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#11
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Nobody knows about RR
Benjamin Lewis wrote:
Depending on the smoothness of the road, you might actually be increasing your rolling resistance by pumping that high. Correct, and I'm sure on some roads that is the case. But typically the roads here are pretty smooth and I'm sure on average the rolling resistance is lower. -as |
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#12
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Nobody knows about RR
Antti Salonen wrote:
Benjamin Lewis wrote: Depending on the smoothness of the road, you might actually be increasing your rolling resistance by pumping that high. Correct, and I'm sure on some roads that is the case. But typically the roads here are pretty smooth and I'm sure on average the rolling resistance is lower. It could well be. It's too bad there aren't more test results available for this. For me, 7-7.5 bar feels pretty good, for bike+rider of about 80 kg. -- Benjamin Lewis Seeing is deceiving. It's eating that's believing. -- James Thurber |
#13
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Nobody knows about RR
as a street rider never ridden a race bike - that chart tells me that a
racer can interpret it but that like it only raises more questions without a solid foundation of race experience. and surely conti isn't about to give its info away. |
#14
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Nobody knows about RR
I thougt that makers of bicycle tires would have experimentally or
scientifically based knowledge as a foundation of their production. Therefore I directed my question about rolling resistance to Continental Tires - and the production manager kindly sent me a reply that is surprisning as well as interesing. If you have access to a decent public library, you should be able to locate many articles on testing rolling resistance. One in particular deals with using coast-down tests to determine tire rolling resistance. The article is "Tire Rolling Resistance Measurements From Coast-Down Tests", SAE #760153. Yes, it is automotive related, but the procedure should work fine. If you check SAE.org, there are many other papers on this topic listed, such as "Determination of Vehicle Drag Contributions From Coast-Down Tests", SAE #720099. You'll probably find that air drag dominates tire rolling resistance at higher speeds. But using coastdown tests, you should be able to figure out if a 25mm tire has higher or lower rolling resistance than a 23mm tire, assuming same rider, same bike, same environment (terrain, wind, temp, etc.), recommended inflation pressures, and same type of tire. My butt-gauge indicates that 25mm tires (Veloflex Roubaix - tubular) grip better, and are more compliant than 23mm tires of the same manufacturer. So, I believe I'm faster in turns, descents. I certainly push harder. The tires are more compliant on rough surfaces, so it's easier to go harder as the ride is smoother. They roll about the same. The 25mm tire is somewhat harder to sprint or climb with since it is heavier, and the diameter is slightly larger. Regards, Rob |
#15
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Nobody knows about RR
On Wed, 15 Jun 2005 12:15:01 +0100, David Damerell wrote:
No, it's not. If you want to maximise speed, you should use in both tyres the maximum pressure that does not cause the increase in RR we see with track-style pressures (eg 170psi), Um, what increase in RR is that? produce an intolerably hard ride; that will be equal in both cases and the 25mm tyre will have lower RR. I don't think either of those conclusions are true. For one thing, a 25mm tire may reach blow-off pressures before it is "intolerably hard", and at that pressure I would assume the RR of the two sizes would be close to the same. -- David L. Johnson __o | A mathematician is a machine for turning coffee into theorems. _`\(,_ | -- Paul Erdos (_)/ (_) | |
#16
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Nobody knows about RR
Thanks for a great variation of insights and interesting considerations.
But it still remains a mystery that there is no available messurements of rolling resistance from 22 mm respectively 25 mm tires with their recommended airpressure. I do undertand that the answer to a simple question may be complicated and will depend on numerous circumstances on the real road. And I do understand that a reduced RR should be seen in relation to higher wind drag and weight. And I do understand, that all these factors have so little impact that it is tempting to end the discussion with the conclusion: It don't mean ****. But I am still curious and I still find the question relevant: In the spring of 2003 the Belgian rider Van Petegem won the Tour of Flandern as well as the Paris-Robaix on 25 mm Continental Competition tires. He must have trusted, that those tires were faster than narrower ones. Did he guess or did he know? Whether you are racing to win or racing to make it through within the time limit, you want the facts that will help you choose the right equipment. The surprising conlusion, that the wider tire has lower rolling resistance, is based on tests of tires of identical construction and identical pressure. The explanation that is given is, that the two tires have a contact area of exactly the same size, but the wider tire has a shorter and wider one, which produces less RR than the narrower and longer contact area. If the result of that test is interesting, then it is even more interesting to make a test of the same two tires with the recommended tire pressure in each. I think the Continental production manager was well aware, that I didn't just want an advice on what tire to choose for my bike. I can´t think of a reason not to give me an exact answer if he knew it. He would not reveal production secrets by saying: ”We have made the test, it shows that the wider tire has a 10 pct. lower RR” – or the opposite. But that is at matter of interpretation, I admit. Ivar of Denmark |
#17
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Nobody knows about RR
On Wed, 15 Jun 2005 11:19:17 -0700, Benjamin Lewis
wrote: wrote: http://w3.iac.net/~curta/bp/velocityN/velocity.html Using the calculator above (the metric version offers rolling resistance and frontal area), let's try a few values and see what we get. The default values predict a brisk 37.18 km/h. Reduce the rolling resistance 5% from 0.0050 to 0.0045, and the speed rises to 37.40 km/h, an increase of 0.22 km/h. But if that 5% reduction in rolling resistance also increased the frontal area from 0.4m^2 to 0.40544m^2, then the speed drops to 37.24 km/h. So the combination of a wider tire that rolls more easily is predicted to increase a rider's speed only 0.06 km/h, or sixty meters in an hour--a convenient 1 meter per minute. I note that for these defaults, the two tires become equal at a little below 44 km/h. (set the power to 473.5 watts) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ (This is assuming no wind and no drafting) Dear Benjamin, I found this memo stuck to your post in my newsreader: # To: Captain Picard #From: Commander G. La Forge, Chief Engineer # #I'd like to make it so, sir, but I left my 473.5 watt #dilithium crystals in my other pants. Maybe that big #Klingon sprinter can help you. Naturally, I harnessed the big Klingon, told him that Lance doubted that anyone with a forehead like a turtle could put out a thousand watts for an hour, and found that the two tires are still just about equal: 57.26 km/h wide (0.40544 25mm frontal) 0.0045 rr (imagined) 57.37 km/h thin (0.40000 23mm frontal) 0.0050 rr (default) Of course, the 10% reduction in rolling resistance is just a vague guess at the best that could be expected in reducing rolling resistance by making the same tire 2mm wider, just as the 0.0054m^2 increase is just a vague guess at the wind drag increase for the wider tire. But if adding 526.5 watts only lets the thinner tire pull ahead 0.11 km/h, then we know why Commander Spock is leaving the calculations to Commander Data. At low and therefore plausible bicycle power levels, there isn't much difference between the two tires. At outlandishly high levels, the tiny differences make even less difference. Which wasn't what I thought. I expected the wind drag to matter more and more relative to the rolling resistance (it does, since the thin tire pulls ahead), but overall it matters less and less in terms of how much it affects the actual speed as power increases. That is, at 1000 watts, neither the tiny extra wind drag of the wider tire nor the little bit of extra rolling resistance of the thin tire can have much effect on the speedometer reading. So thanks for pointing out where the two imaginary tires match--it made me think again. Carl Fogel |
#18
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Nobody knows about RR
15 Jun 2005 14:12:03 -0700, skrev:
My butt-gauge indicates that 25mm tires (Veloflex Roubaix - tubular) grip better, and are more compliant than 23mm tires of the same manufacturer. So, I believe I'm faster in turns, descents. I certainly push harder. The tires are more compliant on rough surfaces, so it's easier to go harder as the ride is smoother. They roll about the same. The 25mm tire is somewhat harder to sprint or climb with since it is heavier, and the diameter is slightly larger. Regards, Rob I use 25 mm tires out of the same belief. Surpisingly the 25 mm Conti 4-Season only weighs 8 grm more than the 23 mm. They are actually 24 mm wide and 25 mm high. Kind regards Ivar |
#19
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Nobody knows about RR
15 Jun 2005 12:15:01 +0100 (BST), David Damerell
skrev: If you want to maximise speed, you should use in both tyres the maximum pressure that does not cause the increase in RR we see with track-style pressures (eg 170psi), or the maximum pressure that does not produce an intolerably hard ride; that will be equal in both cases and the 25mm tyre will have lower RR. Why would you use a lower pressure in the 25mm tyre if the aim is to maximise speed? Because overinflated tires are not faster: they jump too much, and have too little grip. Depending on the character of the road surface you might gain some speed by increasing inflation TO A LIMIT. This would be true for 23 as well as 25 mm. The ideal comparison would be between the two sizes of tires, each with their ideal pressure (for road quality and rider weight). This should be reflected in their "recommended pressure" - not in the same pressure. But you did get a perfectly good explanation of why it is not a sensible question to ask. I still think the explanation was too much common sence and not as exact as I want it. Kind Regards Ivar |
#20
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Nobody knows about RR
Tue, 14 Jun 2005 17:24:24 -0600, skrev:
Reduce the watts from the impressive default 300 to a more modest 150 watts, and the base speed is predicted to be 28.48 km/h, the pure rolling resistance reduced 5% raises the speed to 28.76 km/h, and the final speed with the wider tire's wind drag added drops back to 28.64 km/h--about 0.16 km/h faster, so rolling resistance does indeed matter more at lower speeds, where wind drag isn't so important. It's conveniently about 0.1 mph, or about nine extra feet per minute at around 18 mph. Carl Fogel How I enjoyed this - and the following calculations. I so much want the 25 mm tire to be at least a tiny theoretical bit faster than the 23 mm - and if the advangtage of the wider tire threatens to disappear completely, I will only have to slow down till the reduction in RR again will give me an advantage to those trationals, who ride on narower tires. Regards Ivar |
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