I am currently running 315/30/18's on the rear of my 96 with my 4.30 gears. I have found a good looking set of 17" wheels and tires on craigslist. The rears would be 315/35/17 if I buy them. Would I see too much difference in RPM's going with the 17's instead of my 18's? Guy selling the 17"s is going to switch to 18"s to get his RPM's right when he installs 4.10 gears...I had never even thought about RPM's until he mentioned it...Any thoughts?
17" or 18" rim with 4.30 gears???
- Thread starter Rick98Z
- Start date
I must be retarded cause I can't get the thing to compute it out right lol...
Does anyone run 17" rears with 4.30 gears out there???
Does anyone run 17" rears with 4.30 gears out there???
You would likely not see much of a RPM difference. The 315/30/18 is 25.4" tall tire with a 79.9" circumference and the 315/35/17 is 25.7" tall with a 80.7" circumference. So your looking at about a 5/16" taller tire, which in the tire size to RPM ratio is a pretty insignificant amount. A change of wheel size doesn't affect your gear ratio but a change in tire size will.
I was thinking that it should be a small amount, that's why I was wondering why this guy kept saying he needed to switch to 18"s since he went to 4.10 gears? Unless he tracks the car and wants specific rpms at certain speeds I couldn't figure out where it would be much difference???
I really don't necessarily want to kept my 4.30 gears anyway so can't see where it would hurt anything changing sizes at this point...Thanks for the help thumper!
I really don't necessarily want to kept my 4.30 gears anyway so can't see where it would hurt anything changing sizes at this point...Thanks for the help thumper!
Get the 17's and then some 28in tall M&H dr's. You will thank me later
Doubt I will need drag radials if I read that right...my cobra not going to see track, just weekend fun car 
There will be no difference you can tell.
That guy is full of crap
4.30 gears are great!
That guy is full of crap
4.30 gears are great!
Guess the next question is does anyone know if the american muscle version fr500 17" rim will work with the 13" front Brembo setup? They fit on my current 03 Cobra 17" rims but unsure with the fr500's???
Great! I just noticed when looking on ebay at some FR500 wheels, the 17" listed not for use with big brake kits such as brembo...Was going to try to contact American Muscle to be sure.
Don't know what's hard about it? Type in numbers and hit calculate and you have an answer.
315/35/17 = 25.6" tire height. 25.6" x 4.30 x 60 mph = 3386 rpms in 1:1 aka 4th gear.
315/30/18 = 25.4" tire height. 25.4 x 4.30 x 60 mph = 3413 rpms in 1:1 aka 4th gear.
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Thanks all for the help, just gotta make sure they clear the brembo calipers still. American Muscle told me to buy one wheel and try it out lol...
Why would you run 4.30s on the street, 3.75 tops and I took them out for 3.27 on a 6 speed and 3.08 in the turbo car with an auto. I have a real set of FR500 by Ford and they clear Cobra front brakes but they are 18" not 17". I know the aftermarket FR500 don't have the same clearance as the real one's. I've looked everywhere for the real ones but they haven't made them in a while. Been wondering what my real FR500 in perfect shape are worth, somebody told me just the Ford center cap on them are going for $150.
4.30's were in it when I bought it, I would love to go to 3.73's but funds don't allow it right now
Why would you not? Did you ever drive your Cobra when it was still N/A?
These cars need 4.56 desperately in N/A form.
I have gotten used to the 4.30's really but highway rpms are a little higher than I prefer...
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