Sleeper_08

I've been watching the forum and done some searches but can't find any discussions on the best wheel and tires sizes.

What I am looking for are comments on the best choice for a daily driver used up to four times a year on road courses, both tight ones and long ones (Mosport). I plan to have both a winter and summer set of wheels and tires.

My current plan is to use 18 x 9.5 with 255/45/ZR18 on the front and 285/40ZR18 on the rear for summer. Winter would be 18 x 9.5 with 255/45/ZR18 front and rear and if it really snows I'll take public transit.

The car will be an 08 GT with the 445 HP Roush supercharger.

Thanks.

UrS4

Well if you are serious about the road course thing and you haven't changed any of the suspension stuff, I would stick with the same size tire front and rear so as to keep the understeer to a minimum. Going staggered causes more understeer on the road course and makes the car more twitchy in the corners for snap oversteer.

Depending on your summer weather you should run a max summer or extreme summer tire, like a Kumho MX or something with a tread wear of 200AA. 4 road courses and DD will cause you to wear through tires once a season so figure that into your tire choice. I mean you could go the opposite and run an high performance all season tire with a tread wear of 400AA but you will lose some dry grip but they will last longer.

Sleeper_08

UsS4

Thanks for the response.

My reason for thinking about usingthe larger rear tires was that they would provide greater traction coming out ofthe turns and going down the next straight, especially with the added output of the supercharger.

Later on I plan on lowering the car and doing other suspension upgrades.

Based on this would you still suggest the same size front and rear?

UrS4

All the serious road course guys, like F1Fan, Rodeoflyer, etc all say go with the same tire size all around as it is the most neutral and you have the ability to rotate tires which is key when road racing as certain tracks will cause wear on certain tires (front or rear) and parts of the tire (inside or outside edge). When I had my audi and ran a long course that had more right hand turns than left, I wore my outside shoulder on my front drivers tire and the inside of the rear passenger tire faster and being able to rotate prevents cupping and premature failure. Thus I could run more sessions on the track and more events.

Norm Peterson

Not a simple thing. Withdifferent size tires if you tuneout the understeer with a little more rear roll stiffness you're back to not being able to use the power any sooner, although you might be cornering at a slightly higher speed based on having a little more total grip. I'd expect it to be a little trickier driving up therethough.

If you leave yourself margin for being able to use the power, you'll have the understeer.

Something to keep in mind is all the various fluid temperatures if you'll be running in boost for extended periods of time or with only brief periods of not being in boostand how that might affect your power.

I'd stick with the same sizes and see if there's a problem that needs to be fixed.


Norm

Sleeper_08

Urs4 & Norm

Thanks for the input. The comments about keeping the same size front are rear included things I had not considered. e.g. the ability to 'rotate' front and rear to allow for wear.

Based on the same size front and rear;
1)is 18 x 9.5 with 255/45/ZR18 the optimal size for 18 inch wheels (18" required if I upgrade to GT500 front brakes)
2) what would be the optimal size to replace the stock 235/55/ZR17 to replace the stock all season tires on the stock rims?

Thanks.

Norm Peterson

18 x 9.5 is the widest rim listed as being within the 'acceptable' range for most 255/45 tires. You will get the crispest response and the best support for the tread, though quite possibly the combination could be more sensitive to camber. BTW, that combination is one of at most two options that I'm considering for a car that I have not yet pulled the trigger on, and if it's not obvious at this point, I am a little hardcore about running wheels that are relatively wide for the tires.

I was going to add to my previous post that unless you're running where the rules won't let you run wider wheels,9.5" is a bit on the narrow side for a 285-width tire. I know it's OE on the GT500, but that car is not particularly aimed at the corner-carving market. The Super Snake puts 275 width tires on 10's . . . .

I don't see lots of options on item #2. There are a few 255/50's (8" is an acceptable widththough not particularly wide and supportive for that size - I'd rather see either 8.5's or 9's here), 245/50's (not too many choices either) are slightly smaller but probably of adequate capacity and would be slightly more suitable for 8" wide rims in a handling-oriented application.


Norm

Sleeper_08

Norm

Thank you very much for your response. It was exactly what I was looking for.

Based on your input I'm going to go with 18 x 9.5 and 255/45/ZR18front and rear.

My car arrives mid to late February so by the time I get the wheels and tires organized and installed there should be nicer weather around here to take advantage of them!

UrS4

I will comment on the stock wheels and optimal tire choices.

I would go with a 255/50/17 tire. 8" is optimum for that width tire. There are fewer choices at that width and the price goes up but there are some good tires that come in that size. The bridgestone pilot all season tire is quite good, probably better thansome summer tires so that is one possibility. There are others, you can check popular tire sites like Tirerack.com and discounttiredirect.com etc. etc. and read the reviews that pertain to S197 owners.

RodeoFlyer

245/45/17 is great. There are lots more options and at a lower cost. You wont miss that 5mm I promise.