Notices
General Cycling Discussion Have a cycling related question or comment that doesn't fit in one of the other specialty forums? Drop on in and post in here! When possible, please select the forum above that most fits your post!

Tire Pressure

Old 06-08-22, 09:28 AM
  #76  
fishboat
Senior Member
 
Join Date: Feb 2016
Location: SE Wisconsin
Posts: 1,890

Bikes: Lemond '01 Maillot Jaune, Lemond '02 Victoire, Lemond '03 Poprad, Lemond '03 Wayzata DB conv(Poprad), '79 AcerMex Windsor Carrera Professional(pur new), '88 GT Tequesta(pur new), '01 Bianchi Grizzly, 1993 Trek 970 DB conv, Trek 8900 DB conv

Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 751 Post(s)
Likes: 0
Liked 799 Times in 467 Posts
Originally Posted by LarrySellerz
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
..just goes to show..traditional physics aside, the apple can fall far from the tree.
fishboat is offline  
Likes For fishboat:
Old 06-08-22, 09:42 AM
  #77  
t2p
Senior Member
 
Join Date: May 2022
Location: USA - Southwest PA
Posts: 2,981

Bikes: Cannondale - Gary Fisher - Giant - Litespeed - Schwinn Paramount - Schwinn (lugged steel) - Trek OCLV

Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 1359 Post(s)
Liked 1,803 Times in 1,038 Posts
Originally Posted by beng1
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.
back in the day when we ran 20 and 23mm tires (w/tubes) - we were able to determine (subjectivity) the bikes seemed to roll and feel better with lower air pressure on compromised road surfaces (if not most road surfaces)

but there was one small but significant 'catch' that could quickly ruin your ride: snake bite punctures

if you ran less than 100 psi - you were inviting trouble - especially the larger / heavier riders

today rims and tires are wider - many run tubeless - so they are able to take advantage of this and run lower pressure
.
t2p is offline  
Old 06-08-22, 09:50 AM
  #78  
t2p
Senior Member
 
Join Date: May 2022
Location: USA - Southwest PA
Posts: 2,981

Bikes: Cannondale - Gary Fisher - Giant - Litespeed - Schwinn Paramount - Schwinn (lugged steel) - Trek OCLV

Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 1359 Post(s)
Liked 1,803 Times in 1,038 Posts

Originally Posted by smd4
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.
I might be able to grant your wish !

I can place you at the top of the rapidly growing list for these fine vintage 20 mm Axial Pro tires that have been out of use for 20+ years - with vintage Air-B latex tubes

But they have not been inflated during that 20+ year period - so I cannot guarantee 40 psi let alone 140 psi

Go small or don't go at all !
.
t2p is offline  
Old 06-08-22, 09:51 AM
  #79  
LarrySellerz
Senior Member
 
Join Date: Mar 2021
Posts: 1,964
Mentioned: 23 Post(s)
Tagged: 0 Thread(s)
Quoted: 2644 Post(s)
Liked 474 Times in 344 Posts
Originally Posted by t2p
back in the day when we ran 20 and 23mm tires (w/tubes) - we were able to determine (subjectivity) the bikes seemed to roll and feel better with lower air pressure on compromised road surfaces (if not most road surfaces)

but there was one small but significant 'catch' that could quickly ruin your ride: snake bite punctures

if you ran less than 100 psi - you were inviting trouble - especially the larger / heavier riders

today rims and tires are wider - many run tubeless - so they are able to take advantage of this and run lower pressure
.
I got a pinch flat at 120 psi on 25mm tires last week, had a bunch of groceries hanging off the bike but it was still ridiculous
LarrySellerz is offline  
Old 06-08-22, 09:53 AM
  #80  
icemilkcoffee 
Senior Member
 
icemilkcoffee's Avatar
 
Join Date: Aug 2009
Posts: 2,592
Mentioned: 13 Post(s)
Tagged: 0 Thread(s)
Quoted: 1541 Post(s)
Liked 1,702 Times in 956 Posts
Originally Posted by rclouviere
I’velooked at the silcachart and it seems to be pretty accurate?
It looks pretty accurate to me too. But I disagree that smaller diameter rims require higher pressure. I have a lo-pro bike with 24" front wheels. My wife has a Terry bike with 24" front wheel, and my kids ride bikes with 650c wheels, so we have plenty of non-700c wheels in our garage and I've always pumped up the smaller tires same as the larger tires of the same width.
icemilkcoffee is online now  
Likes For icemilkcoffee:
Old 06-08-22, 10:42 AM
  #81  
ofajen
Cheerfully low end
 
ofajen's Avatar
 
Join Date: Jun 2020
Posts: 1,965
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 642 Post(s)
Liked 1,040 Times in 663 Posts
Originally Posted by smd4
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!
From the article I linked on page 1:

WHAT CAUSES ROLLING RESISTANCE

To go faster, the first step is to identify what exactly is slowing us down. When looking at our tires we are looking at casing losses and surface impedance. Casing losses is the amount of energy that you are losing when your tire is deflected and loses heat. The other major factor sapping energy from the system is impedance losses.

The best way to look at impedance is the amount the system is moved up or down based on a bump. For example, on a perfectly rigid wheel like something found on an in-line skate or skateboard if you hit a 5mm bump, the entire system is lifted 5mm off the ground.


When you move to a pneumatic tire like we ride on bicycles the bump is absorbed largely by the tire and the loss is felt in the heat of the tire deflection like we just talked about. The better the tire and the lower the pressure, the more energy is absorbed by the tire.


We have long been told that higher pressures are faster on the road. We thought that to be true and even “tested” it to be true. This is because all of the testing at that point had been done on roller drums which are extremely smooth surfaces. When the surface is extremely smooth like on a roller or a wooden velodrome casing losses account for the vast majority of rolling resistance which is why you would want to run pressures exceeding 140psi.

When real world testing started to be done by Tom Anhalt, he found that there was a breakpoint pressure. This breakpoint is where casing losses are no longer the leading contributor, but surface impedance becomes the driving force to slow you down. Below you can see his test that follows the same curve as the roller test closely on this “good” pavement surface right up until it doesn’t. The losses in the system shoot back up because it is now the surface impedance that takes over. The rougher the surface, the smaller the tire, the lower that breakpoint pressure is going to be.





These graphs lead us to the question of what pressure should we run. As with almost all marginal gains questions the answer is, it depends. What surface are you riding on, what size are your tires, how much does your system weigh, what kind of bike are you riding; all of these play a factor in the optimal tire pressure for the given conditions.

(remainder of article omitted as it gets more into details about tire types and the Silca calculator)

Also, note the higher slope of the surface impedance dominated part of the curve. This is what leads us to seek to err slightly on the side of “too low” rather than “too high” since the incremental energy cost is less for a given deviation from optimal pressure.

Otto

Last edited by ofajen; 06-08-22 at 10:47 AM.
ofajen is offline  
Likes For ofajen:
Old 06-08-22, 10:48 AM
  #82  
phughes
Senior Member
 
phughes's Avatar
 
Join Date: Mar 2011
Posts: 3,064
Mentioned: 7 Post(s)
Tagged: 0 Thread(s)
Quoted: 1020 Post(s)
Liked 1,252 Times in 724 Posts
Originally Posted by smd4
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!
No one really has to explain that to you, because that is not really why the lower pressure tire has less roling resistance. You simply fail to look past the contact patch, and consider the other variables that factor into the equation. If you would take a moment to actually read without bias, you might actually understand it better. Keep in mind, the lower pressure tire does not always have less rolling resistance, there is more to it than that.

Here is an article I posted before, but I am pretty sure, based on your continued posts showing your lack of understanding of the realities of the issue, that you didn't read it. https://www.renehersecycles.com/myth...ure-is-faster/
phughes is offline  
Old 06-08-22, 11:49 AM
  #83  
70sSanO
Senior Member
 
70sSanO's Avatar
 
Join Date: Feb 2015
Location: Mission Viejo
Posts: 5,772

Bikes: 1986 Cannondale SR400 (Flat bar commuter), 1988 Cannondale Criterium XTR, 1992 Serotta T-Max, 1995 Trek 970

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1935 Post(s)
Liked 2,150 Times in 1,313 Posts
It is pretty simple. The correct answer is based on what is used by those who actually get paid to ride fast.

There is a lot of data and people can argue all they want, but if professional cyclists are riding wider tires that is the most compelling evidence. And that evidence is mirrored in the lack of availability of 700x20 clincher tires that were so prevalent 35 years ago.

John
70sSanO is offline  
Old 06-08-22, 11:57 AM
  #84  
asgelle
Senior Member
 
Join Date: Apr 2006
Location: Albuquerque, NM
Posts: 4,514
Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 1028 Post(s)
Liked 447 Times in 263 Posts
Originally Posted by 70sSanO
It is pretty simple. The correct answer is based on what is used by those who actually get paid to ride fast.
Except, of course, it took something like 10 years for the Pro peloton to come around to what Tom, Josh and others realized right away from Tom's data.
asgelle is offline  
Old 06-08-22, 12:11 PM
  #85  
70sSanO
Senior Member
 
70sSanO's Avatar
 
Join Date: Feb 2015
Location: Mission Viejo
Posts: 5,772

Bikes: 1986 Cannondale SR400 (Flat bar commuter), 1988 Cannondale Criterium XTR, 1992 Serotta T-Max, 1995 Trek 970

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1935 Post(s)
Liked 2,150 Times in 1,313 Posts
Originally Posted by asgelle
Except, of course, it took something like 10 years for the Pro peloton to come around to what Tom, Josh and others realized right away from Tom's data.
There is a real world stubbornness that does take time to overcome.

In golf there is a phrase, "feel is not real" because so many people feel what they are doing is correct, but in reality it is not.

In many sports, one's perception is not close to an actual video of the performance. That is, unless the individual is truly an elite athlete.

John
70sSanO is offline  
Old 06-08-22, 01:29 PM
  #86  
WhyFi
Senior Member
 
WhyFi's Avatar
 
Join Date: Jan 2010
Location: TC, MN
Posts: 39,505

Bikes: R3 Disc, Haanjo

Mentioned: 353 Post(s)
Tagged: 1 Thread(s)
Quoted: 20791 Post(s)
Liked 9,436 Times in 4,663 Posts
Originally Posted by smd4
Anyway, constantly telling folks they're just "wrong" is probably the easiest way to explain things. But thanks anyway.
People generally don't go out of their way to educate the belligerently ignorant. I've previously posted a link to a podcast - one doesn't even need to muster the motivation to *ack* read something - so don't complain to us that you've ignored it.

But, since I'm such a nice, helpful guy, I'll even post it again, for the aggressively lazy - https://cyclingtips.com/2016/08/cycl...and-pressures/

So, there's the water. Are you going to drink?
WhyFi is offline  
Likes For WhyFi:
Old 06-08-22, 02:03 PM
  #87  
billridesbikes
Senior Member
 
Join Date: Nov 2019
Posts: 701
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 347 Post(s)
Liked 418 Times in 250 Posts
@ofajen Otto, Doesn't the Silca site show this is a real but marginal gain?
Crr is the proportional amount of force needed to move some weight some distance at a constant speed.
Let's take me and my bike together are 80kg (before stopping for chicken fried steak).
The difference between the lowest and highest Crr is about 0.001
0.001 * 80kg * 10m/s*s = .8 kg-m/s*s (N)
Or for me about 9-11s difference over a flat 40km at my FTP.
In a TT that would be a little over an hour for me, yes I want those 11s really badly! But daily riding probably not that noticeable.
billridesbikes is offline  
Old 06-08-22, 02:10 PM
  #88  
Koyote
Senior Member
 
Join Date: Sep 2017
Posts: 7,768
Mentioned: 37 Post(s)
Tagged: 0 Thread(s)
Quoted: 6882 Post(s)
Liked 10,873 Times in 4,637 Posts
Originally Posted by WhyFi
People generally don't go out of their way to educate the belligerently ignorant. I've previously posted a link to a podcast - one doesn't even need to muster the motivation to *ack* read something - so don't complain to us that you've ignored it.

But, since I'm such a nice, helpful guy, I'll even post it again, for the aggressively lazy - https://cyclingtips.com/2016/08/cycl...and-pressures/

So, there's the water. Are you going to drink?
I know you know this, but some people come here for confirmation rather than information.
Koyote is offline  
Likes For Koyote:
Old 06-08-22, 02:12 PM
  #89  
WhyFi
Senior Member
 
WhyFi's Avatar
 
Join Date: Jan 2010
Location: TC, MN
Posts: 39,505

Bikes: R3 Disc, Haanjo

Mentioned: 353 Post(s)
Tagged: 1 Thread(s)
Quoted: 20791 Post(s)
Liked 9,436 Times in 4,663 Posts
Originally Posted by Koyote
I know you know this, but some people come here for confirmation rather than information.
I sometimes give the benefit of doubt because I'm such a softie.
WhyFi is offline  
Old 06-08-22, 02:15 PM
  #90  
Koyote
Senior Member
 
Join Date: Sep 2017
Posts: 7,768
Mentioned: 37 Post(s)
Tagged: 0 Thread(s)
Quoted: 6882 Post(s)
Liked 10,873 Times in 4,637 Posts
Originally Posted by WhyFi
I sometimes give the benefit of doubt because I'm such a softie.
Yeah. And then the confirmation seekers end up resentful when they are corrected, and you wonder why you ever bothered trying to be helpful.
Koyote is offline  
Old 06-08-22, 02:21 PM
  #91  
PeteHski
Senior Member
 
PeteHski's Avatar
 
Join Date: May 2021
Posts: 8,175
Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 4274 Post(s)
Liked 4,713 Times in 2,911 Posts
Originally Posted by 70sSanO
It is pretty simple. The correct answer is based on what is used by those who actually get paid to ride fast.

There is a lot of data and people can argue all they want, but if professional cyclists are riding wider tires that is the most compelling evidence. And that evidence is mirrored in the lack of availability of 700x20 clincher tires that were so prevalent 35 years ago.

John
Geraint Thomas mentioned in a recent podcast that he runs around 4.5 bar (65 psi) in his road tyres. He's around 70 kg and probably running 26-28 mm wide tyres (Conti GP5000S).
PeteHski is offline  
Old 06-08-22, 02:45 PM
  #92  
ofajen
Cheerfully low end
 
ofajen's Avatar
 
Join Date: Jun 2020
Posts: 1,965
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 642 Post(s)
Liked 1,040 Times in 663 Posts
Originally Posted by billridesbikes
@ofajen Otto, Doesn't the Silca site show this is a real but marginal gain?
Crr is the proportional amount of force needed to move some weight some distance at a constant speed.
Let's take me and my bike together are 80kg (before stopping for chicken fried steak).
The difference between the lowest and highest Crr is about 0.001
0.001 * 80kg * 10m/s*s = .8 kg-m/s*s (N)
Or for me about 9-11s difference over a flat 40km at my FTP.
In a TT that would be a little over an hour for me, yes I want those 11s really badly! But daily riding probably not that noticeable.
It’s 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

Last edited by ofajen; 06-08-22 at 02:55 PM.
ofajen is offline  
Old 06-08-22, 03:17 PM
  #93  
HTupolev
Senior Member
 
Join Date: Apr 2015
Location: Seattle
Posts: 4,261
Mentioned: 41 Post(s)
Tagged: 0 Thread(s)
Quoted: 1971 Post(s)
Liked 1,297 Times in 629 Posts
Originally Posted by billridesbikes
The difference between the lowest and highest Crr is about 0.001
Or for me about 9-11s difference over a flat 40km at my FTP.
How did you conclude a 9-11s difference? That would be an incredibly low impact for a Crr delta of .001 to have.
HTupolev is offline  
Old 06-08-22, 04:41 PM
  #94  
tankist
Junior Member
 
Join Date: Oct 2006
Posts: 172
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 83 Post(s)
Liked 157 Times in 55 Posts
What about automobile tires? It is a known fact that under-inflated ones result in worse gas mileage.
tankist is offline  
Old 06-08-22, 04:43 PM
  #95  
asgelle
Senior Member
 
Join Date: Apr 2006
Location: Albuquerque, NM
Posts: 4,514
Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 1028 Post(s)
Liked 447 Times in 263 Posts
Originally Posted by tankist
What about automobile tires? It is a known fact that under-inflated ones result in worse gas mileage.
In case you haven’t noticed, cars have these springy, bouncy things.
asgelle is offline  
Old 06-08-22, 05:14 PM
  #96  
phughes
Senior Member
 
phughes's Avatar
 
Join Date: Mar 2011
Posts: 3,064
Mentioned: 7 Post(s)
Tagged: 0 Thread(s)
Quoted: 1020 Post(s)
Liked 1,252 Times in 724 Posts
Originally Posted by tankist
What about automobile tires? It is a known fact that under-inflated ones result in worse gas mileage.
Sure, under the car manufacturer's recommended inflation pressure, which they figured by using the weight of the vehicle, and how it affected the recommended tires. You know, the same way people on this thread have said you figure proper inflation pressure for bicycle tires.

So, if you go under the recommended pressure on car tires, you lose fuel efficiency. The recommended pressure for most cars, is under the maximum inflation pressure for the tire. So you haven't hit on any gotcha, with the exception of confirming what people who actually understand this issue have been saying, tire pressure is based on the weight the tire has to carry. It really is that simple.
phughes is offline  
Old 06-08-22, 06:26 PM
  #97  
cxwrench
Senior Member
 
cxwrench's Avatar
 
Join Date: Jul 2013
Location: Nor-Cal
Posts: 3,767

Bikes: lots

Mentioned: 7 Post(s)
Tagged: 0 Thread(s)
Quoted: 1958 Post(s)
Liked 2,932 Times in 1,489 Posts
Originally Posted by tankist
What about automobile tires? It is a known fact that under-inflated ones result in worse gas mileage.
You didn't really think about this, did you?
cxwrench is offline  
Likes For cxwrench:
Old 06-09-22, 12:48 AM
  #98  
Fredo76
The Wheezing Geezer
 
Fredo76's Avatar
 
Join Date: Oct 2021
Location: Española, NM
Posts: 998

Bikes: 1976 Fredo Speciale, Jamis Citizen 1, Ellis-Briggs FAVORI, Rivendell Clem Smith Jr.

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 395 Post(s)
Liked 857 Times in 422 Posts
Originally Posted by asgelle
I wonder if that was the model used by some clowns to "prove" that lighter wheels are no better than lighter anything-else. Seems like it might be. I had to laugh. I agree with Larry here.

Moreover, the way he's treated here by some folks disgusts me.
Fredo76 is online now  
Likes For Fredo76:
Old 06-09-22, 06:07 AM
  #99  
asgelle
Senior Member
 
Join Date: Apr 2006
Location: Albuquerque, NM
Posts: 4,514
Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 1028 Post(s)
Liked 447 Times in 263 Posts
Originally Posted by Fredo76
I wonder if that was the model used by some clowns to "prove" that lighter wheels are no better than lighter anything-else. Seems like it might be. I had to laugh. I agree with Larry here.
No, the proof that removing weight from wheels makes a trivial difference compared to removing the weight from anywhere else in the system came from direct field testing (the earliest I'm aware of is Kraig Willett's from 2001). The model just explains the empirical finding.
asgelle is offline  
Likes For asgelle:
Old 06-09-22, 06:20 AM
  #100  
PeteHski
Senior Member
 
PeteHski's Avatar
 
Join Date: May 2021
Posts: 8,175
Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 4274 Post(s)
Liked 4,713 Times in 2,911 Posts
Originally Posted by Fredo76
I wonder if that was the model used by some clowns to "prove" that lighter wheels are no better than lighter anything-else. Seems like it might be. I had to laugh. I agree with Larry here.

Moreover, the way he's treated here by some folks disgusts me.
The clowns happen to be correct though.
PeteHski is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.