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Tire Pressure

Old 06-07-22, 08:52 PM
  #51  
phughes
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Originally Posted by LarrySellerz View Post
Bro ride your own ride... I work with physicists all day (im at a national laboratory in group looking for dark matter), there are too many variables to math out the fastest tires. The only reliable test is one done in real world conditions. Some people enjoy thin hard tires.
Working with physicists is not the same as understanding physics.

And if you do indeed work there, as an amateur astronomer I'm jealous.
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Old 06-07-22, 08:55 PM
  #52  
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Originally Posted by asgelle View Post
That doesn't tell anything about the variables in road conditions, its a very complex equation to do correctly, if not impossible.
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Old 06-07-22, 08:57 PM
  #53  
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Originally Posted by LarrySellerz View Post
That doesn't tell anything about the variables in road conditions, its a very complex equation to do correctly, if not impossible.
Not clear on the meaning of validation, are you? Talk to the physicists you work with.
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Old 06-07-22, 08:58 PM
  #54  
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Originally Posted by phughes View Post
Working with physicists is not the same as understanding physics.

And if you do indeed work there, as an amateur astronomer I'm jealous.
Yeah I work at SLAC, one of the particle accelerators. My father is one of the higher ups in an experiment looking for dark matter and during covid they lost manpower and I was available. Bit of nepotism going on
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Old 06-07-22, 09:02 PM
  #55  
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Originally Posted by smd4 View Post
You do realize “smaller contact patch” = less friction = less rolling resistance?
1-Friction forces between a typical sealed road surface and a tire are substantially more proportional to total normal force than to contact area. A small contact area mostly just makes the friction less consistent, i.e. traction can be sketchier.
2-The friction between tire and road surface is mostly static friction, not sliding kinetic friction, meaning that there's not much frictional energy dissipation happening at the interface.
3-The two above points have very little to do with rolling resistance. Ignoring vibration, Crr on a sealed road surface is largely driven by friction internal to the tire (i.e. hysteresis of the casing and tread and whatnot), not friction between the tire and the road surface.

Last edited by HTupolev; 06-07-22 at 09:06 PM.
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Old 06-07-22, 09:09 PM
  #56  
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Originally Posted by LarrySellerz View Post
Yeah I work at SLAC, one of the particle accelerators. My father is one of the higher ups in an experiment looking for dark matter and during covid they lost manpower and I was available. Bit of nepotism going on
Please tell us precisely what you contribute to this project. I'd love to know.
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Old 06-07-22, 09:15 PM
  #57  
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Originally Posted by Koyote View Post
Please tell us precisely what you contribute to this project. I'd love to know.
I'm a technician, today I spent most of my time helping a relatively inexperienced PHD student with some orbital welds (a machine that does welds for you, if you set it up properly.) I live in the bay area where people are still terrified of covid, so there is a severe lack of the normal student labor.

also what does that matter? mind your own business bro. Ride your own ride
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Old 06-07-22, 09:18 PM
  #58  
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I like math it out. I think I'll use it.

In the car repair business, at least back in the day of distributor caps and rotors, they'd say "throw a tune-up on that Chevy". So how about

throw some math on that

I like it. Awesome thread.
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Old 06-07-22, 09:20 PM
  #59  
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Originally Posted by LarrySellerz View Post
I'm a technician,
Then you should stop implying that you understand physics because you work with physicists. You don't understand physics, and you are uninterested in learning from those who do -- that much is obvious from your posts.
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Old 06-07-22, 09:27 PM
  #60  
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Originally Posted by downtube42 View Post
I like math it out. I think I'll use it.

throw some math on that
In grad school, one of the standard texts would offer these hairy mathematical problems, work most of the way through them, and then -- rather than showing the last several steps in solving the problem -- the author would use the line "And the rest is obvious to the casual observer." One day while studying, one of my friends said, "I'm as casual about this as anyone, and it's not obvious to me."
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Old 06-07-22, 09:27 PM
  #61  
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Originally Posted by LarrySellerz View Post
Bro ride your own ride... I work with physicists all day (im at a national laboratory in group looking for dark matter), there are too many variables to math out the fastest tires. The only reliable test is one done in real world conditions. Some people enjoy thin hard tires.
In grad school, I had the good fortune to be able to take two classes on gravitation from Bahram Mashhoon, who, as a gravitational theorist who worked with John Wheeler, was here because we had a research reactor with thermal neutrons and techs who could make working neutron interferometers from single crystal silicon ingots. (Gravity experiments arenít so easy on charged particles where the gravitational interaction is 39 orders of magnitude less than the electromagnetic)

Anyway, Iíve always disliked the notion of dark matter and thought of modern cosmology as a bit of a shambles. Thankfully, Bahramís monograph from 2017 holds some hope that we are better understanding the history dependence and nonlocal aspects of gravitation which actually produce many similar results that some have explained with what seems to me a hand waving notion of dark matter.

Iím not necessarily going to recommend you actually buy a copy and try to work through it but here is the book. Itís an Oxford Press monograph.

https://global.oup.com/academic/prod...c=us&lang=en&#

Otto
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Old 06-07-22, 09:31 PM
  #62  
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Originally Posted by ofajen View Post
In grad school, I had the good fortune to be able to take two classes on gravitation from Bahram Mashoon, who, as a gravitational theorist who worked with John Wheeler, was here because we had a research reactor with thermal neutrons and techs who could make working neutron interferometers from single crystal silicon ingots. (Gravity experiments arenít so easy on charged particles where the gravitational interaction is 39 orders of magnitude less than the electromagnetic)

Anyway, Iíve always disliked the notion of dark matter and thought of modern cosmology as a bit of a shambles. Thankfully, Bahramís monograph from 2017 holds some hope that we are better understanding the history dependence and nonlocal aspects of gravitation which actually produce many similar results that some have explained with what seems to me a hand waving notion of dark matter.

Iím not necessarily going to recommend you actually buy a copy and try to work through it but here is the book. Itís an Oxford Press monograph.

https://global.oup.com/academic/prod...c=us&lang=en&#

Otto
Lol, there are many "alternative" theories of what dark matter is besides the commonly accepted weakly interacting massive particle model, and im not going to argue about it here
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Old 06-07-22, 09:44 PM
  #63  
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Originally Posted by LarrySellerz View Post
Yeah I work at SLAC, one of the particle accelerators. My father is one of the higher ups in an experiment looking for dark matter and during covid they lost manpower and I was available. Bit of nepotism going on
Pretty cool, Larry. During Covid a lot of places needed manpower, many still do. The fact you're still there says something. Nothing wrong with taking advantage of a good opportunity.
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Old 06-07-22, 09:44 PM
  #64  
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Originally Posted by LarrySellerz View Post
Lol, there are many "alternative" theories of what dark matter is besides the commonly accepted weakly interacting massive particle model, and im not going to argue about it here
What would a dark matter bike be like?
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Old 06-07-22, 09:48 PM
  #65  
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Originally Posted by phughes View Post
Pretty cool, Larry. During Covid a lot of places needed manpower, many still do. The fact you're still there says something. Nothing wrong with taking advantage of a good opportunity.
Its almost impossible to get fired from a government job like this, but I try to work hard and do my best.
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Old 06-08-22, 04:37 AM
  #66  
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Originally Posted by skidder View Post
I just look at the sidewall of the tire and see what the manufacturer has imprinted on it. Currently running 700x32 tires and I pump them up to the recommended 80 psi max. I used to run 700x28 that had a max rating of 110 psi.
Probably a reasonable approach if you happen to weigh 350 lbs.
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Old 06-08-22, 04:59 AM
  #67  
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Originally Posted by Daniel4 View Post
In Newton's pendulum, the kinetic energy of the first ball is transmitted through all the balls to the last because they are perfectly elastic and very hard. If the balls were perfectly inelastic, the last ball would not move at all because all of the balls would have absorbed all the energy.

In a hard tire, all the energy is transmitted through and you can feel all the vertical bumps. Not only do you go up and down, you go forward.

In a soft tire, the rubber absorbs all the energy and reduces your forward motion. Try riding on grass and sand where the soft ground is absorbing all the energy. Then compare that with riding on concrete, asphalt or on a perfectly smooth and hard track of a velodrome. The hard surface transmits all your energy.
The rougher the road surface, the more you don't want the vertical force inputs from the road transmitted and absorbed directly by your body. On a paved road that basically translates to vibration and the occasional more abrupt hit from potholes etc. All of which adds to your accumulated fatigue and ultimately slows you down. If the road is super smooth then you can run higher pressures and reduce the hysteresis losses in compressing the tyre. But as the road surface becomes less smooth, it soon becomes more beneficial overall to absorb the road inputs within the tyre rather than through your body. You only have to compare velodrome track tyres with mountain bike tyres to see the two extremes at play. Both are fastest in their element.

Where people get confused is attributing speed with a harder ride. Beyond a certain point it becomes counter-intuitive.

Last edited by PeteHski; 06-08-22 at 05:04 AM.
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Old 06-08-22, 06:51 AM
  #68  
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Originally Posted by Koyote View Post
Sometimes when everyone is saying you're wrong, it's because you are wrong.
And yet, no one can explain how a smaller contact patch has more rolling resistance than a larger one. Guess that explains why my Toyota Sienna feels like it's floating on air!
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Old 06-08-22, 07:10 AM
  #69  
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Originally Posted by downtube42 View Post
I like math it out. I think I'll use it

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Old 06-08-22, 07:14 AM
  #70  
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A Silca engineer, when interviewed, said that if you want to go fast you are much better off running pressure that is lower than higher. And he said this is because although there are gains to be made by running high pressure, they are much smaller than the losses that can occur from vibrations induced in the bicycle from the texture of the road surface. He said that as he and his crew were traveling around the world being technical support at races, they almost never used their tire pumps when adjusting the pressures of bicycles they adjusted for various riders, in almost every case they were letting air out of the tires they looked at.

This engineer said that the only surface that could use higher pressures would be a sanded smooth and varnished velodrome track, an outdoor concrete velodrome, although being very smooth, would not use higher pressure for optimal performance. So the take-away is that anyone riding on any sort of public paved road, is certainly better off running pressure that is low, not so low that there is any danger of damaging the tire in use, but not pumped up to the max pressure that is on the sidewall of the tire.

So I have been riding with lower pressures lately in my road-bikes, not worrying so much about them being pumped up to the sidewall pressure, but having them ten or fifeteen pounds lower. There are a few local courses I ride which have been used for time-trials in past decades, and eventually I will get round to timing myself on them while riding with lower pressures. All the science says that I should be faster with the low pressure, but I do not use any sophisticated methods of measuring, just the stop-watch feature on a wrist-watch over a dozen miles. I am guessing the low pressure will not hurt my speed at all, it may make me a little faster, and it will certainly be a bit less fatigueing, so all I see are advantages.
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Old 06-08-22, 07:18 AM
  #71  
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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.
https://www.amazon.com/Bicycling-Sci...s%2C113&sr=1-1
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Old 06-08-22, 08:17 AM
  #72  
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Originally Posted by cxwrench View Post
^This^
You guys that think high pressure is fast because 'it feels fast' just don't get it.
Again, I'm not a racer. I'm a casual rider. I guess I just opt for a bike that "feels" faster instead of one that "feels" slower. My actual time means little to me. But, feel free to keep on trying to convince me.

Now if I could just find some 700 x 20C clinchers that went to 140.
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Old 06-08-22, 08:26 AM
  #73  
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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's been explained several times, in several ways, throughout this thread. Your refusal to learn does not negate that.


Originally Posted by smd4 View Post
Again, I'm not a racer. I'm a casual rider. I guess I just opt for a bike that "feels" faster instead of one that "feels" slower.
That's your decision. But don't be deluded into confusing your feeling with facts.
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Old 06-08-22, 08:40 AM
  #74  
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With the latest hookless rims like my Zipp 303s wheels, 73 psi is the maximum recommended pressure for any tire. If that's not enough, then you buy wider tires. Zipp's pressure calculator recommends only 51/54 psi for my weight and 30mm tires. I found that a bit too squishy and increased it by 5 psi. Works great. I use 62/66 for 19mm internal width hooked rims and 28mm tires, as recommended by the Zipp calculator.
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Old 06-08-22, 09:17 AM
  #75  
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Originally Posted by Koyote View Post
It's been explained several times, in several ways, throughout this thread. Your refusal to learn does not negate that.
Really?? Here are all the responses I got:
Originally Posted by WhyFi View Post
Ew, David.
Originally Posted by WhyFi View Post
"Doing it wrong" sums it up better. Well, if you're interested in performance, at least.
Originally Posted by WhyFi View Post
If absurdly high pressure is what you prefer - you do you. If you think that it's faster - you're objectively wrong.
Originally Posted by WhyFi View Post
Which is why I qualified my "doing it wrong" with, "if you're interested in performance."
Don't confuse your perception with reality. They're slower, they have a smaller contact patch, and being "less cushy" is the conversion of forward momentum in to upwards momentum.
There's a wide range of optimal, depending upon the rider, the tires, the surface, etc, but 140psi on pavement is well outside of the feasibly optimal range.
Originally Posted by WhyFi View Post
So, if we want the fastest tires, we should be aiming for the least amount of friction between the road and the tire? Cool.
Originally Posted by cxwrench View Post
You're confused.
More confused.
You guys that think high pressure is fast because 'it feels fast' just don't get it. What you're feeling is the very definition of rolling resistance. If you're feeling every little bump and bit of texture it's because the bike AND you are going up and down. Not as efficient as if the bike AND you weren't going up and down. 'Feels' count for very little here, we're dealing with physics. Which are known as the LAWS of physics.
Originally Posted by HTupolev View Post
1-Friction forces between a typical sealed road surface and a tire are substantially more proportional to total normal force than to contact area. A small contact area mostly just makes the friction less consistent, i.e. traction can be sketchier.
2-The friction between tire and road surface is mostly static friction, not sliding kinetic friction, meaning that there's not much frictional energy dissipation happening at the interface.
3-The two above points have very little to do with rolling resistance. Ignoring vibration, Crr on a sealed road surface is largely driven by friction internal to the tire (i.e. hysteresis of the casing and tread and whatnot), not friction between the tire and the road surface.
Originally Posted by Koyote View Post
That's your decision. But don't be deluded into confusing your feeling with facts.
Originally Posted by Koyote View Post
Sometimes when everyone is saying you're wrong, it's because you are wrong.
As you can see, except for HTupolev, there's has been a whole lot of un-helpfulness and un-explanation in this thread, mostly telling me 1) I'm disgusting, 2) I'm "doing it wrong;" 3) I'm wrong; 4) I'm "confused" and "don't get it;" 5) I'm "deluded;" and 6) I'm wrong again. Even HTupolev's explanation leaves room for the apparently impossible fact that a smaller contact area produces less rolling resistance. asgelle provided a link to a book, which may or may not be helpful. But certainly not an explanation.

Anyway, constantly telling folks they're just "wrong" is probably the easiest way to explain things. But thanks anyway.

Last edited by smd4; 06-08-22 at 09:29 AM.
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