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Hard braking down hill blowouts
Is it normal to have blow-outs on a road bike from prolonged hard braking going
about one mile down a steep hill or should superior wheels and tires be able to deal with the generated heat? I have an old panasonic but keep the tires and tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, which are not the best in the world but a heck of a lot better than what my LBS sold me. It is a 27 inch rim and I could not find any better quality tires). But is it the tire/wheel quality at issue? I have been thinking about getting a new bike rather than trying to upgrade this one for a number of reasons (I don't think it's even possible to switch to the current wheel size) but the blow-outs are my biggest justification of expenditure to my wife. Thanks. Ben |
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Hard braking down hill blowouts
Ben Kaufman wrote:
Is it normal to have blow-outs on a road bike from prolonged hard braking going about one mile down a steep hill or should superior wheels and tires be able to deal with the generated heat? I have an old Panasonic but keep the tires and tubes up to date (Performance Bike GT2 Kevlar, rated at 105 lbs, 26TPI, which are not the best in the world but a heck of a lot better than what my LBS sold me. It is a 27 inch rim and I could not find any better quality tires). But is it the tire/wheel quality at issue? I have been thinking about getting a new bike rather than trying to upgrade this one for a number of reasons (I don't think it's even possible to switch to the current wheel size) but the blow-outs are my biggest justification of expenditure to my wife. This is a traditional problem, so much so that bicycles are prohibited down certain roads in the Alps. Zirlerberg above Innsbruck is a classic with six runaway escape ramps for brake failures of trucks. The Würzen Pass from Slovenia to Austria has a long 18% grade. Locally in the Santa Clara Valley we have several tire blow-off descents on Metcalf Road and Hicks and Almaden Roads, each of which has had fatalities on descents. Tandems are noted for this problem, especially if the driver isn't careful to use front and rear brakes equally. For this reason tandems used for mountain touring are best equipped with hub brakes (drums or disks). In the days of tubular tires, that were glued onto rims, glue melted allowing tires to creep and tear off the inflation stem causing rapid deflation. I experienced that effect in the alps ans later had clincher blow-offs on the same stretch of the Gotthard Pass. I instrumented a wheel with pressure sensor and temperature thermocouple to monitor a blow-off but was unsuccessful getting the tire to separate even though temperature reached 150 degC and pressure 125 psi. The mechanism for blow-off is still unclear but it seams the bead material softens and creeps of the hooked bead of the rim. On steep descents after riding through water, I have generated steam that came hissing out of the rim from around the stem as I braked for successive hairpin turns on the Nufenen Pass in the Alps. Jobst Brandt |
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Hard braking down hill blowouts
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Hard braking down hill blowouts
On 28 Mar, 06:35, wrote:
In the days of tubular tires, that were glued onto rims, glue melted allowing tires to creep and tear off the inflation stem causing rapid deflation. *I experienced that effect in the alps ans later had clincher blow-offs on the same stretch of the Gotthard Pass. Not to dispute or anything, but where was that? Down the south side of the old Tremola, perhaps? Sergio Pisa |
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Hard braking down hill blowouts
On 2008-03-28, Ben Kaufman wrote:
Is it normal to have blow-outs on a road bike from prolonged hard braking going about one mile down a steep hill or should superior wheels and tires be able to deal with the generated heat? I have an old panasonic but keep the tires and tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, which are not the best in the world but a heck of a lot better than what my LBS sold me. It is a 27 inch rim and I could not find any better quality tires). But is it the tire/wheel quality at issue? I have been thinking about getting a new bike rather than trying to upgrade this one for a number of reasons (I don't think it's even possible to switch to the current wheel size) but the blow-outs are my biggest justification of expenditure to my wife. Some math I did earlier: http://groups.google.co.uk/group/uk....1d32532f671264 It's probably all wrong off course, but my tentative conclusion from it is that the rims act as heat sinks-- they can soak up quite a lot of energy, enough for most purposes, but they can't really cope with sustained braking. Disks on the other hand have much less heat capacity (because they're smaller) and probably work hotter, so I reckon they might get up to temperature quite quickly and then dissipate more because of the bigger temperature difference with the surrounding air. This would mean they should be better for continuous braking. In any case they won't make the tyres pop off. |
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Hard braking down hill blowouts
On Mar 28, 9:49 am, Ben C wrote:
Disks on the other hand have much less heat capacity Nor do they exchannge heat with the tyre. Sergio Pisa |
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Hard braking down hill blowouts
On 2008-03-28, sergio wrote:
On Mar 28, 9:49 am, Ben C wrote: Disks on the other hand have much less heat capacity Nor do they exchannge heat with the tyre. Indeed. I wonder if they ever melt the grease in the hub though. |
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Hard braking down hill blowouts
Sergio Servadio wrote:
In the days of tubular tires, that were glued onto rims, glue melted allowing tires to creep and tear off the inflation stem causing rapid deflation. Â*I experienced that effect in the alps ans later had clincher blow-offs on the same stretch of the Gotthard Pass. Not to dispute or anything, but where was that? Down the south side of the old Tremola, perhaps? Yes, on the last hairpin turn leading to the Fortezza. Jobst Brandt |
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Hard braking down hill blowouts
Ben C? wrote:
Disks on the other hand have much less heat capacity Nor do they exchange heat with the tyre. Indeed. I wonder if they ever melt the grease in the hub though. Most bicycle disks are mounted on support spiders so flimsy that heat conduction to the bearings is insignificant. Jobst Brandt |
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Hard braking down hill blowouts
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