Community Forums

jimnkarens · 10-07-2013, 06:49 PM

Of the eight tires on a class A, two front, two rear, dual in middle, how should tire pressure be balanced? All same pressure? More in dualies?

jlfbatonrg · 10-07-2013, 07:00 PM

Depends on the weight distribution of the coach. The correct way to determine your optimum tire pressures is to take the coach to a weigh station and weigh the coach preferably all four corners separately.It should be weighed fully loaded. Hope this helps.

Mr_D · 10-07-2013, 07:09 PM

Each of the major tire manufacturers publish an RV tire booklet. It shows how to weigh the rig and gives some of the weight/pressure charts. I have them for Michelin, GoodYear and Toyo. Some tire companies don't publish the charts so then you just inflate to the pressure on the sidewall, which, in most cases, is the minimum pressure to support the maximum rating of the tire.

jimnkarens · 10-07-2013, 07:16 PM

Yes!

Thank you both.

Crabby Mike · 10-07-2013, 08:49 PM

Inflating to the pressure listed on the sidewall would be safe, but likely more than needed, and would probably provide an unnecessarily rough ride. There should be a sticker somewhere in your coach (usually on the wall by the driver's seat) listing the weight ratings for each axle and the entire motorhome, and the tire pressures corresponding to those ratings. Those are the RV manufacturer's recommended tire pressures for your coach, and will likely be less (sometimes a lot less) than the sidewall pressures. If you find that, you'll probably find that the front tires need the most pressure (since there are only two of them), and the dually and tag tires will take much less. Also, though tire pressures may vary by axle, all tires on the same axle get the same pressure.

All of this, of course, is only to get you by until you can get the coach weighed (each axle, and preferably each end of each axle), consult the tire manufacturer's table for your specific tires, and set the pressures where they should be.

jimnkarens · 10-07-2013, 10:12 PM

Thank you. Good info.

dennis45 · 10-08-2013, 12:15 AM

I had trouble finding a place that could weigh each corner. All I could get was front and rear from your typical Weigh Scale.
So, I started with 100 Psi in the rear and 110 in the front. I bought a hand held IR Temp Gun and after running on the road for a couple hours I stopped and checked the temps on each tire and began to experiment with pressures.
Turns out, the Right Side was running hotter than the left on the rear. The fronts were pretty close side to side but running pretty cool.
I raised the Right Rear pressure to 105 and then to 108. Left rear is at 102.
Now, my temps are all in the range of 90-100 deg F on a 75 Deg day. I lowered the fronts to 105 and the temp came up and it rides nicer.
Point is, all these charts are a great starting point but the key is operating temp. If the tire is running hotter it is telling you to raise the pressure to keep the side wall from flexing excessive. If they feel cool, they are over inflated and not flexing as they should to give the proper ride.
Tires should feel warm to the touch after a couple hours on the road fully loaded when properly inflated. Ambient of course will have an effect as to How Warm.
After going through this exercise on a few trips and adjusting my pressures according to temperature, my coach rides and handles like dream.

Mr_D · 10-08-2013, 12:38 AM

Quote:

Originally Posted by dennis45

I had trouble finding a place that could weigh each corner. All I could get was front and rear from your typical Weigh Scale.
So, I started with 100 Psi in the rear and 110 in the front. I bought a hand held IR Temp Gun and after running on the road for a couple hours I stopped and checked the temps on each tire and began to experiment with pressures.
Turns out, the Right Side was running hotter than the left on the rear. The fronts were pretty close side to side but running pretty cool.
I raised the Right Rear pressure to 105 and then to 108. Left rear is at 102.
Now, my temps are all in the range of 90-100 deg F on a 75 Deg day. I lowered the fronts to 105 and the temp came up and it rides nicer.
Point is, all these charts are a great starting point but the key is operating temp. If the tire is running hotter it is telling you to raise the pressure to keep the side wall from flexing excessive. If they feel cool, they are over inflated and not flexing as they should to give the proper ride.
Tires should feel warm to the touch after a couple hours on the road fully loaded when properly inflated. Ambient of course will have an effect as to How Warm.
After going through this exercise on a few trips and adjusting my pressures according to temperature, my coach rides and handles like dream.

Interesting experiment, but NOT what the tire companies say to do and they have engineers that do nothing but test and make the weight/pressure charts for the public to follow.
BTW: all tires across an axle should have the same pressure.

dennis45 · 10-08-2013, 12:48 AM

Quote:

Originally Posted by Mr_D

Interesting experiment, but NOT what the tire companies say to do and they have engineers that do nothing but test and make the weight/pressure charts for the public to follow.
BTW: all tires across an axle should have the same pressure.

I agree, as long as they are carrying the same weight. Is this not the reason for weighing each corner?
IMHO, If the tire is carrying a higher weight it requires a higher operating pressure to prevent the side wall from over flexing. As per the Mfg Tire Chart.
friction caused by sidewall flexing, results in heat. Measure the temperature and you can tell if the side wall is doing its job that it is rated for.

ru499 · 10-08-2013, 04:19 AM

To be honest, I would not inflate my tires just enough to cover the weight I'm carrying just to do away with ride harshness. Having been a truck driver for 40 yrs now, I don't ever recall a trucker adjusting tire pressure for a particular load. On my coach, I run my 22.5 tires at 105psi cold. The pressure will go up to about 115-120 when they are hot. Works for me. Also, when you run more pressure, you may have a harsher ride, but you should have less rolling resistance, better mpg.

As for weighing each corner, well I've never seen that either in trucking. What if you are a little over on, say the right rear. What are you going to do, buy a higher load range tire for that wheel? That would seem kinda silly. If you're right at the load limit of your tires or axels, you probably ought to get rid of some weight or buy a bigger rig.

FormerBoater · 10-08-2013, 06:03 AM

Quote:

Originally Posted by Mr_D

Each of the major tire manufacturers publish an RV tire booklet. It shows how to weigh the rig and gives some of the weight/pressure charts. I have them for Michelin, GoodYear and Toyo. Some tire companies don't publish the charts so then you just inflate to the pressure on the sidewall, which, in most cases, is the minimum pressure to support the maximum rating of the tire.

Make sure all your fillings are secured, all screws tightened to specification etc. if you go this route.

Over inflation is likely the result, hard on the equipment and the tires IMHO.

bdickson · 10-08-2013, 06:05 AM

My sticker said 105 psi all round. I had the coach 4 corner weighed and looked up the tire manufacturers charts. Using the heavier weight on each axle I'm running at 90 front 95 rear. I then installed Crossfires on the duallies so the pressure in each pair of tires is the same.

Setting each side of the coach to different pressures does not sound safe. When I check my temperatures after a run, left and right sides can have a big difference, but that is due to the direction of the sun hitting the rig.

Ray,IN · 10-08-2013, 06:46 AM

Quote:

Originally Posted by Mr_D

Each of the major tire manufacturers publish an RV tire booklet. It shows how to weigh the rig and gives some of the weight/pressure charts. I have them for Michelin, GoodYear and Toyo. Some tire companies don't publish the charts so then you just inflate to the pressure on the sidewall, which, in most cases, is the minimum pressure to support the maximum rating of the tire.

I agree. The RMA (Rubber Manufacturers Association) states over 90% of all tire failures are the result of under-inflation/overloading. Regardless of my coach weight, all the tires are inflated to mfgrs recommendation for coach GVWR.

Post43 · 10-08-2013, 06:53 AM

I have been running 90 lbs in all six of my 22.5 Michelin tires. My coach feels like I'm running cement tires! Not on good roads, but on bad city type side roads. I have added air suspension and new shocks, huge improvement! But still I am going to get the rig weight checked. A quick look at the pressure charts shows as little as 70 lbs at around 4200 lbs!!!
So.... my quest continues.