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Rollin' Stones
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Discussion Starter · #1 ·
Descending this morning got me thinking. How fast can a standard clincher wheel go before it fails? I remember hearing Bobke talk about descents in the Tour where riders reach 65-70mph for short periods of time. Hypothetically, how fast could a wheel go? What would fail first?
 

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Adorable Furry Hombre
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cydswipe said:
Descending this morning got me thinking. How fast can a standard clincher wheel go before it fails? I remember hearing Bobke talk about descents in the Tour where riders reach 65-70mph for short periods of time. Hypothetically, how fast could a wheel go? What would fail first?
Going fast isn't that hard on equipment given good roads, and a rider who knows what line to take through turns. It is the slowing down part which causes problems.
 

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going REALLY fast is hard on equipment. When John Howard set a cycling speed record of 157mph on one attempt the rear wheel blew not because of a blowout but because the centrifugal force on the tire was enough to blow out the valve, requiring a special metal valve cover. Don't know the details of tires etc that he used.

 

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stevesbike said:
going REALLY fast is hard on equipment. When John Howard set a cycling speed record of 157mph on one attempt the rear wheel blew not because of a blowout but because the centrifugal force on the tire was enough to blow out the valve, requiring a special metal valve cover. Don't know the details of tires etc that he used.


Towed to speed and then paced the car...weaksauce. Most of us, given the balls to do it, could likely repeat the feat.
 

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Actual story

stevesbike said:
going REALLY fast is hard on equipment. When John Howard set a cycling speed record of 157mph on one attempt the rear wheel blew not because of a blowout but because the centrifugal force on the tire was enough to blow out the valve, requiring a special metal valve cover. Don't know the details of tires etc that he used.
Actually, he was using lightweight motorcycle wheels, and Schraeder valve inner tubes. When the bike got up to about 140 mph, the centripital force depressed the valve spring on the Schraeder valves and deflated his tires. Nothing special, just the force exceeded the spring constant of the valve. He installed normal valve caps (included a rubber O-ring gasket to seal against the valve stem) and that fixed it.
 

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backinthesaddle said:
Towed to speed and then paced the car...weaksauce. Most of us, given the balls to do it, could likely repeat the feat.
John Howard was a dominant racer of his time and was on the US Olympic Team. "Most of us" never were nor ever will be that fast. Stop kidding yourself.
 

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Kerry Irons said:
John Howard was a dominant racer of his time and was on the US Olympic Team. "Most of us" never were nor ever will be that fast. Stop kidding yourself.[/QUOTE

that's right - John is a legend in US racing - multiple US national champion, 3 time Olympian, and won Hawaii Ironman. He's a fixture in San Diego cycling as well, and a nice guy. I used the example of the tube failing only as a conjecture re the OP about what part of a wheel might fail first at really high speed....
 

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Kerry Irons said:
John Howard was a dominant racer of his time and was on the US Olympic Team. "Most of us" never were nor ever will be that fast. Stop kidding yourself.
Again, the know-it-all gets it wrong.
I never said we could be the equal of John Howard himself, nor exceed his records or palmares.

He DID NOT pace the vehicle UP to that speed. He was towed behind the car up to @55mph and then released to ride in the slipstream. It would have been simply impossible to turn the gear at low speed. He used a double reduction gear, versus a normal bicycle's ratio of 6-ish to 1.
And yes, given the testicular fortitude, most guys who are Cat3 or better could likely do the same. The record now belongs to Fred Rompelberg, a Dutchman who specializes in pacing behind vehicles.

Anyone that's reasonably fit can pace the right vehicle up to 60mph or so. The lack of tall enough gearing to continue the chase/pace becomes an issue at those speeds. Hell, I suck, and paced a Merita bread truck to 55mph one morning. Like Howard said in the 1985 SI article, I just got sucked along by the vortex.

And it's centrifugal force you boob. Outward pressure on the wheel/tire, from the speed of rotation, forced the air out.

Sure, it took fitness and balls of steel, but it's not out of the realm of possibility.
 

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Sucker for carbon
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backinthesaddle said:
Again, the know-it-all gets it wrong.
I never said we could be the equal of John Howard himself, nor exceed his records or palmares.

He DID NOT pace the vehicle UP to that speed. He was towed behind the car up to @55mph and then released to ride in the slipstream. It would have been simply impossible to turn the gear at low speed. He used a double reduction gear, versus a normal bicycle's ratio of 6-ish to 1.
And yes, given the testicular fortitude, most guys who are Cat3 or better could likely do the same. The record now belongs to Fred Rompelberg, a Dutchman who specializes in pacing behind vehicles.

Anyone that's reasonably fit can pace the right vehicle up to 60mph or so. The lack of tall enough gearing to continue the chase/pace becomes an issue at those speeds. Hell, I suck, and paced a Merita bread truck to 55mph one morning. Like Howard said in the 1985 SI article, I just got sucked along by the vortex.

And it's centrifugal force you boob. Outward pressure on the wheel/tire, from the speed of rotation, forced the air out.

Sure, it took fitness and balls of steel, but it's not out of the realm of possibility.
Sucked in by a vortex? What, is your name Dorothy? You weren't sucked in. You just more easily pushed yourself in due to the (relatively) low pressure region caused by the air being displaced by the moving van.

Also, the centrifugal force is fictitious. The phenomenon stems from the object in rotation wanting to follow a straight line path tangent to its curved path. This creates the illusion of a force throwing it outward, but is really just the effects of the rotating object's inertia. There is also a force keeping the rotating object in check (in this case provided by the wheel) This is a real, center-seeking force known as the centripetal force.
 

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cydswipe said:
Descending this morning got me thinking. How fast can a standard clincher wheel go before it fails? I remember hearing Bobke talk about descents in the Tour where riders reach 65-70mph for short periods of time. Hypothetically, how fast could a wheel go? What would fail first?
I've gone 64 mph, and no problem.

I think the tire or tube would fail well before the wheel.
 

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backinthesaddle said:
Again, the know-it-all gets it wrong.
I never said we could be the equal of John Howard himself, nor exceed his records or palmares.

He DID NOT pace the vehicle UP to that speed. He was towed behind the car up to @55mph and then released to ride in the slipstream. It would have been simply impossible to turn the gear at low speed. He used a double reduction gear, versus a normal bicycle's ratio of 6-ish to 1.
And yes, given the testicular fortitude, most guys who are Cat3 or better could likely do the same. The record now belongs to Fred Rompelberg, a Dutchman who specializes in pacing behind vehicles.

Anyone that's reasonably fit can pace the right vehicle up to 60mph or so. The lack of tall enough gearing to continue the chase/pace becomes an issue at those speeds. Hell, I suck, and paced a Merita bread truck to 55mph one morning. Like Howard said in the 1985 SI article, I just got sucked along by the vortex.

And it's centrifugal force you boob. Outward pressure on the wheel/tire, from the speed of rotation, forced the air out.

Sure, it took fitness and balls of steel, but it's not out of the realm of possibility.
sure. lots of people could replicate the athletic component in terms of the wattage required etc., BUT it requires more than balls of steel - I've talked with John a bunch of times about it and the most difficult part was handling the bike and getting the front end/steering worked out. Any bit of unsmoothness from the rider amplified into instability. A speed wobble at 150mph wouldn't be pretty...
 

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skaruda_23 said:
Also, the centrifugal force is fictitious. The phenomenon stems from the object in rotation wanting to follow a straight line path tangent to its curved path. This creates the illusion of a force throwing it outward, but is really just the effects of the rotating object's inertia. There is also a force keeping the rotating object in check (in this case provided by the wheel) This is a real, center-seeking force known as the centripetal force.
http://xkcd.com/123/
 

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Two strikes

backinthesaddle said:
Again, the know-it-all gets it wrong.
I never said we could be the equal of John Howard himself, nor exceed his records or palmares.

He DID NOT pace the vehicle UP to that speed. He was towed behind the car up to @55mph and then released to ride in the slipstream. It would have been simply impossible to turn the gear at low speed. He used a double reduction gear, versus a normal bicycle's ratio of 6-ish to 1.
And yes, given the testicular fortitude, most guys who are Cat3 or better could likely do the same. The record now belongs to Fred Rompelberg, a Dutchman who specializes in pacing behind vehicles.

Anyone that's reasonably fit can pace the right vehicle up to 60mph or so. The lack of tall enough gearing to continue the chase/pace becomes an issue at those speeds. Hell, I suck, and paced a Merita bread truck to 55mph one morning. Like Howard said in the 1985 SI article, I just got sucked along by the vortex.

And it's centrifugal force you boob. Outward pressure on the wheel/tire, from the speed of rotation, forced the air out.

Sure, it took fitness and balls of steel, but it's not out of the realm of possibility.
I guess that just because Isaac Newton called it centripetal force, that's not good enough for you? And you call me a boob?

And I'm just sorry, but no Cat3 is going to get a bike up to 157 mph under any conditions. Of course he was towed, and of course he was behind a streamliner, but it's not something that can be done by "most guys who are Cat3 "

Time for some anger management classes?
 

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Rollin' Stones
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Discussion Starter · #16 ·
Sooooo, back to my original question, the consensus is that the tube or tire would fail first, not the spokes, hub, or rim from constant high speed? I'm not talking a short descent. I mean if a machine could simulate road conditions, at high speed, what would give out/fail first?
 

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mode of failure?

cydswipe said:
Sooooo, back to my original question, the consensus is that the tube or tire would fail first, not the spokes, hub, or rim from constant high speed? I'm not talking a short descent. I mean if a machine could simulate road conditions, at high speed, what would give out/fail first?
I'm still thinking tube/tire before wheel. Wheels are very strong. I once was descending at 45-50 mph following a pickup, and blew out a tire when I ran over, I think, a 2x4 in the road that I couldn't see, as I was too close to the truck. Instant blowout. I had a small buldge in my rim (a Ksyrium).

At higher and higher speeds, I'd not be so concerned about things just flying apart, but what would happen if I hit something, debris, a pothole, that kind of thing. I think that's the kind of failure I'd be afraid of. What happens at 100 mph if you blow a tire? Does it then fly to pieces, and then the bare rim meets the road? I'd think it would get pretty squirrely.

If I were planning on riding 100-150 mph, I'd likely want a stout high quality 26" rim with slick mtb tires. Would want it well balanced. That way, if you do hit something, you have a lot more cushion to absorb and distribute it.

I suppose you could test it by hooking the front end of a weighted bike to the back of a car (or some mechanical equivalent), with the back tire on the ground, then keep driving faster and faster. Shouldn't be that risky. Sounds like a job for Mythbusters.
 

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Fixed said:
I'm still thinking tube/tire before wheel. Wheels are very strong. I once was descending at 45-50 mph following a pickup, and blew out a tire when I ran over, I think, a 2x4 in the road that I couldn't see, as I was too close to the truck. Instant blowout. I had a small buldge in my rim (a Ksyrium).

At higher and higher speeds, I'd not be so concerned about things just flying apart, but what would happen if I hit something, debris, a pothole, that kind of thing. I think that's the kind of failure I'd be afraid of. What happens at 100 mph if you blow a tire? Does it then fly to pieces, and then the bare rim meets the road? I'd think it would get pretty squirrely.

If I were planning on riding 100-150 mph, I'd likely want a stout high quality 26" rim with slick mtb tires. Would want it well balanced. That way, if you do hit something, you have a lot more cushion to absorb and distribute it.

I suppose you could test it by hooking the front end of a weighted bike to the back of a car (or some mechanical equivalent), with the back tire on the ground, then keep driving faster and faster. Shouldn't be that risky. Sounds like a job for Mythbusters.
Uh oh. Here comes the balancing debate again, lol.
 
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