Front tire cupping... Suspension?

[AZ_Scott]

Not my bike...

I ran across a guy with a Hyper S, about 3K miles, and his Corsa III front is quite cupped. He doesn't know why, but I have an idea.

He keeps his tires inflated properly, and he hardly pushes the thing. He's an *older* fellow, and he likes to take it slow and easy, leaving around an inch of virgin rubber on the edges.

So why the cupping? Well, it turns out he's never set up his suspension since the bike was uncrated. The front end is still very soft, and he's around 200 lbs. My theory is that he's using up so much suspension travel in the course of ordinary riding, that the rake is effectively reduced, which causes the front tire to "push", even though he's not even riding aggressively.

I've never had any issues on my Corsa III's (neither has my wife), and I don't recall anyone else having cupping issues that I've read about here.

Later this week, we're going to get his suspension set up and throw a new set of tires on his bike, and we'll see if we can get this thing fixed...

[PedroHM]

what do you class as cupping?

[AZ_Scott]

There's a considerable difference in height between adjacent tread blocks. When you run your hand over the surface of the tire, you can feel the "steps".

The guy says the bike has gotten very twitchy and wiggly as the tire has worn...

[MrDude_1]

that sounds almost 100% like air pressure.... as much as id like to say theres a suspension setup that can cause that.. i have yet to ever find one... no matter what someone tells me about their air pressure...

also, note that if you start to cup a tire, then inflate it properly.. it will continue to cup itself.... at that point the tire is too misshapen for it to not happen...

[AZ_Scott]

The guy runs 32 PSI, which is exactly what I run, and my friend who knows him well tells me he's super anal about that kind of stuff - to the point of checking pressure every single day, which... I mean, come on, I don't even do that...

[PedroHM]

have a look at the tread. is it worn at 45deg on the front edge with a raised sharp lip on the trailing edge?

[Monstaman]

Just a side thought, has it cupped evenly around the circumference of the tire, maybe balance weights have taken a holiday?

Cupping is also a feature of excessive rebound damping ie allowing packing, just a thought

[AZ_Scott]

Originally Posted by PedroHM

have a look at the tread. is it worn at 45deg on the front edge with a raised sharp lip on the trailing edge?

Mmm... Yeah, kind of like that, I suppose. Are you getting that, too?

Monstaman, I thought about missing tire weights, too. I'll have a look when I see him later this week...

[Antigrav]

If the guy is old going slow and cruising as you say the tire isn't even going care at all... It must have been tire pressure intially. My point being if he isn't going fast enough to put some heat and pressure on the tire they won't be effected with cupping unless tire pressure is off. In addition suspension set up is not really important for the most part if a person is going slow... rebound or compression isn't going to help cupping for a person just cruising around... those tire readings that racers go by as far as cupping and stuff are for people on the gas with the bike working hard under them not for and old guy just out for a ride. Probably needs more tire pressure since he is just cruising

[PedroHM]

that wear on the tread is almost certainly too much rebound, wind it right out and bounce it hard till it does 1 rebound only, let him ride it and see how it feels, you can then tweak it on when he needs it.

i just setup my mates front end, he said it transformed the bike. most people seem to run too much rebound damping as it makes the bike feel smooth but it rapes the rubber