Metzeler Z6 front AND rear severely cupped???

[mystahagy]

Howdy,
I've only had my Z6's on for about 3k miles which is nothing for these tires, but both front AND rear have some serious cupping issues. I have checked air pressures constantly at which I was running 33/35 cold. They've gotten worse and worse at an increasing rate, and it makes the bike feel really twitchy, and has REALLY increased turn-in past a comfortable rate. The slightest input and the thing goes over really quick, too quick. All shocks seem ok, and the rear tire is on straight and true. Also, I can't seem to find any play in the front end.
The only thing I can think of is from increasing the preload on my rear shock. Before my tires went crazy, I turned my preload from 4 to 5 about 4 months ago. This was mainly because I ride 2 up a lot. Does anyone have any ideas as to the cause of this? Before the Z6's I was running really old D207's from the previous owner, and they didn't show any signs of this activity.
This really pi$$es me off, these tires have at least 75% tread on them.

[woobie]

Any chance of some pics?

I'll post some of mine later. I took pics when I mounted mine at 22K, then again at 28K and 32K.

I've got about 8700 miles on mine right now. I do have a noticible flat spot from the highway but nothing else yet.

[Junior]

I put around 7000kms on my Z6's and never had a problem. They still had lots of life left when I traded the bike. They were an awesome tire on the Kat.

I've never heard of anyone have cupping issues with them.

[stevnmd]

Umm, I'd guess that 33/35 is low for those tires, and even more so on a heavy bike... I'd guess you should be running 36/38 cold to start, and maybe 36/40.

[mystahagy]

Here's a shot of the rear, doesn't show it very well though. It's night here, I'll try to get a pic in the sunlight tomorrow.

[BISQ]

The only time I've had issues with cupping is via really low pressures. I've never had an issue on the rear.

The increased turn-in is an interesting side effect. I didn't notice that on mine.

Tire pressures, and possibly wheel or steering bearings are the only things I can think of....or maybe even a misaligned rear tire (hmm).

Good luck on that one, bro.

[The CyberPoet]

Re: Metzeler Z6 front AND rear severely cupped???

Howdy,
I've only had my Z6's on for about 3k miles which is nothing for these tires, but both front AND rear have some serious cupping issues. I have checked air pressures constantly at which I was running 33/35 cold.

Those are Suzuki-recommended pressures for the OEM tires (33 front, 36 rear - aka 33/36).
Metzeler's recommendations for the Z6's start at 34 for the front, so minimum air pressure should be 34/36.5 (140lb rider) and go upwards based on load weight. If you're a 200lb rider in gear, you should be at 36/39 or so. If you have a passenger who weighs over 80lbs on the bike regularly (or you weigh in closer to 300lbs than 200lbs), up that even further to 38/40-41 (under 80lbs, split the difference, passenger). Passenger weighs 150+ increase it even further to 39/41 or up to max at both ends as the combined load starts to reach around 440lbs.
Tire cupping always happens as a result of the tires running hot and under-pressurized for that particular load.
You can calculate tire deformation at approximately 1mm per 20kg of extra load. You want to add enough pressure to offset that deformation, without going over-board.
It would also seem the Z6's are much more prone to cupping then the Z4's they replaced (I've never seen a Z4 cup). I've seen two pairs of Z6's cupped so far -- in both cases, the rider didn't keep the pressure high enough (one because of a slow leak at the valve stem; the other because of an inaccurate tire gauge).
Consider contacting Metzeler's US Rep and seeing what he (a) has to say about it, and (b) if he'll replace the tires on a pro-rated basis. I've found him to be reasonable about such requests at times

They've gotten worse and worse at an increasing rate, and it makes the bike feel really twitchy, and has REALLY increased turn-in past a comfortable rate. The slightest input and the thing goes over really quick, too quick. All shocks seem ok, and the rear tire is on straight and true. Also, I can't seem to find any play in the front end.
Before my tires went crazy, I turned my preload from 4 to 5 about 4 months ago. This was mainly because I ride 2 up a lot..

Normally cupping doesn't make any significant difference on turn-in tendencies normally, especially not as easier, smooth turn-in. Sharper turn-in normally occurs because the center section's flat area isn't flat any more (the arc has worn down across both sides to make the arc-profile very sharp, an issue with tires that are constantly on their sides, such as canyon carvering every ride).

Question: When you say they are cupped, are the cupped in the center, or off-center of the tire?
Top-down/front-on pictures of the tires would probably show the issue better.

Cheers
=-= The CyberPoet

[mystahagy]

Re: Metzeler Z6 front AND rear severely cupped???

[quote="The CyberPoet

Question: When you say they are cupped, are the cupped in the center, or off-center of the tire?
Top-down/front-on pictures of the tires would probably show the issue better.

Cheers
=-= The CyberPoet[/quote]

You bring up a good point, and they probably were too low for riding 2-up. It's that twitchyness of it that has me worried. I'd say the deformation is on the side, about halfway between the center and the edge of the tread. I'm at work, but I'll def. try to get some better pictures up later. Thanks for the info, that's a wealth of information as usual, Cyberpoet
I am curious, what's in my tire's future? By increasing pressures to the correct amount, will the deformation still continue? Obviously this is cause for new tires, but I'm a poor college student. Safety comes first, but as long as it doesn't get worse I think I can handle it.

[The CyberPoet]

Re: Metzeler Z6 front AND rear severely cupped???

You bring up a good point, and they probably were too low for riding 2-up. It's that twitchyness of it that has me worried. I'd say the deformation is on the side, about halfway between the center and the edge of the tread. I'm at work, but I'll def. try to get some better pictures up later.

I'm looking forward to the pics. Get both tires, both from straight on, and from 35-40 degrees off center.

If you had said it was only one tire that was doing it, I would suspect that there might be an alignment issue (anything from poorly aligned rear axle to a bent axle or warped rotor), but since you said both are doing it, it would imply the tire pressure is at fault.

I am curious, what's in my tire's future? By increasing pressures to the correct amount, will the deformation still continue? Obviously this is cause for new tires, but I'm a poor college student. Safety comes first, but as long as it doesn't get worse I think I can handle it.

Well, the tires won't get better on their own normally, although some aggressively cheap individuals have been known to take a belt sander or equivilent to a rotating tire to sand down the uneven cupping. My personal opinion is to have you contact Metzeler directly and see if they'll give you any help -- like I said, few people regularly talk to the factory and sometimes they are really helpful about such things (such as providing pro-rated replacements if they can recapture the tires to examine them).

Cheers
=-= The CyberPoet