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Got a blowout, now what are the valve stems made from?
For those not up on the "What did I do today on my 996 thread", I learned how to change the tire on it. I just put on a new set of shoes 1200 miles ago. While I am not a tire expert, it appears the right rear tire lost air and the damage was a result of this. There are no road hazards in the tread, so I wonder if it is the valve stem. Looking at them, they are not the typical rubber ones I am used to. Are these steel? Is there a rubber gasket somewhere? When new tires are put on, do you need specific part to put in a new valve stem? Or will any tire place have these?
You definitely need the metal stems. I'm not sure just any tire place would have them. The metal stems can handle the higher centrifugal forces associated with your TT's high speed capability without bending outward. The rubber stems can't (long term), and could fail due to age and high speeds. Porsche was concerned enough before metal stems were available to put supports on the rim that the rubber stems rested against. On my 993, there is a metal cap that extends over the rubber stem and allows it to rest against the rim; again supporting the rubber stem. Both designs provide support against the centrifugal forces and were solutions to higher speed capabilities before metal stems were available.
Sunset sells the supports that I use on my Fuchs rims. The rubber stem rests against the metal support keeping it from bending outward.
Years ago, I did a calculation that showed the forces created by a 1 gram stem cap at 150mph is measured in pounds not grams. I was bored and curious one weekend.
As far as the damage to your tire, it looks like it lost air then you had to keep driving for a bit. The rim cut that groove in the tire being driven when flat. Your only chance of saving a tire is to pull over as soon as possible.
Last edited by autobonrun; 03-27-2019 at 09:53 AM.
Thanks for the replies. For “regular” cars, you normally get new valve stems when you get new tires. Does this need to be done here? Do I need to call the shop that mounted them and ask if they were done?
All TPMS sensors have metal stems with a greyish cap.
*MOST have metal valve stems.
Did the 996 come with tire pressure sensors?
And if they were already installed on the wheels im sure a tire shop would have just left them as they are not throw away like rubber ones. The gaskets could be leaking tho
Turbo hollow spoke wheels are a different breed. Normal cars of that era had plain old rubber stems. Metal stems were available for "normal" cars for a variety of reasons. Then came TPMS (not the 996) which are available in both rubber and metal stem buts thats for another thread. Since the 996 turbo are hollow spoke they take an odd metal stem which is unique and a typical tire shop will not have them laying around. Perhaps a Porsche specific shop but not your everyday tire shop.
Here is a screen shot from ECT tuning of what they look like.
Had the new tire put on- it’s hard to find a place that will do these. Once removed, the culprit was found. Puncture. I’ve sent them off to the road hazard claim so this should be an easy case.
So, slow leak.........low pressure............sidewall abuse...........rupture. Wish we had TPMS, I can't find any aftermarket versions that don't look cheesy.
Yea exactly. If you find a TPMS solution, please advise. While I am not pleased with having to go through this, I am glad to know it should be covered. $400 is not a cheap tire.
03-27-2019, 12:11 AM
Got a blowout, now what are the valve stems made from?
