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Wheel/Tire Help Needed

allstarcmdr

Member
Joined
Sep 29, 2004
Messages
7
Location
Charlotte,MI
Corvette
1977 Buckskin Tan Coupe and 1987 White Convertible
I have a 1993 vert. , with 17x8.5 frt and 17x9.5 rear wheels. Tires are P255/45zr17 frt and P285/40zr17 rear. A Friend is willing to give me his '99 wheels from his previous vette. MY question is : 1. will his 18x9.5 with P275/40zr18 fit on the rear of my '93 . 2. Should I stay with the P245/45zr17 of his on the frt of my '93 . 3.Would the change to 18" on the rear effect the speedometer calibration ?
Thanks Guys for the info you can give me !!
 

lagasvd

Well-known member
Joined
Sep 24, 2004
Messages
60
Location
Pennsylvania
Corvette
1986 Indy Pace Car
You just need to check the dimensions of the tires. Using the tire size, the first number is the width of the tire, sidewall to sidewall, in mm. To get to inches just divide by 25.4. The second number is the aspect ratio, or the ratio of the sidwall height to the width. To find the sidewall height take this number, divide by 100, and multiply the tire width. The last number is the diameter of the wheel (rim) in inches. To get the overall tire height, multiply the sidewall height by two and add the diameter of the wheel.

P285/40ZR17 are 11.22 inches wide and 25.98 inches tall.
P275/40ZR18 are 10.83 inches wide and 26.66 inches tall.

The "new" tires are slightly narrower (less than 1/2 inch) and slightly taller (just over 1/2 inch). They should fit just fine as far as size goes, don't know about rim offset or lug pattern. Your speedometer will be slightly off due to the different tire height or diameter but now that much to worry about.

Hope this helps.
 

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