Flat Tires, Yikes!
 

I just got this troubling note from the PCA:

"Year: 2004
Total Mileage: 6500
Car Use: General

Question:
I just discovered a nail in the rear tire. Is this true that the tire has to be replaced and cannot be fixed.
Thanks

Answer:
Yes it is true. This applies to many manufacturers and to all "Z" rated tires and above. This is set do to the speed rating of the tires. Having a plugged hole in a tire at high speed can cause a catastrophic failure. Now as a temporary fix it would be possible to patch a hole in the center tread area. Under no circumstance would you ever plug or patch a tire with a hole in or close to the side wall. "


I did not know any of this about tire care with my Boxster. I have looked through the owners manual and such, I thought carefully, and did not know flat tires should not be plugged, at least not as a long-term repair.

When I got the car and took it in for service, there was a nail in one of the rear tires. The Porsche mechanic just pulled it out and did not repair it as it did not leak. He said nothing about being careful or looking out for the tire.

To make matters worse, a week or so later, I got a screw in my front tire which caused a slow leak. I got the leak plugged and have been driving on it since. Monday I go in for four new tires, sounds like I have been way overdue.....


Ed

2000 Boxster
48K
Beatup Pirelli's

Ed,

This has been covered a few times before. What they told you is technically correct, however, they're telling you that for liability reasons. A good plug shouldn't cause you any problems provided that you don't take the car to excessive high speeds since that plug renders the Z rating ineffective. But, it doesn't mean that the tire isn't still useful.

I honestly wouldn't worry too much about it. If you want to get new tires, fine, but feel free to do it at your leisure.

Also, I'm a HUGE fan of Tire Rack (online). I ordered 4 new tires this past Friday - they arrived on Monday - installed on Monday. I saved myself a BOATLOAD of money and got exactly the tires I wanted. Seriously, I can't rave enough about that site.

Good luck.

New Tires
 

I was suprised at how good a price I could get Michellin's through my Porsche dealer was. My local Porsche dealer chages 200.00 more for 4 Michellin's (mounted and balanced) than I can get them for from tire rack. But that extra 200.00 includes shipping, mounting and balancing.

That sounds like a pretty good price to me, especially because I normally hang around when they are doing any work on my car to pick the brains of the mechanic.

I am close to the wear markers at several spots on the rear tires these days and its suprising how much easier it is to get the rear wheels to slide around on corners compared to when I had some tread on the suckers. I am very interested to see how much quieter, if at all, and how the ride compares with the Michellin's I am getting and my current Pirelli's.

Ed

Pete: A "boatload" compared to what?

A couple of yrs. ago I needed to replace two of the four Conti 17"ers and checked Tire Rack vs the shop I typically deal with in Boulder. After including shipping and the cost of mounting and balancing, there was virtually no savings whatever over what I paid the local shop for two tires, with no shipping cost and mtng/bal "included".

I know a lot of folks think Tire Rack is the greatest thing since canned beer, but that just hasn't been my experience. Not cost-wise anyway.

Good point, Ronzi! People should use the pricing knowledge gained from places like Tire Rack, and use that to negotiate a better price with the dealership or local area tire shop. Lots of local tire places do price matching of other advertised pricing (sometimes regardless of the other price not being local).

My experience has been similar to Ed and Ronzi's, in that when I replaced tires I found that Pioneer Porsche pricing was on par with Tire Rack for PS2s, when taking shipping, balancing etc. into account.

This would seem to make sense as when you're dealing with a commodity like Porsche parts you can jack up the price, but for goods that are readily available, like tires, the dealers have to be somewhat competitive.

There is a brochure probably at your dealer that lists Porsche approved tire selections for the Boxster. On the back of the brochure is a statement that any plugs or repairs on the tire nullify the speed rating on the tire. But there is no comment on whether you have to go out and replace the tire altogether.

Hi,

Before anyone gets the wrong impression, a nail/screw through the tread and into the carcass of a Tire does a lot more than simply nulify a Speed Rating. The Tire is compromised - period.

At speed, the plug/patch can work loose causing the carcass to disintergrate. And the extra mass which the plug/patch adds produces a Hot Spot in that area of the tire further raising the possibility of a Blowout and loss of control. The only way I would put a repaired Tire back on a performance car is only to buy enough time (read 1-2 weeks) 'til I could afford to replace it.

Considering the cost of repair and accelerated depreciation to the car should it sustain body/frame damage, the cost of the Tire pales in comparison, and we haven't even mentioned the possibility of injury or worse.

Be Safe , and think of the others you share your car and the road with and replace the tire. It's too bad that tires can be struck down in their prime with lots of tread left, but that's just the way it is sometimes...

Happy Motoring!... Jim'99

So, what your saying is it wasn't such a good idea for me to be doing 150+ mph on a plugged rear tire a few months back. I guess it's a good thing I'm replacing those things soon. A blow out at those speeds wouldn't be pretty.

I had the same experience as Ronzi...I went to Discount Tire and they beat tire rack by a few dollars. The only problem is I mistakenly got the Potenza Re050 instead of the Re050a that is approved by Porsche. Does that make a difference? I highly doubt it because they use the 050 on the MB SLR. Anyway, definately go to your discount tire dealers and price the rubber so you can make an informed decision.

Hi,

Absolutely not a good idea. A repaired Tire should not exceed 65 MPH, 55 MPH for a sustained drive.

Heat is the enemy and with a plug/patch, that area of the tire has more mass and therefore greater heat retention to that localized area, it sheds this heat at a lesser rate than the rest of the tire.

This heat build-up can cause the rubber cement which holds the plug/patch to soften/loosen causing a loss of integrity to the seal of the plug/patch allowing air to leak.

Also, the dynamic forces can cause the plug/patch to work loose altogether, especially with an already softened glue. Also, there may have been severed cords from the puncture all adding up to a fair potential for disaster.

Now does this occur to each and every repaired tire? No. But, not every puncture is the same or every repair for that matter. Some hold better than others depending upon the degree to which the tire was compromised and
the skill and knowledge of the person repairing it. More repaired tires will fail in the manner described than not. Are you willing to take the chance with your car and your body (or those of others)? As I said, no one wants to throw away an otherwise perfectly good tire, but you have to realize that it is no longer perfectly good.

Happy Motoring!... Jim'99

This is a good thread and I totally agree that Be Safe is the mantra here. I am about to pose a technical question but let me be clear I am not trying to argue that plugs are safe, I'm just trying to understand...!

It makes sense that 1) heat build up is bad, and 2) a plug/patch adds mass to act as a heat sink and retain that heat. But my question is how severe is the heat build up at 60, 70, 80 mph really? The rubber cement is designed to survive sustained heat and loads at 150mph. The energy at these speeds is much more than the energy at 75mph thanks to 1/2 mv2 plus dynamic vibration plus any other forces I don't think of. And while the plug adds mass, does it add that much more mass? The heat load at 75mph at the plug itself must be many times more than normal, to match the heat a tire would see at 150mph.

I'm sure there are lots of variable like have been mentioned, the quality of the fix, the size of the patch. So there is a good likelihood that you have a BAD fix and have to lower your speed! That said, DO NOT drive a plugged tire at any great speed! This is not worth experimenting with!

I'm not disagreeing with anyone about potential problems with repaired tires, either patched or plugged.
I will say, however, that along with probably a lot of others on this forum, I have driven on repaired tires on sedans, vans, and trucks for literally years at highway speeds and never had a problem. Was I just lucky? Maybe so, but I also think that the chances of a catastrophic tire failure on a properly repaired tire are pretty low.
Would I drive a repaired tire at high speed? No, as common sense would dictate that the chance of a failure increases with speed, as does the severity of the outcome.
Tire companies and auto manufacturers err on the side of caution. Why? Maybe I'm just a cynic, but I think it's liability in case of litigation.

Ronzi, I agree with a lot of the above, but, the main point of differentiation is the comparison of a regular passenger/truck tire vs. the unique characteristics of a speed rate high performance tire...in particular the way is dissipates heat.

Ahhh, Pioneer - great shop! If you run into Matt Bang, please tell him that his New Jersey customer says hi.

Hi,

I realize what you're saying and I don't necessarily violently disagree with it. But, as a former Fleet Aviator and a past and current SCCA National Competition license holder Safety has always been Center Stage in my activities. And, not to say that my resume' is a prerequisite to being Safety Concious, many people are so as well.

It's probable that a catastrophic failure at high speed is a small percentage, but do you want to be that guy?

But, while many here have agreed that high speed shenanigans are not advisable on a repaired tire, how realistic is this? People spend mega-$$ adding intakes, exhausts, headers, superchargers and the like to make their Boxsters even faster. How willing will they be to geld their car and their efforts because of a repaired tire? Perhaps they do so for a week or a month, but I suspect that soon they return to their old habits totally forgetting or ignoring the fact that they are riding on compromised rubber.

And, just like the tire itself, the repair will degrade with age and use. You may not have a failure in the first few months, but the potential rises with time. In other words, it becomes more compromised with time.

If the tire was punctured relatively early in it's life, given the limited miles many people drive their cars, it could be years before the tire is replaced due to treadwear alone. And, Boxster owners seem to be keeping their cars about 5 years in general (a casual, not scientific estimate). Do you really want to own it for one or two of those 5 years pulling the reigns on it's performance?

As bmusatti points out, these are performance tires on a performance car. A passenger or truck tire may run at expressway speeds, even exceeding them on occaision. But, they do not generally have to repeatedly endure the stresses imposed on a Boxster tire.

Of course, people can do as they wish and ultimately will. But, I cannot, on principal, personally endorse an unsafe practice for someone seeking advise. Especially where the rubber meets the road...

Happy Motoring!... Jim'99

Well spoken Jim. When I'm driving at high speeds I'm not thinking about the rear tire that is patched on my car(though I should be). I guess I should consider myself lucky because I've put some pretty good stress on the tires considering the autocrosses, donuts( ok so what they are fun) and some high speed usage. This thread makes me think of the unassuming guy buying the second hand boxster that has a patched rear tire though. That poor unsuspecting soul just was out for a "spirited" drive then BOOM his tire fails and he is toast because previous owner never mentioned that kinda thing.

It's too bad that tires can be struck down in their prime with lots of tread left, but that's just the way it is sometimes...

- MNBoxster

Good one Jim, a solitary tear rolled down my cheek after reading that one.