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Old 08-21-2010, 11:28 AM   #1
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Tire "cupping"

I posted this over on the Winnebago board last week. As usual with tire problems there was a whole range of comments, suggestions and assertions. The subject is somewhat related to the tire pressure post just below, but not quite. I am kind of frustrated with the situation I am in with these tires now because I still really dont have a "warm and fuzzy" feeling about what the actual cause of this wear was. It may be underinflation, but I continue not to totally believe that, because I inflated the tires to the Michelin Load/pressure tables, and they should know, right ? Anyway, here is the post. Grateful for any knowledgible comments :

"Just noticed some slight cupping of the tread of my front tires. There are appx 5 flat spots about 5" long and 2" wide on the outer section of the tread area of the tire, about equally spaced around the circumference. The remaining tread area is fine, no flat spots. My tires are the Michelin XRVs (255 x 80 R22.5). I have 31,000 miles on the coach, and it looks like this has just happened recently. I have not noticed it previously, and I check my tires often. I keep my tires properly inflated, as per the tire pressure / loadings chart from Michelin. (Last weighing was 4,000 lb weight per front wheel, and I run 90 psi in the fronts. According to the chart minimum pressure required for this loading is 85 psi). Anyone had this happen to a tire, or know what causes these flat spots ?
Thanks

Meurig Davies '07 Meridian 36G"
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Old 08-21-2010, 11:42 AM   #2
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More info

Sorry that this is all so long winded, but to give the whole story, I need to include this follow-up post I made also :

"I just spent the whole morning at my local Freightliner shop, and at Les Schwab later. Freightliner checked out the whole front end. Shocks, tie rods, kingpins etc. Everything. Also checked the wheel bearings end play and checked the front end alignment. Nothing unusual found. Everything in spec. No worn or loose parts. Nothing. The only thing they commented on was tire pressure. Measured at 85 psi. I told the supervisor that I have been running 85 psi pressure (their gauge, 89 on mine) in my front tires, to which he stated that they "never" put less than 100psi in that size tire. He said that anything less than 100psi and "you start getting problems". So I let them take them up to 100psi. Then I went to Les Schwab. They checked the tires and that guy said "could be a number of things, including low tire pressures". Well, all the possible causes he mentioned (except for faulty rubber compound) had already been checked OK by Freightliner, so his conclusion was low tire pressure also. Then I told him I had been running 85 psi. He was wide eyed and said they NEVER put less than 100 psi in that size and type of tire. OK, now for the first 3 years that I owned the coach I actually DID run 100 psi in my front tires. But then I picked up a Michelin publication which shows Load / tire pressure figures. I weigh my coach a few times a year, usually before a long trip, and the front end always weighs 8,000 - 8,400 lbs. The Michelin chart indicates that 85 psi is good for 4,400 lb per single tire, so 85psi is what I have been running in them. Now Freightliner and Les Schwab say that is too low. Go figure. Why would the Manufacturer specify a pressure that is going to damage the tire ?
This is going to be an expensive lesson, because now that the tires have started cupping that is probably going to accelerate the rate of wear considerably, according to the Les Schwab supervisor. (PS - I originally said that only the right side tire was cupping, but on closer inspection today, the left tire has some very slight cupping starting also).
Not happy about this

Meurig Davies '07 Meridian 36G"
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Old 08-21-2010, 10:41 PM   #3
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Not sure what you are looking for? Not sure what size tires either?
My new 19.5"s are Toyo's. Load chart say 90 psi. I tried that first and the bus handled like crap. sidewall says max is 120, so I cranked em up to 115. Bus handles WAY better, good enough for me.
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Old 08-21-2010, 11:19 PM   #4
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If as you say psi (But do you weigh the front axle, right and left separately?) and all parts and alignment is good, then what you have is commonly called "River Wear" River Wear occurs on free rolling tires usually on (front axle) long haul tractors. Manufactures design all sorts of grooves and ribs into the edges of the tires to try to prevent this from happening.

I'm sure if you measure the tread depth of the front tires, compare it to a new tire, you will find you are getting many miles (5K, 6K or more) per 32nd.

IMO with no front end problems and your PSI is correct you have normal wear.
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Old 08-22-2010, 12:14 PM   #5
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Thanks for your response. Actually, after some more research I think what I may have is "Shoulder Step Chamfer Wear". Similar to River wear I think, but the description of step chamfer wear describes exactly what I am seeing on my tires. It too is considered as "normal wear", but there was a comment on one reference I read which said that increasing tire pressure will help. So hopefully the fact that I have increased my front tire pressures from 85psi to 100psi will at least slow down the rate of wear. I am also thinking of swapping the steer tires with two of the rear tires. The rear tires are in excellent condition.

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Old 08-22-2010, 01:54 PM   #6
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Just Wondering I have never seen anything mentioned about tire wear relative to driving in high crosswinds. It would seem to me that with the big Barn Door we are pushing down the road some unusual wear should be seen on the outside edge of the tread. Granted, it would be on both inside and outside, I think. And, making round trips would tend to even out the wear on both curb and street side. Could this tread edge wear have anything to do with crosswind driving?
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Old 08-22-2010, 02:26 PM   #7
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Quote:
Originally Posted by JimM68 View Post
Not sure what you are looking for? Not sure what size tires either?
My new 19.5"s are Toyo's. Load chart say 90 psi. I tried that first and the bus handled like crap. sidewall says max is 120, so I cranked em up to 115. Bus handles WAY better, good enough for me.
You're pretty close to the max pressure for your rims,better check.Most 19.5 are accuride,and the max is 120 psi.You should weigh the coach and inflate to the proper psi,don't go by the sidewall psi.
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Old 08-23-2010, 07:48 AM   #8
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Cupping is generally caused by worn out shocks. I would check that first. Outside tread wear on both sides of the tire would indicate under inflation. Centerline treadwear would indicate over inflation.
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Old 08-23-2010, 08:42 AM   #9
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Here is a link to the Kal Tire website that shows pictures of different tire wear and a list of possible causes.

Kal Tire - Tire Wear Conditions

Possible causes for Cupping/Scalloping are;
  • loose wheel bearings
  • mismounted tire/ wheel assembly
  • out of balance wheel assembly
  • tread design/ tire design
  • worn bearings, shocks, springs or other suspension components
  • mismatched duals
  • inconsistent dual inflation (10 PSI or greater)


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Old 08-23-2010, 09:56 AM   #10
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It is interesting that with all the emphases on weight of the coach and tire pressure that you were told to increase tire pressure to 100 or more at both the tire dealer and the chassis company. This interests me because I have the same tire and the service adviser at the dealership where I purchased the coach said to run 105 psi all the time. The weight and psi charts don't seem to be workable for this tire.

I used the chalk method to double check for the proper psi. Put several wide chalk lines on the tires with kid's sidewalk chalk. Then take a short drive (1/4 mile or less) and check the chalk line to see if it is wearing off evenly. If the chalk is gone from only the outer edges then the pressure is too low. If it is gone mostly from the center the pressure is too high. When I tried this method I had to go to 105 psi to get an even wear of the chalk line. This was with the fuel tank and fresh water tank full, the way that I would normally drive. This convinced me that the dealer was correct. LINK Optimizing Tire Pressure
Hope it works out for you, Joe
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Old 08-23-2010, 10:52 AM   #11
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Originally Posted by azloafer View Post
I used the chalk method to double check for the proper psi. Put several wide chalk lines on the tires with kid's sidewalk chalk. Then take a short drive (1/4 mile or less) and check the chalk line to see if it is wearing off evenly. If the chalk is gone from only the outer edges then the pressure is too low. If it is gone mostly from the center the pressure is too high. When I tried this method I had to go to 105 psi to get an even wear of the chalk line. This was with the fuel tank and fresh water tank full, the way that I would normally drive. This convinced me that the dealer was correct. LINK Optimizing Tire Pressure
Hope it works out for you, Joe

Thanks Joe, I think I will give it a try.

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Old 08-23-2010, 09:19 PM   #12
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Cupping is generally caused by worn out shocks. I would check that first. Outside tread wear on both sides of the tire would indicate under inflation. Centerline treadwear would indicate over inflation.

Actually I may have wrongly defined the problem as "cupping" originally, because that's what I thought it was at the time. However, as I said in a later post it looks like "Shoulder step chamfer wear" more closely represents what I am seeing on the tire, which is not really cupping, as such. So the causes that produce cupping dont really apply to my problem. Also, as I indicated in my second posting, I had Freightliner check all the suspension components for wear, looseness etc. including shocks, and they checked the alignment, which was in spec. So worn out shocks etc is not relevant.


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Old 08-23-2010, 09:26 PM   #13
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Quote:
Originally Posted by azloafer View Post
It is interesting that with all the emphases on weight of the coach and tire pressure that you were told to increase tire pressure to 100 or more at both the tire dealer and the chassis company. This interests me because I have the same tire and the service adviser at the dealership where I purchased the coach said to run 105 psi all the time. The weight and psi charts don't seem to be workable for this tire.

I used the chalk method to double check for the proper psi. Put several wide chalk lines on the tires with kid's sidewalk chalk. Then take a short drive (1/4 mile or less) and check the chalk line to see if it is wearing off evenly. If the chalk is gone from only the outer edges then the pressure is too low. If it is gone mostly from the center the pressure is too high. When I tried this method I had to go to 105 psi to get an even wear of the chalk line. This was with the fuel tank and fresh water tank full, the way that I would normally drive. This convinced me that the dealer was correct. LINK Optimizing Tire Pressure
Hope it works out for you, Joe
Yes, if true about the seemingly arbitrary 100psi that I was told (or 105psi in your case), then it all seems to make nonsense of the Michelin published load/pressure tables.
Go figure.....
Interesting about the chalk method to check for correct psi. Thanks. I will remember that.

Meurig & Mary Lou '07 Meridian 36G
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Old 08-24-2010, 11:51 AM   #14
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Use wide chalk lines for the test...

Quote:
Originally Posted by Meurigd View Post
Yes, if true about the seemingly arbitrary 100psi that I was told (or 105psi in your case), then it all seems to make nonsense of the Michelin published load/pressure tables.
Go figure.....
Interesting about the chalk method to check for correct psi. Thanks. I will remember that.

Meurig & Mary Lou '07 Meridian 36G
If you try the chalk thing I would suggest that you use the large kid's sidewalk chalk and make wide lines. The wide lines are better than using a thin line with regular chalk. You can really see what is happening. I made several on each of three tires tire so that when I stopped at least one of the lines might be showing. I don't think that it is necessary to do all six tires when you have the psi the same in all tires. Maybe two back and one front. Happy travels, Joe
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