I have NEVER had a tire lose air from going over 140.
because the rubber in the valve stem degrades over time. also, look at when you fill the tire and check the pressure, the twisting on the stem. every major tire manufacturer recommends changing the stem with a tire (talking rubber, it is once a year for metal stem race applications). obviously, if you use rubber, you do not need to change stems with your tires if you change every weekend. the reason you never lost air over 140 can be two-fold (actually three, wait for it). one, your valve cap retained enough of a seal to prevent loss (hence race rules if the valve fails, the cap can REDUCE incident) and two, your seal in the stem is still pretty good. same reason you need tires for a certain speed rating, your valve stems should be angled, and not perpendicular. (http://www.calctool.org/CALC/phys/newtonian/centrifugal)
i will admit one fault here, i wrote 140, when i should have written 200 mph. sure most people on this forum will not reach that speed, but a degraded stem is bad news.
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did you also know that you should change your valve stems with every tire change too?
Quote:
Originally Posted by 1/4milecrazy
And why is that?
What do you work for a tire store??
I have NEVER had a tire lose air from going over 140.
Stems once per season is generally good enough.
And yes valve stems can loose air from speed. That is why race orgs require metal caps with orings in them usually. But it is RARE that it happens. I have only heard of it happening on superbikes at places like daytona with stupid fast speeds prolonged as well.
But these same bikes can spin the rear tire on the rim.. and the best riders in the world have been known to spin the front tire on the rim on the brakes too.
Yeah, once a year is sensible. On a race bike, changing the valve every tire is just ridiculous. I would be changing the rear valve stem every 3-5 track days. Not that its expensive or time consuming.
I have had the same valve stems on my truck for over 3 years, I check them regularly. I know that stems are prone to dry rotting. But I dont agree with changing them every tire change, not even on my truck.
My CBR has about 7000 miles on it, and have changed the rear tire 4 times due to flats, I doubt at 7000 miles my stem are rotted.
BTW, I do have angled stems on my track bike.
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Quote:
Originally Posted by GixxerVixxen
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did you also know that you should change your valve stems with every tire change too?
On a car, where you will get 40 or 50 thousand miles out of a set of good tires...of course.. On a bike that can wear through a set of tires in as little as 3 or 4 days or usually around 3000 decent paced street miles.. That would just be wasteful unless you just never ride and they are really old.
On a car, where you will get 40 or 50 thousand miles out of a set of good tires...of course.. On a bike that can wear through a set of tires in as little as 3 or 4 days or usually around 3000 decent paced street miles.. That would just be wasteful unless you just never ride and they are really old.
well nitrous said that he rode street. fwiw, the tires on my streetbike will be 4 years old when i change them, thus i will change stems. yes, 4 years, i bought the bike as a leftover and only put 10k on it in 3 years (deployments plus canadian winter, plus a busy track season). trackbike got rubber stems twice this season, i just kept forgetting the bridgeport angled ones at home all the time.
In the back-to-back JDSA and GNF weekends (or i should say "events", since the GNF actually started Thursday), i went through 10 rear tires and 4 fronts. That is a lot of valve stems.
But Im rarely over 140, let alone a 100. Im a street rider.
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