| Author | Message | ||
| Gary Stadler (Boogiethecat) (68.7.217.217)
Rating: N/A |
I just got back from another 1000 mile trip in "da Crown" and noticed that my front tires have acquired some slight "cupping" on the innermost and outermost tread sections of both front tires, ie both edges of both front tires. I'll try to describe- The tread consists of four sections (three grooves going around the tire) and the grooves are zig-zag. The "cupping" occurs equally on the two outside edges of each tire only and follows the zig perfectly... ie the tire is a tad higher at each point where the tread is widest(less worn at the wide part of the zigs) and a tad lower is at it's narrow points (more worn at the narrow points where the zags occur). There is nothing noticably wrong with the two center tread sections of the tires. The tires are almost new Michelins, there is no pulling or other driver-discernable signs that anything is wrong. Any idea as to what's the cause, or should I even be concerned? This has only become noticable in the last 1000 miles and I've got 10,000 miles on the tires. It's not extreme... had the sun's shadows been in a different place today as I walked by, I probably wouldn't even have noticed it. No other signs of wear are apparent... gary | ||
| BrianMCI96A3 (65.41.212.127) Rating: N/A |
It sounds like they may be slightly out of balance gary, but I'll ask my tire guy on Monday and see what he says. Brian | ||
| Doug (68.83.22.144) Rating: N/A |
out of ballance or a tir not disigned for continuous highway use | ||
| Luke Bonagura (Lukeatuscoach) (12.75.167.205)
Rating: N/A |
Hi Gary: Check your tire pressure. Go to a "Heavy Duty" front end shop and have them check your front tires for balance. At the same time have them check the condition of the king pins, steering ends, shafts, yokes, u-joints. etc. Each worn part in a front end can and will add to poor "Tire Life" I Hope this HELPS!!!! And Happy & Safe Bussin' to All!!! LUKE at US COACH | ||
| Casper (52.128.30.23) Rating: N/A |
Sounds like tire pressure to me. | ||
| Ian Giffin (Admin) (64.228.43.53)
Rating: N/A |
Hi Gary, I have been checking around the internet for related problems and tried to sift through to something that looked reasonable. I don't disagree with the others in this thread, but may I offer that your problem is not dissimilar to several others that I was able to read about. "Cupping", is a fairly common problem that may be caused by, simply, an agressive tread pattern. I have most often seen (or more correctly, heard) this problem from a passing pickup truck where it sounds like its tires are squared off, kinda like "rin, rin, rin, rin, rin" as it drives by. If one examines the tread carefully, as you have Gary, you'll notice the leading edge, or each single tread element that strikes the road first is shaved off, front to back, more so at the front than on the leaving, or rear, of the tread element. I'll try to illustrate this - and please forgive my freehand artwork in an image editor:::  I read where the most common reason for this is because of the aggressive nature of the tread pattern, the leading edge of each tread element hits the pavement with a great deal of force, compared to the force generated as the rear of the tread element leaves the pavement. These forces result in the leading edge of the tread element wearing more rapidly than the leaving edge. Ok, how does this translate into bus terms? You will notice on many commercial long haul over the road coaches that their front tires appear to have no tread at all. The only thing you see is the curcumferencial grooves carved out of the tire. The purpose of this type of tire is to make for a passenger pleasing silent ride. The side effect is that cupping is negligible. Solution? What I have read is very vague. Several of the solutions from tire manufacturer's complainants were to change brand of tire. In most cases, the different brand of tire was an acceptable solution (oddly, one client changed TO Michelins - so the problem is not necessarily exclusive to Michelin - as a matter of fact, I read about more problems with Goodyears). The other solution is to try the treadless over the road coach type tires - which may not be totally satisfactory if you live in snowy areas. As mentioned before in this thread, ensure your tires are properly inflated and that all tires are aligned to the road and to each other, properly. These two things will minimize any negative effects and/or unusual tread wearout situations. I will defer this question to Buswarrior, who is a safety expert, and may be able to enlighten us all on further aspects of this problem... Earth to BW... are you there??? Regards, Ian www.busnut.com | ||
| Bruce Wayne (24.242.117.43) Rating: N/A |
The front end repairman I respect the most told me bad shocks cause it | ||
| mel4104 (208.181.100.74) Rating: N/A |
Bruce your answear is the same as the tire guys at two different bus shops that i asked , they said that the other items mentioned can cause cupping but the first thing they look at are the shocks. they had one that had the wrong rated shocks on it, they were new shocks but the wromg rating and sure ate tires. | ||
| Ian Giffin (Admin) (64.228.43.53)
Rating: N/A |
Bruce & Mel, Ask your shock guys why Gary's tires are cupping on the outside and inside edges but not through the middle 2 tread sections. Seems to me that a shock problem would cause the tire to flatten the full width of the tire. Please explain. Ian www.busnut.com | ||
| Loydd Fones (Tbird) (64.91.108.101)
Rating: N/A |
I think most tire cupping on inner and outer edges is caused by low tire pressure or weak shocks, or a combination of both Tbird | ||
| Gary Stadler (Boogiethecat) (68.7.217.217)
Rating: N/A |
Interesting. I doubt its the shocks as they were replaced with new correct ones 5000 miles ago, and tire pressure is correct for my weight. Ian's answer makes the most sense... in fact I have noticed all along that the front tires make a lot of noise. For my first few thousand miles (basically my first long haul trip) I swore that it was bad wheel bearings, because they make exactly the same sound, kind of similar to the "Buzz" of an L-1011's engines as they take off. But as I drove I noticed that the sound changes a lot with road composition, but not during turns as bad bearings would, and upon inspection the bearings are fine. It's the "agressive" nature of the tread making the noise, and most likely if I was to count the cups and multiply by diameter/speed I'd find that the sound I am hearing is exactly the frequency that the cups are hitting the road. I'm going to do this next and I'll report in. Thanks for the ideas guys~!!! Gary | ||
| Jim-Bob (12.46.52.74)
Rating: N/A |
I have had similar cupping problems on my right front tire. What I found is that the brake drum was badly out of balance on that corner. It actually caused a bounce like an out of balance tire. The drum was so far out of balance that with or without the tire installed, if you put the heavy spot up at 10 or 2 o'clock & let go, it rotates back down to the bottom rapidly only passing 6 o'clock by a little then returning. There was no sign of a missing weight. I went to the truck parts place & told them I had an out of balance drum. They said "None of them are balanced", then modified that after checking in the catalog to: "Well, balanced drums ARE available for $10.00 more, but after the bus has 250,000 miles or so the front end is so worn it doesn't matter"! (How about after 2.5 million miles!!!) Well, I bought the balanced drums, which, by the way do not rotate at all when off the ground. I am going on a test run next week & will let you-all know how she feels at 70. By the way, the balance weights are a 1.5" by 3" piece of 5/16" steel welded to the O.D. of the drum. | ||
| Phil Dumpster (24.16.243.37) Rating: N/A |
Balance doesn't matter if you only go very very slowly. A worn suspension will actually make the symptoms of an out of balance wheel assembly worse. (more looseness) Are those Michelins the same ones that were on the bus when it was a school bus? (I'm assuming this is a Crown school bus, not an atomic or an Ikarus import.) School bus fleets usually use the same tires at all four corners of the coach as a cost and time saving strategy. Since most school busses don't spend a lot of time on the highway at high speed, putting drive tires at all four corners doesn't cause operational problems. Who cares how much noise it makes? It's only school kids.  For highway use, you'll want a tread with continuous ribs around the circumference of the tire so you don't have the noisy problem that Ian described above. Aggressive treads should only be used on trucks that need them. Some steer axle tires have a block tread on the outside edges. If you can hear the tread buzzing while going down the road, the tires are underinflated. By the by, "cupping" usually refers to a spot where the tread is noticably more worn than on the rest of the tire. This is usually caused by the tire bouncing down the road, which can be caused by a number of things. It sounds more like the wear pattern you are seeing is a result of an underinflated tire. For your present tires, try increasing the tire pressure to put more of the weight of the coach on the center ribs and less weight on the outer edges. This should quiet them down a bit as well as make steering easier. If increasing the tire pressure to the maximum permitted pressure doesn't solve the problem, then change to a tire with a high ply rating or load range. An overloaded tire will show the same wear pattern as an underinflated tire. | ||
| FAST FRED (63.234.21.36) Rating: N/A |
I prefer the Blue Roads and have what many would consider very agressive tires all around. The cupping I had ceased after new kingpins and shocks were installed. FAST FRED | ||
| mel 4104 (208.181.100.85) Rating: N/A |
Ian, as in most shops the mech. do not know the physical science reason but over the years the old guys in the shops have go to first things and BC transit and coast mountain transit both say they quick check the front end for wear and the change the shocks. one reason i think they do this is from had this correct the problem many times over the years and a pair of shocks are a lot cheaper and less labour cost first. one tour bus company that i talked to said that they change the front shocks at every second new tire on the front and every third set on the rearjust as a prevent. measure. that is all they said and with a 1000+ buses between them . sorry i could not give their reason . | ||
| Buswarrior (Buswarrior) (64.229.210.89)
Rating: N/A |
Hello all. Sorry, was off to NYC feeding the need for bus driving... Uneven tire wear gets blamed on a lot of things by a lot of people. Sometimes accurately, sometimes not. Here's a list: something is out of balance or alignment, the suspension won't let the tires run true, inflation is wrong, wrong tire for application alignment is a given, the tires have to be pointing in the forward direction, and be relatively upright on the balance front, the tires as mounted on the rims need to be in balance. The installation of the wheel on brake drums also can be messed up, as well as the drums themselves, as noted in an earlier post. All of that spinning mass at the wheel end has to be in balance, or the resulting wobble will wear off the rubber according to the wobble. Warning: there are mechanics out there who may not subscribe to the theory of a completely balanced wheel end. worn suspension, front or rear, will let the tires wander around instead of running true, as noted by Luke. You'd be amazed at the wild tire wear sometimes found on the opposite end of a bus from where the worn suspension really is, and the unneccessary expenditures on the wrong parts... inflate the tire to the pressure recommended for the loads it is carrying, period. choosing the wrong tire for the application is a strike out. more aggressive tread tires are reported to have some difficulty in delivering good service life when installed on the front axle. As posted earlier, a fairly continuous rib around the outside edge is the norm for steer tire applications. Now, for some perspective: Typically, many, or perhaps, most of us, don't drive enough miles to find unusual wear patterns on our tires, since we age them out long before we wear them out. It might be helpful to suggest this: you're probably in good shape if it runs straight on the highway, you can hold it in the lane in the wind with one hand and it doesn't thump or vibrate at speed. These comments are no substitution for proper routine maintenance and inspection of the vehicle by a knowledgeable person. I just want to relieve some worry in those who want to do the right thing, and are still working out what right for you is! keep as much money in your own pocket as is responsible to do so... happy coaching! buswarrior | ||
| Dwight (172.172.21.71) Rating: N/A |
Cupping I have seen has been related to shocks worn, loose, or just plain too small for the job. | ||
| H3Jim (68.105.103.139) Rating: N/A |
HOpe this is not too far off the track, but I had a 1971 Triumph motorcycle that exhibited similar tread wear on the front tire. ie the leading edge was more worn than the following edge. It too had an aggressive tread pattern. At the time the experts determined that it was due to hard or even excessive braking. If that was true, Ian's explaination makes sense. The rear of the pad can squeegee out and not bear so much weight, force, so it escapes some wear, while the front can't flex anywhere, so it bears teh full weight and just wears. I had quite large peaks at the rear of each tread pattern. If it was just a balance problem, or the shocks were worn, the cups probably would not coincide with the tread pattern so precisely. | ||
| TWO DOGS (65.179.201.195) Rating: N/A |
The left front on my Eagle is cupping....I "almost" had the courage to try the brand new golf balls inside it...sometimes...the easy things work..I have to take it into town next month for a trailer hitch...might have them put in while I have it in town...if I can find a good tireman he ought to be able to put them in without removeing the wheel | ||
| DonTX/KS (66.82.9.43)
Rating: N/A |
Let me add some different perspective on this. Several years ago Chrysler Corp did some extensive testing to try to determine the causes of such wear. Their conclusions were that any FREE ROLLING tire will do this as a natural action. I had such a problem on my Kenworth with Michelins on the steering axle, they always replaced them under warranty after checking alignment, shocks, wheel bearings, balance and other causes. Two of us bought new 2001 Saturns, and were dismayed at about 6000 miles the rear (Free Rolling) tires were cupped badly and causing noises inside the car. The owners manual said we should have rotated them at 3 or 4k miles. Most two wheel drive vehicles I am aware of require frequent tire rotations, and this is with NEW shocks, alighment, pressures, etc. Perhaps all we really need to do is put the tires on a drive axle to true them up again. |