JRev

Hello, I'm currently running 245/60/R15 tires with the standard 15' rallye wheels. I was thinking about putting some bigger tires in the rear and was wondering whats the biggest tire that I could fit in the rear without modifying anything in the back except for potentially a bigger wheel size.

Fun71

You can fit some monster sized tires back there, as long as you have the correct wheel backspacing. 295-50-15s fit without any issues (with 5.5"backspacing if I remember correctly - do a search and there should be lots of posts about this) and Brian Trick had some even larger tires on his car.

JRev

Awesome, thanks!

vette442

My V Code '72 Supreme had 305s on it when I bought it in 2002. Scroll down on my website page for a picture of them....

http://highoctaneauto.com/newpage17.htm

Terry

JRev

Looks good, I assume those are 15x7 SSlll wheels?

droptopron

They can't be. A 305 would need a wider wheel than 305.


People have run 275/60 on a stock 7" wheel. I don't like the look (too ballonned IMO) but to each their own.

JRev

Quick question, is there a conversion or way you can determine how wide of a tire will fit on a certain wheel?

Smallhurst

There is not a true chart, but basically you do not want to go over 2" wider than the rim. 1.5" is better. I know guys that can do 8" on a 275 and that looks okay. 9" looks better.

JRev

Sounds good, thanks!

oldcutlass

The tire manufacturer has wheel width recommendations listed for every tire in the specs. These are recommendations and small deviations have been acceptable over the years.

oldsmobiledave

You can't choose a tire size without a discussion of rear axle ratio. If your car has 2.56 or 2.73 gears & you put a 275 60 15 out back you will HATE it off the line if you have a stock SBO.


What is your rear axle ratio?


Now we need to talk about what is under the hood. If it is a 350 2bbl forget a 28" tall tire. If you have a BBO you can turn the 275 60 15 even with 2.73 gears.


Consider your power output & gear ratio before you pick a tire size.

JRev

So it is a 1972 Cutlass Supreme with a stock 350 4 barrel, I am unsure of the rear end, its most likely one of those two, but I have no idea on it specifically. I see your point of the performance issue, can I increase the tire size at all without affecting performance too much or should I just stick with my current 245/60/R15 setup? I just want to give it a more beefy look in the rear like oldschool drag cars. Thanks!

JRev

Sorry, what is a BBO?

oldsmobiledave

BBO = Big Block Olds.


Most likely your car has 2.73 gears. Consider a 255 60 15 tire. it is a good fit on a 15 x 7 rim & fills out the wheel well nicely. Any taller tire & your off the line acceleration will suffer badly.

JRev

Thanks for the advice!

foren6doc

Hello everyone. Once again, I have a quick tire fitment question that I hope the experienced can answer for me. I have a 1971 Cutlass Supreme convertible that I would like to install some different wider tires on the back for much better traction. The wheels that I have are the old vintage American Racing 200S Daisy wheels that measure 15" X 8.5" with a backspacing of 3-3/4". My question is, can I run the Mickey Thompson 3753R Drag Radial tires that are 275/50R15. These tires have a section width of 11.3" and tread width 10.5" and the overall diameter is 26.1". I am worried that the tires might rub on the inside of the rear fender lip. I would like to buy a pair of these for the rear since they are on sale right now and I also need the better traction that the drag radials can offer.


Let me know what you folks think. Will they clear with this backspacing?