big wheels = gear change?
Thread Starter
Pro
Joined: Jan 2005
Posts: 644
Likes: 0
From: Denver Colorado
big wheels = gear change?
I have a 95 coupe w/ ZF6, recently bought new wheels, and noticed a definite change in acceleration, I was curious if anyone here would know what the difference in the gear ratio would be between stock size 275X40X17 compared to a 305X30X19. I want to go with shorter gears to get that acceleration back and some.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
It CAN be figured, nominally, from the tire size, but the best way is to measure the loaded circumference of each tire and figure the percentage difference. Apply that percentage to the gear ratio. It won't be a lot. You can save some time by going to the next lowest ratio. It will compensate for the tires, and then some.
RACE ON!!!
RACE ON!!!
Pro
Joined: Nov 2004
Posts: 641
Likes: 3
From: Long Island NY
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
Originally Posted by artvette
but the diameter of this 19" tire is very close to the 275-40-17....25.9"diameter/800 rev per mile...so change in effective "gear ratio" is very small
I think your problem is the increased weight of the 19" wheel/tire
Do you know the weights?????
BTW even if the actual weights are the same, the weight of the 19" is centered on a larger diameter.....which will slow the car down...
Don't know for sure, but if you have lost performance it is more the result of increase weight and and the larger radius to the center of the weight...
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
Play with this. If the speed for any given RPM is lower it will improve acceleration, if it is higher it will hurt it.
http://www.wku.edu/~nathan.plemons/calc.xls
http://www.wku.edu/~nathan.plemons/calc.xls
Racer
Joined: Jul 2005
Posts: 301
Likes: 0
From: Dallas/Spring Texas
Originally Posted by LT4BUD
Yes, but they don't give diameter, rev per mile for 305-30-19....
but the diameter of this 19" tire is very close to the 275-40-17....25.9"diameter/800 rev per mile...so change in effective "gear ratio" is very small
I think your problem is the increased weight of the 19" wheel/tire
Do you know the weights?????
BTW even if the actual weights are the same, the weight of the 19" is centered on a larger diameter.....which will slow the car down...
Don't know for sure, but if you have lost performance it is more the result of increase weight and and the larger radius to the center of the weight...
but the diameter of this 19" tire is very close to the 275-40-17....25.9"diameter/800 rev per mile...so change in effective "gear ratio" is very small
I think your problem is the increased weight of the 19" wheel/tire
Do you know the weights?????
BTW even if the actual weights are the same, the weight of the 19" is centered on a larger diameter.....which will slow the car down...
Don't know for sure, but if you have lost performance it is more the result of increase weight and and the larger radius to the center of the weight...
I think you hit the nail on the head
Safety Car
Joined: Apr 2003
Posts: 3,793
Likes: 9
From: VA
Originally Posted by BRICHC4
I have a 95 coupe w/ ZF6, recently bought new wheels, and noticed a definite change in acceleration, I was curious if anyone here would know what the difference in the gear ratio would be between stock size 275X40X17 compared to a 305X30X19. I want to go with shorter gears to get that acceleration back and some.
Since you also have a different wheel there are other factors as mentioned above, but regardless of cause a gear change will help.
http://www.miata.net/garage/tirecalc.html
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Pro
Joined: Jan 2005
Posts: 644
Likes: 0
From: Denver Colorado
LT4Bud thanks that makes a lot of sense, so I think 4.10 will do just fine, nathan that spreadsheet is awsome to play with and not just for tire sizes either thanks I saved it if you don't mind.
