Tire Pressure question

[mlpeloquin]

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?

All autos have psi stickers. Ever look up the load/pressure chart for them. I have out of curiosity. The auto manufactures set the psi on the stickers for the maximum load the car is rated for. No I will never adjust the cars tire psi per the load chart. This sounds like an engineer and company lawyer writing this.

[Tskadberg]

Originally Posted by Dennis C.

Michelin does recommend getting a 4 corner weight.

Where have you read this recommendation? Seems like an odd policy as there is basically no place to do this. But for the traveling scales at rv rallies.

[Bill Gail]

As numerous prior post's have noted , unless you know your actual axle weight's you're flying blind .

I weighed our coach loaded for how we travel , 1/4 tank freshwater , empty gray and black water tanks , full fuel and propane along with clothing , lawn chairs , BBQ and assorted sundries . I've weighed the coach with and without the toad , with the boat and trailer attached and with the MG and trailer attached to provide a baseline for tire pressure .This will vary by individual needs .

I then used the Toyo Tire Pressure Chart . These are the Factory "recommended pressures" for the corresponding loads .

As I see it , no "safety factor " increase in pressure is necessary . The Engineers have already allowed for it in the recommended pressure . In fact the tire pressures increase when driving due to ambient temperature and friction , and those pressure increases are engineered into the tire design .

When traveling , I check tire pressures every morning . Seldom is an adjustment necessary .

A good set of tires , in good shape , set at the proper pressure will provide you with many miles of trouble free driving .

[cadillac_al]

So, the consensus is to ignore the manufacturers placard for recommended tire pressures and weigh your rig and find a tire chart for your tires and come up with a percentage to inflate past that recommendation. That makes perfect sense. Those motorhome engineers are probably just flunkies that couldn't get a job at General Motors anyway. Here I've been going by the manufacturer recommendations and having zero problems all this time. Man was I clueless.

[Jon_C]

Originally Posted by Onyrlef

Yes, you certainly could if they’d let you. However the Cat Scale Website very specifically in the block showing how to weigh a motor home states they cannot allow 4 corner weighing. If you were to happen up on an operator who isn’t aware of their policy would be the only way it’s going to happen. According to their site, straddling the scale, for any number of reasons, is a liability issue.

Thanks for pointing this out, it’s been a couple of years since I weighed, apparently the local folks at my scale didn’t know the rules ( They’re the ones who told me how to do it) or the rules changed since.

[ftodaro]

Originally Posted by cadillac_al

So, the consensus is to ignore the manufacturers placard for recommended tire pressures and weigh your rig and find a tire chart for your tires and come up with a percentage to inflate past that recommendation. That makes perfect sense. Those motorhome engineers are probably just flunkies that couldn't get a job at General Motors anyway. Here I've been going by the manufacturer recommendations and having zero problems all this time. Man was I clueless.

I think they needed to make a pathway for those who would not take the time to do it right.

[burgmark]

Originally Posted by Bill Gail

As I see it , no "safety factor " increase in pressure is necessary . The Engineers have already allowed for it in the recommended pressure . In fact the tire pressures increase when driving due to ambient temperature and friction , and those pressure increases are engineered into the tire design .

The safety factor is primarily due to the fact that I have my weight only for each axle, not for each tire position and one side will likely weigh more or less than the other side. Michelin recommends the same pressure for all tires on a single axle, so the safety factor is an attempt to compensate for the heavier side of the MH.

[Onyrlef]

Originally Posted by cadillac_al

So, the consensus is to ignore the manufacturers placard for recommended tire pressures and weigh your rig and find a tire chart for your tires and come up with a percentage to inflate past that recommendation. That makes perfect sense. Those motorhome engineers are probably just flunkies that couldn't get a job at General Motors anyway. Here I've been going by the manufacturer recommendations and having zero problems all this time. Man was I clueless.

Who said “ inflate past that recommendation?” The tire pressure recommendations on your data plate are correlated to the coach’s maximum allowable axle weights and that tire. You can ride from now on with that psi and that tire ( as long as you don’t exceed your max. axle weights) and you’re perfectly fine. Or, you can find your real-time axle weights, consult your tire manufacturers table and adjust your tire pressure accordingly. It’s not either/or. If your data plate recommends x psi on each rear tire @ 12,000 lb. max. axle weight, however your fully loaded axle weight is actually 11,000 lbs. and your tire manufacturers table recommends y psi, you can stay at x psi and be perfectly fine or go to y psi and be perfectly fine.

[Dennis C.]

Originally Posted by Tskadberg

Where have you read this recommendation? Seems like an odd policy as there is basically no place to do this. But for the traveling scales at rv rallies.

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® X® 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.”

[Onyrlef]

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® X® 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.”

That’s what you should do in a perfect world, however in an imperfect world where most reside there isn’t likely an accessible means to determine corner weights. In that likelihood plan B, is to weigh the coach at a Cat Scale, find tire mfg’er’s recommended psi for that tire on that axle, bump it 10% or so to allow for the side to side differential and carry on. I’m thinking no one ever had a tire failure and the guy at the shop said “ If he’d only added two more lbs”. Don’t let perfect be the enemy of the good.

[dperkinstx]

Originally Posted by Old-Biscuit

Get your RV weighed then use the TOYO RV Tire Load Chart

https://www.toyotires.com/media/1475...ion_tables.pdf

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.

[Dennis C.]

Originally Posted by Onyrlef

That’s what you should do in a perfect world, however in an imperfect world where most reside there isn’t likely an accessible means to determine corner weights. In that likelihood plan B, is to weigh the coach at a Cat Scale, find tire mfg’er’s recommended psi for that tire on that axle, bump it 10% or so to allow for the side to side differential and carry on. I’m thinking no one ever had a tire failure and the guy at the shop said “ If he’d only added two more lbs”. Don’t let perfect be the enemy of the good.

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.

[ChrisDParise]

[QUOTE=dperkinstx;6410588]I created this post because I'm installing a TireMinder TPMS and wanted to know what I should set my baseline tire pressures to. /QUOTE]

I love my TireMinder i10 TPMS.
Class C 30.5' Sunseeker 2860DS with 225/16" tires.
Duallys set to 80 psi which is max. Originally set rear baselines the same but quickly found out I was getting high pressure warnings messages at 92-3 psi (+15% over baseline) when hot.

Called Tireminder, btw support is M-F, and they recommended setting baselines to 85 psi.
Haven't had a problem since.

Tireminder manual is great but there's no mention within it on baseline recommendations.

Fwiw, front psi and baseline set to 65 psi and not had problems up there yet

[Crasher]

Originally Posted by dperkinstx

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.

If you don't believe the recommendation that TOYO produced, why did you weigh the coach and get their chart? The drive axle on my Bus weighed 19,800#, similar to yours and called for a similar pressure. I ran 85 psi in them for 50,000 miles. When I replaced them the tread depth was 1/3 less on the inner ribs than the outer ribs. That told me 85 psi was still above the minimum to carry the load. I trust the tire manufacturer to know what is best for me.

Edit: I set the TPMS minimum alarm @ 80 psi. If the weather was going to warm up, I drove slower for a few miles before coming up to highway speed. In the course of a year, I would adjust the pressure no more than once or twice due to OAT changes.