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The definition of the "rolling resistance coefficient" refers to some "Figure 1", in which "F is the rolling resistance force". But in the Figure 1 ( http://en.wikipedia.org/wiki/File:Rolling_Resistance_2.png) F is "some towing force applied to the axle". It is no clear if it is some force pulling the wheel that compensates the effect of the rolling resistance, of it is the force that provokes the wheel to loss energy and eventually stop. — Preceding unsigned comment added by 186.135.53.190 ( talk) 00:44, 11 October 2014 (UTC)
I'm going to change "g" in that equation to for normal force. I think that would be more general. Fresheneesz 20:17, 27 May 2006 (UTC)
Shouldn't there be slope or angle mentioned in the formulas? Friction[kinetic] = u[k] * N = u[k] m g cos(theta) and Energy = u[k] m g d cos(theta) I thought. Victor ( talk) 07:08, 17 August 2010 (UTC)[User:Victory2006]
That external link at the bottom is very interesting, is Crr's relationship with temperature not well documented? This would be something that should be on this page. Fresheneesz 23:05, 27 May 2006 (UTC)
It is well documented. see for example SAE paper 800090. Reading off the graph .025 at -20 deg C, .012 at 30 deg c, .009 at 80 deg C Greglocock 22:44, 23 September 2006 (UTC)
The term 'slip', referred to road vehicles, is equivalent to 'creep' of railway wheels (see adhesion railway), it appears that automotive engineers don't talk to railway engineers.
It is a misnomer because the region of contact is not subjected to actual sliding, but elastic distortion, the figure of 11% is indicative of the condition where the tyre forces arising from the shear stress in the region of contact are sufficient for gross slippage to occur. Wheel forces arise from the elastic distortion of both the wheel and supporting surface at the region of contact.
This cyclic distortion results in energy loss, particularly in materials which have high internal friction such as rubber, so rubber tyres on asphalt have higher rolling loss than iron tyres on steel rails, because the internal losses are higher, and a much larger volume of material is affected by the distortion.
There is some partial slippage at the edges of the region of contact, which adds further to the losses, but the region is effectively stationary, so that adhesion is governed by static friction, which is usually greater than sliding friction.
I think what is meant in the article is the fundamental kinematic property of the wheel to transfer the motion of the vehicle relative to the surface from the region of contact to the hub, where greater control of the friction loss is achievable, hence roller bearings and lubrication.
Despite its superficial simplicity, the humble wheel is quite a sophisticated machine when studied to any depth. Gordon Vigurs 10:46, 4 June 2006 (UTC)
This table does not cite an original source. If it is known where the values originated, please cite.
I was able to get a copy of the source for the passenger rail car coefficient, written by Astakhov. I'm entirely new to Wikipedia but I've uploaded it to the Wikipedia commons and allowing someone much more familiar with Wiki standards to include it in the references section. https://commons.wikimedia.org/wiki/File:Pages_from_397774.pdf — Preceding unsigned comment added by Ironchief ( talk • contribs) 14:47, 21 November 2017 (UTC)
From the formula given it seems that the rolling resistance is independent of the speed of the rolling object. Is that correct?-- 129.70.14.127 12:07, 11 May 2007 (UTC)Quixy
Yes, pretty much. At very high speeds things get more complicated, but to within the normal sort of testing accuracy it doesn't change significantly with vehicle speed. That is, in a fuel economy model they don't normally have a speed sensitive contribution to rolling resistance. Anything small would be masked by the aerodynamic drag from the wheel, which is quite significant above 80 mph. Greglocock 07:25, 12 May 2007 (UTC)
Note that it's the rolling resistance FORCE that's independent of speed. The energy used is the force times the distance moved, and that's also independent of speed. If you go faster, though, you're moving more distance in a given time, and you need more energy in a given time, and energy per unit time is power. So you do need a bigger engine as you go faster... but it doesn't run as long. —Preceding unsigned comment added by 123.2.171.243 ( talk) 09:19, 20 April 2009 (UTC)
If you go faster, though, you're moving more distance in a given time, and you need more energy in a given time, and energy per unit time is power. So you do need a bigger engine as you go faster... but it doesn't run as long.
Thats not necessarily true, of you modify the gear ratio (if the application is geared) you can achieve a higher speed with the same or less energy. — Preceding unsigned comment added by 209.127.10.18 ( talk) 01:41, 2 October 2011 (UTC)
- Rolling resistance of rubber tyres is speed dependent! Tyre is polymer, every polymer has creep behavior. Therefore young modulus of polymer depends on bending frequency! — Preceding unsigned comment added by 188.120.195.255 ( talk) 21:48, 11 February 2015 (UTC)
Shouldn't this article be renamed to "Rolling friction". That s what its called in physics. Also the rename is needed to be consistent with Friction article. Firestonetireguy 17:22, 9 September 2007 (UTC)
The person who said kinetic/sliding friction is greater than rolling/static friction is totally wrong. The coefficient of sliding friction is much less than static/rolling friction. That is why good car brakes doesn't skid to a stop when you hit the brakes. Furthermore, sliding is much more efficient on a lubricated surface, hence rocket sleds use sliding sleds, and not wheels. Edited and fixed this portion by adding this:
"Rolling friction/static friction is much greater than sliding friction. The coefficient of rolling/static friction is greater than that of sliding/kinetic friction. Static friction prevents motion. This is why car wheels roll to a stop instead of skidding in order to stop as soon as possible. Also, rocket sleds using sliding sleds instead of wheels since sliding friction is much less. ...However, rolling/static friction does not create heat, since it prevents motion.
"Rolling friction depends on the coefficient of rolling friction between the two materials (µr) and the normal force (N) of the object. The force of kinetic friction depends on the coefficient of kinetic friction between the object and the surface on which it is moving (µk) and the normal force (N) of the object. For any pair of objects, the coefficient of kinetic friction is usually less than the coefficient of static friction." -MSN Encarta"
Edit it if you want to make it more concise.
Intranetusa 05:13, 9 October 2007 (UTC)
The section "in braking" seems to me a tangent at best, more appropriate for an article on the physics of braking. I think it should be at least moved later in the article if not moved to the brake article (which is rather thin at the moment). Any thoughts? Ccrrccrr ( talk) 03:50, 14 December 2007 (UTC)
What sources do you have for the steel wheel/steel rail values?
I have found specific ranges in between 0.0002 and 0.0005 for c. 30" diameter wheels. That's 2e-4 to 5e-4, mainly from the following two sources:
-Gordon, David W. Bicycling Science. Cambridge, Mass. : MIT Press, c. 2004. (They computed a range of 0.0002-0.0005)
-Williams, John A. Engineering Tribology. New York : Cambridge University Press, 2005. (This one has a value of 0.0004, but doesn't specify a size but it strongly implies a regular-size railroad wheel)
It is my belief that the latter value in the first source, 0.0005, is often rounded to 0.001. Just my two cents, hope it's correct.
Additionally, how does Fatigue Cracking relate to Rolling Resistance in rail applications? — Preceding
unsigned comment added by
209.127.10.18 (
talk) 01:27, 2 October 2011 (UTC)
""Over inflating tires (such a bicycle tires) may not lower the overall rolling resistance as the tire may skip and hop over the road surface. Traction is sacrificed, and overall rolling friction may not be reduced as the wheel rotational speed changes and slippage increases."" Reasonable men might conclude that if a tire is hopping and skipping, those moments would be marked with ZERO rolling resistance (yes, zero traction, as well--but this isn't a safety article now, is it?). —Preceding unsigned comment added by 75.37.224.235 ( talk) 16:29, 13 September 2009 (UTC)
The effect of rough surfaces transferring forward momentum to vertical momentum - which gives rise to vibrations that are eventually dissipated in various ways - may not be the same as 'rolling friction', but it is part of what is considered 'rolling resistance'. One reference I could find about this on the internet is this: http://janheine.wordpress.com/2010/10/18/science-and-bicycles-1-tires-and-pressure/ , which is written by an author of an article in Bicycle Quarterly, I have not seen that article directly but it should contain the numbers as well. It is also generally considered the cause for the lower rolling resistance of mountain bike tires with lower inflation pressures on rough surfaces, which is mentioned in the Schwalbe article already referenced in the wiki, but much more clear in the full report that appeared in the German Mountainbike magazine and of which an English translation can be found here http://www.mtbonline.co.za/downloads/Rolling_Resistance_Eng_illustrated.pdf . This report also provides strong evidence for the claim that wider tires have lower rolling resistance. — Preceding unsigned comment added by 145.94.178.86 ( talk) 14:31, 19 June 2014 (UTC)
How do you know this ins't due to better aero rather than Crr? Greglocock ( talk) 01:43, 12 January 2012 (UTC)
Moved from deleteed section "Small wheel size?"
The LGV-Est world speed record ini 2007 (the one which achieved 357 mph) was done specifically under special conditions, and one of those conditions was that they used, in fact, larger-diameter wheelsets for the train than usual. —Preceding unsigned comment added by Facial ( talk • contribs) 06:57, 2 March 2008 (UTC)
Large drive wheels reduce the rotational speed of all mechanical components, surely a desirable design feature. The consideration of rolling resistance might be nominal as all other train set wheels remained much smaller than the driven wheels. 75.37.224.235 ( talk) 16:33, 13 September 2009 (UTC)homebuilding
Being a successful competitor in the ultimate speed challenge soap box derby races mentioned in the article (wins in 2010 and 2011) and having developed a system for evaluating the rolling resistance of such wheels, I can attest from direct experience to the following:
Wheels with solid polymer tires of similar construction and identical tire materials and cross sections were tested at diameters varying from less than 4 to greater than 7 inches. Over a significant part of this range the rolling resistance was not a function of diameter. There is a point where rolling resistance appears to increase with decreasing diameter but for much of that range the rolling resistance was constant with diameter which is counter to the unsupported broad assertion the smaller wheels have higher rolling resistance.
Mark c estes ( talk) 00:49, 4 April 2012 (UTC)
Moved from deleted section"Rolling friction depends on the wheel radius!!!": Incorrect statements have been deleted such as support for the discredited "Coulomb's law" or claims that rolling resistance doesn't depend on the wheel radius (which is only approximately true for pneumatic tires on a hard surface over a limited range of radii).
The American equation [Coulomb's law] is obviously not a physically based formula but a nonsense-formula of the type that is so common in the US (just think of SEER, for instance, comparing BTU per hour with watts instead of just giving a non-dimensional efficiency number). The equaiton given by Andrew is obviously invalid outside the US, and thus does not belong in Wikipedia except for US consumption. Also, the article should consider that narrower wheels are more efficient (as anybody having used bikes with different tire widths has noticed). I don't know exactly why, that is why I went here, but it is not explained. I guess it is because a smaller surface of rubber is being deformed per time. Could someone take care of this? —Preceding unsigned comment added by 67.191.4.25 ( talk) 01:41, 22 December 2009 (UTC)
Note by David Lawyer (May 2012): The debate (much of which I removed) had 2 sides and both were wrong. One side thought that rolling resistance is independent of radius (correct for pneumatic tires on hard pavement) while the other thought is was inversely proportional to the radius. See #Depends on diameter written by me, which resolves the debate, using literature on the subject that the people in the debate didn't know about.
In particular, the diagram, the formulae and the statement "The above equations don't include variation of rolling resistance with speed. This is a reasonable simplification but measurements at different speeds show some variation"
I plan on removing the following formula (and text): The force of rolling resistance can also be calculated by[1]: F=(Nb)/r
where F is the rolling resistance force (shown in figure 1), r is the wheel radius, b is the rolling resistance coefficient or coefficient of rolling friction with dimension of length, and N is the normal force (equal to W, not R, as shown in figure 1).
Equating the above two equations, and solving for b, gives b = Crr·r. Therefore, if a source gives rolling resistance coefficient (Crr) as a dimensionless coefficient, it can be converted to b, having units of length, by multiplying Crr by wheel radius r.
The above formula is based on the disgraced "Coulombs law" impling that rolling resistance is inversely proportional to the wheel diameter (in this case the radius r). It's been shown to be wrong (see the section I wrote on diameter). Someone later showed that b = Crr x r which is correct but it's just a tautology. So I plan to delete it all. One of the previous formulas correctly shows it to be inversely proportional to the square root of the radius. 99.135.20.235 ( talk) 01:48, 8 March 2012 (UTC)
‰ is something like % only it means parts per thousand. Although it's not on keyboards it's a Unicode symbol and can be copied and pasted. Then one can say that automobile rolling resistance with ordinary tires is about 10‰ while in the 1950's it was 20‰ and that for a loaded rail freight car it's only 1‰. We could show both Crr (as a ratio) and Crr as parts per thousand (‰) in the table, but I would like to avoid using the direct ratio entirely and state that to get the Crr coefficient, one just moves the decimal point of the ‰ by 3 places to the left (multiplies by 0.001). This unit is sometimes called pounds per thousand pounds or kilograms-force per metric ton. 66.81.123.252 ( talk) 21:49, 22 March 2012 (UTC)
An alternate proposal would be to use Newtons/tonne (metric ton). But conversion of this back to the coefficient is not so simple since one has to divide by gravity g. — Preceding unsigned comment added by 99.135.20.235 ( talk) 02:46, 21 March 2012 (UTC)
view, although most people in the US don't know what it means. 16 April 2012 (UTC) -David Lawyer
I quote from above: "no one else uses either % or parts per hundred". If that were true, it would be a problem. But it's not true. Examples: [1], [2] (last paragraph in first column), [3] slide 8, [4], question 10, [5], [6], p. 8, [7] on pages ~23, 25-28.
I just added a picture illustrating the hysteresis effect. Further I would like add another picture showing plastic deformation (e.g. a wheel on soil, leaving behind permanent depression), if I can find the time. Besides that I would like to suggest some restructuring of the article. In my opinion we could do more to separate the different effects. Therefore the section "Rolling resistance can mean different things" could be moved up: directly after "primary causes"? The section on physical formulas could be moved down? It should be clearer about the phenomena that are incorporated here, instead of just quoting the external sources. Finally I suggest to remove sub-headers such as "Wheel bearing resistance", making slightly bigger paragraphs. Okay? Edwinv1970 ( talk) 15:45, 2 June 2012 (UTC)
Don't remove the sub-header which I created "Wheel bearing resistance". Other subheadings I was going to add were: Pure rolling resistance, Energy lost due to shaking the earth, Energy lost due to shaking the vehicle, Losses due to sliding of the wheel on the rail (mostly due to hunting). While automobiles have such losses, I don't think anyone has estimated them. So this section will be only for trains since the Russians did it for railroads during the Soviet era. I stopped because I want to use units of parts per thousand. Writing Crr= 0.0003 is not as easy to comprehend as Crr=0.3‰. David S. Lawyer 07:22, 4 July 2013 (UTC)
Most of the work on rolling resistance is experimental and not theoretical, often resulting in empirical formulas. Thus I think the topic of rolling resistance belongs to the "Transport engineering" wiki category and is part of the wiki project of "Civil engineering" both of which I've added to the talk page. However, it started out under the physics heading. Should it be removed from the Physics project? I added a link to it from the "Railway engineering" article, which is just a bunch of links to other articles. I think it's fine to continue to cover rolling resistance here for all types of vehicles since it facilitates comparisons. David S. Lawyer 00:38, 4 November 2013 (UTC) — Preceding unsigned comment added by Dlawyer ( talk • contribs)
-I would think automotive or mechnical engineering would be the best home for this article. AresLiam ( talk) 01:10, 4 November 2013 (UTC)
- Absolutely... Mechanical Engineering. That's what they do. Civil engineers deal with things that are static. — Preceding unsigned comment added by 2600:100D:B02B:A80B:8DE3:D324:81CA:8A06 ( talk) 02:20, 22 December 2015 (UTC)
Assuming "Coulomb's Law" is widespread, I suppose it is notable enough to be here. It does not, however, need to be scattered all over the article. Any mention of it should be prefaced by a note that it is incorrect. — Preceding unsigned comment added by SllipsLacimech ( talk • contribs) 21:13, 28 January 2014 (UTC)
http://indiatransportportal.com/wp-content/uploads/2016/02/india-rolling-resistance-itp-feb-2016.pdf is dead. I found something similar at https://www.slideshare.net/ArnaudRenard3/india-rolling-resistance-and-fuel-saving-2016 but I don't know whether it is the same and whether this is a canonical link. — Preceding unsigned comment added by TN ( talk • contribs) 12:21, 14 November 2017 (UTC)
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I cannot find support for these claims in the cited source:
Guiggniani doesn't seem to devote much space to rolling resistance or bicycles. Also, I am unfamiliar with this use of the word "precession", and I can't find where Guiggniani uses the word at all. - AndrewDressel ( talk) 13:03, 23 May 2018 (UTC)
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The definition of the "rolling resistance coefficient" refers to some "Figure 1", in which "F is the rolling resistance force". But in the Figure 1 ( http://en.wikipedia.org/wiki/File:Rolling_Resistance_2.png) F is "some towing force applied to the axle". It is no clear if it is some force pulling the wheel that compensates the effect of the rolling resistance, of it is the force that provokes the wheel to loss energy and eventually stop. — Preceding unsigned comment added by 186.135.53.190 ( talk) 00:44, 11 October 2014 (UTC)
I'm going to change "g" in that equation to for normal force. I think that would be more general. Fresheneesz 20:17, 27 May 2006 (UTC)
Shouldn't there be slope or angle mentioned in the formulas? Friction[kinetic] = u[k] * N = u[k] m g cos(theta) and Energy = u[k] m g d cos(theta) I thought. Victor ( talk) 07:08, 17 August 2010 (UTC)[User:Victory2006]
That external link at the bottom is very interesting, is Crr's relationship with temperature not well documented? This would be something that should be on this page. Fresheneesz 23:05, 27 May 2006 (UTC)
It is well documented. see for example SAE paper 800090. Reading off the graph .025 at -20 deg C, .012 at 30 deg c, .009 at 80 deg C Greglocock 22:44, 23 September 2006 (UTC)
The term 'slip', referred to road vehicles, is equivalent to 'creep' of railway wheels (see adhesion railway), it appears that automotive engineers don't talk to railway engineers.
It is a misnomer because the region of contact is not subjected to actual sliding, but elastic distortion, the figure of 11% is indicative of the condition where the tyre forces arising from the shear stress in the region of contact are sufficient for gross slippage to occur. Wheel forces arise from the elastic distortion of both the wheel and supporting surface at the region of contact.
This cyclic distortion results in energy loss, particularly in materials which have high internal friction such as rubber, so rubber tyres on asphalt have higher rolling loss than iron tyres on steel rails, because the internal losses are higher, and a much larger volume of material is affected by the distortion.
There is some partial slippage at the edges of the region of contact, which adds further to the losses, but the region is effectively stationary, so that adhesion is governed by static friction, which is usually greater than sliding friction.
I think what is meant in the article is the fundamental kinematic property of the wheel to transfer the motion of the vehicle relative to the surface from the region of contact to the hub, where greater control of the friction loss is achievable, hence roller bearings and lubrication.
Despite its superficial simplicity, the humble wheel is quite a sophisticated machine when studied to any depth. Gordon Vigurs 10:46, 4 June 2006 (UTC)
This table does not cite an original source. If it is known where the values originated, please cite.
I was able to get a copy of the source for the passenger rail car coefficient, written by Astakhov. I'm entirely new to Wikipedia but I've uploaded it to the Wikipedia commons and allowing someone much more familiar with Wiki standards to include it in the references section. https://commons.wikimedia.org/wiki/File:Pages_from_397774.pdf — Preceding unsigned comment added by Ironchief ( talk • contribs) 14:47, 21 November 2017 (UTC)
From the formula given it seems that the rolling resistance is independent of the speed of the rolling object. Is that correct?-- 129.70.14.127 12:07, 11 May 2007 (UTC)Quixy
Yes, pretty much. At very high speeds things get more complicated, but to within the normal sort of testing accuracy it doesn't change significantly with vehicle speed. That is, in a fuel economy model they don't normally have a speed sensitive contribution to rolling resistance. Anything small would be masked by the aerodynamic drag from the wheel, which is quite significant above 80 mph. Greglocock 07:25, 12 May 2007 (UTC)
Note that it's the rolling resistance FORCE that's independent of speed. The energy used is the force times the distance moved, and that's also independent of speed. If you go faster, though, you're moving more distance in a given time, and you need more energy in a given time, and energy per unit time is power. So you do need a bigger engine as you go faster... but it doesn't run as long. —Preceding unsigned comment added by 123.2.171.243 ( talk) 09:19, 20 April 2009 (UTC)
If you go faster, though, you're moving more distance in a given time, and you need more energy in a given time, and energy per unit time is power. So you do need a bigger engine as you go faster... but it doesn't run as long.
Thats not necessarily true, of you modify the gear ratio (if the application is geared) you can achieve a higher speed with the same or less energy. — Preceding unsigned comment added by 209.127.10.18 ( talk) 01:41, 2 October 2011 (UTC)
- Rolling resistance of rubber tyres is speed dependent! Tyre is polymer, every polymer has creep behavior. Therefore young modulus of polymer depends on bending frequency! — Preceding unsigned comment added by 188.120.195.255 ( talk) 21:48, 11 February 2015 (UTC)
Shouldn't this article be renamed to "Rolling friction". That s what its called in physics. Also the rename is needed to be consistent with Friction article. Firestonetireguy 17:22, 9 September 2007 (UTC)
The person who said kinetic/sliding friction is greater than rolling/static friction is totally wrong. The coefficient of sliding friction is much less than static/rolling friction. That is why good car brakes doesn't skid to a stop when you hit the brakes. Furthermore, sliding is much more efficient on a lubricated surface, hence rocket sleds use sliding sleds, and not wheels. Edited and fixed this portion by adding this:
"Rolling friction/static friction is much greater than sliding friction. The coefficient of rolling/static friction is greater than that of sliding/kinetic friction. Static friction prevents motion. This is why car wheels roll to a stop instead of skidding in order to stop as soon as possible. Also, rocket sleds using sliding sleds instead of wheels since sliding friction is much less. ...However, rolling/static friction does not create heat, since it prevents motion.
"Rolling friction depends on the coefficient of rolling friction between the two materials (µr) and the normal force (N) of the object. The force of kinetic friction depends on the coefficient of kinetic friction between the object and the surface on which it is moving (µk) and the normal force (N) of the object. For any pair of objects, the coefficient of kinetic friction is usually less than the coefficient of static friction." -MSN Encarta"
Edit it if you want to make it more concise.
Intranetusa 05:13, 9 October 2007 (UTC)
The section "in braking" seems to me a tangent at best, more appropriate for an article on the physics of braking. I think it should be at least moved later in the article if not moved to the brake article (which is rather thin at the moment). Any thoughts? Ccrrccrr ( talk) 03:50, 14 December 2007 (UTC)
What sources do you have for the steel wheel/steel rail values?
I have found specific ranges in between 0.0002 and 0.0005 for c. 30" diameter wheels. That's 2e-4 to 5e-4, mainly from the following two sources:
-Gordon, David W. Bicycling Science. Cambridge, Mass. : MIT Press, c. 2004. (They computed a range of 0.0002-0.0005)
-Williams, John A. Engineering Tribology. New York : Cambridge University Press, 2005. (This one has a value of 0.0004, but doesn't specify a size but it strongly implies a regular-size railroad wheel)
It is my belief that the latter value in the first source, 0.0005, is often rounded to 0.001. Just my two cents, hope it's correct.
Additionally, how does Fatigue Cracking relate to Rolling Resistance in rail applications? — Preceding
unsigned comment added by
209.127.10.18 (
talk) 01:27, 2 October 2011 (UTC)
""Over inflating tires (such a bicycle tires) may not lower the overall rolling resistance as the tire may skip and hop over the road surface. Traction is sacrificed, and overall rolling friction may not be reduced as the wheel rotational speed changes and slippage increases."" Reasonable men might conclude that if a tire is hopping and skipping, those moments would be marked with ZERO rolling resistance (yes, zero traction, as well--but this isn't a safety article now, is it?). —Preceding unsigned comment added by 75.37.224.235 ( talk) 16:29, 13 September 2009 (UTC)
The effect of rough surfaces transferring forward momentum to vertical momentum - which gives rise to vibrations that are eventually dissipated in various ways - may not be the same as 'rolling friction', but it is part of what is considered 'rolling resistance'. One reference I could find about this on the internet is this: http://janheine.wordpress.com/2010/10/18/science-and-bicycles-1-tires-and-pressure/ , which is written by an author of an article in Bicycle Quarterly, I have not seen that article directly but it should contain the numbers as well. It is also generally considered the cause for the lower rolling resistance of mountain bike tires with lower inflation pressures on rough surfaces, which is mentioned in the Schwalbe article already referenced in the wiki, but much more clear in the full report that appeared in the German Mountainbike magazine and of which an English translation can be found here http://www.mtbonline.co.za/downloads/Rolling_Resistance_Eng_illustrated.pdf . This report also provides strong evidence for the claim that wider tires have lower rolling resistance. — Preceding unsigned comment added by 145.94.178.86 ( talk) 14:31, 19 June 2014 (UTC)
How do you know this ins't due to better aero rather than Crr? Greglocock ( talk) 01:43, 12 January 2012 (UTC)
Moved from deleteed section "Small wheel size?"
The LGV-Est world speed record ini 2007 (the one which achieved 357 mph) was done specifically under special conditions, and one of those conditions was that they used, in fact, larger-diameter wheelsets for the train than usual. —Preceding unsigned comment added by Facial ( talk • contribs) 06:57, 2 March 2008 (UTC)
Large drive wheels reduce the rotational speed of all mechanical components, surely a desirable design feature. The consideration of rolling resistance might be nominal as all other train set wheels remained much smaller than the driven wheels. 75.37.224.235 ( talk) 16:33, 13 September 2009 (UTC)homebuilding
Being a successful competitor in the ultimate speed challenge soap box derby races mentioned in the article (wins in 2010 and 2011) and having developed a system for evaluating the rolling resistance of such wheels, I can attest from direct experience to the following:
Wheels with solid polymer tires of similar construction and identical tire materials and cross sections were tested at diameters varying from less than 4 to greater than 7 inches. Over a significant part of this range the rolling resistance was not a function of diameter. There is a point where rolling resistance appears to increase with decreasing diameter but for much of that range the rolling resistance was constant with diameter which is counter to the unsupported broad assertion the smaller wheels have higher rolling resistance.
Mark c estes ( talk) 00:49, 4 April 2012 (UTC)
Moved from deleted section"Rolling friction depends on the wheel radius!!!": Incorrect statements have been deleted such as support for the discredited "Coulomb's law" or claims that rolling resistance doesn't depend on the wheel radius (which is only approximately true for pneumatic tires on a hard surface over a limited range of radii).
The American equation [Coulomb's law] is obviously not a physically based formula but a nonsense-formula of the type that is so common in the US (just think of SEER, for instance, comparing BTU per hour with watts instead of just giving a non-dimensional efficiency number). The equaiton given by Andrew is obviously invalid outside the US, and thus does not belong in Wikipedia except for US consumption. Also, the article should consider that narrower wheels are more efficient (as anybody having used bikes with different tire widths has noticed). I don't know exactly why, that is why I went here, but it is not explained. I guess it is because a smaller surface of rubber is being deformed per time. Could someone take care of this? —Preceding unsigned comment added by 67.191.4.25 ( talk) 01:41, 22 December 2009 (UTC)
Note by David Lawyer (May 2012): The debate (much of which I removed) had 2 sides and both were wrong. One side thought that rolling resistance is independent of radius (correct for pneumatic tires on hard pavement) while the other thought is was inversely proportional to the radius. See #Depends on diameter written by me, which resolves the debate, using literature on the subject that the people in the debate didn't know about.
In particular, the diagram, the formulae and the statement "The above equations don't include variation of rolling resistance with speed. This is a reasonable simplification but measurements at different speeds show some variation"
I plan on removing the following formula (and text): The force of rolling resistance can also be calculated by[1]: F=(Nb)/r
where F is the rolling resistance force (shown in figure 1), r is the wheel radius, b is the rolling resistance coefficient or coefficient of rolling friction with dimension of length, and N is the normal force (equal to W, not R, as shown in figure 1).
Equating the above two equations, and solving for b, gives b = Crr·r. Therefore, if a source gives rolling resistance coefficient (Crr) as a dimensionless coefficient, it can be converted to b, having units of length, by multiplying Crr by wheel radius r.
The above formula is based on the disgraced "Coulombs law" impling that rolling resistance is inversely proportional to the wheel diameter (in this case the radius r). It's been shown to be wrong (see the section I wrote on diameter). Someone later showed that b = Crr x r which is correct but it's just a tautology. So I plan to delete it all. One of the previous formulas correctly shows it to be inversely proportional to the square root of the radius. 99.135.20.235 ( talk) 01:48, 8 March 2012 (UTC)
‰ is something like % only it means parts per thousand. Although it's not on keyboards it's a Unicode symbol and can be copied and pasted. Then one can say that automobile rolling resistance with ordinary tires is about 10‰ while in the 1950's it was 20‰ and that for a loaded rail freight car it's only 1‰. We could show both Crr (as a ratio) and Crr as parts per thousand (‰) in the table, but I would like to avoid using the direct ratio entirely and state that to get the Crr coefficient, one just moves the decimal point of the ‰ by 3 places to the left (multiplies by 0.001). This unit is sometimes called pounds per thousand pounds or kilograms-force per metric ton. 66.81.123.252 ( talk) 21:49, 22 March 2012 (UTC)
An alternate proposal would be to use Newtons/tonne (metric ton). But conversion of this back to the coefficient is not so simple since one has to divide by gravity g. — Preceding unsigned comment added by 99.135.20.235 ( talk) 02:46, 21 March 2012 (UTC)
view, although most people in the US don't know what it means. 16 April 2012 (UTC) -David Lawyer
I quote from above: "no one else uses either % or parts per hundred". If that were true, it would be a problem. But it's not true. Examples: [1], [2] (last paragraph in first column), [3] slide 8, [4], question 10, [5], [6], p. 8, [7] on pages ~23, 25-28.
I just added a picture illustrating the hysteresis effect. Further I would like add another picture showing plastic deformation (e.g. a wheel on soil, leaving behind permanent depression), if I can find the time. Besides that I would like to suggest some restructuring of the article. In my opinion we could do more to separate the different effects. Therefore the section "Rolling resistance can mean different things" could be moved up: directly after "primary causes"? The section on physical formulas could be moved down? It should be clearer about the phenomena that are incorporated here, instead of just quoting the external sources. Finally I suggest to remove sub-headers such as "Wheel bearing resistance", making slightly bigger paragraphs. Okay? Edwinv1970 ( talk) 15:45, 2 June 2012 (UTC)
Don't remove the sub-header which I created "Wheel bearing resistance". Other subheadings I was going to add were: Pure rolling resistance, Energy lost due to shaking the earth, Energy lost due to shaking the vehicle, Losses due to sliding of the wheel on the rail (mostly due to hunting). While automobiles have such losses, I don't think anyone has estimated them. So this section will be only for trains since the Russians did it for railroads during the Soviet era. I stopped because I want to use units of parts per thousand. Writing Crr= 0.0003 is not as easy to comprehend as Crr=0.3‰. David S. Lawyer 07:22, 4 July 2013 (UTC)
Most of the work on rolling resistance is experimental and not theoretical, often resulting in empirical formulas. Thus I think the topic of rolling resistance belongs to the "Transport engineering" wiki category and is part of the wiki project of "Civil engineering" both of which I've added to the talk page. However, it started out under the physics heading. Should it be removed from the Physics project? I added a link to it from the "Railway engineering" article, which is just a bunch of links to other articles. I think it's fine to continue to cover rolling resistance here for all types of vehicles since it facilitates comparisons. David S. Lawyer 00:38, 4 November 2013 (UTC) — Preceding unsigned comment added by Dlawyer ( talk • contribs)
-I would think automotive or mechnical engineering would be the best home for this article. AresLiam ( talk) 01:10, 4 November 2013 (UTC)
- Absolutely... Mechanical Engineering. That's what they do. Civil engineers deal with things that are static. — Preceding unsigned comment added by 2600:100D:B02B:A80B:8DE3:D324:81CA:8A06 ( talk) 02:20, 22 December 2015 (UTC)
Assuming "Coulomb's Law" is widespread, I suppose it is notable enough to be here. It does not, however, need to be scattered all over the article. Any mention of it should be prefaced by a note that it is incorrect. — Preceding unsigned comment added by SllipsLacimech ( talk • contribs) 21:13, 28 January 2014 (UTC)
http://indiatransportportal.com/wp-content/uploads/2016/02/india-rolling-resistance-itp-feb-2016.pdf is dead. I found something similar at https://www.slideshare.net/ArnaudRenard3/india-rolling-resistance-and-fuel-saving-2016 but I don't know whether it is the same and whether this is a canonical link. — Preceding unsigned comment added by TN ( talk • contribs) 12:21, 14 November 2017 (UTC)
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I cannot find support for these claims in the cited source:
Guiggniani doesn't seem to devote much space to rolling resistance or bicycles. Also, I am unfamiliar with this use of the word "precession", and I can't find where Guiggniani uses the word at all. - AndrewDressel ( talk) 13:03, 23 May 2018 (UTC)
References