Can't remember how it raises or lowers the gear ratio based upon the size of the tires diameter.

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Founder of the Greater Cincinnati F-Body Association
Greater Cincinnati F-Body Association
1988 Yellow Trans Am GTA
Click here for photos

 

Tire size doesn't change your gear ratio. If you have 3.08's, for example, they will always be 3.08's. Going to a taller tire tire will have the same effect as installing a higher gears, such as 2.73's.

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82 camaro--original steering wheel, brake/gas pedals, seats--everything else modified
82camaro

 

It can be called a poor mans gear swap. Lets say you have 3.08 gears and 26" tall tires. To do a tire swap for better accelleration you would have to go to a 24 or 25" tall tire (not a good choice since a shorter tire has a smaller contact patch on the ground.

For better economy you would go to a taller tire. Putting on 28" tires would be like dropping those 3.08's to 2.77

Drag racers will squeeze the tallest tires they can into the wheel well then adjust the rear end gears to compensate for them.

Again as an example. You have 3.08 and 26" tires. putting in 3.73 gears an 28" tires will have little change on your rpm. The rpm at 60 mph will be close to the same so the engine is still working in it's original powerband.

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87 IROC-Z SuperPro ET Bracket Race Car
461 naturally aspirated Big Block

Best ET on a time slip: 11.242 altitude corrected to 10.69
Best MPH on a time slip: 121.52 altitude corrected to 127.76
Altitude corrected rear wheel HP based on power to weight ratio: 504.5
Best 60 foot: 1.546

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
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87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley