Tire Pressure?

Mule · March 2, 2004

I have searched this and some other sites for a direction on tire pressure. 1995 GMC 4-door Yukon with BFG 305/70R16 Mud Terrains. Max on sidewall is 50 PSI. Rancho RSX9000 shocks on the medium setting.

Dealer - use what is on the door jam

Discount Tire - use 50 PSI

Jiffy Lube - Use 50 PSI

4X4 shop - use 34-36 PSI

4x4 shop #2 - use 30-32 PSI

Toyo web site - 40 PSI front, 55 PSI rear

And the list goes on. The truck weighs around 5300 pounds. Any thoughts and why?

Imkunfused · March 2, 2004

Id use whats on the door jam.. Would never run the max, because when the tires heats up.. the pressure will go up.

Machine · March 2, 2004

Hi -

Don't use what's on the door - that information was for the stock tires that came with the Yukon. I believe those were 245/75/16 and 265/75/16's. Your max inflation on the sidewall of your mud terrains indicate the maximum tire pressure allowed...

My max on my 305's is 65psi and I run them at around 50 when the truck is not pulling something.

Try running them at around 37-40psi and observe the wear.

seadoons · March 2, 2004

I have 285/75/16 BFG all terrains that I run at 40PSI. Like the previous post said, the door jam numbers are for the stock tires (which were small). It won't hurt to run it as high as the sidewall of the tire says, but remember, that is the COLD tire pressure...so if you are going to put it that high, do it when the tire is cold (like in the morning).

I am not 100% sure, if the tire says 50PSI cold, the tire really can handle more than that, there is just a buffer in there for the higher pressure from when the tire heats up.

PFarkas · March 3, 2004

Call the tire manufacturer (1-877-788-8899). BFGoodrich happens to have good end-user technical support available, even if they are owned by a French company.

Since you asked, I'll tell you what I would do. It's not gospel. I am no tire expert. I will not be held accountable if your truck flips over or you don't like what I have to say.

Estimate (or better yet, measure with a scale) the front and rear axle weight of your truck.

Look at the MAX LOAD rating of your tires, in pounds. This is the maximum amount of weight that each of your tires is rated to handle safely when the tire is inflated to the maximum PSI, also specified on the tire. At lower pressures, the tire will handle less load.

Figure out the amount of load that each tire will need to support, in pounds. Divide this by the MAX LOAD rating of the tire. Multiply this fraction by the MAX PSI rating of the tire.

The result is probably pretty close to where you ought to air your tires to. That makes sense, except for the part where the load carrying ability of a tire doesn't scale linearly with it's pressure.

That's one way.

Another one is to inflate them to the point where the outside of the tread just begins to come away from the pavement, then air down until you have a reasonably uniform contact patch with the pavement. Some people drive through chalk or dust and look at how evenly the tread gets chalky/dusty to confirm that they have it right.

My truck weighs 6400 pounds. I estimate a 60front/40rear weight distribution. My tires are rated at 50PSI max, 3415 pounds@50PSI. I run my fronts at 32PSI and my rears, when the bed is empty, at 28 (which is a little higher than it needs to be for the rears). According to the math, I should run the fronts at 28 and the rears at 18, which I tried, but the tires felt awfully soft.

Running my tires at these pressures, my treadwear is very uniform and after 53,000 miles, they are in pretty good shape. I expect to get another 20,000 out of my BFGs.

Over-inflating your tires will certainly lead to premature tread wear. Under-inflating them will also lead to premature treadwear and will not allow the tire to safely support as much of a load.

It's better to error towards over-inflating (but not beyond the tire's max rated PSI) than it is to under-inflate.

Mule · March 3, 2004

Great responses and reasoning. I am going to go mid-30's as a starting point. I did the math linear thing equation and it came out to 30 front and 28 rear. The Yukon is close on 50/50 balance since the rear is 400 lbs heavier from the metal, seats, extra doors, etc (from GM).

Thank you!!!

Mule · March 11, 2004

UPDATE:

I talked to BFG this morning. They put me on the phone with a tech. Original tires were 245/75r16 with 35 PSI (per the door sticker). Those tires at that PSI had a load rating of 1700 lbs. So, you need to at least maintain that on the 305/70r16. At 35 PSI on the new tires, they have a load rating of 2270, so 35 PSI is enough.

Now, higher is acceptable based on load, driving conditions, ride, etc. But she warned against going any lower. Since I have probably a few hundred pounds in accessories and lift kit, I think I will use 35 PSI as a minimum. Maybe a little higher.

Machine · March 11, 2004

Great, now that you know, you can play with the pressure and find the most comfortable / reliable psi. I bet you'll find that the upper 30's - low 40's will give you the best results. Just keep observing the tread wear...If they look worn on the outer tire - you're running too low. If they look worn in the middle - they're too high

93Stocker · March 11, 2004

Mule,

If BFG is using the OE tires on the door sticker as a basis for their recommendation, the tire load limit for a P245/75R16 at 35 psi. cold inflation pressure is actually 2065 lbs. For an LT245/75/R16 at 35 psi. it's 1700 lbs. (For the P-metric tires, "loads have been reduced by a service factor of 1.1 for passenger tires used on light trucks..." from the tables we've talked about in the off site emails. For the P245/75/R16, 2271 lbs. is listed many places as the maximum load at 35 psi. Dividing 2271 by 1.1 equals the 2065)

KJ

Mule · March 11, 2004

KJ,

I looked at the BFG website at the original tires (Long Trail T/A) and you are right on the pressure/load of the original. But it was a P-tire used on a light truck, so is the 1700 number or the 2065 number my starting point?

If it is the higher number, then is 35 PSI not really a minimum, but less? Bottom line is that I am in the mid-high 30's and it seems to be right.

93Stocker · March 12, 2004

If BFG used the 1700 number and you told them the door sticker was for a P245/75R16 tire, I'd question the accuracy of anything else they said. For a good comparison you might contact The Tirerack. I've read several good comments about their tire savvy. If you're not shopping for tires they may not be too interested in answering your questions. But, what the heck, only one way to find out. There is an 800# or email option at:

http://www.tirerack.com/about/contact.html

Good Luck!