DCP

I bought a set of HTR Z III. I have had them for about six months. They seem to develop a flat spot while sitting for a while and as a result are pretty lumpy driving along until they warm up. It is especially noticeable when I am at the track and start driving with lower pressures.

Before I buy more of these, I am trying to figure out whether it is a characteristic of the tire or mayble I got a defective one or ones. Anyone one else with these tires have a similar experience?

No HTwo O

I think it's mainly because of your lower than OEM tire pressures.

Are they road forced balanced? If the flat spotting is reversible, after warming up, you're fine.

DCP

Not road forced balanced. I run the recommended pressures in normal driving and it is there then too. It is more noticeable at the lower pressures, but it is always there. I think I may have a defective tire, but wanted to see whether others had the same experience before I reach that conclusion.

ivangene

I did notice a few times where I thought they seemed a little flat for a mile or two nithe morning. I figured it might have something to do with my garage floor (rubber) but agree the higher presures helped.

No HTwo O

You could have a defective tire (out of round??) but if they were road forced balanced (as they should be) it would have found it.

Talk to Damon at the Tire Rack or PM him. Where did you purchase?

ivangene

I am guessing the OP feels the flat spot at low speeds in the morning...which balance would most likely not effect

right?

DCP

It is most noticeable at low speeds in the morning, but I can feel it anytime the car has been sitting for a while. At the lower pressures, you can feel even if the car has been sitting for only a short while and then it is very noticeable at higher speeds too.

I bought them at Tire Rack. I need rears now and am trying to decide whether to buy new rears or a complete set of something else.

morganabowen

When you say sitting for a long time, are you referring to hours, days, weeks etc., etc. I have them on my 996 and have not noticed that. My car does sit for several days on occasion since I go to the office only two or three times a week I'm changing to the Pirelli next week

No HTwo O

DCP, whatever you decide, in the future, make sure your tires are a matched set (don't mix brands and models) and road forced balanced. Run pressures closer to OEM spec. Track days are different.

All tires and all wheels have "high" spots and "low" spots. When dynamic road forced balanced, these are off-set, and the result is a much better balanced tire.

You may actually have a true "flat spoted" tire too. Did you ever lock 'em up on the track, and wear a flat spot into the tire?

My cars sit for 6-8 months during winter hibernation. Tires are over inflated per the manual (about 58 PSI). I never have flat spotting issues. PS2's on the Boxster and Kumho on the Turbo.

No HTwo O

Really? Pirelli is netorious for flat spotting over a Michelin, for example. FYI.

DCP

At street pressures, the car has to sit for hours for the lumpiness to appear. At lower pressures, it just has to sit for 30 minutes. Thanks for that info; I think I have a bad tire. I will get new Sumi rears and if does not go away, I will talk to Tire Rack about replacing the fronts.

I preferred the PS2's I used to have, but I am tracking more and it is just too expensive to continue that habit.

DCP

Thanks. I would not mix brands, although I will put new rears on with worn fronts. I do not want to start the usual debate on the recommended pressures, but I do use the recommended pressures except at the track. The flat spot (or tire defect) was evident from right after the install, so I am certain that I did not put a flat spot on the tires.

rpm's S2

They are relatively soft and can get a bit out of round if sitting for a few days. I had them on my 968 and it was always a bit lumpy for the first few miles in wintertime until they warmed up. Fairly common with summer tires, though a bit more noticeable with the Sumis.

DCP

That is interesting. I never noticed this with the PS2's. Perhaps that is why they cost twice as much. Never noticed either on the Dunlop Diezza Star Spec's that I have on a BMW. That is from the same company as the Summi's and a more aggressive tire.

fpb111

On the track I use the flat spot lumpiness as an indication of "tires are too cold to push hard". When the vibration goes away = time to start 'havin sum fun'.
On the street it is still a good indication that the tires are cold and full traction is not yet available. (Hoosiers)