Under-inflated Tires

We all know that under-inflated tires produce excessive heat and damage the tire. We also know that most D rated tires have a maximum inflation rate of 65 lbs. and E rated tires usually have a maximum inflation of 80 lbs. So my question is, what constitutes an under-inflated tire? When is a tire low on air? 5% under the max rating, 10% under the max rating? I run my trailer tires at the max air pressure but I really am curious to know when is a tire considered low enough to cause excess heat and damage.

I always thought it was considered underinflated when it exceeded 10% of max pressure rating, not max load rating. If that truly be the case, a D rated ST tire with max pressure of 65 p.s.i. would be underinflated at 58 p.s.i.

TC

Mopar_Earl wrote:A tire is under-inflated when the load is higher than the pressure in the tire. A tire will carry X amount of weight at X amount of pressure. Say you run 70 psi in a E-range tire, you can run 3130 lbs on that tire but the more weight you add without adding more air pressure you'd be under-inflated.

Example

ST235/80R16E load and inflation:
2730 @ 55 PSI
2870 @ 60 PSI
3000 @ 65 PSI
3130 @ 70 PSI
3260 @ 75 PSI
3420 @ 80 PSI

I run 70 to 75 lbs in my E-range tires on my trailer (I don't run 80 lbs as E-tires are overkill and I don't need 3420 lbs of load per tire)

I run 70 to 75 lbs in the rear tires of my truck when towing (70 lbs as per Dodge)

I run 45 lbs in the rear tires of my truck when not towing (as per Dodge)

I run 60 lbs in the front tires of my truck at all times (as per Dodge)


Earl

Well said. I run about the same in my trailer. Ford requires 80 in the rear and 50 in the front. I run 62 in the front and 80 in the rear. 62 is a little high because the Ford she get's the wonders but it sure helps the gas mileage. That is the other concern with under inflated tires. The gas or diesel miles per gallon.

TC wrote:I always thought it was considered underinflated when it exceeded 10% of max pressure rating, not max load rating. If that truly be the case, a D rated ST tire with max pressure of 65 p.s.i. would be underinflated at 58 p.s.i.

TC

Interesting quote.

Here's another one to ponder.
In the shade and cool I inflate to 65.
Sitting in the sun it may go up to 70.
Should you deflate to 65 before you take off?
What about the normal heat build up of the road and sun ?
Are the tires over inflated then ?

That is interesting. I would like to hear all the answers.

Since Phillip started 'Here's another one to ponder' We just moved from Blairsville, GA elevation 2500 ft to Colorado Springs, CO elevation 6000 ft the cold air pressure in the tires on my wife's car went up 6 PSI. Jim

Stanford wrote:Since Phillip started 'Here's another one to ponder' We just moved from Blairsville, GA elevation 2500 ft to Colorado Springs, CO elevation 6000 ft the cold air pressure in the tires on my wife's car went up 6 PSI. Jim

Yes elevation effects air pressure.


Earl

When I checked my tires Friday, the tire was at 80psi cold in the shade and cool of the morning. By the afternoon in the sun, it was 96psi.

I am curious. What tire pressure inflator do all of you use? The one I use takes forever to inflate a tire to 65 psi

I use one that inflates in seconds....My shop air compressor with a 60 gallon tank. I usually only have to kick it up from around 55-60 up to 65 from the winter storage time. Usually it's a couple psi low in the summer.

My tanks a 60gal with the 175lbs pump, sears brand.

I check in the morning before I leave. Make sure sun has not heated the tires Once I set I forget until I get home. Just check them once in a while with the thump method. AC is carried once in a while but only when I need for something else.

Scruffy puts the tire pressure sensors on all 8 tires before we leave for a trip. First thing each morning that we travel, we check the pressures. Then it's up to the sensors to keep us informed all day.

Tater

Time for a Miller.