Talk:Rolling resistance
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[edit] Additions
I have added phisical formulas and a table with some examples and in the text correlation with emergency brake. --138.89.56.7 18:14, 16 May 2006 (UTC) Dieter
- I removed the paragraph about the "correlation" because it had no source and I don't think it's correct. Rolling resistance is fundamentally different from simple friction, as described in the article. Something that's firm but rough has a high sliding friction but low rolling resistance, and something that's squishy but smooth has a low sliding friction but high rolling resistance. —Keenan Pepper 21:27, 16 May 2006 (UTC)
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- I don't that thats right either, the smoother a surface, the lower the rolling resistance. Think about the difference between riding a bike on smooth concrete vs rough asphalt - or even riding a bike on a bed mattress. The bed mattress would have the highest rolling resistance because its "squishy". Fresheneesz 20:17, 27 May 2006 (UTC)
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- ...Right, the mattress has a high rolling resistance because it's squishy, not because its surface is rough. It doesn't matter how smooth it is for rolling resistance. Even if you put the smoothest silk sheets on that mattress, it would still be hard to ride your bike on it, because most of your energy goes into compressing the mattress and heating it up. —Keenan Pepper 21:07, 27 May 2006 (UTC)
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[edit] g vs normal force
I'm going to change "g" in that equation to FN for normal force. I think that would be more general. Fresheneesz 20:17, 27 May 2006 (UTC)
[edit] Temperature
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)
[edit] Definition of 'slip'
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)
