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#1
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Zipp marketing...
Yes, I know, marketing is knowing how to make bull**** sound good, but...
"All Zipp clincher rims are designed to work their best below 125 psi tire pressure. Pressures above 125 psi (8.5 bars) can actually increase rolling resistance." _Increase_ rolling resistance? Uh, okay? They're not saying that their clincher rims are weak, are they? No, not at all. "Finally, our bearings are smoother because they simply are rounder than anything else that is currently available. The industry standard allows for balls that are round to within 50/1000th of an inch (which we think is laughable). Even "benchmark" hubs have bearings that are round to only 25/1000th of an inch. We knew that there was still room for improvement which is why our ball bearings only vary 10/1000th of in inch in roundness. You certainly can't see the difference, but you will defiantly feel it." Total BS. So much total BS that someone doesn't know how big 1/1000'th of an inch is. FIFTY thousandths out of round is industry standard? Right. 10 thousandths of an inch out of round is a friggin' mile in bearing terms. The cheapest ball bearings are still some of the most accurately machined parts ever made, and to say that their bearings are within 10 thousandths of an inch accurate, well, they're not saying much about themselves. That said, the idea of a dimpled disk and dimpled rim is sound. Golfers discovered this decades ago, which is where I suspect they got the idea. -- BMO |
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#2
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Boyle M. Owl wrote:
Yes, I know, marketing is knowing how to make bull**** sound good, but... "All Zipp clincher rims are designed to work their best below 125 psi tire pressure. Pressures above 125 psi (8.5 bars) can actually increase rolling resistance." _Increase_ rolling resistance? Uh, okay? They're not saying that their clincher rims are weak, are they? No, not at all. "Finally, our bearings are smoother because they simply are rounder than anything else that is currently available. The industry standard allows for balls that are round to within 50/1000th of an inch (which we think is laughable). Even "benchmark" hubs have bearings that are round to only 25/1000th of an inch. We knew that there was still room for improvement which is why our ball bearings only vary 10/1000th of in inch in roundness. You certainly can't see the difference, but you will defiantly feel it." Did they /really/ write "defiantly", or is that your Freudian typo? |
#3
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"Boyle M. Owl" wrote in news:9flfe.2619$Ay3.1046
@lakeread06: "All Zipp clincher rims are designed to work their best below 125 psi tire pressure. Pressures above 125 psi (8.5 bars) can actually increase rolling resistance." _Increase_ rolling resistance? Uh, okay? Interesting. It's plausible that the marketing hacks of a ^tire^ company might say that, but coming from a ^rim^ manufacturer? That's odd. Or maybe the rolling resistance thing is a smokescreen to obscure what they don't want to admit? As in maybe they are worried their rims might fail at 125 psi or higher? |
#4
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Boyle M. Owl wrote: Yes, I know, marketing is knowing how to make bull**** sound good, but... "All Zipp clincher rims are designed to work their best below 125 psi tire pressure. Pressures above 125 psi (8.5 bars) can actually increase rolling resistance." _Increase_ rolling resistance? Uh, okay? This makes sense to me. On any road that's not perfectly smooth, the surface will cause the bike to vibrate. Vibration takes energy to happen, and that energy needs to come from somewhere. That energy is taken from the rider & bike's forward momentum. Thus, a rougher surface will require more energy to traverse. This is what happens when you transition from smooth pavement to rough chipseal- you'll slow down or start pedaling harder (using more energy) to maintain your speed. A pneumatic tire's purpose (among others) is to provide cushioning between the rider/bike's mass and the road surface. At low pressure, the tire's structure is flexing and twisting, dissipating energy as heat (feel a car tire right after it's stopped- it'll be warm). At normal pressure, the tire should not flex excessively, but it should absorb the irregulaties of the road surface without passing them on to the bike & rider. At high pressure, the tire becomes rigid and unable to absorb these irregularities, passing the vibration on to the bike & rider. Inflating tires to very high pressures has the same effect as riding on chipseal: more energy is consumed vibrating the rider & bike, thus slowing them down. If extremely rigid tires were beneficial, we'd all be riding around on non-pneumatic urethane tires or tubes. AFAIK, every attempt at producing a non-pneumatic tire has been met with similar reviews: harsh-riding and slow. Example: Back in the late '70's, in the halcyon days of human-powered vehicle competitions, one or two vehicles featured disc wheels that used inside-out "V" belts as tires. Non-pneumatic, extremely narrow, extremely rigid. Steve Ball's "Dragonfly" topped out at 49 mph one year. The next year, with no other changes except a switch to conventional tubular tires, he reached 52 mph- an enormous step, considering that at those speeds the majority of drag is air resistance, not rolling resistance. I suspect, though, that Zipp's statement is a CYA on their part. Extremely high pressures might fatigue the bond between the aluminum rim and the carbon structure, and possibly the carbon itself. Jeff |
#5
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On Sun, 08 May 2005 05:48:51 -0400, "Boyle M. Owl"
wrote: Yes, I know, marketing is knowing how to make bull**** sound good, but... "All Zipp clincher rims are designed to work their best below 125 psi tire pressure. Pressures above 125 psi (8.5 bars) can actually increase rolling resistance." _Increase_ rolling resistance? Uh, okay? [snip] Dear Owl, Theory predicits and tests show that rolling resistance can increase with higher pressures: " . . . yes, there are lots of test numbers to back it up. It is the same reason a suspension bike (or car) is faster over rough ground - less mass must be accelerated when bumps are encountered, thus saving energy and reducing momentum loss. Every little bump that gets absorbed into your tire (another reason that supple, handmade casings roll faster than stiffer, low-thread-count casings) is a bump that does not lift the entire weight of you and the bike. You feel fast on a rock-hard tire for a similar reason that people like the feel of stiff brakes (V-brakes with the levers set on low leverage). The brake feels good and stiff because you are doing more of the work. If you increase the leverage, the brake feels spongy, because the extra mechanical advantage allows a modest pull to squish the pads. When you ride a tire at 170psi, the bike feels really lively and fast. That is because you are being bounced all over the place by the surface roughness of the road. However, every time you are bounced, energy you applied to the pedals to get you up to speed is lost. Also, you have less control of the bike, so it feels like it is going faster, even though it isn't. Ever notice how driving down the highway at 75mph in an old Jeep feels crazy fast, and you can cruise smoothly along at 100mph in a nice Saab or BMW and feel like you are going maybe 60mph unless you are looking at stationary objects passing by? There is simply no question about it; rolling resistance tests conducted with bicycle tires rolling over surfaces akin to normal road surfaces always indicate the lowest rolling resistance at pressures a lot closer to 100psi than to 170psi! Years ago, for example, I saw results like this at the Continental tire factory. I was told of similar results at a number of other tire factories I have visited. --Lennard Zinn http://www.ottawabicycleclub.ca/phpB...pic.php?t=137& Carl Fogel |
#6
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Bill Sornson wrote:
only vary 10/1000th of in inch in roundness. You certainly can't see the difference, but you will defiantly feel it." Did they /really/ write "defiantly", or is that your Freudian typo? HAHA No, man, I just cut and pasted. It's there on the page. -- BMO |
#8
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"Boyle M. Owl" wrote
carlfogel wrote: There is simply no question about it; rolling resistance tests conducted with bicycle tires rolling over surfaces akin to normal road surfaces always indicate the lowest rolling resistance at pressures a lot closer to 100psi than to 170psi! Years ago, for example, I saw results like this at the Continental tire factory. I was told of similar results at a number of other tire factories I have visited. --Lennard Zinn Carl Fogel Well, Zinn outvotes me. (I've got one of his books) I find it curious though that track riders pump up their tires well over 100psi if that's the case. I'm a big fat guy, and I find that the higher pressure definitely helps, though. The ride I get now is similar to when I used to be a teenager and much thinner riding on 80psi tires. No, I don't get bounced around at 125-145psi. BMO I think the fact that the rolling resistance of a wheel depends to a great extent upon the road surface is often overlooked. If the surface is really smooth, such as the rail of a high-speed railway, then tire flex is the energy absorber. You probably would be better off without a pneumatic tire. However, with a rough surface, a wheel with a tire that absorbs some of the roughness is probably more efficient. But I don't know how to calculate the trade-off. As a thought experiment, assume you were to glue a pencil to the road every couple of feet and then ride over them at speed. If the tire has no "give", then every time you hit a pencil, the whole bicycle and part of the rider gets lifted into the air. Which takes a lot of energy and slows you down. But a big balloon tire will absorb the bump without slowing you down. Of course, the constant flexing of the big balloon tire absorbs energy. What works best on a smooth track may not work best on chip-seal. My guess is that I would go a touch faster with less pressure in my tires. Some day I might try it. |
#9
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On Sun, 08 May 2005 19:49:11 -0400, "Boyle M. Owl"
wrote: wrote: There is simply no question about it; rolling resistance tests conducted with bicycle tires rolling over surfaces akin to normal road surfaces always indicate the lowest rolling resistance at pressures a lot closer to 100psi than to 170psi! Years ago, for example, I saw results like this at the Continental tire factory. I was told of similar results at a number of other tire factories I have visited. --Lennard Zinn http://www.ottawabicycleclub.ca/phpB...pic.php?t=137& Carl Fogel Well, Zinn outvotes me. (I've got one of his books) I find it curious though that track riders pump up their tires well over 100psi if that's the case. I'm a big fat guy, and I find that the higher pressure definitely helps, though. The ride I get now is similar to when I used to be a teenager and much thinner riding on 80psi tires. No, I don't get bounced around at 125-145psi. Dear Owl, Look at this calculator's table for the coefficient of rolling resistance, which defaults to an asphalt road: Wooden Track 0.001 Smooth Concrete 0.002 Asphalt Road 0.004 Rough but Paved Road 0.008 http://www.analyticcycling.com/ForcesSpeed_Page.html The surface of a wooden track is considerably smoother than an ordinary road, so higher tire pressures do indeed reduce rolling resistance. When reading tables of rolling resistance for tires like this one . . . http://www.analyticcycling.com/Force...esistance.html .. . . remember that the values were determined by spinning down with the inflated tire pressed against "a smooth steel drum," not actual asphalt. Other tables like this one may roll the tires on a flat surface . . . http://www.legslarry.beerdrinkers.co.uk/tech/JL.htm .. . . but the "speed of rolling is slow so that aerodynamic forces do not come into play," which suggests that there wouldn't be much bouncing. In any case, we do in fact get bounced around at 125-145 psi, just as we get bounced around at 80 psi. It's just that we have to be rolling fairly fast to notice the difference on an ordinary road, something that Zinn's comment assumes. The difference would not be something a rider would be likely to notice, any more than a rider would notice a change of 1 mph at 20 mph without a speedometer or stop watch. If we rolled along like snails at only 5 mph on the ordinary road surface, then the 170 psi tire would probably have less rolling resistance than the 100 psi tire--the bouncing effect that confuses things at speeds of interest to racers would be greatly reduced. Carl Fogel |
#10
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