I was thinking of putting C5 wheels on my 86 TA. I know that the stock tire sizes for the rear are 275/40/18 but i wanted to try and use 295/35/18. Is this too wide and will they stick out too far? Any objections?

 

it won't handle as well plus the less sidewall makes the tire look too small for the car

 

Don't forget that you need adapters to put C5 wheels on there, not sure what size though. I had C6 wheels on mine and needed 2" adapters for those. 295's should fit but you'll have to do some hammering. For the big wheel/small sidewall to look right you def got to lower it 2-3". Later.

 

Youll do some hammering to fit 275/40/18's in there with a 2" spacer

Just around the LCA front mount, nothing major

 

Unless there are some clearance issues with 18s that aren't present with 17s, the 275s will fit fine on the rear. The 295s would interfere with the area around the bumpstop in the fender wells. Also, if the backspacing isn't just right, the tire might rub on the outer lip as well. That's about the only thing I'd be worried with. If you already have the 275s on the back, the 295s might change the balance of the car's handling since it would (theoretically) have more grip in the back.

 

Installed the the 275 40 18's today with 2" spacers. Fit perfect! No rubbing or alterations needed. Thanks for your help.

 

Something I hadn't thought about earlier, but that wheel/tire combo is about an inch taller than the stock would be. Your speedometer will be reading slower than your actually going. I think the correct size for the speedo to be as accurate as possible is 275/35R18.

 

10mm is .3937", nowhere close to an inch

Ive paced my 275/40/18's against the "Your speed is:" signs and its accurate to my speedometer

 

where did 10mm come from, and yes the tire combo is 26.7" our speedos are callibrated for 26" when his speedo reads 60mph it will be closer to 61.6 mph, i think, not too bad

 

The second number isn't in MM. It is the aspect ratio of the width of the tire to its sidewall height. ie: a 275/40 will have a sidewall of .40x275= 110mm while a 275/35 will have a sidewall of ~96. It's not quiet an inch figuring it that way (40 vs 35), but I got my number of 1" from this tire size calculator. It shows a 275/40R17 as 25.7 while a 275/40R18 is 26.7. The 275/40 has a 110mm sidewall and you are putting it on a wheel that is 1" larger in diameter, so it will be taller than stock.

I guess I should have said it will be off a little- something like 2-3mph @ 60. But the faster you go, the more it'll be off.