Cupping Rear Tires

[motocommuter]

All,

Last three rear tires have been cupped real bad. One Michelin Pilot GT & two Avon Azaros. Bike (2002 C10) now has 91k on it, new rear bearings, swing arm is torqued to spec, tires were mounted & balanced by a local private shop. Front end has fork brace, Sonic 1.1 w/15 weight oil, fork preloads at first line. There is no noticeable wobble/play on the front or rear tires when they are off the ground. Front steering seems to be fine, no clunking. Keep the rear tire at 42psi and front at 40psi.

On the list to do is to replace the oil in the rear shock, new swing arm bearings and replace the bushing on the top of the rear shock. Question, do the needle bearings on the linkage wear out or need any type of maintenance?

Also, I've been fighting a sway (ball bearing dance) when the bike is in dirty air (like around semis, suvs, strong wind, etc), thinking the rear tire cupping is related.

So, anyone have thoughts on what is causing it? Or have past experience with rear tires cupping?

Kurt

 

[smithr]

In your own words describe what cupping is or what the tires look like?

My bike dances behind trucks and such but not more then I expect.

 

[motocommuter]

The current tire looks like the center is raised with the sides worn. You can visually see the tire sections sticking out in a "scallop" like fashion.  The previous tire was just "scalloped", can remember the pilot GT, but my tire installer did comment on how cupped it was even though there was thread left.

The current tire you can actually feel the ridge/edge when you lean the bike over. I'll see if I can post a picture of it.

The ball bearing dance is any time im on the interstate. My cousin, with 40 years of riding experience, commented how scary my rear tire looked when he was following me.

Kurt

 

[smithr]

No expert here but most times I have seen that problem the tire was run way to low in pressure.  Could your gauge be wrong?  Is the bike loaded to the max?  I run 42-44 in the rear with avons and never had that.  If your rear end linkage is not right though then all bets off.  Is there play in the swing arm?

 

[2linby]

Your description is cupping for sure. The front I've experienced, but never on the rear tire. More often than not I've "flattened" the rear (square tire) from too much super-slabbing.

I also suspect, along with smithr-scad, your running pressures are the culprit.

 

[gr8scott]

IIRC, the posted tire pressures (look at the decal under the seat) are 36 front/41 rear. Could be off a few psi, but I think your front tire is pumped too high. If your front tire is wobbly (running on ball bearings) due to over-pressurization, it may cause the rear to look like it's swaying too, as it tries to follow the front tire.

 

[roaster]

I felt the same wobbley feeling on the highway on my '06.  cagefree was here this weekend and noticed the cupping of my tires, although there was 32 pounds of pressure. I have upped the pressure to 40 pounds and I am testing it.  I really can't put the $ into new tires but I need to. After we realized my fairing wasn't the culprit I leaned back to the tire concept.
I still have a bunch of tread though, which pisses me off.
When can I tell that its TIME or that its no longer safe??? Anything concrete?

 

[Ranger Jim]

I agree with the comments that you're tire pressures may be wrong.

 

[DeansZG]

Gents,
  Get a good wood rasp, park the bike on the centerstand, set down on the floor, straddling the rear tire.  Start profiling the tire w/ the rasp, knocking down the high spots..... Have done that w/ a couple of rear tires & sometimes to the fronts as well....
**note**  you can also use an orbital sander, but you have to be careful not to remove too much tire.

 

[rje_cne]

I agree with the comments that you're tire pressures may be wrong.

The tire pressures listed are for the Dunflop K701s.  The pressures will vary for other tires.  I run 42/42 and haven't had any cupping on the rear.  I would suspect it has to do with the rear shock and it not keeping the tire firmly on the road.

 

[gr8scott]

I agree with the comments that you're tire pressures may be wrong.

The tire pressures listed are for the Dunflop K701s.  The pressures will vary for other tires.  I run 42/42 and haven't had any cupping on the rear.  I would suspect it has to do with the rear shock and it not keeping the tire firmly on the road.

I disagree.

Tire sidewall pressure markings are max ratings for the tire, not the rating for a specific mounted application on a bike. The tire manufacturer does not know, nor does it care, what bike the tire goes on. They cannot provide all PSI ratings for all mounted applications (brands/models of bikes the tire may fit). The connie weighs in at something like 700-800 pounds depending on rider and baggage. You certainly would not want to run tire pressures like 36/41 PSI on a lighter bike.

36/41 PSI is what is required in a tire to support the weight and load of the Concours. Lighter bikes need less PSI.

Scott

 

[willyp]

Right. But we can also adjust our pressure for ride and riding style preferences. Not to exceed the pressure marked on the tire. I would also think a larger tire, all other things equal would need a little less pressure, due to the larger area supporting the weight.

 

[rje_cne]

I agree with the comments that you're tire pressures may be wrong.

The tire pressures listed are for the Dunflop K701s.  The pressures will vary for other tires.  I run 42/42 and haven't had any cupping on the rear.  I would suspect it has to do with the rear shock and it not keeping the tire firmly on the road.

I disagree.

Tire sidewall pressure markings are max ratings for the tire, not the rating for a specific mounted application on a bike. The tire manufacturer does not know, nor does it care, what bike the tire goes on. They cannot provide all PSI ratings for all mounted applications (brands/models of bikes the tire may fit). The connie weighs in at something like 700-800 pounds depending on rider and baggage. You certainly would not want to run tire pressures like 36/41 PSI on a lighter bike.

36/41 PSI is what is required in a tire to support the weight and load of the Concours. Lighter bikes need less PSI.

Scott

Well, they did the specs for the design of the K701.  The Avons have a much different construction and sidewall set up, hence different pressures.  Ride a Avon front at 36 psi and it will cup quickly.  Went through my first Avon front because of that.

 

[gr8scott]

Right. But we can also adjust our pressure for ride and riding style preferences. Not to exceed the pressure marked on the tire. I would also think a larger tire, all other things equal would need a little less pressure, due to the larger area supporting the weight.

Don't forget there is more weight on the rear tire. That's why it's pumped to 41 vice 36 front.

I think the solution to the original problem then (remember the original problem?) is to run less PSI in the front, and a few more in the rear.

 

[Dumb A$$]

I have been running 36 in my front and it is cupping so yesterday I went up to 42 to see what happens next. Not sure where the rear was, I think 36 also and it is starting to wear funny. It went up to 42 also. I'll see how it turns out. Both still have a lot of tread left and need to get more life out of them.

 

[2linby]

For me (most of the time) 39 psi front and 41psi rear works.  However if I am "packed" I up the rear to 43 psi.

 

[motocommuter]

Do you all think this might be the issue???

Kurt

 

[Ranger Jim]

Well, overhauling the rear shock sure won't hurt but I still think your tire pressures are wrong.  I run 38/42 on my Avon Azaro/Storm combo.

 

[motocommuter]

Jim,

I am running the rear at 42. This last tire was cupped in two weeks on a trip that I did 5,540 miles on.  I checked the pressure every couple days.
I don't think running the front 2psi more that what you are would cup the rear that quickly.

I hear what you all are saying about tire pressure, but I don't think that is it. I've got new rear to put on, so we'll see what happens when I head up to VT.

Kurt