 4th/5th gear.
At 31", you get 21/30 per 1000. In other words, less than 1/2 mph per 1000 rpm in 4th.
A 4.10 puts you at 22/31 in 4th and 5th with a 30" tire, so you are correct with your initial estimate.
At 65 mph, in 5th/4th the 30" tire should run 2223/3130 rpm, the 31"er 2151/3030.
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