The real reason that clincher PSIs top out at 120 is...
07-09-08, 01:11 AM
#26
Bicycle Repair Man !!!
One of the most common things I deal with at the shop is folks asking me what pressure they should run in their tyres and it really isn't as much a matter of what the tyre says regarding minimum and maximums but rather, at what pressure does the tyre lose it's ability to offer deflection ?
The max pressure is dictated by the tyre and rim and in many cases, filling the tyre to the max decreases performance in that they lose their ability to absorb shock and can become sketchy in turns as they bounce off things when they should be absorbing road shock. A tyre that is set at too high a pressure for the bike's rider will also make the ride very harsh.
In the off road world lower tyre pressures have been proven to increase performance and speed over uneven terrain... this is where minimums come into play and for many it becomes a case of how low can you go ?
As a lighter guy I never run my road tyres at their max (cause I get beaten to death) and run my off road tyres at their minimum or even a little less as the odds of my causing a pinch flat are pretty slim...like me.
The max pressure is dictated by the tyre and rim and in many cases, filling the tyre to the max decreases performance in that they lose their ability to absorb shock and can become sketchy in turns as they bounce off things when they should be absorbing road shock. A tyre that is set at too high a pressure for the bike's rider will also make the ride very harsh.
In the off road world lower tyre pressures have been proven to increase performance and speed over uneven terrain... this is where minimums come into play and for many it becomes a case of how low can you go ?
As a lighter guy I never run my road tyres at their max (cause I get beaten to death) and run my off road tyres at their minimum or even a little less as the odds of my causing a pinch flat are pretty slim...like me.
07-09-08, 01:14 AM
#27
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Hell I have a pair of michelin PR3's right now on a spare wheelset being "stretched out" @ 130psi and I can easily deflect the sidewall by pinching on it with my fingers. I've had 145 psi on my reynolds wheels and vittorias and I've been able to see the sidewalls bulge at the contact points as I ride. I don't need a caliper to tell me that they deflect... but I have a pair of calipers that measure down to 0.0005", a very accurate pressure gage, and I'm north of 150. Are you willing to put money on that?
07-09-08, 05:40 AM
#28
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07-09-08, 05:42 AM
#29
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07-09-08, 06:58 AM
#32
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There is an old article in the Velo News Tech base that describes HED's research into pressure rise due to heat in the tires/wheels after a long downhill by pro level riders. The quick take.........300/400degf resulting in pressure rises in excess of 25lbs over what you originally put in. HED's response was to lower their static pressure limits to something on the order of 130psi.
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07-09-08, 07:30 AM
#33
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You LBS has it right.
There are many tires and rims that will stand up to pressures in excess of the 130psi you mention but when a failure does occure (due to pressure) it is almost always due to a rim sidewall failure.
07-09-08, 07:36 AM
#34
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Zipp rates their 404 clincher rims to 125 psi max. The new Pro3Race are 116 psi max rated. Higher pressures are usually a rim strength issue like others have said.
07-09-08, 07:37 AM
#35
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Whatever the tire manufacturer's reason for deciding on a psi rating, the reason that you shouldn't inflate your tire that hard is that it's going to make even a high quality light everything bike ride like garbage. You may as well put solid rubber tires on it.
07-09-08, 06:20 PM
#36
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07-09-08, 06:42 PM
#37
Portland Fred
Not true. I've ridden Open Corsas over 140 psi, and the ride is not only good, it's smoother than what some tires deliver at 100 psi.
07-09-08, 09:38 PM
#38
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I no longer ride on rubber. Instead I've fashioned 23mm hoops of teak that I wrap around my rims. No flats and hardly any rolling resistance.
(according to an ebay bike store mgr).
07-09-08, 09:44 PM
#40
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I ride at 85psi and outroll just about everybody on the hills. Low pressure makes cornering a dream too...
07-09-08, 10:06 PM
#41
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07-10-08, 04:21 PM
#42
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07-10-08, 06:33 PM
#43
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