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Old 04-08-2012, 11:17 PM   #1
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Tire Pressure / Temp Increases when Driving

I realize that tire pressures and temp will increase when driving however, what is an acceptable icrease? My current front Michelein XZA2 energy 295s will go from 117 cold to 131. The rear goodyears G670 from 95 to 105. So what is aceptable? should I put more air in the fronts? I do have 4 corner weights and according to the chart 117 is 5lbs above the chart pressure for the front weight. Both fronts will go up the same increae in pressure.
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Old 04-09-2012, 06:13 AM   #2
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Just had my first real experience with a TPMS last summer for about 8000 miles. I get pressure increases to approximately 20 PSI higher than my cold set temp when driving. Waking up to my normal 105 psi in FL with temps around 90 oat then a couple days later seeing 98 psi with 65 degree oat was confusing at first but became run of the mill over a couple months. I never adjusted the pressure and when I got back to FL had the same pressures I left with.
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Old 04-09-2012, 06:49 AM   #3
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Not an issue the way you have them distributed, but you added another variance by using different tire types. I think you'll have to work it out by observaton during the seasons. This spring traveling South I started with 40 degree oat/cold temp and watched tire temps go to 100 degrees as the air temp went up to 80 degrees and the sun heated the road (the pressure went from 80PSI to 95PSI as well. During the sumer, staying close to a centeral loaction, I usually see cold temps at 85 deg climb to 105 to 110 during a 90/95 degree day. So a 20 degree increase isn't an indication of a problem and using 2 different tire types could explain why one set gets hotter than the other (front vs. back, vs traction/friction). So ii don't have your answer, but hope this gives you something to think about.
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Old 04-09-2012, 10:26 AM   #4
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Always consider pressure measured only at ambient temperatures. Manufacturers account for normal pressure increases from that basis in their sidewall ratings.

Temperature is what the pressure is all about. The pressure reduces flex which is where the temperature increase in operation comes from.

Your tire materials will suffer when tire pressure gets much over 140F. I am not very familiar with MoHo tires but the materials are the same for all tires, I think. I like to keep my tires at about 120F and I find that sun and road heat may make for a difference of 10F to 20F between sides sometimes.

Note that, while environment will make some difference, tire temperature on the road is mostly due to operational factors and will stabilize at 100F - 120F or so if you have the pressures right.

The weight on the tires is easily seen in tire temperature differences in my experience.

The key is that if you have a tire running hot, it needs air. That may be because of a leak or because it is carrying too much load or because the vehicle speed is too high for circumstances.

In a TPMS, tire temperature is a bit harder to measure. That is why some mount inside the tire so that they can monitor temperatures as well as pressures.

I make it a point to do a walk around with an IR thermometer on my rig during breaks to check tire and hub temperatures. Any significant temperature differences clue me in to a potential problem. I've discovered leaks before they went totally flat and loose brake springs that way.
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Old 04-09-2012, 02:54 PM   #5
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The tire pressure should build up should be about 10% from cold to running hot. If you start at 100 psi cold and check the pressure after running for 15 minutes or so at cruising speed you should see no more than 110 psi. If you do then you need to add air to the tire as the tire is running too hot.
Conversely if you start at 100 psi cold and still have 100 psi after running at speed you can lower the pressure. In this case the tire is over inflated and is not able to flex as it is designed. This will cause tire problems in addition to a harsh ride.
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Old 04-09-2012, 03:03 PM   #6
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Increase the front by 2 lbs
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Old 04-09-2012, 07:10 PM   #7
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10-15 psi increase is typical for tires that are 80-120 psi when cold.
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Old 04-10-2012, 10:35 AM   #8
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2nd the IR thermometer. I check tire temps at stops with one from RadioShack. I am less concerned with absolute temp than with relative temps between tires. If the steer tires are within 5 degrees of each other which can be accounted for by sun, I am happy. I expect to find inner duals running 5 to10 degrees hotter than outers due to their position.

I once checked the hot pressure and found it 20 degree higher than at ambient after an hour run at highways speeds. Haven't bothered to check it since.
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Old 04-10-2012, 11:45 AM   #9
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Tire Pressures

Here is the post I submitted last year. I do not know how to refer to the post with a link so I am posting it again here to try to help dispell some of the misunderstandings regarding tire pressures. If someone could explain how to make a link to a post for future use I would appreciate it.

I worked for Michelin and Yokohama Tire corporation for 15 years or so. I say that so that what I say next will have some credibility. The correct tire pressure is based upon the size of the tire, the load it is to carry at a given speed, at a given temperature. Tires are put together with heat and pressure and they will come apart the same way.
The pressure listed on the sidewall of the tire is the maximum pressure for the tire's maximum load based upon highway speed as measured before running (cold). A tire running across Michigan in the winter is under considerably less stress than the same tire running across the desert in the summer.
The manufacturer inflation guides are the minimum pressures to be run for the weights listed. To be sure you have enough air pressure, check the pressure before starting out. Then stop when you have been running at speed for at least 15 to 30 minutes. Immediately check the pressure. If it was 90 when you started and is no more than 99 when you stop, you are running enough air. A 10% pressure build up due to heat is appropriate. If it is more than 10% you need to add air. This will allow the tire to run cooler and actually lower the operating air pressure when you check later.
If the tire does not build up any pressure after running it, you can safely lower the air pressure and allow the tire to perform better and last longer. However, it is always better to error on the high side.
One more plus using this system to check for proper pressures is that even if your air gauge is not calibrated properly the 10% rule still works.
See ya down the road.
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Old 04-10-2012, 03:36 PM   #10
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I know I'm going to get blasted for this, but, here goes:

My TPMS monitors air pressure and air temperature inside the tire, not the tire itself, the air inside. But it is incredibly useful, I see my tire pressures rise from 80 cold to around 90 running down the highway. But when its 100 out and the highway is 130, it gets really high (temperature). I thought at one time after I first installed the TPMS there was something wrong with my co-pilot front tire brakes, I was paranoid about the temperature going up 10 or 15 degrees. It was all ok, no brake problem, just typical temperature rise with rolling down the road. But it sure made me think something was wrong at the time.

My TPMS alarms at 15% over cold pressure set psi, which on my back 4 is 80 and on the front is 90. It also alarms at a fast pressure loss too. Love my system so far.
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Old 04-10-2012, 03:43 PM   #11
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Quote:
Originally Posted by BryanL View Post
Always consider pressure measured only at ambient temperatures. Manufacturers account for normal pressure increases from that basis in their sidewall ratings.

Temperature is what the pressure is all about. The pressure reduces flex which is where the temperature increase in operation comes from.

Your tire materials will suffer when tire pressure gets much over 140F. I am not very familiar with MoHo tires but the materials are the same for all tires, I think. I like to keep my tires at about 120F and I find that sun and road heat may make for a difference of 10F to 20F between sides sometimes.

Note that, while environment will make some difference, tire temperature on the road is mostly due to operational factors and will stabilize at 100F - 120F or so if you have the pressures right.

The weight on the tires is easily seen in tire temperature differences in my experience.

The key is that if you have a tire running hot, it needs air. That may be because of a leak or because it is carrying too much load or because the vehicle speed is too high for circumstances.

In a TPMS, tire temperature is a bit harder to measure. That is why some mount inside the tire so that they can monitor temperatures as well as pressures.

I make it a point to do a walk around with an IR thermometer on my rig during breaks to check tire and hub temperatures. Any significant temperature differences clue me in to a potential problem. I've discovered leaks before they went totally flat and loose brake springs that way.
BrianL, this is a great and informative piece you have written here. It is very easily understood and appreciated by me very much. Thanks!!

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