How to interpret Tire Size Calculator?
12-19-2003, 04:03 PM
#1
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Thread Starter
How to interpret Tire Size Calculator?
I've done some calcs but I'm confused about what to do with the calculated % change in tire diameter. Is it a bad idea to have different rolling diameters from the front versus the rear? I'm guessing it's ok for a C2, but would this be bad for a C4? And what amount of % difference is acceptable?
Tire size calculator
I'm very confused about what size tires to buy...
Tire size calculator
I'm very confused about what size tires to buy...
12-19-2003, 04:37 PM
#2
If you keep the f/r ratio similar to stock, then you should be fine. So if you get 295's in the back, then you should probably get 235's in the front. Play around with the different aspect ratios availabe in the tire that you want and compare the ratio with the stock ratio.
On my TT ( and probably your C4 ), the rears are slightly smaller, to make the visous coupling always apply some torque to the front axle.
On my TT ( and probably your C4 ), the rears are slightly smaller, to make the visous coupling always apply some torque to the front axle.
12-19-2003, 04:39 PM
#3
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It's bad to have a difference front to rear on a C2 also, since the ABS calculates a different speed front-rear as a loss of traction and will interfere with braking. Also, remember that having smaller overall diameter on the driven wheels will react like a lowering of the gear ratios (which can be great as long as you're consistent F-R) and vice-versa...
12-19-2003, 06:24 PM
#4
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Thread Starter
So there are 2 issues with tire diameter:
1. Too much difference sets off ABS sensors. Someone posted that the 964 manual says not to exceed 6% difference in tire radius. Ok. (thanks Kim)
2. C4 viscous coupling. Jeff- the stock narrow-body 18" rear tires have the SAME (or slightly larger) diameter as the fronts (225/40 and 265/35). Stock 17" sizes also have the same diameters front to rear (205/50-17 and 255/40-17). So I'm still wondering if it's harmful to the viscous coupling to have a couple % difference front to rear.
1. Too much difference sets off ABS sensors. Someone posted that the 964 manual says not to exceed 6% difference in tire radius. Ok. (thanks Kim)
2. C4 viscous coupling. Jeff- the stock narrow-body 18" rear tires have the SAME (or slightly larger) diameter as the fronts (225/40 and 265/35). Stock 17" sizes also have the same diameters front to rear (205/50-17 and 255/40-17). So I'm still wondering if it's harmful to the viscous coupling to have a couple % difference front to rear.
12-20-2003, 03:39 AM
#5
Burning Brakes
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When I wrote that calculator I was thinking it's usefulness would be just for comparing the difference between the size of the tires currently on a car versus some different tires, like going from 16" to 17" wheels.
I didn't realize it, but you can also use it to calculate the difference between your front and rear tires if they are different sizes, Duh. Learn something new every day.
I'm sorry I can't be of help with your question Eric.
I didn't realize it, but you can also use it to calculate the difference between your front and rear tires if they are different sizes, Duh. Learn something new every day.
I'm sorry I can't be of help with your question Eric.
