GEAR RATIO

[DURA-MAX3]

If i changed my tire size from the 235 or whatever the stock size was, and put on 265's what is my gear ratio now. how do you figure it. thanks...

[Heartbeat Hauler]

DURA-MAX3,
Go to this web site:

http://www.prestage.com

and under resources choose car math, then go to calculate gear ratio. You have to know gear ratio - i.e 3.73, transmission - (whatever your overdrive ratio is), RPM and tire height in inches. This should let you experiment with different tire sizes.
Good luck.
JP smile.gif

[ 09-20-2002: Message edited by: Heartbeat Hauler ]</p>

[SoCalDMAX]

Try www.4lo.com. They have tire size calculators as well as gear change calculators.

Regards, Steve

[afp]

Also, remember that loaded roll-out is the number you really want. The tire diameter posted on the tire is just the mold size, and even the actual measured diameter will not be the same as loaded rollout.

Blaine

[DmaxMaverick]

DURA-MAX3

I think the answer you are looking for is 3.56 (approximately, according to manufacturer's posted numbers). That means that with stock tires, you would have a 3.56 rear end to get the same gearing. It will make your speedo read about 4.5% slower than with the stock tires. 50 mph on the speedo will be about 52-53 mph ground speed.

All tires, even from the same manufacturer, will not be the same circumference. The only way to calculate the exact ratio would be to measure the roll out before and after. Convert the difference into %. The % will be the same for all measurements, be it ratio or speedo accuracy.