#31
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I concluded some time ago that the move to wider tires for the road was largely driven by the search for something...anything...that could mitigate some for the extra stiffness that was characteristic of the uber-oversize tubed frames that have come into fashion. It was convenient that a larger tire could be run at a slightly lower pressure for some comfort gains without a big hit in increased rolling resistance.
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#32
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#33
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#34
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The only organization I know of that has published the results of bicycle tire traction tests is Tour Magazine, which periodically does wet weather tire traction tests. These tests consist of rolling down a hill and then riding around a corner on pavement that is constantly being wetted with a water sprinkler. The tester rides through the corner at increasing speeds until the tires slip out (and the rider falls). The test rider wears padded clothing, and rides a special bike that allows them easily jump off if the tires slip, but it should be obvious why this kind of testing isn't done very often. |
#35
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When Flo set about designing their carbon clincher rims, they needed to model the shape of both the tire and wheel together. Based on their previous testing, and the tests published by others, they discovered that the Continental 23mm GP4000 tended to test well aerodynamically, so they based their aerodynamic model around that tire. After Flo produced their new wheel, they tested it in a wind tunnel with a variety of tires, and not surprisingly, it had nearly its best performance with the 23mm GP4000 (that's what they designed it for, after all). But when they combined aero drag with rolling resistance, they found that the wider 25mm GP4000 had a lower total drag - the lower rolling resistance of the wider tire more than made up for the extra aero drag. I have no reason to doubt Zipp's claim that 23mm tire has the lowest drag on their wheels, if only aero drag is considered. But when you add in rolling resistance, I wouldn't be surprised if an excellent rolling, but slightly wider, tire ended up being better. Particularly if compared to a poorly rolling 23mm tire. It used to be that riders selected tires based on which gave the best aero performance with their wheels. But in the future, I suspect that it will be the other way around - riders will select wheels, based on which gives the best aero performance with their tires. And we'll see aero wheels getting wider, to better match wider tires (this is already happening). |
#36
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Since you're an aviator, maybe you'll appreciate the analogy between the pressure sweet spot, and the speed/power curve for air drag: Tire Air Pressure vs. Rolling Resistance: Aircraft Speed vs. Power |
#37
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Then, starting in the early '80s, people started believing that narrow, high pressure tires must be faster, and tires and rims capable of handling high pressures started being made. During the time that frame tubes started growing in size/diameter, typical tire widths started shrinking and tire pressures increasing - 23mm tires became common, and many were even riding 20mm tires, at pressures up to 120 psi or more. The move toward wider tires today isn't to mitigate the extra stiffness of modern frames (even the old frames from yesteryear had too much vertical stiffness to provide much shock absorption) - its to mitigate the ridiculously high pressures that people been using during the last few decades. |
#38
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As to rolling resistance, you are correct that there are many different variables. I've got a bike incoming that is designed as an "All Road" road bike and I'm wondering where I'll end up with the tires. I'm thinking probably 35mm. They'll still probably be ridable on the roads but not too narrow for my liking on unpaved roads. The 38s I'm running now are almost a tad too big for me and sometimes feel a bit sluggish. I'm not yet ready for the 650x50s that some folks enjoy! |
#39
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It's great to get insight from someone who legitimately knows what they are talking about and is willing to take the time to help the average punter who most certainly is not Cancellara, Wiggins or Sagan Curious as to your thoughts on that margin of error though. With such small changes to pressure required in moving from 23-25 or even 25-28, one wonders if the average floor pump/pressure gauge is up to the task! I choose butyl tubes simply because the pressure I start a ride with is likely to be the pressure I finish it with. While I enjoyed running latex tubes for a while, if I went out on a century and had a stop for lunch/coffee, I'd find my pressure had dropped so much that any RR gains of the latex tube were probably negated and even inversed towards the end... |
#40
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ZIPP:
The aero improvement of the 23mm tire over a 25mm+ tire outweigh any relative losses in rolling resistance. When Si on GCN did a KOM hillclimb challenge video, Zipp also recommended 23's as the fastest tire width. Quote:
The new standard / minimum tire size is 25-26mm. The old standard of 23mm is dead. NOTE: When I say 25mm, I mean the INFLATED size on a modern clincher rim (so the tire label probably says 23mm). Anything under a measured 23mm, on a modern wide rim is DEFINITELY dead, short of some rare special cases. The ‘What Should I Use’ Cheat Sheet -If you’re a pro, aspiring pro, or just super-duper fast, use a tire that’s labeled 23mm (inflating to 25-26mm). -If you’re an average, middle-of-the-pack person, trying to be competitive and have fun, use a tire that’s labeled 25mm (inflating to 28-29mm). -If you’re a fat-tire-lover like me, and want to feel like you’re riding a magic carpet, use a tire that’s labeled 28mm (inflating to 31-32mm). With any luck, more new wheels will emerge, making this a legitimate aerodynamic choice. https://www.slowtwitch.com/Tech/What...018__6822.html |
#41
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As for latex, look at the modern latex, we sell tubes made by Vittoria which have a new formula with graphene in them and leak so much slower than the old ones. When we plotted Cancellara's roubaix run in 2010, we measured his tires to have nearly 1psi per hour loss.. so we tuned pressures so they would be perfect a few hours into the race when he was on the worst cobbles.. The new generation of latex tubes might lose 4-5psi per 24 hours, and will save you 2-5 watts per tire which is a bigger savings than a full ceramic bearing upgrade for about 1/50th the price!! |
#42
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Seems that tire size needs (or should be paired with) rim inner - outter measurements?
A GP 4000 25mm on a rim that is 17 id - 25 od vs same tire on a rim that is 20 id - 28 od will perform very different, no? Maybe we all drink the cool aid and spend more $ to gain one watt? Quote:
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#43
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My general understanding is, in cross-section, a U shaped tire is more aero than a O shaped tire. Personally, I just don't sweat it. I like geeking out and webwheeling about it but in reality... In a race, I just care about conserving energy. Light, aero wheels w/ tires I trust. Someone said, generally all XXmm depth wheels are about the same aero savings. So yeah, there are just so many other factors in a race, to me, it just doesn't matter. For PR's, 'baseline' matters more. I want to keep my equipment consistent. I note, if I try for a PR, did I use my carbon wheels or alloys. That way, I can just focus on my physical gains. So, in that regard, it doesn't matter what you own. In all honesty, the biggest gains I feel are when the tires are new. New Rubino Pros feel great! New Sworks tires feel awesome! When they start flat-topping? I'm sure you loose more watts there than anything else. |
#44
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You are correct, that next to having the proper size tire for your rims, replacing them as soon as they begin to show wear makes a very big difference!! |
#45
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Surface roughness - rough surfaces increase suspension losses, which can be mitigated with wider tires Speed - rolling resistance is a larger percent of drag at lower speed, so decreases in rolling resistance with wider tires may outweigh losses due to aerodynamics; conversely, aero drag increases with the square of speed, so narrower tires may be best at the highest speeds. Rider weight - rolling resistance is proportional to rider weight, whereas weight doesn't affect aero losses, so the wider tires may be better for heavy riders, and narrower tires may be better for lighter riders Crosswinds - wind drag in cross winds is increased when the tire width is greater than rim width, so narrow tires may be best in strong cross winds. For 135 lb. Caleb Ewan doing a 45 mph final sprint with a crosswind, Zipp's recommendation for a 23mm tire is certainly correct. But for a 210 lb. rider doing a Grand Fondo at 18 mph, a 25mm or 28mm tire is probably more optimum, even on the same wheels. |
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