Brand New Tires

[Dthomas9572]

Today I had installed 8 315 Michelins on my 1998 Featherlight. I plan on this weekend as advised on this thread to run by CAT scales and weigh the coach loaded. As per Gils advice and picture in an earlier thread I am going to make sure I am splitting the three axles on the three scale pads.

I am then going to go back leaving the right side off the scales. I am assuming that getting the weight of just the left side, by doing the math I should have the weight on each side.

I had the installer put 110 on the drive and 100 on tag and drive. This seemed to be a pressure recommended by some POG members.

Any more advice on how to proceed to get the best tire pressure for my coach?

Thanks

[BGLogistics]

David I recently weighed mine. Didn’t do side to side. Fuel tank full 160 gal, holding tanks empty, water tank probably at least half full 165 gal capacity. Other than that bus completely empty other than me. 15698

[Gil_J]

Yes, you can do wheel position weights with a CAT scale, but it's a PITA due to the framework for the CAT advertising sign over the one end of the scale. Because of that frame you might be challenged to get the coach on the same pressure plates with one side barely off the scale. If you can't do this you'll have to do 2-3 weighings. You'll have to back the coach up so that you aren't up to the CAT Scale sign frame. If you're lucky, the steers will be on one platform and both the tag and drives will be on another. If this is the case, I'd call it good. There's not much of a chance that the side to side difference is much between the drive and tag so an aggregate weight on one side of the combined drive and tag should be good enough. Otherwise, you'll have to back on the scale to get the drive and tags off the one side of the scale and on 2 different pressure plates.

[Gil_J]

Billy, no wonder those 40 footers are rocket ships. You're around 10K lighter than a lot of us.

[BGLogistics]

I may need to install a drag 'chute.:)

[Joe Camper]

Pipe dreams. 10200 steer 12000 drives 30000 CGVW with a 1 ton van in tow. Yesterday I drove from Chicago to OK City on 90 gal of fuel. It was 820 miles.

If u think I'm bragging just wait till I go to a 3.08 rear end gear. I predict 11mpg may be more.

[Joe Camper]

I'll have to build a custom push bumper on it so I can help all my buddies up the mountain. Figure out some way to latch onto the back of one of them buses without getting all that pretty polished stainless smudged up

[Joe Camper]

Enough of the thread creep. Back to tires. I know this is totally unrelated to buses and is purely for entertainment value.

15699

These tires are take offs from a friend of mine's dump truck although they look like retreads they're not their whole tires. I put them on there three or four years ago when I first bought the Peterbilt when I had a million other things to do. Only God knows how many miles were put on these tires before I put them in play. I've got over 40,000 more on it in the last 3 years. Look at the amount of Bulge on the sidewall. I got to that point by dropping the air pressure down until what I felt was a good-looking bulge in a sidewall developed. There's 55 lb of air in those tires that's where they've been for the last 40,000 miles and that's where they will stay. Look at the wear pattern it's absolutely at the perfect pressure.

I can't describe the huge difference in the ride by having them here. The lowest pressure that they show on the Air to weight charts stops at 70 PSI but at that pressure they say the tire can still carry twice what I've got on it and at 70 there was absolutely no bulge evident.

So what do you think about all them apples.

They're starting to finally wear down enough to where I'm going to have to Rattle his cage again and get me another set.

I love telling this story to my bus Buddies and watching them cringe.

Hanging around with all you guys is as much fun as you could possibly have without removing your pants.

[Joe Camper]

How much air pressure does Michelin say you need in a 315 - 80 to carry 5100 lb? 85??

What is the lowest suggested air pressure Michelin says you can put in a 365??

[Dthomas9572]

All,

I have not completed side to side yet. But I am

Steer. 14460 (Michelin says 100 )
Drive 19540.00. (Michelin says 85)
Tag. 11760. (Michelin says 85)

Sound right?

[Gil_J]

100psi is for a max of 14,380, 105psi is correct.

Not knowing the side to side imbalance I'd up the steers at least +10psi over recommended or 115psi.

[Dthomas9572]

Thanks Gil,

I have my drive and tag at 100, that ok?

[Joe Camper]

I got a question. If Michelin says 85 PSI to put your drive tires for when your axle load is 19500 on that axle and it'll carry 23,500lb on an axle at 85psi in those 4 tires, why would you put 100? And in addition u r still 4000lb under (19500 your drive axle) the axle load they say it can carry at 85, they say 23500. Why would u go up to 100psi??

I think I have the answer.

Dave tell me on your chart what Michelin says is the correct air pressure for a 315 80 with 10500 lb on the axle or 5250 per tire, thanks.

The 365's what does it say you need to put in to carry 5250 lb a tire?

I looked the chart stops at 85 is the lowest pressure they give you.

[Joe Camper]

I think when you get into these EXTREME single tire axle loads that you guys experience with these heavy front ends on these buses, over-inflating them is almost as dangerous as under-inflation. I would not put an extra 10 psi in the Steer tires just because of the unknown because you're not sure exactly what you have side to side. I would go weigh it side-to-side and I would put exactly the amount of air in the front tires that Michelin said you need for that weight. I would see what the heavier of the two Steer tires had on it and that's what I would put in both of them exactly not one pound more, not in the Steer tires. The drive tires not so critical.

It wouldn't be difficult to do that at most truck stop scales don't worry about what's on the back for this particular weighing, just pull it up and whatever scale pad that you can land on with the steer Tire one on and one off just set the brakes right there and go get a weight with the bus half on and half off the scale with just a steer Tire in play. If u can do it bus all on great, but not required for what u seek. All the trucker's watching you will think u r out of wack but that's okay because we all know we're all nuts anyway. Before you pull on a scale find a spot to park and go in and talk to the girl that's going to be doing it and let her know what you're going to do that's all.

I would also ABSOLUTELY put a product on the streer tire rims to keep the bead in place in the event of a blowout. Prevost should have these devices on these buses right out of the factory.

[Joe Camper]

Just to give a comparison to the trucking industry. When you have a commercial vehicle operating in a state that allows truck trains and you can put 20000 pounds on the steer axle legally 425s are the standard. U will not see truck trains with 365s. Local haulers too, garbage trucks, cement trucks, 20000lb steer, 425s r the standard tire.

When you've got a single tire axle, AND it's a steer axle, that is close to 15,000 pounds even though you have 315 - 80s that's an extreme load for that tire. And when you have a single Tire steer axle that's approaching 20,000 lb, and you all know who you are, even though you have 365 that's an extreme load for those tires.

Be careful, in every way. We want to see the shiny side up.

[Dthomas9572]

Joe,

Yes I agree and will weigh the steers side to side in the morning. The way you explained it that will be easy to do. My reason (which I have NO confidence in) for the 100 in drives and tag is in reading the multitude of threads on this site seem to say it is safer to have more pressure then to be under inflated. I know the ride can be stiffer, but that is not an concern to me, only safety.

So I understand the steers I will weigh side to side and put the exact pressure. On the tag and drive I still am confused...100 ok? Safe?

What are the bead protectors you are referring to?

[Gil_J]

Joe,

The short answer is that Michelin doesn't publish an axle weight inflation chart for RVs. So, if you don't know what the wheel position weight is you can't determine the minimum pressure for the actual weight.

The second thing to remember is that underinflated or over loaded tires is the number 1 non road hazard reason for tire failure.

[Joe Camper]

Yes to both of u. The reason u should go 100 in the drives is because u can. It is a testament to the unbelievably smooth ride of the prevo. A 15lb change in tire pressure in any other vehicle would be a really noticeable change in spring rate and ride but prevo is so smooth u can not feel the difference. Another reason, should u have 1 of the 2 drives go flat at 100psi the other will get u off the road and 2 safety. On your steering axle keep to the pressures more closely.

I regularly see 15 and 20yr old prevo with around 100000 miles with original shocks and when I let the owner know they r amazed and understandably so, because of the unbelievably smooth ride even with the bad shocks.

Front blowout protection devices....

There's a recent thread on the topic one these products there were 2 mentioned someone help I'm in the middle of pulling up anchor no time to look.

[Dthomas9572]

Hello,

I weighed the side by side and the steer left tire pressure was 7400 lbs. No one in coach. Assuming me in the drivers seat (200 lbs). My wife on couch (135 lbs). then I am at 15135 if I double the weight. So according to tire pressure calculator I am at 105 lbs. Add 70 more lbs I am 110 for correct pressure.

is that the correct target for steers for me?

Thanks

[Gil_J]

I'm not sure I'm following you. Based on your earlier post it looks like the heaviest side on the steer axle is 7,400 and you weigh 200 that needs to be added. So, using the Michelin RV Tire Inflation guide, that goes by wheel position weight, you need to support 7,600. The chart shows you'll need 110psi to support 7,610 pounds. 100psi only supports 7,440 pounds. This will be the same pressure for the tire on the opposite side given the heaviest tire position determines the minimum inflation pressure and all tires on a shared axle must be inflated to the same pressure.

https://www.michelinrvtires.com/reference-materials/load-and-inflation-tables/#/