70-442-W30

When I picked up our new megavan from the dealer, the tire pressure was set at around 80 psi all the way around. About halfway to the coast on a trip to winterize our camper, I stopped to see what the door sticker said because the bumps were a bit, well...bumpy.

According to the sticker, the tires were supposed to be at 50 psi for the front, and 80 psi for the rear. So, I lowered them down to 60 for the front to see if I noticed a big difference. It did soften the ride quite a bit. But the 50 vs 80 seemed like too big of a difference to me, so I stopped at 60.

I know when I tow our camper with this and get the weight distributing hitch all hooked up, the front tires will need to go back to 80. But for now, I'm good with the 60.

So I was wondering, for anyone out there who has a larger vehicle, do you have a such a huge psi differential between the front and rear tires on your sticker? This seems a bit extreme to me. That's 30 pounds.

rustyroger

Who would know better than the manufacturer?. Well if it's a Ford on Firestone tires then it's the tire makers.
But it's quite normal for big differences between front and rear on RVs and commercial chassis'.
If you want to be certain you are running at optimum pressure get the axles weighed at a weighbridge and email the tire makers and ask them what they recommend.

Roger.

RROLDSX

I believe it is the load rating E tires (10 ply) that you need to have for the heavier loads. The tires themselves will have the load rating on them that you need to comply with. You can soften the ride on the lower load (like the front tires) by reducing the pressure to the 50 to 60 range then increase the rear as required for the load without exceeding the ratings. I also like to match the air bag pressure to the tires. It seems to give better stability w/o all that rocking and rolling. Once I'm done hauling the load I reduce the air pressure for better ride Control back down to 50 or 60.

70-442-W30

Yes, that's what I have...the load rating E 10 ply. I just was wondering if anyone else had a sticker inside the door with such a big difference between the front and back recommended pressures. I've never owned any other vehicle where it was such a big difference between the two.

Pic below.

RROLDSX

That's loaded. Reduce the pressure when unloaded in the back otherwise you'll rattle you teeth out of your head. If you are running air bags you should reduce the pressure to no less than 5 psi without a load.

Indy_68_S

Haven't had that large a difference F/R, but I've never had a new heavy duty hauler.

Not uncommon.

Seems like these days brand new vehicles have the tires way over inflated for transport/delivery. The dealer is supposed to adjust them during pre-sales prep, but they don't.

When I picked up our (then new) '11 Outback the tires were all at ~ 50 psi. Normal is mid 30's. It was kinda like driving on ice all the way home....very 'dancy'.

RROLDSX

Also, when you are adjusting your tire pressures up for a load you want to have the load already on otherwise 80 psi in an unloaded truck will become too high for the tire and could cause catastrophic failure once loaded.

70-442-W30

Not trying to argue with you here, but I wanted to share what I found. The Cooper Tire site says the numbers on the placard are the minimums. The numbers on the tire sidewalls that list the max load weights are the maximums. See here:

http://us.coopertire.com/Tire-Safety...-Capacity.aspx

So, in my case the minimum recommended pressure for the rear is 80 psi (placard) and that is also the maximum according to the tire sidewall, 3000 lbs at 80. The front has the minimum pressure of 50 psi, although the tires are the same size and specs as the rear and can do 3000 lbs at 80.

That does seem strange though to have such a high rear pressure. I wonder if Nissan just transferred the data over from their NV3500 cargo vans because on those you would probably want the higher psi rear all the time due to them being used commercially. Or maybe Nissan needs to have this showing as 80 psi rear due to not knowing how many passengers it will have loaded at any given time.

Common sense says that if the front tires aren't going to overheat at 50 psi and a light load, then the tires on the rear aren't going to overheat at 50 psi and a light load either. And that would be a way softer ride....

I don't have airbags. Would be nice though. I might have to check on that, although my camper only has around 750 lbs of tongue weight and less than that with the W/D hitch hooked up. Probably not needed unless sagging really bad.

jaunty75

I don't think this is true at all. When you load any vehicle, you are compressing the springs, not the tire volume. The only way to increase the pressure inside the tire is to add more air or actually shrink the tire's internal volume, and I don't think that happens when a tire is loaded by any reasonable load.

It's an easy enough experiment to do. Measure the tire's pressure with the vehicle unloaded, then load the vehicle and measure the tire pressure again. I'll bet that there will be no difference.


Here's a thorough explanation of the issue, complete with diagrams and everything.


Does car tire pressure change with weight of car load?

https://physics.stackexchange.com/qu...ht-of-car-load

RROLDSX

You are repeating what I have said. The 5 psi minimum was for the air bag pressure unloaded. Tire wall ratings must be followed closely for maximum pressures not to be over inflated.

70-442-W30

When you said, "That's loaded" I thought you were referring to the tire pressures listed on the placard as the pressures you would need if loaded for max payload. But as I said, those numbers, according to the link I posted, refer to the minimum psi required at all times on the vehicle.

Regardless, it still is a mystery to me why the rear minimum pressure is at 80 on the placard, and the maximum pressure on the sidewall is listed at 80. Maybe it has something to do with the government testing and rollover ratings. Because these vehicle types don't have mandatory EPA fuel economy ratings, I know it has nothing to do with that.

Or maybe it has to do with the vehicle's angle into the wind.

wyogf45

FWIW, I just put another set of new tires on my 2005 Chevy 2500. I use it to pull our 3 horse slant goose neck horse trailer. It has the 8.1 motor with the Allison transmission. I have run the same tires for several years. Cooper Discover AT 3. Load rating E. Loaded, I run 80 PSI rear and 60 PSI front. Unloaded I run it at 60 PSI front and rear to improve the ride. I have never had any unusual wear issues or safety concerns. I've been trading at the same tire shop for 30 years and have had this exact conversation with the owners on more than one occassion. I also got a second opinion from the mechanic I have used for 30 years and his opinion is basically the same. His only difference is he thinks 50 - 55 PSI is fine. I have run at this PSI also without any problems.

70-442-W30

I appreciate the feedback and may consider going to the 60 psi front and rear myself. That is unless anyone here can see any real danger in it.

RROLDSX

As WOGF posted, these 10 ply tires are pretty tough and are pretty forgiving. The numbers become more important when flirting with maximum loads and pressures.

70-442-W30

Just went to 60 front and 70 rear. Feels perfect. Bumps aren't that bad and wind/big rigs don't push me around on the highway as they did. I will inflate to max sidewall pressure when towing though.

joe_padavano

Sorry, I don't buy that. The tires will distort to achieve the required contact patch shape under load. The internal pressure won't change that much, and frankly, it changes more due to heating from use than a full load will ever cause it to go up.

70-442-W30

I've never heard that anywhere else but here either.

However, there is great debate whether or not max pressure (as posted on the sidewall) should be used when towing a heavy load. Many in the camping forums do it both front and rear and some just increase the rear. My take on it is that if you are using a weight distributing hitch then some of that is going to be transferred to the front, and airing the tires up to max pressure helps to keep the guesswork out of it.

I'd be interested in knowing your opinion on it.

ELY442

I use to be a truck mechanic for a lumber company and they have tractor trailers, flatbeds, and other trucks. These tires takes 110-120 psi. These tires generate a lot of heat so the air pressure rises when they are hauling lumber, sheetrock and other building materials. I only fill the tires 10 lbs less before reaching maximum specs. The drivers noticed the difference and told me that the truck does not ride that hard or bouncy.