Optimum tire air pressure

Topic: Optimum tire air pressure (Read 1198 times) previous topic - next topic

Optimum tire air pressure

October 06, 2020, 01:13:10 pm

1998 U270 with Toyo 295/75R 22.5 tires. What's optimum tire pressure for best ride, but still save tire wear.

Re: Optimum tire air pressure

Reply #1 – October 06, 2020, 01:19:13 pm

To be the most accurate, you should get a front and rear axle weight reading. Then you can use the PSI per the tire manufactures rating. The weight of your coach will make a difference of the pressure to use.

Re: Optimum tire air pressure

Reply #2 – October 06, 2020, 01:30:46 pm

Quote from: MarkC – October 06, 2020, 01:19:13 pm

To be the most accurate, you should get a front and rear axle weight reading.

To be even more accurate, you should get your coach 4-corner weighed. Otherwise, you are just guessing at what pressure to run.

Why? If one corner of your coach is significantly heavier than the other, then the tire pressures on that axle should be based on the weight of the heavy end of that axle.

Escapees SmartWeigh program is a well known service. 4-corner weighing is also available from other vendors.

SmartWeigh · Escapees RV Club

Re: Optimum tire air pressure

Reply #3 – October 06, 2020, 01:45:42 pm

Quote from: Chuck & Jeannie – October 06, 2020, 01:30:46 pm

To be even more accurate, you should get your coach 4-corner weighed. Otherwise, you are just guessing at what pressure to run.

Escapees SmartWeigh program is a well known service. 4-corner weighing is also available from other vendors.

SmartWeigh · Escapees RV Club

RVSEF is another that does 4-corner weighing

Why Weigh?

Some NIRVC (National Indoor RV Centers) locations also have the ability to do 4-corner weighing. Lewisville, TX is one. Not sure about the others.

Until one has at least axle weights and preferably 4-corner weights, inflate per the manufacturer load/inflation tables, assuming GAWR is what each of your axle weighs. 'Tis better and safer to be somewhat overinflated than underinflated at all (the latter causes damage to the tires).

(ETA the data plate by the driver's seat lists pressures based on GAWR for the OEM tires, which would no longer be applicable)

Re: Optimum tire air pressure

Reply #4 – October 06, 2020, 02:26:06 pm

Quote from: Chuck & Jeannie – October 06, 2020, 01:30:46 pm

To be even more accurate, you should get your coach 4-corner weighed. Otherwise, you are just guessing at what pressure to run.
Why? If one corner of your coach is significantly heavier than the other, then the tire pressures on that axle should be based on the weight of the heavy end of that axle.
Escapees SmartWeigh program is a well known service. 4-corner weighing is also available from other vendors.
SmartWeigh · Escapees RV Club

Bus companies, fire dept, most truckers just max the tires, That what I have always done and happy with it.

If you base the tire pressures on the weight of each corner, then you will chase the weight depending on the amount of diesel, propane, grey and black water tanks and the weight/way you load your coach for each trip. Adding weight to one corner in the front will take weight off the opposite corner in the back.

And yes, it rides just fine at 110 psi. Handles well and stops quickly too.

And for those who talk about contact area, etc, do you think fire departments and bus companies compromise public safety? Keeping the public safe is their job. We are talking real world here, not armchair theories.

Pierce

Re: Optimum tire air pressure

Reply #5 – October 06, 2020, 02:33:01 pm

I'm at 100 in front and 95 in rears. After trying different pressures, This is the best overall for mine. 1996 U295-36footer, 31,000 loaded. Mt TST monitor system shows 107 at 65 on fronts and 100 in rears

Re: Optimum tire air pressure

Reply #6 – October 06, 2020, 07:06:03 pm

Maybe someone with a very similar coach could post their weights .
Take the weights and check your tire inflation chart. Add 5 pounds just cuz until you find a scale.
100 should be safe until then imho.
My old minibus is 80x 6😍

Re: Optimum tire air pressure

Reply #7 – October 06, 2020, 07:41:46 pm

If you are smooth roads everything from the correct pressure on up works ok. Rough roads? The correct rides better

Re: Optimum tire air pressure

Reply #8 – October 06, 2020, 07:45:05 pm

Guys,

There is a reason that the tire manufacturers went to the time/trouble/$$ to publish PSI/Load tables. They KNOW that proper PSI depends on actual load.

Can you inflate to PSI on the sidewall-- sure! But hopefully (because you do NOT want the tire loaded to their absolute capacity) that will be well over-inflated. Read that HARSH RIDE.

Re: Optimum tire air pressure

Reply #9 – October 06, 2020, 08:08:59 pm

Overinflated results in running on a narrower center part of the bead. Depending on design any self steering parts of the design are lessened. Plus hydroplanes easier. Skitterish on ice

Re: Optimum tire air pressure

Reply #10 – October 06, 2020, 08:52:39 pm

I've settled on 90# front and rear, when I ran across a free scale in Montana last month everything was how it should be and at 23,400# loaded, a ton and half below max.

Re: Optimum tire air pressure

Reply #11 – October 06, 2020, 09:40:48 pm

Cold psi will be stamped on the tire.. I follow that to the letter with 80,000 lb truck to 30.000 lb coach. Under inflated tire will over heat in hot weather. Tire mfg stamps that information for a reason.

Re: Optimum tire air pressure

Reply #12 – October 06, 2020, 10:08:04 pm

I know that tire pressures are something everyone has a different opinion on. I will say that on a 2800 mile trip that we just finished last week, and the first with my TPMS, I did find this out...................
Previously, I had ran with the recommended PSI on the side of the tire and the pressure would increase about 10 PSI from cold to hot tires.
Halfway through the trip in NAC, I had the coach weighed and based on the axle weights, we able to drop the pressure 15 PSI on the rear and 10 on the front.
The ride improved DRAMATICALLY(wife noticed right away, and she didn't even know I reduced the pressure) and the tire heat reading was exactly the same. Did the last 1800 miles of the trip and enjoyed the ride difference. No wandering, no tire over heating, very happy with the change.

Re: Optimum tire air pressure

Reply #13 – October 06, 2020, 10:20:24 pm

Quote from: MarkC – October 06, 2020, 10:08:04 pm

I know that tire pressures are something everyone has a different opinion on.

While true, the FACTS presented by the tire manufacturer's inflation tables for actual weight is the correct answer.

Said another way, please trust the engineers who designed your tires-- they are a better information source than our opinions.

Re: Optimum tire air pressure

Reply #14 – October 06, 2020, 10:22:52 pm

Quote from: MarkC – October 06, 2020, 10:08:04 pm

I know that tire pressures are something everyone has a different opinion on. I will say that on a 2800 mile trip that we just finished last week, and the first with my TPMS, I did find this out...................
Previously, I had ran with the recommended PSI on the side of the tire and the pressure would increase about 10 PSI from cold to hot tires.
Halfway through the trip in NAC, I had the coach weighed and based on the axle weights, we able to drop the pressure 15 PSI on the rear and 10 on the front.
The ride improved DRAMATICALLY(wife noticed right away, and she didn't even know I reduced the pressure) and the tire heat reading was exactly the same. Did the last 1800 miles of the trip and enjoyed the ride difference. No wandering, no tire over heating, very happy with the change.

Be sure to check the pressures cold, if you lowered the pressures 10 lbs while hot you need to recheck cold.

Re: Optimum tire air pressure

Reply #15 – October 06, 2020, 10:30:20 pm

Thanks Craneman, yes, everything was done cold, first thing in the morning before hitting the road.

Re: Optimum tire air pressure

Reply #16 – October 06, 2020, 10:33:40 pm

I has not checked my tire pressure before our current trip other than thumping on the tires and visually looking at the amount of "squash" that the Michelin's normally show if correct. 97/87. Appeared to be a little low. Not much. A little.

The drive, over a thousand miles, confirmed my visual inspection. Slight vagueness. Slightly more body wiggle in sharper radius road speed turns.

Finally got out the precision powertank digital tire gauge and filler.

92.3 and 93 on the front versus 97.0.

Backs were 83,83, 83 and 79 versus 87.

600 miles later the vagueness was gone allowing 10mph better entry speeds in big medium speed corners and the self centering was noticeably improved. Less steering corrections needed.

Only after every worn or out of adjustment part was replaced and the steering box rebuilt and the wheel bearings set to .001 and .003 respectively could I get back to what countless new unihomes I had driven long ago drove like.

No play in steering wheel. Minimal corrections needed and light pressure was all that is needed.

I feel a tiny "tic' in the steering wheel turning quickly from left to center to right a bit.

Pretty sure the zirks in the column may need greasing. Do not know if the shop hit them or knew they existed.

Sold a lot of coaches new that you could drive from the bottom of the steering wheel.

My customers appreciated that I handed them a straight driving, easy to drive coach that did not tire them out if they needed a long day behind the wheel.

ORED's took more work New and required shop fixes before selling.

I found if any coach drove perfectly it sold for more money every time. If a customer shook his head sideways that normally cost me and my store money.

The tire pressure is very important among other things.

Too high the coaches wander. Especially in cross winds.

Too low they are vague in turns to me.

Mine drives straight as an arrow now even in light winds.

Only took 8 years and 40k miles.

My curse is that I drove a hundred or more of these new and remember the drives too well

Get the pressure exactly right then move on to the other parts.

You may remember my post when you get everything back to new specs and the tires correct I feel

Re: Optimum tire air pressure

Reply #17 – October 07, 2020, 03:08:42 am

Quote from: craneman – October 06, 2020, 10:22:52 pm

Be sure to check the pressures cold, if you lowered the pressures 10 lbs while hot you need to recheck cold.

But "cold" varies with air temperature and altitude. I try to pick a happy medium rather than chase cold pressures each morning.

Re: Optimum tire air pressure

Reply #18 – October 07, 2020, 09:53:07 am

I don't find any difference in tire pressures at ambient temperatures. Running at highway speeds in hot weather I can see 50 degrees increase in tire temps with significant pressure change.

Re: Optimum tire air pressure

Reply #19 – October 07, 2020, 11:39:49 am

Whatever anyone decides, in my humble opinion, most important is equal across the back four.

97 U295 36' Toyo's, been all over the place with pressures. Happy at 90 PSI cold all around. Verified by Les Swabs as OK.Rides and steers nice. Tire wear fine...Check periodically with Pyrometer.

Wall plate is way lower, and tires side wall is way higher.

Cheers
Chris

Re: Optimum tire air pressure

Reply #20 – October 07, 2020, 12:54:04 pm

Tire manufactures recommend pressure based on tire load AND same pressure both sides. If in doubt run at a higher pressure, but don't exceed max pressure marked on tire sidewall and on rims. Never run underinflated as this will heat up the tire due to excessive sidewall flex and destroy it.

Keith

Re: Optimum tire air pressure

Reply #21 – October 07, 2020, 04:41:39 pm

Once you decide on the cold air pressure, don't chase it during the day.

No, we don't suffer from a "HARSH RIDE" at 110 psi. Neither one of us would tolerate that. At max pressure our fire trucks never had an uncomfortable ride and bus companies don't drop pressures to make customers happy. Have you ever been in a tour or Greyhound bus that rode badly?

We had service day once a week on each apparatus. Each tire was checked to make sure it was inflated to the maximum listed on the sidewall.

H rated tires will give a rough ride at 120 psi and may be a little harsher at lower pressures.

Re: Optimum tire air pressure

Reply #22 – October 07, 2020, 07:16:33 pm

Harsh ride is relative to the roads you are on. La freeways are a test in my opinion. Shocks, tires, pressures become very important. Long ago as a manager when I test drove a coach I purposely did not look at the tire brands.

After the drive before exiting the coach I mentioned whether the coach had Michelin's or something else.

100% accuracy.

This is on my local la roads and the local freeway.

Part the ride, part the steering, part the road noises and part the amount of steering correction needed.

I had many customers laugh and then I took them on a unihome drive.

Made many deals that way. Nothing in a rv drove as well.

Prevost is so heavy that no small movements feed back.

I do understand the money issue. Seen a lot of line haul big rigs with Michelin's on the steering axle. They may have something else on the rest of the axles although

Re: Optimum tire air pressure

Reply #23 – October 07, 2020, 08:42:44 pm

Bob,

We both live in California with the potholes, cracks, etc. Up north has the weather to make things even worse. Although, states like Michigan make our roads seem like the Autobahn. Detroit has streets that can destroy any SUV's suspension especially around the GM factory.

Here is a list of truck tires and their ratings:

I've been working on tires for about 7 years and here is my list of best commercial truck tires...

1. Bridgestone – Overall they have have the best line of tires. The Lp. 22.5 R197 is the best trailer tire on the market. The 287 is the best steer tire on the market. The 726 is the best drive tire on the market. You can't go wrong buying a Bridgestone tire. The casings are also great. You should be able to cap a casing multiple times.

2. Hankook – Quietly becoming 1 of the bigger tire companies in the world and for a good reason. They make great tires. They make an excellent trailer tire in Lp. 22.5 and 11R22.5. They make good tires in 17.5″ as well, for low-boy trailers. They also make make an excellent large steer tire such as a 315R22.5 or a 385R22.5.

3. Goodyear – I give them high marks because they make a very good casing. You may get mixed results with the new tires but if you re-cap your tires you get a great value for your dollar. They make some nice drive tires in 22.5″.

4. Firestone – The 455 is a great trailer tire. The steer tires are not great but you could do a lot worse. The 663 is a good drive tire and firestone also makes good casings that re-cap well.

5. Michelin – The most expensive/overrated tire. Michelin casings don't stand the test of time. They are know to dry-rot faster than most other tires. Their beads tend to break or crumble if they have to be removed from the rim, usually making them junk. Besides the poor casings they do make one of the better super-singles on the market. If you're going to spend the money on Michelins don't put them on something that isn't being used year round, full-time.

6. Continental – They make the best deep tread drive tires for rough terrain driving. They also make great 17,5″ trailer tires. The casings are pretty good but not great. You should get at least 1 recap out of a casing.

7. Yokohama – They make pretty decent drive and trailer tires in 22.5″. Steer tires are average. The beads on the casings crumble much like Michelins when you remove them from the rim. This can make them unusable.

8. BFG – Much like a Michelin but cheaper. The tires seem to wear fine but the casings don't last. They do make a good Lp. 22.5 trailer tire, just make sure you use up the tread before the sidewalls start to deteriorate.

9. Aeoulus – A little known off-brand, they make a good drive tire and their casings can usually be re-capped more than once, making this cheaper tire a good choice. I wouldn't use an off-brand steer tire though, but it depends in the truck. Aeoulus tires are almost always heavier than other tires of the same style and size. I don't really know if that is good or bad, but you definitely notice it when stacking them.

10. Kumho – They make a durable 315R22.5 drive tire for heavy trucks such as a garbage truck. Those casings also recap well. The steer tires they make in the 315 size are OK but not for the 18-wheeler.

This is all just based off of my opinion from working with these types of tires. I've worked in a re-cap shop and I do fleet service work now.

Pierce

Re: Optimum tire air pressure

Reply #24 – October 07, 2020, 09:31:00 pm

Pierce that list has interesting info. This was compiled by you?

My info was that the Michelin's x steel cross belt non overlapping construction was unique in the industry. The thinner sidewall that shreds on a flat and allows the tire to come down square on the tread block to not flip flop and lose control was also unique.

Everyone else then and I think now has thicker sidewalls to support the tread block if the pressure is lost.

Michelin's look like squashed tires on the bottom if everything is correct.

The rest barely show the bulge on the bottom. Thicker sidewalls.

Every unihome or Unicoach made came with Michelin's. 32 years.

Does anyone disagree that this is a money issue?

The poster mentioned Michelin dry rot if not used regularly.

My Xza-2's had cracks from low use. Made fot a moving heavy truck.

My Xza-3+'s have none. Seems to have fixed that issue.

My fmca high volume dealer said when he took the 2's in trade that he had never seen that on rigs. They got driven.

I needed 7160# load tires that with my weight could be run at less than 100 psi

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