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Tire Air Pressure


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Just bought new shoes for my 07SGT, ended up with Michelin Pilot SS.. 275/35/20 Rear, and 255/35/20 Front.

 

The tire shop that did the install recommneded that I inflate to 48psi all around, not to exceed 51 psi. This is the highest tires pressure that I have ever run.... In any car.

 

Driven a few miles so far, and the tires themselves are fantastic, i like them better than the original BFG KDW's. Grip in amazing, corning is fantastic, and much smoother.

 

Releative to the tire pressure, just interested in what the advantages/disadvantages would be to running this high of a pressure..

 

The thinking of the shop guys was that this would give me better longevity and tread wear, especially since I cannot rotate them.

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My sense is you will wear the centers of the tires with that kind of pressure. Did you get a second opinion from anyone? Those are pretty extreme pressures. When I am not able to bring my track tires and run street tires on the track (255 front, 285 rear), I run 39 psi front and 36 psi rear (measured hot) and I arrived at those setting for my particular car after a ton of experimentation at the track. I will be interested in what others have to say.

 

Jim

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In my opinion that is way too high. That sounds like the max pressure for the tire. I have the razors on my car, 20's, an i run 37 psi all around, since you have a wider tire in the rear i would go up to about 40 in the rear. This is what i have found works well for that type of setup in my experience. The other guys are right though, the only benefit from running that high pressure is slightly higher mileage, but you have the potential to wear the center of your tires quicker. That's my 2 cents.

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Same old screed: You have two manufacturers involved, each with slightly different motives. The car folks want you to run 32 PSI all around, and they hope the slightly rough ride of a Mustang will be somewhat mitigated by (relatively) low pressures, so first-time walk-on-the-lot shoppers will not be put off by having their teeth rattled when traveling over modern pot-holed roads. The tire folks pretty much say (but not in so many words) "Go with what your manufacturer recommends". That keeps them kind of liability-free, in a way, and according to your installer, keeps you coming back for more tires more often.

 

Higher tire pressures are actually necessary for high-speed or heavy-load uses. The "Maximum" pressure numbers are referenced to load capability. Tire Rack has dozens of semi-technical articles that cover this kind of thing, including how many more pounds pressure for however much faster or heavier you are going.

 

There is a little support for higher pressures in larger-diameter tires: those twenty-inch rims might be a little less likely to get bent if a stiffer tire distributes some of the sharp impact loads around the rim rather than let the rim take a concentrated blow which could certainly cause a failure of integrity.

 

For my part, street tires on track are inflated like Jim said: 39-37 hot, 285-40s on square 18x9.5 rims; street uses I like the fronts just a bit higher than the backs because of the sense of quicker response, so they are usually 35, while the rears are 32 for comfort. I don't care that much about MPG numbers, but I do raise everything by three pounds if I'm traveling for more than a couple of hours at a time.

 

There is a sticker out there, may actually be a legitimate GT500 item, that says something to the effect that if you plan on driving at more than 120 MPH for extended periods it is important to carry 40 PSI in your tires.

 

You'll get all kinds of advice from official and not-so-official "experts"; all you can do is weigh the evidence and opinions, and do what seems best to you. As a long-time car user and tire-wearer-out, I recommend you start with the car manufacturer's recommendation and work from there. Something, some combination of pressures, uses, and expectations will strike you as right, and you'll be happy.

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Thanks for the great advise, the consesus seems to be this is indeed too high. I did notice in the brief ride that I took, that the rear of the car seemed to possess a few more rattles with the 48 psi pressure.

 

I may try to step the pressures back down, perhaps in the 35 - 40 range, and see how she feels.

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At the pressures your running, according to the Michelin website each tire has a load capacity of 1400 to 1600 lbs! Seems extreme to me. It appears that if you ran 32 psi in each tire you'd be fine. If it were me that is what I'd do. Tire dealers and car dealers typically over-inflate.

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My sense is you will wear the centers of the tires with that kind of pressure.

 

 

Ditto.

 

Not only that but high tire pressure WILL increase your stopping distance, and especially with ABS.

 

48psi is HIGH, I don't care what size tire you have on the car. I'm assuming the 51d you say the dealer mentioned is the MAX tire pressure with the MAX load, as listed on the sidewall??? Take that load weight and you can determine what pressure to use if you know the weight on *that* particular tire.

 

Are the tires the same size as what came on the car? If so, the sticker on the B-pillar is what you should go with. Even if not (I assume NOT because they are 20's) I'd stick close to the mfgr's. recommended tire pressure.

 

I'd have to double check but I think my 2010 GT500 recommends 36psi (COLD) but it's a little heavier than your SGT if I understand right.

 

I know when I drop my 18" KR tires down to 20psi my traction increases tremendously. But I don't want to wear the outers out so I keep them at 32psi (what the KR B-pillar label said).

 

High pressure will wear out the center of your tread faster, low pressure will wear out the outside tread faster.

 

If you have a IR thermometer you can take a ride down the freeeway for a few minutes than check the temp across the width of the tread. It should be EVEN all the way across. If it's hotter in the center, you're overinflated. If it's hotter on the outsides, you're under-inflated.

 

I set my grandson's car up *strictly* by tire temps and that's where I'd get our best times (asphalt oval tracks). Even temps across each tire with 6 degrees hotter Rt. Front (SLIGHT push).

 

 

Phill

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