Tire Pressure question

[Onyrlef]

Originally Posted by Dennis C.

I’m not saying it’s easy or practical. I’m just passing the information along.

I also use “Plan B” as I have axle weights at the CAT Scale but not corner weights.

Same here

[RVStitchy]

Originally Posted by Ray,IN

That is red is, to me BS. Do you ever do that with your autos, which has tires inflated to the Federal Safety Placard?

Agree it is BS. But you can't compare auto tires to RV tires. Thicker sidewalls design for higher loads does allow a degree of adjustment for actual weight.

[DaveMan]

I have a question on RV dual rears - I typically set both the inner and outer to the same tire pressure (in my case 85 psi) but i notice the inner always runs hotter than the outer (which results in a higher tire pressure on the inner. Does anyone run their inner at a slightly lower tire pressure? Is the difference in temperature and resulting pressure a cause for concern and increased wear?

Dave

[Jon_C]

Originally Posted by DaveMan

I have a question on RV dual rears - I typically set both the inner and outer to the same tire pressure (in my case 85 psi) but i notice the inner always runs hotter than the outer (which results in a higher tire pressure on the inner. Does anyone run their inner at a slightly lower tire pressure? Is the difference in temperature and resulting pressure a cause for concern and increased wear?



Dave

I run mine at same pressure. That small difference in psi under load won’t hurt anything. Ive got 25k miles on mine wear is even.

[twinboat]

The inner tire runs a bit hotter because of the brakes being in it.

No, you do not adjust for that. All rear tires run the same psi.

[Dennis C.]

I agree with the comments above. Run the duals at the same pressure.

[bentjm]

Originally Posted by dperkinstx

I created this post because I'm installing a TireMinder TPMS and wanted to know what I should set my baseline tire pressures to. The nearest CAT scale is 30 miles away. A round trip would cost me $50 in fuel alone. Meanwhile, there's a metal recycling place 2 blocks from where I store my RV, so I went there to have my RV weighed (I'll stop at a CAT scale some other time when I drive by one). I have a full tank of fuel, the water is about 1/4 full, and the black & grey tanks are close to empty (I always leave a few gallons in each after flushing).
I drove just the front tires onto the scale. The printout they gave me says 11,580 lbs. Then I drove across the scale, leaving only the rear tires on. The printout says 19,200.
My coach has Toyo 295/80R22.5 tires. Using your Toyo inflation table, I divided my front weight (11,580) by 2, giving me 5790. I decided to go with the 6285 number on the chart (95 PSI) because I'd rather have a little too much air in the tires versus not enough, plus the fact the copilot wasn't with me, I might put something in the forward bays, etc.
I assume I must divide that weight by 4, giving me 4800 (dividing by 2 is 9600, which is heavier than anything on the chart). According to the chart that puts me at 80 PSI. I think that's far too low. I decided to go with 95 PSI in the rear tires and see how the ride is.

If my calculations are unreasonable, please let me know before my next 300 mile trip.

95 psi on the rear is too high. 85 psi is where you should be based on the table. I consistently weigh in at 19,700 +/- on my rear weight and run 85 psi with no problems.

[Vibeman]

Tire threads, like engine oil threads, generate a lot of responses. I like reading these and getting a feel for the range of thinking on a topic. I want to add my recent experience to this thread since tire pressure not only affects load carrying capacity, but handling too. My Thor coach tire placard states to carry 82 psi in all tires. Stated GAWR is 7,000# on front axle and 12,000# on rear axle. I have Goodyear G670 RV tires. The Goodyear tire pressure chart for my tire starts at 80 psi, that is the minimum recommended pressure. I have weighed my coach fully loaded and know my axle weights and never overload. For simplicity and a safety factor I have been carrying 90 psi cold in all tires. I have onboard TPMS.
We are enroute now from Michigan to south Texas. 2 days ago, going west on I-30 in Arkansas I had near perfect driving weather, cool, sunny, very little wind, and very nice road conditions. Many trucks though. I was still noticing the front end feeling skittish when getting passed by semi’s. My TPMS read 107 psi on the front tires. In other circumstances I might have blamed pavement conditions, crosswinds, or steering play and just soldiered on. Instead, as a little test, at my next rest stop I let out 5 psi from both front tires. Within 15 minutes I was right back on the same road, the same conditions, same speed, but now with a very noticeable improvement in handling. I would not call it a night and day difference, but still very noticeable. I feel this is about as close as I could get to a test with controlled conditions.
UPSHOT: I still feel adding a little extra pressure to tires as a safety factor is ok, but it can have drawbacks too.
Since I know my axle weights, I could run all my tires at 80 psi ( the lowest Goodyear recommended pressure) and STILL have a margin of safety according to the Goodyear chart. Even more so because Goodyear has probably already added their own safety factor to their charts, over and above what their testing would actually warrant. It could also be that Thor even added their own 2psi safety factor too!
For the rest of the way down this year I will stick with 85f and 90r but on the way back north, in warmer weather, I may do a little more careful testing. BTW, I do carry an air compressor with me.

[Tskadberg]

Originally Posted by Dennis C.

This recommendation is found in the Michelin RV Tires Guide For Proper Use and Maintenance for my new tires. Pages 12 - 16 outline the various types of scales and provide information on how to weigh each corner of the coach. Additionally, these pages provide information on how to read the weight and inflation charts to properly inflate tires.

Here are a couple of quotes from the guide:

“Even though the weight of the total axle is within the axle rating, it may be overloaded on one side, which means an overloaded wheel position. That’s why side-to-side weighing is required.”

“Let’s consider an RV running on 275/80R22.5 MICHELIN[emoji768] X[emoji768] LINE ENERGY ZLRG tires, with actual corner weights of 5,400 lbs. on the left front tire, 5,175 lbs. on the right front tire, 8,500 lbs. on the left rear duals, and 9,200 lbs. on the right rear duals. For control of the RV, it is critical that the tire pressures be the same across an axle. Therefore, we must “overinflate” the right front tire and the left rear duals. Checking the load/inflation table below shows that a cold tire pressure of 95 psi will support 5,510 lbs. on a single front tire.

To determine the pressure for the rear duals, again take the heaviest position, in this instance the right rear weighs 9,200 lbs. The load/inflation table below shows that a cold pressure of 85 psi will support 9,380 lbs. on 2 dual tires. It is important to note that the cold inflation pressure for the tire must never exceed the maximum inflation rating that is stamped on the wheel.”

Still an insane recommendation as there are only traveling 4 corner scales. All RV are suppose to chase these traveling scales around? It’s pointless recommendation if there are no means to follow it.

[Dennis C.]

Originally Posted by Tskadberg

Still an insane recommendation as there are only traveling 4 corner scales. All RV are suppose to chase these traveling scales around? It’s pointless recommendation if there are no means to follow it.

The guide shows how to weigh your coach at a CAT scale by positioning the coach with only one side on the scale, as mentioned above. I think some CAT scales have space for this and some do not. Additionally, a heavy duty scale that’s capable of weighing each corner can be purchased for home use for under $1,000. It’s not something that I feel the need to purchase, but it’s an option if someone is really concerned about this issue and doesn’t mind spending that much money.

[Tskadberg]

What is the biggest difference anyone has found on a 4 corner weight?

[Jon_C]

Originally Posted by Tskadberg

What is the biggest difference anyone has found on a 4 corner weight?

My rear axle had 500lbs heavier on passenger side, mostly due to batteries. Only 100 lbs difference on steer axle.

Measured on my local cat scale 2 years ago which I understand from this thread is no longer allowed.

[Crasher]

Originally Posted by Tskadberg

What is the biggest difference anyone has found on a 4 corner weight?

My Bus was close to 1,000# heavier on one rear and 800# off on one front. It has four ride height valves and the dealer was able to get the steers within 100# and the rear within 500# which is well within accepted parameters.

[grassy]

I weigh, and my pressures are based on the weight..