Tire Size question for 95
Thread Starter
Drifting
Joined: Dec 2003
Posts: 1,493
Likes: 94
From: Westfield MA
Tire Size question for 95
I have a 95 that came with 8.5" rims up front and 9.5" rims in back and 255/45 and 285/40 tires. I am thinking of getting new wheels that are 9.5" all around with 275/40 tires. Then I could rotate them at least front to rear.
From what I can tell, the 275 tires are 25.7" in diameter and the 285 tires are 26.1
Is this enough to make a difference to the cars computer or speedometer? Should it be reprogrammed? Is the ability to rotate front to rear not a big deal?
From what I can tell, the 275 tires are 25.7" in diameter and the 285 tires are 26.1
Is this enough to make a difference to the cars computer or speedometer? Should it be reprogrammed? Is the ability to rotate front to rear not a big deal?
Race Director
Joined: Oct 2005
Posts: 11,771
Likes: 177
From: Rolla Missouri
2021 C4 of the Year - Unmodified Finalist
St. Jude Donor '10 thru '25
You'll be just fine with the 275/40-17 tires. Those were stock sizes on a lot of C4's
Here is a quick formula to calculate tire sizes
((2 x Tire Size x Aspect Ratio) / 2540) + Rim Diameter
Using the above formula:
((2 x 285 x 40) / 2540) + 17 = 25.97637
((2 x 275 x 40) / 2540) + 17 = 25.66141
That is 0.31496" difference, which will not make enough difference in the speedometer to worry about.
Note: There might be slight differences in sizes between brands of tires. The above will get you a good average though.
Here is a quick formula to calculate tire sizes
((2 x Tire Size x Aspect Ratio) / 2540) + Rim Diameter
Using the above formula:
((2 x 285 x 40) / 2540) + 17 = 25.97637
((2 x 275 x 40) / 2540) + 17 = 25.66141
That is 0.31496" difference, which will not make enough difference in the speedometer to worry about.
Note: There might be slight differences in sizes between brands of tires. The above will get you a good average though.
Le Mans Master
Joined: Sep 2003
Posts: 5,874
Likes: 0
From: Littleton CO
I planned on doing the same thing, but the shop installed four 285/40's instead of the 275/40's I had asked for. Not sure why, but I didn't notice for weeks. They fit just fine and look rather cool up front and the diameter is even less (more?) of a non-issue.
The 285's might still be harder to come by, though. A couple years ago, they were scarce.
The 285's might still be harder to come by, though. A couple years ago, they were scarce.
Pro
Joined: Mar 2005
Posts: 666
Likes: 0
From: Walton KY
I have been running 275/40-17s on 17x9.5 A molds for years with no trouble. Mine is lowered 1.5 inches and in very hard turns my tires rub the hood. I noticed front end push was almost eliminated by the wider fronts and barely noticed the skinnier tire out back....mostly because I was running a cheaper tire with the 275s. (BFG vs. Sumitomo)
Thread Starter
Drifting
Joined: Dec 2003
Posts: 1,493
Likes: 94
From: Westfield MA
I planned on doing the same thing, but the shop installed four 285/40's instead of the 275/40's I had asked for. Not sure why, but I didn't notice for weeks. They fit just fine and look rather cool up front and the diameter is even less (more?) of a non-issue.
The 285's might still be harder to come by, though. A couple years ago, they were scarce.
The 285's might still be harder to come by, though. A couple years ago, they were scarce.
Le Mans Master
Joined: Oct 2004
Posts: 7,706
Likes: 485
From: Everett WA
C4 of Year Finalist (appearance mods) 2019
My 95 (due to the Z07 option) came with 9.5" and 275x40 on all 4 corners so this should be absoluetly no problem for you. Yes you can rotate from front to back to extend the life of the tires.
You can if you want to pay the extra $$ run 285x40 on all 4 corners
You can if you want to pay the extra $$ run 285x40 on all 4 corners
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Thread Starter
Drifting
Joined: Dec 2003
Posts: 1,493
Likes: 94
From: Westfield MA
thanks
Safety Car
Joined: May 2002
Posts: 4,659
Likes: 82
From: Toronto ontario
I have a 95 that came with 8.5" rims up front and 9.5" rims in back and 255/45 and 285/40 tires. I am thinking of getting new wheels that are 9.5" all around with 275/40 tires. Then I could rotate them at least front to rear.
From what I can tell, the 275 tires are 25.7" in diameter and the 285 tires are 26.1
Is this enough to make a difference to the cars computer or speedometer? Should it be reprogrammed? Is the ability to rotate front to rear not a big deal?
From what I can tell, the 275 tires are 25.7" in diameter and the 285 tires are 26.1
Is this enough to make a difference to the cars computer or speedometer? Should it be reprogrammed? Is the ability to rotate front to rear not a big deal?
Burning Brakes
Joined: Aug 2001
Posts: 797
Likes: 2
From: Westminster MD
Keep in mind that GM went to the smaller front wheel/tire combo in an effort to reduce "tramlining", where the car will want to follow the ruts in the road.From 1989 thru 1992 they all came with the 17x9.5 all-around combo. In 1993 they dropped the fronts down to 8.5 unless the car has a suspension package (Z07, Z51)
I regularly switch between a 9.5/8.5 "stock" street set and a 17x9.5 (with 275's) all around for autocross. No computer, ABS, etc problems.
I regularly switch between a 9.5/8.5 "stock" street set and a 17x9.5 (with 275's) all around for autocross. No computer, ABS, etc problems.
Burning Brakes
Joined: Apr 2009
Posts: 1,185
Likes: 33
From: Charlotte Michigan
My '93 Ruby came with the stock wheels of 8.5 front and 9.5 rears with no tires and the wheels that were on it were Z06 9.5's with the 275's on the front and the 285 stock size on the rear. So I needed the rear replaced so I went with the 275's on all 4 wheels. 92 and earlier models came with 275's on all 4 with the 9.5 rims. I don't like the Z06 wheels and hope someday to change to zr1's spoke wheels as my first choice or c5 or c6 spoke wheels 17X9.5's. Along with the economy of being able to have tire rotation from front to rear is a big part of it also.
