Tire pressure question

[noJeepshere]

I am travelling this weekend and the weather is supposed to get pretty sketchy this weekend where I am going. Right now I have the tires on my Yukon up to their full pressure rating, or what they should be for it. My question is: can I safely let out some of the air (from 35 psi to 25-30 psi) and still be good to go on the freeway? I know there will be a bit of a loss of fuel economy, but at 65 I get around 20 mpg, so a slight loss won't be a big deal. I just wonder what will happen to the tires being run low like that. Any input will be great, thanks in advance.

 

[pseudomike]

Lot of variables, the actual tires, size, number of plys in sidewall and so on. I run 33" yokohama load range E on my Tacoma around 22PSI though they indicate 70PSI on the sidewall. I do this because the tires are too stiff for a truck that light that came with p-metric tires from the factory. Your Yukon is heavy so you may have different reults.

 

[noJeepshere]

It came with 245/75-16s, then when I bought it I put 265/70-17s on it and the guys at Les Schwab put them to 35 psi, said that's what it was supposed to be at. IIRC, the owners manual says the same thing.

 

[colbystephens]

i will go out to a trail, air down to 10psi and often have to cruise the freeway home at that pressure - or at least to the nearest gas station. this is with radial 38" TSL's, and did the same with 35" mtr's. going down to only 25 or 30 PSI will absolutely be fine - but i doubt that it will give you any better traction than 35PSI.

25 is still pretty darn full. my wife's car recommends running the fronts at 20 and the rears at 25. granted, it's a VW bug - so it's super light weight. however, that's just to say that 20 isn't really that low for a light-truck or passenger car.

if i were you, and i were concerned, i'd drop it down to 25 PSI and if the weather actually gets nasty on the road - drop it down to 15. The initial 25 PSI is only so that you don't have to get out and sit out there in the cold waiting for your tires to drop a whole 20PSI in one sitting.

 

[George_Pimpdaddy]

i always though that you would generally get the best traction and fuel with the pressure on the door?? seems silly to air down on the highway when it can affect your safety

 

[colbystephens]

the pressure on the door is the best combination of comfort and fuel economy. in theory it would have something to do with keeping the tread perfectly flat on the ground, but radial tires have enough sway in the side walls that you typically don't have problems keeping the tread on the ground even at maximum tire pressure. i care very little about comfort compared to fuel economy, so i always run my tires at max PSI on the highway.

it's not unsafe to run tires at 15-20 on the highway (or even lower, really). you're only going to lose a bead if you get a side-load on the side wall, and that shouldn't happen on the highway. i just use more caution around corners. ofcourse, we air down for the trail and this creates all kinds of weird and heavy lateral loads that cause us to lose beads on the trail (though, i've yet to experience that great event...) knock on wood.

 

[USSkoval]

it's not unsafe to run tires at 15-20 on the highway (or even lower, really).

What about Wilderness AT's on Furd Explorers?

So lowering pressure will help even when driving in plain 'ol bad weather? I didn't realize that. I'm also one of those people that always runs max pressure listed on the sidewall.

 

[colbystephens]

i don't know anything about ford explorers - those have a tire reputation unique to them.

traction is directly related to the surface area of the tire in contact with the ground. so, any time your tires are low it will increase your traction. there's no reason to do this on the road, however, unless the road is in super terrible shape (i.e. snow, ice). it sacrifices fuel economy and tire life to run them low on the pavement because there's added friction, thereby heat, thereby wear. it hurts your fuel economy because there's effectively more rolling resistance.

i guess you could liken running a radial tire at low pressure to running a bias ply tire at regular pressure in terms of how it would affect your fuel economy and tire wear...

 

[4X4HIGH]

the pressure on the door is the best combination of comfort and fuel economy.

it's not unsafe to run tires at 15-20 on the highway (or even lower, really). you're only going to lose a bead if you get a side-load on the side wall, and that shouldn't happen on the highway.

The correct air pressure for a tire comes from info that is ON THE TIRE and not in the door jamb especially if the tires are not the factory tires that came on the vehicle.

It is very unsafe to run a tire with too low or too high of a pressure. Either way will build extra heat and can make the tire explode. Tires that are low on air pressure at highway speeds are dangerous enough because now there is way to much side wall movement happening.

 

[chulisohombre]

my tires are load range e rated for 4000 lbs per tire.so i only have them at 30 in the front and 25 in the rear.unless you are carrying a lot of weight,they do not have to be aired up all the way.also you will get really weird wear pattern in the center of the tire if they are max aired up.

 

[colbystephens]

The correct air pressure for a tire comes from info that is ON THE TIRE and not in the door jamb especially if the tires are not the factory tires that came on the vehicle.

It is very unsafe to run a tire with too low or too high of a pressure. Either way will build extra heat and can make the tire explode. Tires that are low on air pressure at highway speeds are dangerous enough because now there is way to much side wall movement happening.

you're right, but the question is what is "too low"... too high is obviously over the max range. on the highway, i doubt you get that much side wall movement because the roads are usually pretty straight, so there's no lateral loading of the tire. also, if you need your tires that low on the highway, you won't be going fast enough for it to be a big deal.

i don't like driving home at 10psi... but i do it, and have never had a problem.

 

[DEMON44]

the max psi listed on the sidewall is for max load capacity. on an LT tire.

if you're not AT max tire load you do not have to run max psi.

 

[jms]

... on the highway, i doubt you get that much side wall movement because the roads are usually pretty straight, so there's no lateral loading of the tire....

Yes, you do get a lot of sidewall movement with an underinflated tire at highway speeds, and it has nothing to do with lateral loading.

Look at a tire at low air pressure at standstill: the sidewall is bulged out at the point of contact with the road, due to the weight of the vehicle. But the sidewall of the tire opposite the point of road contact is not flexed or bulged outward. Roll the tire one revolution, follow the sidewall at one fixed spot, and you'll see the sidewall at that spot move - flexed outward at road contact, not flexed, flexed out again.

It takes 600 (or something like that...) revolutions of the tire to cover one mile - so in one mile, the tire sidewall goes thru 600 cycles of flexing outward and coming back. That can generate heat; at trail speeds, that heat dissipates easily. At 60 mph, that is 1 mile per minute, or (if we stay with the number above) 600 flex cycles per minute, or 10 flex cycles per second, heat is not only generated rapidly, but doesn't dissipate as easily any longer. So you have a lot of sidewall movement with an underinflated tire. There's always some movement in the sidewall, but you'll get more with lower tire pressure.

Whether this is going to kill a tire is dependent on many variables, tire pressure / speed / tire size / ambient temperature / sidewall construction / tire materials come to mind.

 

[colbystephens]

wow. cool, i stand corrected!