Tire Pressure Thoughts

[ken1mod]

Gentlemen,

 

I notice on this great site that many of us install larger tires on our trucks. I also notice quite a few complaints about ride harshness.

 

i was in charge of a fleet of load carrying and towing trucks for 25 years and have come to know tires and their characteristics.

 

Tires need to be inflated to the pressure that matches the load applied to them. Tire stores also almost always over inflate new tires. They typically inflate the tire to the maximum allowed pressure as stated on the tire itself. This is very often severe overinflation resulting in poor braking, handling and ride harshness.

 

For example, my silvy door sticker recommends 35 psi all around. This is the pressure that gives the correct tire patch to the ground with the full rated load in the bed. With this pressure the tire is quite over-inflated with no load. This is clear when looking at the dust pattern that is sometimes visible on the tire after driving. Only about half the width of the tire is touching the road on the rear tires. The front is OK because bed load does not affect front tires very much.

 

I lowered the rear pressure to about 28 and the result was very positive in all respects.

 

If I looked around, I could probably find load range F tires that would fit my wheels. These will have a max pressure on the tire itself of 120 lbs. This would be the correct pressure if I loaded that tire to 3000 lbs. This tire on the front of my truck should still be inflated to 35 psi.

 

Another point. Larger tires require lower pressure for a given load. If you install bigger feet, you need to find a tire pressure chart that gives correct pressure for that size tire at the applied load. Maybe if anyone finds one of these, they can post a link.

 

Chevy used to include a chart in the owners manual that listed correct pressures for specific axle load. They don't seem to do this any more.

 

Anyway, I hope this info will help those of us with ride harshness issues. An unloaded pick-up needs substantially lower rear tire pressure than sticker.

 

My first exposure to this concept came from when I had a '69 VW bug. The front end is absurdly light and the correct tire pressure was something like 15psi.

 

Ken

[OUMike]

Gentlemen,

 

I notice on this great site that many of us install larger tires on our trucks.  I also notice quite a few complaints about ride harshness.

 

i was in charge of a fleet of load carrying and towing trucks for 25 years and have come to know tires and their characteristics.

 

Tires need to be inflated to the pressure that matches the load applied to them.  Tire stores also almost always over inflate new tires.  They typically inflate the tire to the maximum allowed pressure as stated on the tire itself.  This is very often severe overinflation resulting in poor braking, handling and ride harshness.

 

For example, my silvy door sticker recommends 35 psi all around.  This is the pressure that gives the correct tire patch to the ground with the full rated load in the bed.  With this pressure the tire is quite over-inflated with no load.  This is clear when looking at the dust pattern that is sometimes visible on the tire after driving.  Only about half the width of the tire is touching the road on the rear tires.  The front is OK because bed load does not affect front tires very much.

 

I lowered the rear pressure to about 28 and the result was very positive in all respects.

 

If I looked around, I could probably find load range F tires that would fit my wheels.  These will have a max pressure on the tire itself of 120 lbs.  This would be the correct pressure if I loaded that tire to 3000 lbs.  This tire on the front of my truck should still be inflated to 35 psi.

 

Another point.  Larger tires require lower pressure for a given load.  If you install bigger feet, you need to find a tire pressure chart that gives correct pressure for that size tire at the applied load.  Maybe if anyone finds one of these, they can post a link.

 

Chevy used to include a chart in the owners manual that listed correct pressures for specific axle load.  They don't seem to do this any more.

 

Anyway, I hope this info will help those of us with ride harshness issues.  An unloaded pick-up needs substantially lower rear tire pressure than sticker.

 

My first exposure to this concept came from when I had a '69 VW bug.  The front end is absurdly light and the correct tire pressure was something like 15psi.

 

Ken 

 

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Very interesting. So you said you lowered your rear tire pressure to 28 lbs. What made you decide to do this. I run stock tire sizes and was kinda curious if I was running proper pressure. I run 35 lbs all the way around. Would I benefit from lowering the rears to 28?

 

Thanks

[ken1mod]

Sir,

 

What made me adjust my rear tire pressure down was when I was looking at my rear tires after a rain storm and it was apparent that the rear tires were making a bicycle-like contact pattern on the road. That aint right and the ride was definitely harsh. The truck also seemed to not stop as well as it should with the anti-lock working overtime quite often.

 

I would never write this type of post if I were not completely comfortable with the concept that air pressure must match the load applied to the tire. I used to live by this principle. As I said earlier, Chevy used to publish a table of pressures in the manual that on our 1 ton chevy vans varied from 45 psi empty to 75 psi fully loaded for the rear tires. This was with load range e tires. The front tires always carried the recommended 45 psi.

 

If you lower your rear pressures to 28, you will note that the tire is still round as a robin, acutally tighter looking than the front tires.

 

Experiment a bit, I think you will like the results.

 

Remember that you must increase tire pressure if you are planning to carry a heavy load. I rarely carry anything in my truck and find that 28 is the right number for me.

 

Ken

[bigdogxx]

My 05 with a set of bfg ko tires still stock size were loaded up to 45 psi by my mechanic not sure why that much but i lowered to 40 psi all the way around, should i bring them even lower to 35 front and 28-30 in the rear?If it smooths out the ride im all for it, 85% of the time the bed is unloaded with no weight in it.

[mmmikkke]

Great intro, Ken. A lot of guys can use this kind of info.

[sledr]

I run all 4 Duelers at 35 PSI. I get great mileage and the ride is slightly rougher than the 32 PSI the dealer previously set them at.

[OUMike]

Sir,

 

What made me adjust my rear tire pressure down was when I was looking at my rear tires after a rain storm and it was apparent that the rear tires were making a bicycle-like  contact pattern on the road.  That aint right and the ride was definitely harsh.  The truck also seemed to not stop as well as it should with the anti-lock working overtime quite often.

 

I would never write this type of post if I were not completely comfortable with the concept that air pressure must match the load applied to the tire.  I used to live by this principle.  As I said earlier, Chevy used to publish a table of pressures in the manual that on our 1 ton chevy vans varied from 45 psi empty to 75 psi fully loaded for the rear tires.  This was with load range e tires.  The front tires always carried the recommended 45 psi.

 

If you lower your rear pressures to 28, you will note that the tire is still round as a robin, acutally tighter looking than the front tires.

 

Experiment a bit, I think you will like the results.

 

Remember that you must increase tire pressure if you are planning to carry a heavy load.  I rarely carry anything in my truck and find that 28 is the right number for me.

 

Ken

 

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Yea I very rarely carry anything in my truck, and I live in Houston. Frequent heavy rain is common. I think Imma drop my rear pressures and check it out.

 

Thanks a lot!

[lerbud]

i agree with lowering the pressure. i always lower mine to about 30 all the way around. always seems to ride smoother that way. too much air rides way too rough.

[mmmikkke]

Everybody should go to a Cat scale at a truck stop, go inside and ask for instructions to get weighed, find out your front and rear axle weights, and then set tire pressures for empty-running accordingly.

[asilverblazer]

This is what I used to do when my truck did duty as my daily driver. Now that I use it strictly for towing I keep it at 35 all around, but before hand I was running the recommended pressure up front and around 30PSI in the rear. Now that I have an air compressor I am more willing to experiment with different pressures, than I used to, going to 7-11 for free air gets old after a while.

[ken1mod]

Guys,

 

I might also point out that I am not a freak for smooth ride. I am usually more interested in handling. My girl friend even likes a firm ride (?).

 

But an overly harsh ride and skipping and bouncing of the rear end is no fun either.

 

I will try to find a pressure vs loading chart. Maybe the tire manufacturers post those.

 

You might try what I did, under certain road conditions there is a beautiful picture on the tire of the contact patch from the road dust. I believe it is correct for the whole tread to be in contact with the road, not just the center. Do you agree?

 

Ken

[OUMike]

Guys,

 

I might also point out that I am not a freak for smooth ride.  I am usually more interested in handling.  My girl friend even likes a firm ride (?).

 

But an overly harsh ride and skipping and bouncing of the rear end is no fun either.

 

I will try to find a pressure vs loading chart.  Maybe the tire manufacturers post those.

 

You might try what I did, under certain road conditions there is a beautiful picture on the tire of the contact patch from the road dust.  I believe it is correct for the whole tread to be in contact with the road, not just the center.  Do you agree?

 

Ken

 

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Question.

 

In doing this have you noticed any difference in longevity of your tires? I ran this buy a couple buddies and they said it was a good idea, but should chew tires up quicker. Have you found this to be accurate? The thinking is...better grip = more friction = faster wear. What you guys think?

[97whitez71]

Is this the type of chart you are talking about?

 

Tire Chart

 

Look on page 7

[phire]

i agree with lowering the pressure.  i always lower mine to about 30 all the way around.  always seems to ride smoother that way.  too much air rides way too rough.

 

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But it does give you better fuel mileage!

[ken1mod]

The tire wear point is a good one. Doesn't correct inflation yield best tire mileage? I am only and strongly advocating correct, textbook tire inflation. I would never run any tire underinflated.

 

My point is that the sticker is correct only for full rated bed load and results in overinflation for unloaded use. Isn't overinflation bad for wear, besides beating up the truck. My 265 continentals wear great, no visible wear at 10,000 miles. I was going to rotate them last week but they looked so perfect that I postponed the project.

 

Ken