Rear Tire Cupping!

[malcolmblalock]

Hello all. I was just washing the bike and noticed that my rear tire is cupping quite a bit on the left side. The right side may show a very small bit of cupping, but not like the left.

 

The tires are Pirelli Angel ST, size 180-55-17, and they are the "heavy duty" (my words) designation. They currently have about 8K miles and look pretty good. The wheel seems to run true, and there's no wobble in rear hub. All seems normal to me except the cupping. Bike has 21K miles (09 RT).

 

I understand the left side wearing a little more than the right, due to crowning in the roads. I live in a flat part of the world and do a lot of highway and interstate (translate--non-curvy) roads, so the center is worn more than the sides.

 

Just wondered if anyone else had noted a cupping rear tire. I've had front tired on various bikes in the past that cupped, but never a rear.

 

Any ideas on what's causing it?

[Matts_12GS]

Check your tire pressures...

[malcolmblalock]

Yeah, I forgot to mention that I keep up with tire pressures pretty regularly. I keep the front at 35 and the rear at 39. I use a TireGard monitoring system, and keep it on when riding. Pressures have not been "low" (below 36). This is where I've always run my tires (gauge and TireGard are within 0.5 psi).

 

It's just a weird thing to me--I've never had or heard of rear tires cupping, and wanted to know if others have seen it and how/if they found a cause.

[Matts_12GS]

Every tire I've had cup has been due to pressure issues, but I'm not too familiar with Angels.

 

After 8K miles, aren't they getting into the replacement window?

[XTrooper]

I too have a 2009 RT shod with Pirelli Angel ST tires.

 

Your tire pressures, especially the rear tire pressure, seem low to me and that may be the problem. I keep my front tire at 36-37 and my rear at 44-45. At the 2500 mile mark, the tire wear is even.

 

BTW, I'll be tickled pink if I get anything close to 8000 miles out of my tires.

[ScottM]

I have Michelin PR 2s and just notice left sided cupping on rear tire. Fronts are OK and I keep 36 in front and 40 in rear. Have had front cupping issues with Bridgestones but not with the last 2 PR2 fronts. No clue on what is causing the rear cupping...never had that happen before and have not seen it written up in forums.

Scott

 

[malcolmblalock]

I'm an old guy (63) and don't ride hard. My rear tires usually go 11-13,000 miles before changing out. Fronts go closer to 20k miles. So, 8K miles is about 2/3 worn out.

 

I'm not concerned about changing it out prematurely, but do wonder why it's cupping.

 

And on tire pressures, I pretty much follow the manufacturer's recommendations. I know that too much pressure causes more center-tire wear and low pressures cause more sidewall wear. These tires were pressured like all of the tires over my entire history of 1200 RTs, which now is roughly 80k of riding.

 

Maybe it's the Angel ST? It's the first of this brand and type I've ever used. Have tried Michelins, which wore out way fast. I like the ME Z6s, but with the center of the tire containing no wear indicators, I got tired of guessing when it's worn out.

[CoarsegoldKid]

 

Just wondered if anyone else had noted a cupping rear tire.

Any ideas on what's causing it?

Have U got a picture to show. And as Matt stated an air pressure check maybe in order.

[Guest Kakugo]

Contact Pirelli and ask to talk with a tech. They will be able to advise you regarding tyre pressures. If they have doubts they'll send a field rep to check on your tyres.

When I bought my first set of Michelin PR2 I run them at BMW recommended pressure for solo riding (2.2 bar front and 2.5 bar rear) and the bike felt pretty "weird".

A phone call to Michelin solved everything: they advised me to run it at 2.5 bar front and 2.9 bar rear, the maximum recommended by BMW. They even explained me why.

Worked for me and may be worth a shot.

 

[CoarsegoldKid]

They even explained me why.

 

What was their explanation? So we can stop guessing.

[Guest Kakugo]

They even explained me why.

 

What was their explanation? So we can stop guessing.

 

All their latest road going tyres (PR2, Power Pure etc) have very, very soft construction requiring high pressure to operate properly.

This is mostly due to a request by Japanese manufacturers which want tyres to be run at a single pressure (differently from BMW with their "pressure according to circumstances" attitude).

This contrast with ultra-stiff track tyres which require very low pressure to operate properly (Power One's should be run at 2.1 bar front and 1.9/1.5 bar rear according track temperature).

[CoarsegoldKid]

Still guessing why. My experience seems to agree with higher pressures.

Power One's are like limp rubber bands compared to PR2s.

[CoarsegoldKid]

My bad. I checked my Ducati tires and they are not Power Ones. They are Pilot Power 2CT and are limp compared to the sport touring PR2s of B spec.