typesredline

Hey guys. I don't put a ton of miles on my 2013 GT, so I am just now becoming due for her first set of new tires. I already know I'm going with extreme contact sports. But the size is another question.

If I stay square, I'd do 265. I want to stick as close as possible to the stock height of the brembo set up. And want to keep the brembo wheels. So going 275 is A just barely fits the wheels and B too big for the front imo and would affect turn in.

That said, I'd like to supercharge her within this new tire sets life. I already have terrible traction as is. So even though the new tires are a billion times better than stock and slightly wider. With 550ish whp, I'm pretty sure 265's won't cut it. So my thought was to get the 10" brembo style wheels from AM for the rear (pc to match) and run the oem 255/40 up front and the almost identical height 295/35 in the rear. I think that would give me enough traction.

But my concern is going staggered. What else needs to be done to get the neutral handling back? Bigger rear sway? Or do you think that tire in 265 would give sufficient traction when supercharged?

Bert

I think the 265 in a real sticky tire like Michelin Pilot Super Sport would be pretty good but still probably will spin fairly easily with the supercharger.

The "neutral handling" really only matters when you are at the limits of cornering capability and the car starts to either push (understeer) or spin (oversteer). This almost never happens on the street unless you are way beyond the limits of good judgment. As long as both ends are still stuck it really doesn't matter.

But yeah a stiffer sway bar out back supposedly can bring it back into balance.

The other consideration is tire rotation; can't do it if staggered.

EF1

Staggered vs square usually depends on personnel preference and intended use. People who road course tend to stay square, while the drag racers are more likely to go staggered. I have run 275/40R19 on my stock Brembo wheels with good results on the street. They have done okay on the track for a novice driver (me), but I am starting to out drive them. The last time out I was starting to get some sidewall roll. I just went to a 275/35r19 set up on 10" wide wheels. They are a little shorter than the stock tire size, but not much. I have only put a few street miles on them so far, but like the feel for far.

The staggered set up will lead to some understeer which you should be able to correct with suspension set up. A lighter front or heavier rear sway bar should correct it.

Siber Express

275/40 19 square on mine, the only effect on turn in is 1.21 to the left and 1.17 to the right on the G Meter before it breaks loose, and that is the rear not the front, the Continental D/W's stick pretty good.
BTW the 275/40's are the same height as the CS/GT 245/45's.

typesredline

Good point. But I'm not to worried about rotation. I haven't ever rotated the stock tires. To little usage. Currently, the tread is fine. But they're beginning to dry rot 😂. I do about 2-3k miles a year. Unfortunately this isn't by choice. I have a daily driver that is very much needed in what I do.

Ideally I'd like to do both. But even if I did, overall use would be 90% straight line stuff. I remember reading your post about the side wall roll. I want a good amount of tire on each side of the wheel. So if I went over 265 it would be on wider wheels.

Any suggestions on which rear sway? There's so many. Adjustable. Non adjustable. Etc.

Yeah I'm a big fan of the extreme contact tires. Keep in mind these would be the new(ish) sport which replaced the DW's. They crush them in all categories and test slightly better than the PSS's but not as good, or expensive as their successor, the 4s. Also the brembo's run 255/40 which are 27" tall. 275/40 ends up .75" taller. I know ppl do it. But I want them the same. 265/40 is .3" taller than stock. But if I went staggered, the front would obviously be the stock height, and the 295/35 would be .1" taller.

typesredline

I think I'm leaning staggered for the extra meat and look.

So I think my follow up question is, would you guys see any issue with the spread of 255 front and 295 rear. Also like I asked above, which rear sway would be recommended? Could I just do the boss 302 rear since that had a 255/285 staggered set up?

TheReaper

The AM Brembo wheels that I have seen are not the same color as the factory wheels.

laserred38

Nor do they fit the factory center caps.

FWIW, I'm running 295/305 MPSS and even with TC turned on, I still have lots of wheelspin in 1st and 2nd, set to 30psi. And I'm only about 420whp, N/A.

EF1

That is what is fun about modding these cars. There are so many choices that you can make it your own. The 255/295 staggered looks good in my opinion. I would go with an adjustable rear sway bar to allow you to tailor the handling to your liking. I have the Steeda competition adj sway bars on both ends of my car. You will play with them a little in the beginning. Once you figure out what you like you will leave them alone.

typesredline

Correct. They make a charcoal in 18" and the 19x10 that I'd be getting are black. I have a local powder coater that will make them match the oem gunmetal.

I'm fine with the all black center caps they come with. Wheel spin with 305's and NA is interesting. I guess even with the 295's I could expect some spin once supercharged. But I'm sure it would be much less than with 265's right? Because if the difference in width is irrelevant with that much power as in they'd both equally spin the same, it's easier to just stay square at 265. Being that I wouldn't need new wheels and powder coating and sway etc.

laserred38

If you like your stock wheels, I'd just stick with them and do your square setup. I ran 265/40 square for a bit on stock wheels and I think they were the perfect size for our cars. The unfortunate part of it is it's not a common size, so if you need a replacement immediately, it'll have to be ordered. I think that's why Ford went a little smaller with the 255/40s. 275/40s are very common but I ran those for a bit too and they're just a little big for the stock wheels.

If you're set on going bigger, I'd just get 4 all new wheels of a different design so you feel like you made a substantial change. Maybe some RTRs or 6GRs, 19x9.5 or 19x10 all around and 285/35s.

typesredline

Well that's just it. I want it to look like I didn't make a change at all. Plus I'd rather only need to buy 2 wheels. Not too worried about availability since I have the second vehicle.

Would the 265's supercharged be useless? That's honestly the only reason I'd go with 295's in the rear is for more patch. But if they would still spin a ton, it wouldn't be worth it.

Gabe

Traction is more dependent on the tire compound, not so much the tread width.
You have cars launching front-wheels-in-the-air on 275's because of the tire compound and construction.

laserred38

This...

typesredline

Interesting. So you're saying that a tire like the EC Sport in 265 will hook as well (or as poorly) as the same tire in a 295?

5.M0NSTER

So the question really is what tire compound do you want to use? I mean for the street use of a mostly NA 5.0, 265 Conti DW will do just fine. You add 150hp with a blower and I would want to go as wide as possible and as sticky as possible.

laserred38

FWIW, Roush puts 275/35/20 Continental Contact Sports on 20x9.5s on all Stages of their Mustangs, including the supercharged ones.

Bert

The size of the contact patch and the compound of the tire both matter.

The contact patch thing is a little confusing because technically it is the same for the same tire pressure regardless of the width of the tire: total contact patch area ~ (weight of car, lb) / (tire pressure, lb/in^2). As the contact patch gets wider, it also gets narrower to yield the same area. So theoretically the only way you can increase the contact area is to reduce the tire pressure.

But for practical purposes the width does make a difference; that's why the track guys are constantly trying to get the widest wheels and tires under the car that they can possibly fit. I can't explain exactly why, but believe that the 305's or 295's are going to transfer more torque to the ground without breaking traction than the 265's, all else being equal (same compound).

typesredline

Good info guys. Thank you.

759Rider

Also remember contact area increase (or decreases) as a function of diameter as well as width. Longer contact patch vs. wider contact patch.

I haven't done the math to figure out how (for example) a 1/2" increase in height affects contact patch vs. 10mm of width, but it would be interesting.

Here is a sweet little calculator that will do the work for us:
http://bndtechsource.ucoz.com/index/...alculator/0-20

What this shows is that my 275/40-19s have a slightly larger contact patch than a 285/35 of same diameter. You can do the same math for any size tire. It's really a fun little app.

Check it out.

:-)