Tire pressure increases

[Mike T Phillips]

43 ft holiday rambler imperial 2008

i start out with all my 8 tires at 100 psi that was Recomended by my tire installer. After a trip of 25 miles all the pressure has increased aprox 10 psi except the front two.  the driver side increases to 120 psi and the passenger side front goes to 127 aprox.   It  never has gotten over 135 psi.      The temp increases aprox 15 degrees on all the tires.       Is this something I need to have checked and what could be wrong 

[96 EVO]

What size front tires?

If 295/80, I don't think 100psi cold, is enough!

I have a similar size coach, and inflate my steer tires to 115psi.

[klcdenver]

That is normal for pressure to increase with heat. If you are using a aftermarket TPS they are not precise accurately. They are designed to basically only tell you of a pretty fast loss or rise in pressure giving you time to get stopped before a catastrophic condition. 

[timaz996]

It is important to weight your coach and run the cold pressures from your tire manufacture listed for those axle weights. The tire pressure increase for the front is higher then I would expect. Until you weigh it look at the placard that lists tire pressures by your driver's seat and us those. A tire pressure that is too low will run hot and over flex the side wall. Go to your tire manufacture's web-site and look up your tire model.

[Tom Cherry]

3 hours ago, Mike T Phillips said:

43 ft holiday rambler imperial 2008

i start out with all my 8 tires at 100 psi that was Recomended by my tire installer. After a trip of 25 miles all the pressure has increased aprox 10 psi except the front two.  the driver side increases to 120 psi and the passenger side front goes to 127 aprox.   It  never has gotten over 135 psi.      The temp increases aprox 15 degrees on all the tires.       Is this something I need to have checked and what could be wrong 

Bottom Line…. Look at the Driver’s tire plate data and inflate, cold, as in the early morning, right before the sun starts radiating and increases the temperature.

Then weigh it per the instructions in the manual.  The TAG setting is critical.  Most run around 40 - 60 pounds…but that is MEMORY.  Any truck scale with no guard rail on one side and a flat, NOT elevated scale pad will do.  Get the weights for the entire rig…all three axles…individually. Then pull back on with one side OFF the scale pads and repeat.  Subtract the second side from the total…bingo. INDIVIDUAL corner weights.

UNLESS you have the SmartTire of the TPMS sensors on a band inside the wheels, the temps are meaning.  They are just measuring the ambient around the valve stem….

If you inflate to the recommended pressures, say, 115 on the steers, then you will run in the upper 120/low 130.  Tires FLEX.  You need to drive at least an hour for the tires to “get to the thermal equilibrium” temperature. That is when the tires flex and build up heat but the rotation and fresh air dissipate the heat….in other words…STABILIZE.

Many TPMS have alarms you can set…anywhere from 15 - 25% above the set point.  Typically 18 - 20 PERCENT….not PSI…

Your inner rears will run 3 - 5 PSI hotter than the outers.

NEVER, EVER trust a tire shop to know the “correct pressure” for a Motor Home.  They deal in truck tires and load them up.

 

[Ivylog]

Your tire installer is wrong. Until you can weigh use 110F 100D and 80T with it’s regulator set at 40.

[David Pratt]

23 hours ago, Mike T Phillips said:

43 ft holiday rambler imperial 2008

i start out with all my 8 tires at 100 psi that was Recomended by my tire installer. After a trip of 25 miles all the pressure has increased aprox 10 psi except the front two.  the driver side increases to 120 psi and the passenger side front goes to 127 aprox.   It  never has gotten over 135 psi.      The temp increases aprox 15 degrees on all the tires.       Is this something I need to have checked and what could be wrong 

Tires are a major concern to everyone, whether it be a motor-home, travel trailer, truck, aircraft or even a bike. All of us want to maintain and service our tires to get the most life from them.

I am most conscious about proper tire care, tire inflation, heat, load limits, speed ratings to name a few things of importance. Somethings about tire care are very simple and in most cases other things get more difficult because of lack of knowledge or experience.

Tire Maintenance and Tire Care is always a Discussion we have at the Gathering.

I learned a lot about tires mostly because of my experience in auto racing and maintaining my own aircraft. 

Tom Cherry and Frank McElroy mentioned Thermal Equilibrium. I would venture to say that most folks have never heard of it, let alone understand it. Thermal Equilibrium is the one most important issue we dealt with in our race cars. It alone can determine how the car handles and tire life/wear. Thermal Equilibrium sounds like it is more heat related but, the air pressure in the tire is what regulates it more unless some outside development was in play, such as overheated brakes, bearings, heat from the sun and road surface temperature.

Since I purchased my first Motor Home, my first project was always to weight the coach and establish the correct tire pressures. When TPMS came on the scene it made the job much easier.

One of the methods that is always discussed is to have the coach weighed on all corners and establish the maximum axle weights to establish the correct air pressure for each tire on that axle based on the heaviest corner on the axle. Tires should be inflated to the same pressure on that axle with a minor exception.

Once I have established the Load factors for each axle and the base line air pressure I will take it to the next step which does take time and some driving. This is where Thermal Equilibrium and how it effects tire performance comes into play. I take the coach out on the highway and at highway speed 60 - 65 MPH I travel one hour and log the tire temps, Then again at 1.5 hours and log the temps again at the 2 hour mark and monitor each hour after that.

Under most normal circumstance the one hour mark will be your tire blow up pressure.This is the point where the tire pressure has achieved Thermal Equilibrium. At this point forward your tire pressures should be stable with little change.

That one hour tire pressure(blow up pressure) will be different depending on what air you use to fill your tires. The blow up pressure will be higher if you fill your tires with just air and will be lower if you fill and maintain your tires with Nitrogen. The ideal Blow Up pressure should be no more than +/- 20% max.

The second step is to lower the tire pressures in each tire 2-3psi below the baseline tire pressure in step one and take it on the highway again repeating the first step and logging the temps.

The third step is to repeat the first step again but raise the tire pressure 2-3psi above the baseline tire pressure in step one.

Compare the one hour blow up pressures. If the blow up pressure is higher in step two it indicates a low base line temp. In step 3 If the pressure is lower that would indicate to much pressure. If your using Nitrogen to keep your tires inflated your average blow up pressure will be 12-14% above your base line pressure. If you fill you tires with just air the blow up pressure will be 14-20% higher than you base line pressure. Raise or lower the baseline tire pressure to where your blow up pressure is is with in the percentages and stays stable for the duration of your trip.

An Example; My baseline pressure in my Steer Tires is 115psi and the blow up pressure stabilizes at 128psi. Drive Axle tires baseline pressure are105psi and the blow up pressure is 118psi. The tag axle tires baseline pressures are 95psi and blow up pressures are 107psi. these pressures are consistent whether I am on the road two or five hours.

As noted in prior posts about the inner drive axle tires having a higher pressure than the outer drive axle tires this is not uncommon, there is a lot of heat generated by the engine and transmission being funneled through that area. but a 30% jump above the base line pressure is and indication something else is going on.

When I was doing the tire pressure tests I saw that the inner drive axle tires blow up pressure would be 3-4psi higher than the outside tires. So I started to adjust the inner baseline pressure down until the inner tires would be at the same blowup pressure. My base line pressure on the drive axle tires are; L/Outer-105psi, L/Inner-103psi, R/Inner-102psi, R/Outer-105psi. One hour Blow up pressure is stable at 118psi.

All the tires on my coach are filled and maintained with Nitrogen.

My TPMS also measures heat. I very rarely pay any attention to it. Your tire psi will warn you of a problem with the tire long before the temperature will.

With the race cars the only time we are concerned with the tire temps is when we changed the tires in the pits. We would measure the temps across the tires along with the tread depth. The tires temps would tell us how the tire was contacting the track surface(GRIP) and if we need to make any alignment/suspension adjustments.

[timaz996]

From Dave: "When I was doing the tire pressure tests I saw that the inner drive axle tires blow up pressure would be 3-4psi higher than the outside tires. "  This is why I run Crossfire on my duals. When you change the pressure, you change the circumference. One tire taller then the other creates friction...heat. The Crossfire doesn't let the good tire loose much air (10 psi max) if one tire blows. 

[Paul J A]

WEIGH YOUR COACH. Four , or Six corner weight is the best, but single axle weights will be OK too. Fuel and water full. Black and grey tanks empty with your stuff on board. CAT scales at many truck stops. Tell the clerk you want to weigh a coach. There is an intercom at the scale so you can communicate with the clerk. There will be 3 platforms for3 axles. Steer axle on the  first, Drive on the second, and if applicable, Tag on the third. Keep the ENGINE Running, so you stay at Ride Height. Get the print out from the clerk. IF you have a tag axle, you may have to adjust your DOWN pressure to move weight as needed, and after adjusting your down pressure on the tag, REWEIGH the coach.  Now go to YOUR tire Mfg. inflation charts for the correct COLD inflation.

 

 

 

 

[Jetjockey]

The sunny side will be higher temps and pressures