Schrader valves
Plano Dude
http://www.roadbikeaction.com/Most-Popular-Stories/content/67/3777/Five-Things-About-Valve-Stems.html
that during John Howard's Bonneville speed runs he kept getting soft
tires because the Schrader valves were creeping open during his runs
due to centrifugal force.
You can buy plenty of out of the factory cars now that can easily
eclipse the 100 mph that supposedly caused the problem. Same for
motorcycles and of course race cars. I have seen tires with speed
ratings, but never heard of speed ratings for Schrader valves.
Sounds to me like the story is a crock. Anyone have something
different to add?
DirtRoadie
> It has been a long standing storyhttp://www.roadbikeaction.com/Most-Popular-Stories/content/67/3777/Fi...
> that during John Howard's Bonneville speed runs he kept getting soft
> tires because the Schrader valves were creeping open during his runs
> due to centrifugal force.
>
> You can buy plenty of out of the factory cars now that can easily
> eclipse the 100 mph that supposedly caused the problem. Same for
> motorcycles and of course race cars. I have seen tires with speed
> ratings, but never heard of speed ratings for Schrader valves.
>
> Sounds to me like the story is a crock. Anyone have something
> different to add?
Just an observation- A schrader valve in a bicycle rim is typically
oriented directly radially. Not so for autos.
That would affect the forces tending to open (and/or inhibit opening)
the valve.
But I don't know about motorcycles.
In any case one wonders why there would not have been valve caps in
place.
DR
thirty-six
> It has been a long standing storyhttp://www.roadbikeaction.com/Most-Popular-Stories/content/67/3777/Fi...
> that during John Howard's Bonneville speed runs he kept getting soft
> tires because the Schrader valves were creeping open during his runs
> due to centrifugal force.
>
> You can buy plenty of out of the factory cars now that can easily
> eclipse the 100 mph that supposedly caused the problem. Same for
> motorcycles and of course race cars. I have seen tires with speed
> ratings, but never heard of speed ratings for Schrader valves.
>
> Sounds to me like the story is a crock. Anyone have something
> different to add?
Th typical valve lift off speed was calculated at around 140mph. Good
valve caps make this irellevant. Tyres go soft with speed due to heat
generation. Different rubber compounds are typically specified, which
are very thin, for speed record trials. I seem to recall regular
moped tyres were used. Mopeds typically have a maximum speed of 30 or
40mph by law, but may be capable of 50mph (for which the regular tyres
will be capable performers).
carlgr...@gmail.com
> that during John Howard's Bonneville speed runs he kept getting soft
> tires because the Schrader valves were creeping open during his runs
> due to centrifugal force.
>
> You can buy plenty of out of the factory cars now that can easily
> eclipse the 100 mph that supposedly caused the problem. Same for
> motorcycles and of course race cars. I have seen tires with speed
> ratings, but never heard of speed ratings for Schrader valves.
>
> Sounds to me like the story is a crock. Anyone have something
> different to add?
Dear PD,
Howard's single flat occurred on a 150 mph run (not 100 mph), with a
vertical valve stem (not an angled car valve stem).
A thread that discussed the details:
Cheers,
Carl Fogel
Fred Flintstein
Car valve stems travel a smaller radius.
There are good reasons to hate on John Howard but I'm
not sure this is one of them.
Fred Flintstein
Plano Dude
wrote:
> On 2/9/2011 6:58 PM, Plano Dude wrote:
>
> > It has been a long standing story
> > that during John Howard's Bonneville speed runs he kept getting soft
> > tires because the Schrader valves were creeping open during his runs
> > due to centrifugal force.
>
> > You can buy plenty of out of the factory cars now that can easily
> > eclipse the 100 mph that supposedly caused the problem. Same for
> > motorcycles and of course race cars. I have seen tires with speed
> > ratings, but never heard of speed ratings for Schrader valves.
>
> > Sounds to me like the story is a crock. Anyone have something
> > different to add?
>
> Car valve stems travel a smaller radius.
>
> There are good reasons to hate on John Howard but I'm
> not sure this is one of them.
>
> Fred Flintstein
I wasn't hating on JH. Very rarely do stories and rumors get started
by the person in question. Look at the Jobst/helmet thread by
Clitorius Vaginus, for example.
Anton Berlin
This is all nerdy bike talk - why can't some of you eggheads calculate
how much force and friction it actually does take for a girl to suck
the chrome off a trailer hitch. That's the kind of math we can all
appreciate.
Simply Fred
> This is all nerdy bike talk - why can't some of you eggheads calculate
> how much force and friction it actually does take for a girl to suck
> the chrome off a trailer hitch. That's the kind of math we can all
> appreciate.
I'd have thought you'd be calculating your share ratio on Liz.
Brad Anders
This seems like an ideal episode for the "Mythbusters" guys. Maybe
Kari or Scottie could be the test subjects.
DirtRoadie
wrote:
Interesting discussion and the G-force figures all seem accurate.
But I didn't follow there where it was stated:
" The short pin weighed only 3 grams, while the long pin weighed 4
grams:
http://i39.tinypic.com/302x9gg.jpg "
Looks to me like there's a decimal point missing from the 3g and 4g
figures. For comparison I quickly weighed 5 complete Schrader cores
(not just pins) at ~ 4g = .8 g each.
The 3000g (~6.6 lbs) spring force just sounded high to me. And,
indeed, loading a digital scale with partially compressed Schrader
core I get something more in the range of <400g. That's rough since I
was simply holding the valve pin against the scale platform. So that
somewhat offsets the apparent 10x error in pin weight above
But one thing that seems to not have been discussed in the thread is
the additional effect of tire pressure in keeping the valve closed.
Using .01 sq. in. as the affected area and 70 psi as the tire pressure
there's another 317g worth of valve closure force - perhaps nearly
matching doubling the spring force.
I have no firm conclusion. There are too many guesstimates involved.
But there doesn't seem to be any clear reason to suggest that the
original claims were false.
DR
Michael Press
<f01ee97d-4777-4907...@z31g2000vbs.googlegroups.com>,
DirtRoadie <DirtR...@aol.com> wrote:
Effects you did not mention and are very difficult
to even estimate are cyclic and stochastic
forces from rotation, bumps, and vibration.
--
Michael Press
DirtRoadie
> On Thu, 10 Feb 2011 10:22:53 -0800 (PST), DirtRoadie
>
> I ask as there are available today, off the shelf, tire pressure
> monitoring systems rated to around 180 MPH, and probably some rated to
> higher speeds, that are used by competition cars. It would seem as
> though running on the salt flats would be a logical place for them as
> I would think a high speed run would tend to raise pressures somewhat.
> There are also pressure control systems that adjust tire pressure
> automatically while running, mostly used by circle track cars, I
> believe.
>
> By the way, in the past valve caps incorporated a seal so that
> tightening them firmly sealed the valve completely. Sadly no longer
> common.
Past? Yes ancient.
References:
http://sportsillustrated.cnn.com/vault/article/magazine/MAG1119704/index.htm
(note the media "spin" on the air loss issue P. 2)
Also
http://www.youtube.com/watch?v=Py94okBKDU0
To simplify, the question was just now posed (again?) as to whether
the air loss issue was myth or fact.
So there has been some more numerical flogging based upon best
guesses.
In Mythbusters parlance, the air loss seems plausible.
DR
thirty-six
> (note the media "spin" on the air loss issue P. 2)
>
> To simplify, the question was just now posed (again?) as to whether
> the air loss issue was myth or fact.
> So there has been some more numerical flogging based upon best
> guesses.
> In Mythbusters parlance, the air loss seems plausible.
>
> DR
My cousin came off after decelerating from in excess of 150mph. It
seemed that tyre deflation was likely the cause of his fall at over
100mph.
DirtRoadie
Details?
DR
Plano Dude
I'm betting the cause was gravity.
thirty-six
Yes, but he was thrown off the bike because of wobble. Machine was
destroyed all bar the trick bits.