I currently have 17" x 9.5" C6 wheels on all four corners with 275-40-17 Cooper Zeon tires. I would like to get some wider tires to handle the power of my new motor.
Two questions.

What is the widest tire I can get on my 17" x 9.5" wheel and still get the same OD as my existing tires?

If I get a pair of 18" rims, what is the widest tire I can get that while maintain my existing OD?

 

By "handling power" I guess you mean off the line.
In this case, wider isn't better because you'll get a shorter/stiffer sidewall which creates more tire shock. Try going to a softer compound.

 

Yeah, I am speaking about off the line using street tires. I completely understand that stick DR's will do the trick at the track.

 

You don't necessarily have to run DR's. Some street tires are softer than others too.

 

Going to a wider tire does not have to make the sidewall shorter/stiffer. A 285/40-17 would have a slightly taller sidewall than a 275/40-17. While the 285 diameter is slightly greater, it is still within the range of the stock tires used on the V8 4th Gens. And a 315/35-17 (which won't fit correctly on a 9.5" wide wheel) will have the same sidewall height as a 275/40-17.

 

It appears that if I run 285-40-17 then I will gain around 3/8" more tread width over the current 275-40-17. Of course it will also be about 1/4" bigger in diameter too.

 

You have to look at the exact specs for the tires you plan to buy. The tread width is not specified anywhere in the tire "size", and can vary all over the place. If you look at all the 275/40-17's available, I suspect you would find that while the sidewall dimension varies only slightly, the tread width probably varies by almost one inch from the narrowest to the widest tread. There are 285's that have narrower tread than some 275's.

And, tread width is not the only factor determing traction. As noted above, hardness of the tread compound, tread design and all the other factors that go into the tire's design will affect traction. Again, you will find that some of the highest rated tires for dry traction are not necessarily the ones with the widest tread.

Tire diameter will also vary slightly for any given size.... the overall diameter for a 275/40-17 will vary by +/- 0.10". A "large" 275 may not be too much smaller than a "small" 285. Theoretically, its a 10mm (0.40") difference in diameter between the two, but theory and reallity are not necessarily the same.

 

Injuneer, thanks for the responses.

I am staying with the Cooper 2XS Zeon tires since they have worked very well in the past. All other things being equal the 285 should be a tad wider than the 275 according to the calculator which may make better traction, then again may not. I imagine it cant hurt to try.

 

injuneer, I am facing the same type delimma. I have a 400 rwhp 383 with a built trans and 9inch. I am going to get some new wheels/tires and really need traction. This car sees time on the road in good weather but thats it. I want to be able to hook up the best I can without a slick. My thoughts are 17x11 zr1's with ? or 17x9 zr1's with ?. Or even some 18's in the rear with ? I heard et streets are the deal but don't see anything bigger than 275/40/17 although nitto seems to make more size options. Any input you have would be of great value.
Thanks

 

if you want better traction, id suggest a better tire. sure youve had good luck with the coopers, but try something higher on the food chain and you will see

 

I have cooper zeons and can spin them till my 94Z could get a collector plate! If one was faced with the decision of 315/35/17 dr on 17/11 rims or 285/40/17 on 17/9.5 what would you choose knowing a priority is straight line traction?

 

I guess I am confused by this statement.