Tires: About tires, judgement call, hunter road

Question
Hello, two questions here:
1 I replaced 4 tires into my car (Porsche 18 in. Contis 225-40 front, and 265-35 rears)when the shop tried to balance them in a Hunter Road force machine, it showed that 2 of them were marginal due to out of round, I am still waiting for the replacements, but I really feel the car great, Do you think that tires can be defective?
2 One of the "good" set had a screw about 1.5 inch to the sidewall, they said it was repairable and they did, they even mentioned that the tire is even "stronger" now due to the patch, I am concern about that because I really drive fast the car, the question is if a tire repaired can lose its z rating or something similar?, thank you very much


Answer
Fenando,

"Out of round" is a judgement call.  In other words, how much is too much?  Some vehicles are really sensitive and some aren't and what determines the point at which the Hunter machine judges how much is too much is based on experience of what causes vehicles to vibrate.  Obviously you are correct in questioning this as you're not feeling anything.  So, no, those tires are not defective.


I'm a little unclear about where the hole was.  I'm going to assume the hole was in the tread, because if it was in the sidewall, the tire is not repairable.  And again, you are right, a repaired tire is something you should be concerned about.  The problem is that on top of the normal risks you take with tires - there might be a hidden defect in the tire or there is debris in the road that could cause a blowout - adding the fact that the tire was operated underinflated for some period of time and the fact that the tire has a discontinuity in the structure are things that multiply the risks involved.  

I should tell you that tire manufacturers have a variety of different stances regarding repairs vs speed ratings.  I think the differences of opinion revolve around how each manufacturer percieves the risk involved.  My take is that operating a tire over 100 mph is not something I'd want to do with suspect equipment - and a repaired tire would be suspect.  

Hope this helps.