Tire question?
01-26-21, 04:00 PM
#26
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What matters for tire selection isn't the rolling resistance of the tire versus the aerodynamic drag of the whole system. It's the rolling resistance of the tire versus the difference in aerodynamic drag caused by the tire selection. If you change to a tire that's 10W-faster-rolling but 5W-higher-aero-drag at 20mph, you're going to save 5W at 20mph regardless of whether the rider's body is in a tuck that's producing 100W of aero drag or an upright posture that's producing 170W of aero drag.
01-26-21, 04:08 PM
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01-26-21, 04:53 PM
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So why do racers use such skinny little tires? Rolling resistance isn't everything. At roughly 15 miles per hour on a flat road, air resistance surpasses all of the other factors that are holding you back combined. As you r speed increases beyond 15 MPH, the importance of air resistance becomes progressively more and more significant. Skinny little tires have less frontal area and consequently less air resistance than wide ones.
I assume there is a rubber compounding factor to rolling resistance but the only thing I know for sure about that is that carbon makes tires both black and wear longer. Look at little kids bikes - boy's bike tires, which are black, wear at least 3 times as long as little girl's bikes that have white tires.
I assume there is a rubber compounding factor to rolling resistance but the only thing I know for sure about that is that carbon makes tires both black and wear longer. Look at little kids bikes - boy's bike tires, which are black, wear at least 3 times as long as little girl's bikes that have white tires.
01-26-21, 05:11 PM
#29
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You will overwhelm that 5W through more aerodynamic drag at 22 or 23 mph (using imaginary arbitrary made up numbers made up for this discussion)
01-27-21, 08:59 AM
#30
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I have no idea what "pretty small" means, but I do know that the difference in rolling resistance between tires can be 10 W or more (and of course, that's totally independent of what may be going on aerodynamically). I also know how hard I have to work to improve my power by 10 W.
Also:
1. A ten watt difference between comparable tires is pretty extreme and hardly representative of what an average person would be debating when looking at, say, $50 28mm slick tires.
2. The point stands that relative to aerodynamic drag, rolling resistance is small potatoes.
3. We are talking about a guy on a hybrid here, not some finely honed roadie with a power meter eeking out every marginal gain.
01-27-21, 11:35 AM
#31
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I kindly ask that you reread my post. I'm not saying rolling resistance is something every cyclist everywhere should ignore, which seems to be what you're implying.
Also:
1. A ten watt difference between comparable tires is pretty extreme and hardly representative of what an average person would be debating when looking at, say, $50 28mm slick tires.
2. The point stands that relative to aerodynamic drag, rolling resistance is small potatoes.
3. We are talking about a guy on a hybrid here, not some finely honed roadie with a power meter eeking out every marginal gain.
Also:
1. A ten watt difference between comparable tires is pretty extreme and hardly representative of what an average person would be debating when looking at, say, $50 28mm slick tires.
2. The point stands that relative to aerodynamic drag, rolling resistance is small potatoes.
3. We are talking about a guy on a hybrid here, not some finely honed roadie with a power meter eeking out every marginal gain.
1. 10w difference is extreme? I dunno about that...First, let’s be clear that we’re talking about per pair, since a) that’s how we usually do tires and b) because 10w saved is 10w saved regardless of single or pair. Second, in ‘19, BicycleRollingResistance.com found a +5w per tire difference between Vittoria’s Corsa Speed G+ 2.0 and their Corsa G+ 2.0, as well as between Schwalbe’s Pro One TT Addix TLE and their Pro One Addix. Those tires are generally available within $10 of each other, so they’re classed the same by price. When you look at Tom Anhalt’s 18mph gravel tire resistance tests, he finds Challenge Strada Bianca 30c rolling at 25w/pair and their Gravel Grinder Race 38c rolling at 40w/pair, so a 15w difference there. I’m with asgelle on this: saving 10w every 30secs spent at 18mph (that’s how BRR tests) is a really big deal, and accrues into serious energy over the course of ride, energy that can be spent reaching whatever goal one sets for themself, like cleaning a climb in record time.
2. I don’t know which “aerodynamic drag” you’re talking about— the frontal area of a narrow tire compared to a wide tire, the drag of the wheel and tire, the drag of the complete bike, or the drag of the complete bike+rider system— but it doesn’t matter, because as cyclists, there’s only so much we can control or are willing to change, so if you want to go faster or further or save energy, you’ve got to take the small potatoes. Getting more aero by going from the bar flats to the drops may only save 13w (at 28mph)— see here—so it’s not as though saving 10w at the tires at 18mph is quantitatively small potatoes (i.e. a lot less watts) despite the fact most of our energy is used to fight system aero drag. Sure, the study also found that really hunkering down in the drops at 28mph saved about 45w, and I don’t know about you, but the amount of time I spend at 28mph hunkered down in the drops hammering it out is effectively zero, and certainly nothing compared to the time I spend riding at 18mph.
3. That we’re talking about someone on a hybrid does not change the benefit of energy savings; we all want and can notice that. I agree with you here, though, in that I don’t think the OP needs to worry about the wide/LP vs. narrow/HP thing when looking at showroom bikes, and I think it’s especially problematic for the OP to do that without regard for tread type (as indicated in the OP). Tires can be changed easily, and the OP can almost certainly get more efficient (and lighter) tires aftermarket than what will come fitted to any bike they’re looking at. I think it’s far more important for the OP to look that the tread type is suited to their needs than to worry about wide vs. narrow, because for nice, smooth surfaces, they don’t need tread lugs sapping energy, and should prefer a smooth or lightly textured tread.
01-27-21, 11:43 AM
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Skinny rock hard ultra high pressure tires do not flex over a bump. They force the bike and rider to rise. That takes energy from forward motion, hence they are actually slower that a wider lower pressure tire that will flex. Simple as that.
01-27-21, 01:17 PM
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I definitely understand what you’re getting at, but simple it ain’t!
01-27-21, 03:27 PM
#35
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Quadratic and cubic functions use an exponentiation operation, but the argument is the base, like:
f(x) = a*(x^b)
A function being "exponential" means that the argument is used as the exponent, like:
f(x) = a*(b^x)
f(x) = a*(x^b)
A function being "exponential" means that the argument is used as the exponent, like:
f(x) = a*(b^x)
Last edited by HTupolev; 01-27-21 at 03:32 PM.
01-27-21, 04:05 PM
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Simple as that? Define “skinny.” Define “ultra high pressure.” Explain why a pair of 35c Conti Terra Speed TRs at equal pressure require 10w less power to maintain 18mph than 40c Schwalbe G-One Allround Super Ground Speedgrips. 🙃
I definitely understand what you’re getting at, but simple it ain’t!
I definitely understand what you’re getting at, but simple it ain’t!
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01-28-21, 10:30 AM
#39
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There's plenty of rolling resistance info on this website. https://www.bicyclerollingresistance...on-32-37-40-47
Fat tires still have more rolling resistance than 25-28mm racing tires. The old 23mm is just about dead, with most pros riding 25-28mm at lower pressures than they used to.
I'm just now getting into 28mm michelin tubeless tires on my two road bikes. For a 140 lb rider, recommend pressures are as low as 60 psi with 19mm internal width rims. I put 70 front and 75 rear in mine. After 1000 miles or so, I calibrated my old silica pump gage and found that it read 8psi higher than the true pressure, so I was riding with a lot less pressure than I thought. Michelin lists 73 psi as the recommended minimum.
Fat tires still have more rolling resistance than 25-28mm racing tires. The old 23mm is just about dead, with most pros riding 25-28mm at lower pressures than they used to.
I'm just now getting into 28mm michelin tubeless tires on my two road bikes. For a 140 lb rider, recommend pressures are as low as 60 psi with 19mm internal width rims. I put 70 front and 75 rear in mine. After 1000 miles or so, I calibrated my old silica pump gage and found that it read 8psi higher than the true pressure, so I was riding with a lot less pressure than I thought. Michelin lists 73 psi as the recommended minimum.
