tire pressure

I would say check the tires and depending on what type of ride you want and your driving style fill accordingly. I run 40 PSI in my tires, but i would rather have a more stiff ride and better gas milage/tire life then having a plush ride and less gas milage and have the tires wear out faster. I have heard people running anywhere from 26 to 41 PSI.

At 40 psi you will be getting better mileage but you are going to run the inside of your treads off way before the outside. I cannot see how you can get increased tire mileage that way. The tradeoff of better gas mileage over tire life may make it worth it at today's pump prices, but you have to be experiencing a much rougher ride.

There is a trick you can do to determine precisely how much pressure to keep in your tires for your particular vehicle. It will give you the best tradeoff possible between mileage, tire life, and comfort. Make sure you use an accurate tire guage so that once you learn this pressure you know it is correct.

With a cold vehicle and cold tires, air them up way over pressure. 40 psi would certainly be there. Take a chalk and mark a chalk line sideways across the tread of a front and rear tire. Drive your vehicle several yards (30-60 or so should do it). Now look at the chalk marks.

You should see the inside of the chalk marks worn off but the outsides should still be showing. In other words, the bowed out overinflated tire was wearing the middle of the tread and not touching the outside of the tread.

Release a couple of pounds of pressure from the tires and repeat the experiment. Continue until the complete chalk marks wear evenly. (You might want to lose another pound to make sure the entire tire is bearing down across the tread once the entire chalk mark disappears at the same time). You have now determined the tire pressure at which you are keeping the entire tread on the road.

Under this pressure you are wasting available fuel economy, generating excess heat, and prematurely wearing the tread. Over this pressure you will get better mileage at the cost of comfort and decreased tread life. Keeping at this pressure will wear the tire evenly and thus extend its life to its greatest extent and offer the best compromise possible between gas mileage, comfort, and safety (you'll have your whole tread on the road). The pressures may be a couple of pounds different between front and back for your particular vehicle application.

A caveat: this needs to be done on NEW tires as soon as you buy them. If you have already logged 25,000 miles on overinflated tires all you will be doing is verifying the exceessive pressure you have already been using (in other words, the chalk line will wear evenly even though the middle of the tread may be quite a lot shallower than the outside tread).

[Edited by GJarrett on 11-30-2000 at 07:18 AM]

hey, thanks for the info...i just got new tires TODAY and i'll be doing the experiment TOMORROW...lol :exp: i had to try the new icon i love these guys ok, enough grr

One thing to add to Gerald's response:

When you drive with the chalk line, drive in a straight line (no turns.) Since turning puts the tire in a funky position, the chalk will wear off differently.

Good Advice but...

All good advice from the folks above but do yourself a favour Minek. Swap those (Firestone?) Wilderness pink pearls for a set of better rubber. Shredded one on a tame logging road and bent the aluminum wheel. Add money and stir. If you live in the land of wind and rain like I did on the We(s)t coast of British Columbia and drive on those tires, you could end up with a trophy for "Best in class" in unlimited hydroplane. Bin there, done that on a blustery day a couple of years ago on a wet road at 80kms/hr (50mph). Drove into the tire guy (he lived..yuck, yuck) and put a set of Michelin XCX/APT's or others on. Huge difference. Could save your life.

Cheers

I have 10,000 on my tires and they seem fine. The tires are wearign pretty eaven;y, but the front end of my Explorer does need an alingment so thats the only thing. The rears are wearing very evenly and the centers seem ok...the tires say 41PSI cold rated pressure on the sidewalls so thats what I have run...on our ford van the tires were rated at 50 so we ran 48 and the OUTSIDES of the ries still wore more then normal. I thought the high pressure would prevent that...oh well...my tires are fine except the the alingment issue, but the shops say no alingment till ther ball joint is fixed and I can't fix the ball joint for a few more weeks. ALso I tried that chalk thing beofre, but I was in a driveway and it was too small so I gotta go out on the back roads and do that test. personally i wouldn't run less then 35 PSI because I find that the sides bow more...(especially on a tire with soft sidewalls) i have BFG Long Trails and they are a pretty tough tire in terms of rigidity and they have a LONG treadwear.

That makes sense. I don't run nearly as much (28 psi) but I have the BFG AT's with a triple ply sidewall and they are way oversize. I can't remember but I think I was running 32psi on the stock Firestones.

On my 98 XLT the sticker on the end of the drivers door says to use 26 psi front and back. I find this hard on the power steering pump, but the ride is smooth. I found that 30 psi front and back works good for both ride and ease of steering.

Also keep in mind that tire pressure increases with temperature. The tire wall usually has the maximum pressure rating. Most of the time, it does not state that this is a cold max pressure. Since it is very hard to know how hot the tires will ever get (asphalt in the summer), it is always a safe bet to run much lower than the max. Over-inflation could be the cause of tread separation on the ATX tires. I see a lot of vehicles with the AT style Firestone tires including Subaru's Forester. I sure hope that Firestone is not selling "a bill of goods" to all of these car manufacturers. So far the AT's I have are wearing fine, but as they age, they seem to be getting noisy in town.

I still see ATX's in parking lots, but I have only seen them on older Explorer's, interesting. I know that Ford went from Firestone ATX's to Goodyear then back to Firestone AT's in 98. Anyone remember the "Firestone 500" tire days?

Anyway, enough rambling, 30psi works for me.

uh

I'm not trying to get into an i-know-it-all contest on tires here, but i just wanted to say in response to GJ's chalk line idea (good idea btw) that from my (limited) experience with tires, the entire width of the tire doesnt/shouldnt contact the road...just a small oval called the "contact patch" does so.
It sounds like the idea would work great on all but radial tires...though maybe someone worked it out and making sure the entire surface contacts the road at cold pressure and no speed works out to the right pressure for the best "contact patch" when actually driving..i.e. tires spinning. Just a thought I had.

i dont think thats true. Tires dont ride on a small oval, they wouldnt get enough traction. Just like racing slicks, the more surface area, the better grip of the road you have. Same would go for offroading, the more grip on the dirt you can get, the better.

Maybe I'm wrong, but isn't the tire pressure stamped on the sidewall of the tire the max pressure that is allowed with these particular tires and not the recommended tire pressure? I don't think it's neither smart nor usefull to inflate the tires to the max of their capacity.

BTW, I,m running 32 psi with my 31" BFG MTs.

Tire pressure is different for different vehicles. My mom had dualler AT tires on her 94 E150 van. Max cold pressure was 50 and we ran them at 46 or 48. guess what..the tires still got rounded off, showing underinflation. That van just weighs so much that it eats tires no matter how full you have them. Now we just got new tires and they only have a 40PSI max cold pressure. i predict they will be rounded off on the sides by the time they have 20,000 miles.
As for my Explorer, i now have about 18,000 miles on my BFG Long Trails, and they are wearing good. i used to run 40 in them to prevent the sides getting rounded like it does on the van, but since the Explorer doesn't weigh that much I lowered the pressure down to 36 or 38. i have tried to run them at 30 as some of you do, but it just makes the tire buldge too much and gives for a soupy ride. i prefer the truck to be nimble and responsive. i think that the door sticker pressure is what is recommended for the tires that came on the vehicle from the factory. WHen you get new tires then that sticker is no longer valid. Every tire is different and i think that tire pressure is really up to the driver. i didn't think that the explorer would handle so much different with just 8 PSI less in the tires, but it did. Each driver needs to just use what they think, watch tire wear, and fill them until the truck gives the type of ride they are looking for.
SOrry for the long post...just my thoughts

I have 265/75/16's on mine. I used a load inflation chart and then did the chalk test yesterday. I'm running 31 psi up front, And 33 psi in the rear.

mine is stamped 26 psi cold. i wondered why i had that floaty feeling on mine and checked the air pressure. i saw it had 40 in it so i let it out to 28, it drives like a dream now.
just my 2 bits

Originally posted by snooper0069
mine is stamped 26 psi cold. i wondered why i had that floaty feeling on mine and checked the air pressure. i saw it had 40 in it so i let it out to 28, it drives like a dream now.
just my 2 bits

Click to expand...

That door sticker that says 26 is wrong..ford sent out new stickers that said the mionimum was to be 30 psi cold. This is to prevent blowouts.

The guy at the tire store told me I should run my 31x10.50 15's BFT AT KO's at 35, the sidewall says 50 max so I bought what he said. But we live at or near 7000 feet and a buddy said who has Toyota Truck said he thought that living up here might have someting to do with it but he has pretty much worn his BFG's out over the past few years, and says he runs his at 45 pounds unless he's out in the snow cutting wood. He suggested I start at 45 pounds, so being new to the moutains I'm going to give it a try at 45 for awhile anyway. He has a compresser and after he increased the pressure to 45 the X did seem to turn easier and pick up speed better, but we'll see. I have to say I was surprised since in my past 32 - 35 was where I stayed with my older trucks tire pressure.

bump, excellent information

Thanks for the info I just put passenger tires on a 2wd 97 ex rides like a dream and quiet. My door jamb says 26 tire store guy said run at 35. Doesn't look as mean without the michelen 30x9.5 but rides better.

in all my cars I'm running 32PSI i it gives me best all around traction i need for city/hwy driving