March 31, 2019, 12:46 PM
Digger660Tire hight
How much if any difference will it change the gear ratio form a 108 1/4 tire to a 109 3/4 tire?
March 31, 2019, 09:08 PM
Tom396The revolutions per mile will change. You can't actually change the gear ratio without physically changing the ring and pinion. I know that you meant what effective change, but it just bugs me when it is referred to as "changing the ratio". Take care. Tom Worthington
April 01, 2019, 08:36 AM
Lenny5160The difference between those two numbers is all you need to know.
109 3/4 is about 1.4% larger, so you will get about 1.4% more distance traveled for each rotation of the driveshaft.
April 01, 2019, 08:56 AM
Mike RietowHypothetically, if you have a 4.10 gear and went from a 34.5 tire to a 35, the effective gear would be 4.03.
April 01, 2019, 09:44 AM
FootbrakeJimWhat are you trying to figure out with tire rollout difference? RPM change at stripe, or?
You might want to check out this site:
Wallace Racing CalculatorsApril 01, 2019, 03:25 PM
Digger660trying to see if it will slow the car down on 60 foot. sorry for any confusion
April 01, 2019, 03:48 PM
FootbrakeJimIMHO, the amount of change in your 60' is usually not going to be a lot for that difference in rollout. But it depends a lot on the converter, and the camshaft/torque curve of your engine. Even tire pressure will affect how much difference you'll see. If you've got a broad flat torque curve, and a loose converter, it may not change a bit. I made a 2" difference in tire height and it didn't change my short times at all, though it did affect RPM at stripe.