Wide vs Less Wide Tires, Another View
09-13-17, 07:18 AM
#151
Senior Member
One thing I have often wondered regarding drumtesting is how well they represent reality. For one, as have been noted, their surface does not represent real roads well, second the drum pulls the wheel at a steady pace. > No real power transfer through the wheel/tyre outside of whatever power i required to spin the wheel, similar to coasting. > Would the results be any different if in stead the wheel pulled the drum at, say, an average of 200w and would it affect if the results if power was pulsed like a real pedalling motion. Im betting everybody on the forums have heard the "swish, swish, swish, ..." from a road bike tyre going at decent power. That is not accounted for.
09-13-17, 07:58 AM
#152
Senior Member
Drum testing is only meant to measure Crr. It's been shown that relative performance of tires is the same as with road testing up to the point where the tire is unable to follow the road surface. The othe things you mention either don't affect Crr or are unrelated to it.
09-13-17, 08:34 AM
#153
Senior Member
Some facts:
Tires at the same psi will have the same area contact patch. This is basic physics. Pounds per square inch, multiplied by the area of contact, gives you the weight the tire is supporting.
Larger tires at the same psi as smaller tires give less rolling resistance. Rolling resistance is proportional to the circumference of the tire contact patch. For the same area contact patch, the smallest circumference of that contact patch is a circle. Larger tires have a more circular contact patch than smaller tires, so larger tires give less rolling resistance.
On a perfectly smooth surface, higher psi inflation gives less rolling resistance by decreasing the contact patch area, thus decreasing the contact patch circumference. A marble will roll longer on a wood floor than a bouncy ball.
Why have small tires? Because smaller tires can support higher tire pressures. Higher pressures on smooth surfaces give low drag.
Why have larger tires? Because larger tires can support lower tire pressures. Lower pressures on rough surfaces give low drag (suspension effect).
Small tires have minimum pressures due to the carcass deflection leading to pinch flats. Larger tires have maximum pressures due to the tension force on the carcass tearing it apart or blowing a clincher tire off the rim.
If you are riding a smooth velodrome, small tires (19mm is most common) at very high pressures are best (most are 160-200psi). If you are riding very rough roads (cobbles/gravel, for instance, or off-road cyclocross/mountain biking), large tires (30mm+) at low pressures are required (most are 30-60psi). In between is in between... hence the popularity of the 23 and 25mm road cycling sizes. You can still inflate to moderately high pressures of 100-120psi, but you can maintain some suspension effect.
Tires at the same psi will have the same area contact patch. This is basic physics. Pounds per square inch, multiplied by the area of contact, gives you the weight the tire is supporting.
Larger tires at the same psi as smaller tires give less rolling resistance. Rolling resistance is proportional to the circumference of the tire contact patch. For the same area contact patch, the smallest circumference of that contact patch is a circle. Larger tires have a more circular contact patch than smaller tires, so larger tires give less rolling resistance.
On a perfectly smooth surface, higher psi inflation gives less rolling resistance by decreasing the contact patch area, thus decreasing the contact patch circumference. A marble will roll longer on a wood floor than a bouncy ball.
Why have small tires? Because smaller tires can support higher tire pressures. Higher pressures on smooth surfaces give low drag.
Why have larger tires? Because larger tires can support lower tire pressures. Lower pressures on rough surfaces give low drag (suspension effect).
Small tires have minimum pressures due to the carcass deflection leading to pinch flats. Larger tires have maximum pressures due to the tension force on the carcass tearing it apart or blowing a clincher tire off the rim.
If you are riding a smooth velodrome, small tires (19mm is most common) at very high pressures are best (most are 160-200psi). If you are riding very rough roads (cobbles/gravel, for instance, or off-road cyclocross/mountain biking), large tires (30mm+) at low pressures are required (most are 30-60psi). In between is in between... hence the popularity of the 23 and 25mm road cycling sizes. You can still inflate to moderately high pressures of 100-120psi, but you can maintain some suspension effect.
__________________
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"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
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"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
09-13-17, 09:46 AM
#154
Senior Member
That's beyond the scope of Crr testing. Your questions relate to the kinetic model which as I've said has been validated repeatedly.
09-13-17, 09:48 AM
#155
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That is neglecting any hysteresis from different casing, rubber (and gas) and speed/rate of deformation. Car run-flats get a bit taller at speed. Just looking, I can see the cheap stiff tires hold the bike up with no PSI while the supple ones are flat. At 5PSI they's be different too.
Last edited by Doge; 09-13-17 at 09:51 AM.
09-13-17, 10:03 AM
#156
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Thanks, that's helpful
Some facts:
Tires at the same psi will have the same area contact patch. This is basic physics. Pounds per square inch, multiplied by the area of contact, gives you the weight the tire is supporting.
Larger tires at the same psi as smaller tires give less rolling resistance. Rolling resistance is proportional to the circumference of the tire contact patch. For the same area contact patch, the smallest circumference of that contact patch is a circle. Larger tires have a more circular contact patch than smaller tires, so larger tires give less rolling resistance.
On a perfectly smooth surface, higher psi inflation gives less rolling resistance by decreasing the contact patch area, thus decreasing the contact patch circumference. A marble will roll longer on a wood floor than a bouncy ball.
Why have small tires? Because smaller tires can support higher tire pressures. Higher pressures on smooth surfaces give low drag.
Why have larger tires? Because larger tires can support lower tire pressures. Lower pressures on rough surfaces give low drag (suspension effect).
Small tires have minimum pressures due to the carcass deflection leading to pinch flats. Larger tires have maximum pressures due to the tension force on the carcass tearing it apart or blowing a clincher tire off the rim.
If you are riding a smooth velodrome, small tires (19mm is most common) at very high pressures are best (most are 160-200psi). If you are riding very rough roads (cobbles/gravel, for instance, or off-road cyclocross/mountain biking), large tires (30mm+) at low pressures are required (most are 30-60psi). In between is in between... hence the popularity of the 23 and 25mm road cycling sizes. You can still inflate to moderately high pressures of 100-120psi, but you can maintain some suspension effect.
Tires at the same psi will have the same area contact patch. This is basic physics. Pounds per square inch, multiplied by the area of contact, gives you the weight the tire is supporting.
Larger tires at the same psi as smaller tires give less rolling resistance. Rolling resistance is proportional to the circumference of the tire contact patch. For the same area contact patch, the smallest circumference of that contact patch is a circle. Larger tires have a more circular contact patch than smaller tires, so larger tires give less rolling resistance.
On a perfectly smooth surface, higher psi inflation gives less rolling resistance by decreasing the contact patch area, thus decreasing the contact patch circumference. A marble will roll longer on a wood floor than a bouncy ball.
Why have small tires? Because smaller tires can support higher tire pressures. Higher pressures on smooth surfaces give low drag.
Why have larger tires? Because larger tires can support lower tire pressures. Lower pressures on rough surfaces give low drag (suspension effect).
Small tires have minimum pressures due to the carcass deflection leading to pinch flats. Larger tires have maximum pressures due to the tension force on the carcass tearing it apart or blowing a clincher tire off the rim.
If you are riding a smooth velodrome, small tires (19mm is most common) at very high pressures are best (most are 160-200psi). If you are riding very rough roads (cobbles/gravel, for instance, or off-road cyclocross/mountain biking), large tires (30mm+) at low pressures are required (most are 30-60psi). In between is in between... hence the popularity of the 23 and 25mm road cycling sizes. You can still inflate to moderately high pressures of 100-120psi, but you can maintain some suspension effect.
Thanks, that's helpful
09-13-17, 10:08 AM
#157
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Some facts:
Tires at the same psi will have the same area contact patch. This is basic physics. Pounds per square inch, multiplied by the area of contact, gives you the weight the tire is supporting.
Larger tires at the same psi as smaller tires give less rolling resistance. Rolling resistance is proportional to the circumference of the tire contact patch. For the same area contact patch, the smallest circumference of that contact patch is a circle. Larger tires have a more circular contact patch than smaller tires, so larger tires give less rolling resistance.
On a perfectly smooth surface, higher psi inflation gives less rolling resistance by decreasing the contact patch area, thus decreasing the contact patch circumference. A marble will roll longer on a wood floor than a bouncy ball.
Why have small tires? Because smaller tires can support higher tire pressures. Higher pressures on smooth surfaces give low drag.
Why have larger tires? Because larger tires can support lower tire pressures. Lower pressures on rough surfaces give low drag (suspension effect).
Small tires have minimum pressures due to the carcass deflection leading to pinch flats. Larger tires have maximum pressures due to the tension force on the carcass tearing it apart or blowing a clincher tire off the rim.
If you are riding a smooth velodrome, small tires (19mm is most common) at very high pressures are best (most are 160-200psi). If you are riding very rough roads (cobbles/gravel, for instance, or off-road cyclocross/mountain biking), large tires (30mm+) at low pressures are required (most are 30-60psi). In between is in between... hence the popularity of the 23 and 25mm road cycling sizes. You can still inflate to moderately high pressures of 100-120psi, but you can maintain some suspension effect.
Tires at the same psi will have the same area contact patch. This is basic physics. Pounds per square inch, multiplied by the area of contact, gives you the weight the tire is supporting.
Larger tires at the same psi as smaller tires give less rolling resistance. Rolling resistance is proportional to the circumference of the tire contact patch. For the same area contact patch, the smallest circumference of that contact patch is a circle. Larger tires have a more circular contact patch than smaller tires, so larger tires give less rolling resistance.
On a perfectly smooth surface, higher psi inflation gives less rolling resistance by decreasing the contact patch area, thus decreasing the contact patch circumference. A marble will roll longer on a wood floor than a bouncy ball.
Why have small tires? Because smaller tires can support higher tire pressures. Higher pressures on smooth surfaces give low drag.
Why have larger tires? Because larger tires can support lower tire pressures. Lower pressures on rough surfaces give low drag (suspension effect).
Small tires have minimum pressures due to the carcass deflection leading to pinch flats. Larger tires have maximum pressures due to the tension force on the carcass tearing it apart or blowing a clincher tire off the rim.
If you are riding a smooth velodrome, small tires (19mm is most common) at very high pressures are best (most are 160-200psi). If you are riding very rough roads (cobbles/gravel, for instance, or off-road cyclocross/mountain biking), large tires (30mm+) at low pressures are required (most are 30-60psi). In between is in between... hence the popularity of the 23 and 25mm road cycling sizes. You can still inflate to moderately high pressures of 100-120psi, but you can maintain some suspension effect.
09-13-17, 10:50 AM
#158
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Except his first point is demonstrably wrong, as proven by anyone who has a floor pump, a caliper and two tires with different casing stiffness.
But don't let reality get in the way of a good first principles lecture.
But don't let reality get in the way of a good first principles lecture.
09-13-17, 10:50 AM
#159
Senior Member
09-13-17, 10:51 AM
#160
Senior Member
He wrote a lot so it must be right. Plus he said "Fact."
09-13-17, 11:02 AM
#161
Senior Member
Depends on how you truly define PSI...'pounds per square inch.' Are we talking about purely air pressure on the inside of the tire, or are we more concerned about the force the outside of the tire exerts on the ground in total? Which can also be measured, just not as easily as sticking a gauge on the valve.
If bike and rider weigh 200 lbs, and you have a 2 inches square contact patch, the tire is exerting 100 psi against the road. There's no way around this, and holds true 100%.
09-13-17, 11:21 AM
#162
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Oh come now you know he meant the air pressure inside the tire. He just wanted to lecture, anyone who says "This is basic physics" is looking to elevate themselves first and foremost and not contribute to the general knowledge base.
09-13-17, 11:43 AM
#163
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Even worse, your FLO Cycling link shows different contact patch areas with the same tire at the same pressure (different rim width).
Reality is a hassle sometimes...
09-13-17, 11:48 AM
#164
Senior Member
That is neglecting any hysteresis from different casing, rubber (and gas) and speed/rate of deformation. Car run-flats get a bit taller at speed. Just looking, I can see the cheap stiff tires hold the bike up with no PSI while the supple ones are flat. At 5PSI they's be different too.
Don't generalize. Numbers. Calculate these values and show they are significant to make your argument. Don't just wave your hands around. If you need to justify an argument for first order principles (rolling resistance) with second order effect (tire casing) you've already lost. Obviously I can make a large tire and a small tire with the same casing materials and buildup.
__________________
Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
09-13-17, 11:52 AM
#165
Senior Member
I can always make a large tire and a small tire from the same casing. Most tires come in different widths made from the same casing.
__________________
Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
09-13-17, 11:54 AM
#166
Senior Member
I can always put the large tire and the small tire on the same rim. I do this a lot.
__________________
Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
09-13-17, 11:56 AM
#167
Senior Member
I lecture on basic physics when I see people clearly getting the physics wrong. This is all basic stuff; any permutation can be done on both large and small width tires to cancel the effect.
__________________
Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
09-13-17, 12:05 PM
#168
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Yes, the casing supports some weight. Pretty negligible in the case of a bicycle tire. Bicycles do not go very fast in the scheme of things and tires, even the heaviest duty casings, are very flexible compared to steel belted car tires.
Don't generalize. Numbers. Calculate these values and show they are significant to make your argument. Don't just wave your hands around. If you need to justify an argument for first order principles (rolling resistance) with second order effect (tire casing) you've already lost. Obviously I can make a large tire and a small tire with the same casing materials and buildup.
Don't generalize. Numbers. Calculate these values and show they are significant to make your argument. Don't just wave your hands around. If you need to justify an argument for first order principles (rolling resistance) with second order effect (tire casing) you've already lost. Obviously I can make a large tire and a small tire with the same casing materials and buildup.
Two tires of the same dimensions and PSI feel very different at speed, esp speed on rollers.
Last edited by Doge; 09-13-17 at 12:09 PM.
09-13-17, 12:20 PM
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This sounds a lot like "who are you going to trust, me or your lying eyes?"
I can tell you don't have a lot of experience off-road or with tubeless tires.
I don't know how I or others could calculate the contact patch at 30mph on different tires.
Last edited by Spoonrobot; 09-13-17 at 12:23 PM.
09-13-17, 12:30 PM
#170
Senior Member
True. On bikes with cast iron tyres the air pressure inside the tyre is insignificant ;-)
09-13-17, 12:38 PM
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09-13-17, 01:47 PM
#172
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I believe the areas of the contact patches will be the same, though the shapes will be different. The tire with the stiffer sidewall, I imagine, will have a narrower patch because the sidewalls are stiffer, and as a result, the patch will be longer (front to back).
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09-13-17, 01:52 PM
#173
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I agree, except there can be a slight difference in area also if one tire is stiffer. Think of a solid rubber tire with aquarium size air tube in the middle, small contact area. But this is limited by how much weight the un-inflated tire can hold up without collapsing, so I don't imagine that it's very much. Perhaps not even measurable with normal bike tires.
09-13-17, 02:12 PM
#174
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It seems the discussion wider is better leaves out an important consideration. Weight. I'm never riding a constant speed. I'm always going up and down hills so I am constantly having to accelerate to get back to speed. So just because a wide tire might roll with less resistance it does not necessarily overcome it's disadvantage of using more of my energy because it is heavier. Mass in rotation takes more energy to accelerate than mass going in a linear direction.
But neither am I on the side of skinny tires either. I'm just saying there is a factor left out that is one of many other factors that need to be compromised on. There is no one right answer.
But neither am I on the side of skinny tires either. I'm just saying there is a factor left out that is one of many other factors that need to be compromised on. There is no one right answer.
09-13-17, 02:15 PM
#175
Senior Member
I agree, except there can be a slight difference in area also if one tire is stiffer. Think of a solid rubber tire with aquarium size air tube in the middle, small contact area. But this is limited by how much weight the un-inflated tire can hold up without collapsing, so I don't imagine that it's very much. Perhaps not even measurable with normal bike tires.
__________________
Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter
Last edited by Brian Ratliff; 09-13-17 at 02:18 PM.