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Tire Pressure

Old 06-10-22, 01:52 PM
  #151  
tomato coupe
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Originally Posted by rydabent View Post
The big thing to remember is that if you are the person that has to have your tires at the absolute max on the sidewall, temperature will change it a lot. Your say 120 pounds in your garage, will go a lot higher in the summer riding on black top roads. Black top roads can get burning hot, and then if hilly, add extra heat from riding your brakes down hills. On a 100 degree day, riding down a long hill riding the brakes can cause the tire to go bang. And that would happen probably at a good speed. You would actually be "bleeding" off speed with your hip and arm.
Temperature induced pressure changes aren't that large. If you pump your tires to 100 psi at 70F, and then encounter 100F temperatures on the road, the pressure increase would be less than 6 psi.
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Old 06-10-22, 02:46 PM
  #152  
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Originally Posted by rydabent View Post
The big thing to remember is that if you are the person that has to have your tires at the absolute max on the sidewall, temperature will change it a lot. Your say 120 pounds in your garage, will go a lot higher in the summer riding on black top roads. Black top roads can get burning hot, and then if hilly, add extra heat from riding your brakes down hills. On a 100 degree day, riding down a long hill riding the brakes can cause the tire to go bang. And that would happen probably at a good speed. You would actually be "bleeding" off speed with your hip and arm.
Not really.
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Old 06-10-22, 03:31 PM
  #153  
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Originally Posted by ofajen View Post
Its not the term for energy loss in the casing you really have to watch out for. As I mentioned, the slope of the surface impedance term above the break point is much steeper, so running too high increases the energy loss at a much greater rate.

Also, that graph is for a surface where the break point is 115 psi for a 700x23 tire. The surface impedances I ride on are a lot more.

Otto
Thanks Otto. So at the inflection point it's kind of where the road surfaces starts t to dominate rather than the casing deformation?

Originally Posted by HTupolev View Post
How did you conclude a 9-11s difference? That would be an incredibly low impact for a Crr delta of .001 to have.
Um no, it actually is really small? The rolling resistance coeff is literally the force required to move some weight some distance. We can find out how much force is required to over-come the rolling resistance.

F = Crr * W * d (where W is weight and d is distance)
To roll myself and my bike one meter (80kg together) requires force of 3.1N-m = 0.004 * 80kg * 9.8m/s*s * 1 m
If the Crr increases to 0.005 then the force is higher: 3.9N-m

In a TT I would be putting down around 260W, that is 260N-m force at the pedals at any instant. Meaning about 1.2% of the force is being used to overcome the rolling resistance for optimum tire pressure, and 1.5% of the force for the worse tire pressure. I think in a 65min TT it would result in ~11s penalty (~.3% slower), all other things being equal. Even if you're casually riding around at 100W your rolling resistance is still a minor factor as far as speed is concerned so you might as well make your tire pressure something comfortable.
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Old 06-10-22, 03:36 PM
  #154  
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Originally Posted by billridesbikes View Post
Um no, it actually is really small? The rolling resistance coeff is literally the force required to move some weight some distance. We can find out how much force is required to over-come the rolling resistance.

F = Crr * W * d (where W is weight and d is distance)...
No, no, no, no, no.
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Old 06-10-22, 03:51 PM
  #155  
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Originally Posted by billridesbikes View Post
The rolling resistance coeff is literally the force required to move some weight some distance. We can find out how much force is required to over-come the rolling resistance.

F = Crr * W * d (where W is weight and d is distance)
No, Crr*W is the force. If you multiply by d you're calculating the work overcoming that force over that distance.

If you want power, multiple F by your speed.

Meaning about 1.2% of the force is being used to overcome the rolling resistance for optimum tire pressure, and 1.5% of the force for the worse tire pressure
(~.3% slower)
When aerodynamics are dominant, speed-versus-power doesn't follow a clean direct proportionality.
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Old 06-10-22, 05:21 PM
  #156  
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I wonder why the rolling resistance guy doesn't throw a rough surface on his drum, even once, to experimentally address the topic of smooth drum vs relatively rough roads.

I expect the answer is, he's confident enough in his current results, and it's his test. But it would be nice to see data from a controlled environment on the subject.
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Old 06-10-22, 05:45 PM
  #157  
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This thread went exactly the way I thought it would.
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Old 06-10-22, 06:38 PM
  #158  
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Originally Posted by downtube42 View Post
I wonder why the rolling resistance guy doesn't throw a rough surface on his drum, even once, to experimentally address the topic of smooth drum vs relatively rough roads.
I've seen drums made of diamond plate meant to simulate a rougher surface.
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Old 06-10-22, 06:56 PM
  #159  
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Originally Posted by tomato coupe View Post
I've seen drums made of diamond plate meant to simulate a rougher surface.
unless the wheel is suspended and weighted properly to simulate the system, theres no point. A smooth roller captures the relative performance of tires on rough surfaces below the breakpoint pressure and if the wheel is fixed or not correctly mounted, wont get the breakpoint right.
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Old 06-10-22, 06:59 PM
  #160  
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Originally Posted by asgelle View Post
unless the wheel is suspended and weighted properly to simulate the system, theres no point.
Why wouldn't it be?
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Old 06-10-22, 09:44 PM
  #161  
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Originally Posted by tomato coupe View Post
Why wouldn't it be?
Texturing the drum can theoretically allow you to characterize the hysteresis consequences of more complex tread deformation than a smooth drum, although it's not obvious how much value there is in practice with doing this.

If you're asking about characterizing consequences of inadequate suspension (i.e. due to overinflation), a typical drum setup won't do this because nothing is being suspended. Usually the wheel is just given some static preload before being locked in place for the test. No energy is expended deflecting things upward because that deflection isn't happening, and most of the loads that would be getting deflected upwards don't even exist in the system.
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Old 06-11-22, 08:07 AM
  #162  
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Originally Posted by tomato coupe View Post
Temperature induced pressure changes aren't that large. If you pump your tires to 100 psi at 70F, and then encounter 100F temperatures on the road, the pressure increase would be less than 6 psi.
Black top can get a lot hotter than you say. If you google it they say at 85 degrees black top can get to 140 degrees. What would it be on a 105 degree day???
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Old 06-11-22, 09:17 AM
  #163  
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Originally Posted by rydabent View Post
Black top can get a lot hotter than you say. If you google it they say at 85 degrees black top can get to 140 degrees. What would it be on a 105 degree day???
Even if the blacktop is at 140, your tires don't get to 140.
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Old 06-11-22, 10:20 PM
  #164  
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Originally Posted by smd4 View Post
And yet, no one can explain how a smaller contact patch has more rolling resistance than a larger one.
It doesn't, but a wider tire deflects less, even with lower pressure.
https://schwalbetires.com/technology...rolls%20better.
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Old 06-12-22, 07:30 AM
  #165  
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Im amused to report that I had a flat mid-ride yesterday, replaced the tube, re-inflated until it seemed rideable and had what felt like a good ride home.

Turned out I was running the 700x32 rear tire at 40psi on what Silca would call Category 1 gravel. For my total weight, recommended pressure is more like 59 psi or higher.

I should carry a pressure gauge for these occasions.

Otto
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Old 06-12-22, 09:12 AM
  #166  
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Originally Posted by ofajen View Post
Im amused to report that I had a flat mid-ride yesterday, replaced the tube, re-inflated until it seemed rideable and had what felt like a good ride home.

Turned out I was running the 700x32 rear tire at 40psi on what Silca would call Category 1 gravel. For my total weight, recommended pressure is more like 59 psi or higher.

I should carry a pressure gauge for these occasions.

Otto
I always carry a pressure gauge in case I encounter hors categorie gravel.
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Old 06-12-22, 09:30 AM
  #167  
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I have no issue with re-hashed threads.

A: As high as you can go without bouncing.

Higher pressure for the same setup always provides lower rolling resistance until the tire cannot absorb the road imperfections. Then lowering the tire until it can [absorb road imperfections] will provide lower resistance.
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Old 06-12-22, 09:43 AM
  #168  
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DUH!!! I'll put my 2 cents in...
I run several different tires on the few bikes I have. Some are with big and some with thin small tires.
I look at the side of the tire where it's embossed the MAX and MIN psi for the tire and I subtract 5 to 10 psi.

That's it. If I need a change I am really not changing my pressure, I am changing my wheel set...
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Old 06-12-22, 09:43 AM
  #169  
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We don't talk so much about rotating mass anymore. If you just want speed, look at what the pros are riding on good pavement. From what very little I see of pro races the pavement looks pretty nice (except for the obvious rough stuff). I ride pavement that is in good to excellent condition, I see no need for wider, lower pressure, heavier tires for everyday use. My biggest efforts are climbing at slower speeds.
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Old 06-12-22, 01:20 PM
  #170  
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Originally Posted by zandoval View Post
DUH!!! I'll put my 2 cents in...
I run several different tires on the few bikes I have. Some are with big and some with thin small tires.
I look at the side of the tire where it's embossed the MAX and MIN psi for the tire and I subtract 5 to 10 psi.
The only problem I see with that is that max pressure is often just what pressure the manufacturer is afraid the tire might pop off the rim, and has nothing to do with speed, handling, or comfort.
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Old 06-12-22, 04:12 PM
  #171  
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Originally Posted by urbanknight View Post
The only problem I see with that is that max pressure is often just what pressure the manufacturer is afraid the tire might pop off the rim, and has nothing to do with speed, handling, or comfort.
I imagine marketing people in the bike tire industry are struggling. One upon a time the goal would have been to claim the highest max tire pressure the engineers and lawyers would allow. Now if you project that rock hard high psi image, you're excluding customers. Maybe claiming 90 psi or so is the sweet spot - but then say words like supple and smooth. If you want to attract the "I'm not a racer" demographic, then maybe drop that advertised max down to 70 psi and give it an adventurous name. People eat that **** up.
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Old 06-12-22, 04:35 PM
  #172  
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I'd like to see the hystericalesis of a skinny rider vs a fat rider. The vertical motion isn't merely absorbed in the tire's carcass.
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Old 06-12-22, 06:02 PM
  #173  
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Originally Posted by downtube42 View Post
I imagine marketing people in the bike tire industry are struggling. One upon a time the goal would have been to claim the highest max tire pressure the engineers and lawyers would allow. Now if you project that rock hard high psi image, you're excluding customers. Maybe claiming 90 psi or so is the sweet spot - but then say words like supple and smooth. If you want to attract the "I'm not a racer" demographic, then maybe drop that advertised max down to 70 psi and give it an adventurous name. People eat that **** up.
It's too bad the people eating it up confuse "max" with "recommended"... including me way back when I was 125lb and had no business putting 140psi in a tire.


Originally Posted by GhostRider62 View Post
...hystericalesis...
I learned a word today!
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Old 06-13-22, 03:48 AM
  #174  
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Originally Posted by downtube42 View Post
I imagine marketing people in the bike tire industry are struggling. One upon a time the goal would have been to claim the highest max tire pressure the engineers and lawyers would allow. Now if you project that rock hard high psi image, you're excluding customers. Maybe claiming 90 psi or so is the sweet spot - but then say words like supple and smooth. If you want to attract the "I'm not a racer" demographic, then maybe drop that advertised max down to 70 psi and give it an adventurous name. People eat that **** up.
Is any of this ^ true? Fake reality is everywhere these days.
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Old 06-13-22, 03:50 AM
  #175  
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Originally Posted by venturi95 View Post
We don't talk so much about rotating mass anymore. If you just want speed, look at what the pros are riding on good pavement. From what very little I see of pro races the pavement looks pretty nice (except for the obvious rough stuff). I ride pavement that is in good to excellent condition, I see no need for wider, lower pressure, heavier tires for everyday use. My biggest efforts are climbing at slower speeds.
So that will be 25 or 28c at around 4.5 to 5 bar then.
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