sms302

I have a 2012 GT that has been lowered about an inch but otherwise has stock GT wheel/tires and brakes. I have started doing track days and need something better than the OEM 235/50/18 P zero neros.

I am going to stay with 18 inch wheels due to cost and and availability. My questions as to my various options are as follows:

1) If I keep the stock 18 X 8.5 wheels, what is the biggest/widest (reasonable) tire size?

2) If I go with a dedicated set of mounted track tires I could go to a 18 X 9 inch wheel, what is the biggest/widest (reasonable) tire size?

3) I have been told that 2008 and 2009 GT 500 18 X 9.5s wheels will work on a 2012 GT, is this correct, and if so, what is the recommended tire size?

4) Finally, what is the real world difference between the tires I could put on a 8.5, 9, and if they would work, 9.5 inch wheel? In other words, since cost always matters, where is the point of diminishing returns, while I should get a big bang for the buck going to sticky tires, how much bang is there in the increasingly wider tires for an amateur on a road course.

Entaille

I don't understand why you'd even want to spend the money on an upgrade for half of an inch of width.

truthfully, you could keep your stock wheels and get a sticky summer tire instead of those all season tires, and you would notice a hell of a difference. tire compound is a huge factor, you'll be amazed once you swap to summer tires. how many times have you gone, are you still improving your lap times or are you hitting a wall? if you aren't hitting a wall .. burn those tires down to no tread, no sense in wasting them.

yes, the 18x9.5 GT 500 wheels will work on your car. there are a lot of wider, affordable wheels for your car actually, http://www.americanmuscle.com/2010-mustang-wheels.html carries a lot of them. you probably won't need more than 275 rear tire unless you increase your power - I would draw the 'cap' at that point. you need to decide if you want to stay with a square setup too or if you want to go staggered.

sms302

Thanks, and you have hit the nail on the head, I don't want to spend the money on a marginal upgrade, and so am trying to figure out what is worth changing.

I am not hitting the wall yet at the track and could keep the OEMs on it for awhile, but since I will presumably hit that wall before they are worn out (they are basically new), my thought was to switch to a soft summer tire and keep the OEMs for trips or bad weather (it does rain and sometimes snows at track days). And so then the temptation is to say that since I need another set of wheels I might as well go to 9 inch if that would give me meaningful improvement. But if say, a 255 summer tire on a 8.5 wheel is enough of an improvement over my OEMs for the foreseeable future, I can pick up factory take offs even cheaper than the reasonable prices for 9 inch aftermarkets. But if going up to 275s really helps, I would go with the 9s. BTW, I will keep it square.

UrS4

Several observations. I can tell you have a non-track pack and non brembo car. You will not hit a wall before you go through one set of tires and tires will not be your first wall. Abilty will. Brakes will be your first wall if your ability continues to improve.

Cost is always an issue but it depends on you as to whether a return (improvement in lap times, driver confidence, and overall fun) is diminishing.

So in my opinion, the things that are going to improve your laps times are going to be:
Driver mod
Driver mod
Driver mod
Better brakes (beit pads, bracke ducting, BBK, etc)
Driver mod
Stickier rubber
Driver mod
I think you get my point.

Now with all things being held constant (ie driver mod, brakes, etc) and the only thing that improves your lap time is purely related to tire compound and tire width, the point of diminishing returns is only something you can decide. For example if you say the point of diminishing returns is spending more than $100 dollars more in better tires for less than a 2 second improvement in lap time. For someone else, it might be spending more than $200 more in tires for every 1 second in improved lap time.

I would argue that on a road course, a 275 to 285 wide tire is plenty and would still yield an improvement in lap times before the weight of the tire and the increased weight of the wheel (implying you would be only using a stock Ford wheel) would negatively impact your overall straight line speed or lengthen your braking zone (due to increased unsprung mass overwhelming your stock brakes)

Now as far as what tire width you can use on a stock 8.5 wheel, you could easly go to a 255/45/18
A 275/40/18 will fit on a 9 inch wide wheel
A 285/40/18 will need a 9.5 inch wide wheel for road course use, you could probably slap them on a 9 inch wide wheel and be safe on the street.

Go to tire rack and you can see that there are recommended wheel widths for each sized tire. For every 1/2 inch decrease in wheel wide from the recommended value, the same sized tire will be squished and the contact patch narrowed. Conversely, for every 1/2 inch wider, the contact patch will increase. For example, the contact patch of a 275 tire mounted on a 9 inch wide wheel will be very similar to a 255 tire mounted on a 9.5 inch wheel.

I would recommend a cheap 9.5 inch wide wheel like a GT500 wheel with a sticky 200 UTQG rated 255 wide tire. Those wheels are cheap and the tires are cheap at that size too. This way as you could go with a wider tire later if you find you are willing to pay more for those improved lap times.

eolson

My stock wheels were the 06' 8.5x18 bullits, and I put the max size of of 255/45/18 summer Goodyear F1 eagles on them, and being Supercharged to 435HP, they power gripped great and cornered great for that level of power. I'd keep your stock wheels and go with quality 255/45/18's (height diameter 27", your stocks are 27.2") all around. Erik

Norm Peterson

As mentioned, 255/45-18. Expect a little more ultimate grip but slightly "softer" cornering response than what you're accustomed to.


I can think of only two situations where going only half an inch wider makes much sense. Either you are competing in a class that has a 9" maximum wheel width restriction, or you like the appearance of the 9 enough better to write the cost off against appearance preference. I think a 275/40 is a legitimate fit, but is awfully wide for 9". Personally, I wouldn't go past 255/45 here.


You can legitimately run 255/45 (the GT500 front tire for those years), 275/40 (several folks run this even though 9.5 is not all that wide for this size tire), 285/40 (GT500 rear, may or may not rub if you try to run this size up front), and 295/45 on the rear only (if you don't mind "taller). There are other sizes (such as 265/40) if you don't mind having a slightly shorter tire.


I think that ultimately comes down to specific tire availability in each of the various sizes.

If it matters any, I'm running 255/45-18's on 18 x 9.5 GT500 wheels for three seasons out of the year. Goodyear Asymmetrics. They've seen a track day and some autocrossing.

I'm considering 275/40's next time around or for a dedicated track tire/wheel package - but I'm looking pretty hard at getting a set of 18 x 10's if I do.


Norm

sms302

Thanks everyone, I think my take away is to not go crazy with tire/wheel mods, I can either do nothing and run my OEMs down to nothing, which is of course the cheapest and easiest solution, or alternatively, put 255/45/18s summer tires on my OEM wheels. Then, if my ability and continued interest level warrant it, I can always get wider wheels and correspondingly wider tires later.

So, to throw out a controversy bomb, what is everyone's opinion on which 255/45/18s tires to buy, bearing in mind that unless and until I find extremely cheap factory take offs I will stick with one set of wheels. Car is not DD but does see some street use.

UrS4

Goodyear F1 supercar are relatively sticky and pretty cheap.

Entaille

http://www.tirerack.com/tires/survey...=true&filter=y

if it's helpful in your decision.

sms302

That chart is incredibly helpful, and was not something I was just going to bump into at the tirerack website.

I have multiple votes for F-1s, and seems like a good bang for the buck. Local mustang tuner loves Nittos, anyone have any experience with them, in the size I am talking would be the NT555s?