Tire Pressure

[chris cross]

It's 3:00 in the afternoon and I'm leaving in the morning. My front tires are set at 110 psi. The rears are at 100 psi. The next day, our departure day, and at 8 am. the front tires on our tire system read 100 psi. and the rears are 8/9 psi. lower. Question??? should I inflate the tires to the psi. they were at 3:00 yesterday? If I add 10 psi. to the fronts, will they be 120 psi ??? Saftey is a primary concern, but a very hard ride is no fun.
Thanks,

[chris cross]

It's 3:00 in the afternoon and I'm leaving in the morning. My front tires are set at 110 psi. The rears are at 100 psi. The next day, our departure day, and at 8 am. the front tires on our tire system read 100 psi. and the rears are 8/9 psi. lower. Question??? should I inflate the tires to the psi. they were at 3:00 yesterday? If I add 10 psi. to the fronts, will they be 120 psi ??? Saftey is a primary concern, but a very hard ride is no fun.
Thanks,

[OldForester]

Chris,

If you have the Toyos, you are probably set 10 psi too low. On my 2006, Toyo put a placard in the front of the coach on the firewall behind the generator slide that said 120 psi in the front and 110 psi in the rear cold, and also issued a statement to WRV per previous threads on this forum that this is where the Toyos need to be set no matter what the load.

We have 28000 miles on our 2006 and have been following this advice and so far it works well. We have days, depending on the outside temperature and air pressure (big difference with altitude) where we might be 115 to 124 in the morning on the fronts and 106 to 112 in the rear when cold, based on our SmartTire system. We periodically verify with our tire guage and find it to be very close.

So your temperature and air pressure outside, depending on altitude, will vary the pressure. You are probably safe to drive in the short term, but if you have the Toyos, you should get up to the tire pressure on the placard in the front of the coach, which will probably be 120 in front and 110 in the rear. If you have Good years or another brand, you can adjust the pressure to the weight of your coach and the temperature and air pressure.

It is very common on our coach to have 10 psi of difference between a warm sunny afternoon and a cool morning in our tires. I always start with the temperature in the morning when it's cool and before there's a lot of sun on the tires, as my "cold" temperature.

[chris cross]

Thanks Old Forester: We do run the Goodyear G670 and the pressure calls for 110 front and 100 rears. You did answer my question about the temp. and the pressure.

[Old Scout]

I dont think altitude is a determinate of internal air pressure in a tire--except to the extent that lower external air pressure at altitude might allow a tire to slightly expand in size/volume. Believe air/tire temp is the primary variable. "Cold inflate tire to 120#" at 20 degrees is vastly different than at 70 degrees. Even on a moderately cool morning, the difference in tire pressures between the sunny and shady sides of the coach is dramatic. It seems the only thing that is clear here is that you cant check tire pressures once tires have attained operating temperature.

[OldForester]

Old Scout,

You can check tire pressure all the time with something like SmartTire, if the vehicle is moving, including when it's hot. My front tires will go from 120 psi cold to 140 to 142 psi when warm on a 80 degree day, and my temperature will go up to 150 or so. As long as it's under 200 I don't have a lot of concern.

I find my front tires on a 45 degree morning are around 115 psi in the front at 4000 feet, like in Van Horn, Texas, and 120 psi in the front at 300 feet in Palm Springs, CA, at 45 degrees in the morning before the sun has had an impact on them. The rears go from 110 to about 104-105 on the same situation, and I just checked this again at both places in the last two weeks without adding air to them. I've also found at 7500 feet I lose about 7 to 8 lbs.

So I think altitude makes a difference, and I try to compensate by keeping my air at the 120 psi front/110 rear when I'm closer to sea level, which is true for me in Palm Springs and when I'm home near Tacoma, WA.

Now I have found that air temperature does make a big difference to your point. My front tires on the sunny side of the coach will gain 10 lbs going from early morning at 45 degrees with no sun to 75 degrees and sun later in the day in Palm Springs.

My point of view is that both temperature and altitude matter; try to get the tires set at a lower altitude at a reasonable temperature and leave them alone and watch them on a tire pressure monitoring system like SmartTire, or similar, if you have it.

[Dale777]

Chris,

Tire pressures are supposed to be set to the designated temperatures when the tires are cold. Now, what does "cold" mean? According to tire manufacturers, "cold" means 68 degrees ambient temperature.

If you set the tire pressure to the designated pressure, say when the ambient temperature is 105 degrees, then you have too little tire pressure. If you set the tire pressure to the designated pressure, say when the ambient temperature is 32 degrees, then you have too much tire pressure.

Also, I've found that tires on the side of the coach while it is at rest in the really warm sun will have tire pressure as much as 5 psi higher than the shaded side. Through experience and trial and error, you can learn to compensate for ambient temperature.

I've found the best time to set tire pressure is very early in the morning before the sun has had any effect on one side of the coach versus the other and when it is cool outside, in the vicinity of 68 degrees.

[Springtime]

On the topic of tire pressure, I would appreciate hearing from anyone who has a Tire Pressure monitoring system on their Class A. It is something that I am looking to purchase for our new 2008 Winnebago Adventurer. The dilema is that I have receive several quotes but the prices have been all over the board, ranging from $300 to $1,200. What can I expect to pay as a reasonable price? I am willing to pay for a good quality dependable system, but at the same time, don't want to be ripped off with an inflated price.
Thanks for your advice.

[OldForester]

Springtime,

There a number of systems out there. We installed SmartTire when we bought our coach. We also installed the transmitters on our Toad so we would know the pressure and temperature in it going down the road.

I believe SmartTire is probably near the high end of the price range you quoted. So there may be others that work just as well and are cheaper.

I really like SmartTire because I know pressure, temperature, and deviation from whatever norm I set for each on a continuous basis. I can see the change in temperature and pressure while I'm driving. And if the the Toad develops a flat tire I know about it right away before it damages the rim. It gives a "beep" and a red warning light whenever anything is out of the normal range I set and tells me which tire.

The bad thing about SmartTire is that it takes longer to install, having to dismount the tires and put a clamp and transmitter in each wheel. And when you change tires on the Toad, the installer must be careful not to damage the transmitter. But this is not a major event.

The other thing about SmartTire is you have to get the vehicle rolling for a ways (usually a mile or two for me) before all the transmitters fully connect with the display. So when I sit for an extended period, like a week or so, I usually check the tires with a guage before I start.

So, I would give SmartTire a high recommendation -- it tracks closely with my manual pressure guage and has operated superbly over two years and 28,000 miles. My only repair issue occurred when one clamp broke on one inside dual and I had to replace that clamp at a Camping World store.

[jerry davis]

Our coach did not come with a monitoring system so I installer the Doran unit which has small sending units that are screwed onto the valve stems. Obviously the installation is a snap as the tires do not have to come off the rims.

This unit gives me continuous pressures on both my toad and the coach and also gives off an alarm when pressure drops more that 15%. I think the total cost was about $750 including the sensors for the toad.

The sensors have been on for three years now and I have not had to replace any of them. The one drawback is that you have to send the sensors back to the factory to have the batteries replaced. But Doran says they are getting 5-6 years out of the batteries.

[takepride]

There is a pretty good synopsis of what's available and the differences on page 62 of the February 2008 FMCA magazine. Also online at fmca.com

The basic differences are:
<UL TYPE=SQUARE><LI>inside rim vs. stem mount

<LI>pressure vs. temperature and pressure

<LI>antennae vs. no antennae

<LI>pricing[/list]
Some folks believe the temperature is very important and point out that when mounted inside the rim, they cannot be stolen. Others feel it's better to have something affordable rather than nothing at all.

The article also lists all the websites for the various companies. Have fun comparing!

[NorCal Hal]

We have the Doran Pressure Pro system (PPS)on the 2006 which we transferred over from the 2003. I feel it has a couple of advantages over the Smart Tire system (STS) WRV offers.

The PPS, as an earlier writer said, has the small transmitters that you screw onto each tire valve stem. The STS transmitter is inside the tire attached by a band around the wheel.

I like the portability of the PPS. I bought ten transmitter caps (six for the coach and 4 spares)and I can switch the four on the tow from the Jeep to the truck depending on which vehicle I want to use.

The inside monitor (receiver) is also portable. I have taken the entire system out of the motorhome and used it on the truck and a trailer I was using when I helped our daughter move. In fact, we had a low tire on the trailer that wasn't obvious when we left but the PPS alerted us to after a few miles. I was able to stop and add air preventing what undoubtedly would have been a blow out on the freeway.

Some say that the STS had an added advantage in that it also gives the tire's air temperature. I personally don't see that as an advantage. The only high temeperature you need to be concerned with is when the tire overheats due to low air pressure and the low pressure indicator, not the temperature sensor, will warn you when the pressure drops below 5% of the established PSI you set.

I had problems with the PPS sensors working on the inside rear duals until I got rid of the cheap valve extentions that came on the coach.

After setting the tires at the recommended pressures, while traveling down the highway I can cycle though the individual tire readings and clearly tell which tires are in the sun or shade by the PSI differences.

[NorCal Hal]

Another advantage of the Pressure Pro System.

If you set your tire pressures at 60-70 degrees and wake up some morning to 20-30 degrees the tire pressures may be low enough to activate the low pressure alarm.

If this occurs (and it has for me) you can either silence the alarm and drive a few mile until the tires warm up and the tire pressure increases OR if you intend to be spending some time driving at those temperatures you can unscrew each sensor for 30 seconds then re-install. The sensor now has the new "low pressure" setting as it's base setting.

When you drop down in elevation or move to a warmer area where the tire pressures return to your original pressures, the sensor setting will still be fine as pressures the higher than the base setting does not cause an alarm.

The ONLY affect will be that the tire pressures now have to drop another few PSI over the 15% before the alarms sounds.