Tires' "Radial Force Variation" (Pirelli P-zero Rosso)

[Costas]

There are quite a few threads already on vibration, or shimmy, but my problem is specific to a tire model and I believe it involves "Radial Force Variation" - an issue that is not discussed so often. This is why I am starting a thread to focus specifically on the N3 Pirelli P-Zero Rosso's.

I am currently on my fourth(!) set of these tires (225/40/18 fronts and 265/35/18 rears). Under normal street driving, always with the manufacturer's recommended pressures, the tires eventually develop what feels like flat spots but is more properly described as "radial force variation". The shake can be very intense and disconcerting - enough to make you worry about tire integrity and overall safety.

Severity is not constant - it depends on tire temperature (I believe) and it is much worse after having decelerated from high speed, e.g. from 120mph (I am in Europe). The shimmy is present when braking, rolling, or accelerating but it is felt only past 70 mph or so. It does not go away at higher speeds but it becomes less intense due to the higher frequency. It does not feel like coming always from the front wheels.

Hard cornering or repeated hard braking have, intermittently and to a varying degree, succeeded in alleviating the problem, only temporarily: It returns with a vengeance either the next day or after a bit of driving.

Testing (over months) with combinations of different rims and tires has excluded every other possible cause. Brake rotors were replaced, wheel bearings too, anything rubber in the suspension is good. Balancing also seems perfect. (Unfortunately no shop here has a balancer that exerts a force on the tire - like the Hunter in the USA). In short, putting different tires on my rims (even if they are used), without changing anything else, solves the problem immediately.

I have not moved to a different brand/model because the local Pirelli distributor have already replaced the tires thrice(!) for me - free of charge (do they know something is up?). This last set was fine for a couple of months and, for no apparent reason, it now developed the problem.

I would appreciate any suggestions on how to escalate this issue with Pirelli or any insight into what might be up with the p-zero rosso (where there any "bad" batches that have found their way into the market?).

I should say that grip and response are very good in general so, if not for this problem, the tire would be excellent.

Edited December 9, 2009 by Costas

[stephen wilson]

I'd say "free" tires are worth exactly what you paid for them if their performance unsatisfactory, buy another brand.

Just my 2 cents,

Steve

[Costas]

Steve, I agree, but I had paid full price for the first set of tires :-) Only the replacements (due to this problem) were free. I am going for another brand, for sure, but I am curious as to what is going on with the Pirellis. I mean, just the fact that the distributor replaced them three times is odd.

[stephen wilson]

Yes, your problem does seem odd. I don't recall ever seeing posts about problems with these tires. You could try a general Google search for Pirelli P-zero tire problems.

Good luck

Steve

[infocusf8]

I've had the P Zero Rossos on my car since I bought it and have had no problems with them at speeds up to 130 mph on the track. The only problem I had was suspension related causing a shimmy at 70 mph and they needed a balance and a new alignment for my driving style. They are wearing evenly across and the only complaint I have is they are rough riding sons a guns but that is to be expected with that low a profile tire. It does seem odd that they keep replacing your though but I wish I could get a free replacement on mine as it is almost time for replacements.

[Costas]

It could have been a bad batch of Pirellis. I have since replaced them with Goodyear Eagle F1 Asymmetrics and there is no shimmy at any speed. I gave the last set of Pirellis to a friend (who also has a Boxster S) and they shake on his car, too.

BTW, for a street tire, the F1 Asymmetric's grip is impressive.

[stumpjumper]

mine do the same thing, my shop told me they did it at speed but I'd so rarely taken it on a smooth highway that I'd thought it was just uneven pavement...

Michelin PS2's will be replacing them shortly, once I have some fun destroying the rears :)