Tire Pressure

[DLane]

I am driving my first DP home from the dealer I purchased it from and have been monitoring tire pressure since I know this is important. I've noticed that the pressure after driving the coach for an hour or so is around 15 lbs more than my readings before starting out in the morning. Is this normal?

I also learned a lesson. One evening after arriving at my destination and checking into a hotel, I checked the tire pressure an perhaps an hour later and found it to be higher than necessary based on measured weights at each wheel. So, I let out air to obtain the pressures I desired (keeping pressure equal on each side of each axle). When I checked in the morning with an outside temperature around 10 - 15 degrees, I noticed the pressure had dropped in all tires about 5 lbs and were about that much below the pressure I wanted. I checked again after an hour on the road and the pressures were all up about 10 lbs above the minimum needed for the measured weight of the coach. This is the 15 lb increase I mentioned above. So, I learned to be careful when letting air out of the tires assuming I should only do this when the tires are cold. I also learned how long it takes to add air to the tires at a diesel truck stop.

I also felt the outside right rear tire after arriving at my destination today since it is on the heavier side of the rear axle and noticed if felt warm. Next I felt the left rear outside tire and noticed if felt cool. This concerned me until I checked the front tires. The front left (heavier side of the axle this time) felt cool while the right front felt warm like the right rear. Then I realize the sun was shining on the right side of the coach. Although the temperature outside was in the 20s at the time, I assume the warmth on the right side tires was due to the sun. Does that sound logical, or should I be concerned or check anything else?

[Nathan Focht]

If you search here you will find lots of topics about tires. But, get your coach weighed loaded. It is best to get the weight at each corner. Then you can go online and look up your model tire. The manufacturers have charts that will tell you the exact pressure to run on each axle.

A few key points on tires:

1. Always check pressure when cold before you start the days drive.
2. Always make sure the pressure is the same on all tires on the same axle.
3. Watch for damage (tears, nails, etc.) and wear (tread issues or cracking) before each days drive and I check while fueling.
4. Be careful what you put on your tires and check with the manufacturer.
5. If you change the weight or distribution of the weight in your coach, get it weighed and adjust pressures as needed.

Finally, the heat is normal and that is what is actually changing the pressure in the tires. The rubber flexes as you drive to absorb the road abuse. This flexing produces heat. The heat raises the temp of the air in the tire which then increases the pressure. This is why they say to check cold. The manufacturer designs this fluctuation into their tables. There are people that use a heat sensor to watch the tire temps but thinks like the sun, road heat, exhaust, etc. can affect the temp in each time.

Hope that helps.

[GaryKD]

Hi DLane,
For me, everything you posted is normal. My tires need air about once a year. That is in the Winter, when it gets cold. No more than 5 lbs puts them back to where they should be. Come Spring, it get warmer, and I let the air out. That's about it. The rest of the time they hold to the PSI I put in them. Consider purchasing are tire monitoring system. One can check the tire PSI from the drivers seat.

["007"]

Here is a link that will help you also so far every thing you have asked is normal

MICHELIN TIRE

[Digital Boy]

Good advice from Nathan. Just remember, the ambient (outside) temperature will determine the cold tire pressure at that time.

You don't have to add or remove air every day, just when the weather cools sufficiently for an extended period.

For example: I run 105 lbs in the front and 100 lbs on the rear tires. A couple of years ago I left Pigeon Forge, TN for a Newmar rally in Essex Junction, VT. It was September, I think.

The temps in VT dropped about 25+ degrees from TN. During a tire safety presentation I asked the Michelin and Goodyear reps whether I should increase my PSI in VT if I'm heading south to FL. They both agreed that I should not increase tire pressure if I'm going south. I didn't and once I was back in the southeast the pressure was back to normal.

[RVDude]

The Michelin link above is broken...
The correct link is
http://www.michelinrvtires.com...ference-material.jsp

In particular page 89 of the RV Tire Databook in the link above has the temperature correction tables - ONLY IF you check your pressure in a heated/cooled garage and then operate them at a different temp.

For clarity in the context of inflation "cold inflation pressure" means the pressure of an undriven tire at the outside ambient temperature - like all the posts above say. Air will change about 1 psi per 10 degree F. And of course, NEVER let the air out of a driven (hot) tire, the pressure is always measured cold (undriven).

So yes, if you filled to 105psi in sunny 90F Florida and then drove to sunny 0F Colorado, in the morning, your pressure will be about 105 - 9 = 96psi. You will need to add air to bring that back up to 105 as your new ambient operating temperature is now 0F. And of course if you drive the other way with ambient correct pressure, you will need to remove air (cold, undriven measurement) when you get back to 90F Florida.

As Digi Boy indicated, don't take this to extremes by adjusting for every 10 degree outside temp change every day. When you get to your new ambient, adjust then.

[DLane]

Thanks all for your constructive comments. My inclination is in line with your advice and I now am confident in how to maintain tire pressure.

["007"]

Thanks for the repaired link RV Dude.

[DAN L]

DLANE:
consider the TST TRUCK wireless tire pressure and temperature monitor system. peace of mind for about $300.
now i can run my tire pressure closer to the minimum for my weight giving me a better ride without compromising a safety cushion in case of a leak.

[KenSherwin]

Just to add confusion to an otherwise clear subject (oh wait a minute..... that's backwards) When you leave sunny 2.4 ft elevation Florida with properly aired tires, then show up in sunny 5280 ft. elevation (to pick a nice round number) Colorado, the reduced ambient air pressure will compensate somewhat for the lower temperature. It doesn't make very much difference, but I just had to stir the pot.

[RVDude]

ken - Touche!

Let's see, pv = nrt, or is it v1/t1=v2/t2 or is it pv/t=c or is it, e=mc^2 or is it i=e/r or, or, or, or, what the heck, it's all of them!

[Max Hubrich]

DLane,

I just installed the system DanL mentioned. I haven't made a trip yet but I am amazed at the temperature swings I see just parked, watching the tires on the sunny side vs the shady side. When a cloud passes by, the temp will drop 4-5 degrees almost immediately and then rise back up when the sun reappears. I will equalize all my tires in a sunless environment--- early morning or evening, from now on. We have a forum member that is a distributor. We are glad you are so concerned with operating your rig in a safe manner.

Good luck,

[RVDude]

I suspect those wild temp swings (when a cloud passes by) are because the senders are external, valve stem mounted? I don't see temp swings when a cloud passes by using the internal Smartire system. I suspect, those swings are one drawback to stem mounted senders????