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Tire Pressure Do's and Don'ts


A lot of guys think they know how to properly fill aftermarket tires to the right pressure, but it amazes me how many so called "mechanics" have NO CLUE how to determine the correct tire pressure for any given vehicle with other than stock tires on it.

Here's the deal, with different tires than came stock on your vehicle, you should go by what the tire manufacturer says for how much pressure should be in it, not what the door sticker says. That door sticker has NO WAY of knowing you changed tires and wheels, and no way of knowing what KIND of wheels and tires you changed to!  In most cases it should be around 5 psi or so lower than their recommended max to give a better ride (not so stiff or bumpy) and to ensure the center of the tread doesn't wear out. Too low of a tire pressure will cause the outer edges of the tire to wear, beside the point that too low of a pressure can (and often does) cause a blow out, which can be deadly at freeway speeds and it will make your car sway and roll in corners as the soft sidewalls flex. But then again, there are times when you WANT very low tire pressures for some driving, such as 4 wheeling, mud or rock crawling, drag racing, etc.

Let me give you an example to prove my point; Let's say you have a 68 Camaro and the door sticker says the factory tire pressure should be 32 psi, but you decided to put-on a set of cheater slicks. Are you going to look at that sticker and shove 32 psi into those soft / sticky tires when you hit the race track?, or are you going to look at what the tire manufacturer recommends putting in it? If you put 32 psi into a set of slicks, (or even street legal DOT cheater slicks) like that, they'd be as hard as a rock and would bulge the center out, causing you to lose about half the footprint they're supposed to have. We don't run 32 psi in race slicks. Normally we have about 7 - 9 psi in a full race slick, and 10 - 15 psi in a DOT cheater slick (on average). Set them at what the door jam sticker says and you'll be riding on overinflated balloons and will have no traction what so ever.

Think of it like this; when I build a monster engine for a guy's car, should he go by the factory manual for how much, and what kind of oil it should have in it, and for what kind of spark plugs to use and what the timing should be set at? Hardly. Replacing your factory wheels and tires with aftermarket one's is no different!

A tire will never blow out by being fully inflated (shy of running over a nail or something). What kills most tires and causes most blow-outs is not having enough pressure in them. This is why when you drive down the freeway and you see big chunks of semi truck tire in the road, that is from UNDER-INFLATION which caused too much sidewall heat and the tire separated. When the tires aren't aired-up enough, the sidewalls flex. The faster you go, the more they flex. Flexing causes heat. Heat causes things to get soft and break down. Take a piece of steel coat hanger and bend it. No big deal... you can bend it. Now bend it rapidly over and over again. By about the 20th time you bend it rapidly, the hanger breaks in two. That was from flex friction. Tire sidewalls do exactly the same thing when they are under inflated. They get hot, weak and come apart, especially if they are carrying a heavy load. 

Of course you don't want to over inflate either or the ride will be harsh and bumpy because the tire gets harder the more you inflate it, as well as the tread area "bulges" and will cause the center to wear out quicker then the edges. In most circumstances try running about 5 psi or so lower than max listed pressure for normal driving. This will give you a good footprint, good traction, and a decent ride without the risk of having a blowout.  If you want a smoother ride when you are done carrying that heavier than normal load, let about 5 psi or so more back out and you should be good to go again for everyday normal driving. Obviously vehicles vary, as do tire sizes, load ratings, profiles, sidewall thicknesses, etc, so use this as a simplified guide to the overall picture. 


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