Tyre grip VS tire rolling resistance

[amouzouris]

Ideally you want a tyre to have the highest grip possible...but have a low rolling resistance....
(rolling resistance is how much resistance there is to turn the tires...a lower rolling resistance will improve fuel consumption and engine wear...also they say that 1 in 5 petrol refills is because of the tyre rolling resistance (talking about road cars now) if you let a car stop itself, without applying brakes and by turning off the engine, a tyre with the least rolling resistance will stop much later)

so here is my question... how do they engineer into the tire a high grip level but with a low rolling resistance??? they seem to contradict each other..

[raymondu999]

My physics is rusty - but wouldn't it be more a case of the tyre surface generating tyre grip, but the rolling resistance coming from the axle to the wheel? Or some such. I could be talking rubbish.

[amouzouris]

My physics is rusty - but wouldn't it be more a case of the tyre surface generating tyre grip, but the rolling resistance coming from the axle to the wheel? Or some such. I could be talking rubbish.

yes..indeed there is rolling resistance between the axle and the wheel....but there also is between the tyre and the road surface!

[raymondu999]

Is there? I always thought that it was ok to have higher tyre grip because the friction between road and tyre is pushing the car forwards anyways, or at leas the values would be negligible. I'm quite sure the axle-wheel relationship would provide most of the retardation.

[mx_tifoso]

...between the tyre and the road surface!

Which is what should be the only consideration here.

And they do seem to contradict each other, but seemingly this is the big push now in both road and race applications. A quick google search yeilded a good start:
http://ask.metafilter.com/128129/How-do ... resistance

[amouzouris]

i actually watched the michelin mega-factories documentary and they said that they are trying to reduce the rolling resistance between the tire and the road! they claim that it is quite a significant one!

[amouzouris]

...between the tyre and the road surface!

Which is what should be the only consideration here.

And they do seem to contradict each other, but seemingly this is the big push now in both road and race applications. A quick google search yeilded a good start:
http://ask.metafilter.com/128129/How-do ... resistance

thats very good! thank you mx!

[raymondu999]

Ditto. Thank you mx! I'd vote you up - but I haven't got rep

[xpensive]

The rolling resistance of a tyre is pretty much an anaolgy to a roller-bearing, xcept for the viscous losses unless it's raining of corse,
where the loss is very much in the hysteresis inside the tyre material itself. This phenomena takes place as the rubber and chord is continously deformed and re-deformed, as a certain amount of energy is lost in each sequence. Compare with a coil-spring being heated up when compressed and relaxed at a high frequency, like a valve-spring, that's "hysteresis".

Wiki is your friend, scroll down to "Elastic hysteresis"; http://en.wikipedia.org/wiki/Hysteresis

But in addition to that, there are all sorts of micro-movements and slippage, and as a consequence friction, between rubber and road.

[mx_tifoso]

Xpensive, how does that tie into the relationship with grip?

[xpensive]

Xpensive, how does that tie into the relationship with grip?

Point being that rolling resistance has little to do with the friction between rubber and road.

[amouzouris]

i understand what elastic hysteresis is...
it can easily be explained by this graph:

the curve on the top is the curve produced when the material is stretched which is described by the force applied vs the extension of the material...the curve below is the curve produced when the material is unloaded...and since force (N) x distance(m) = work done (J) the area of the graph between the 2 curves is the energy dissipated as heat when the material returns to its original shape... this would have to do with degradation... so it is related to grip levels but not related directly with my question!

EDIT: so as the tyre is loaded and unloaded it loses energy and it degrades...

[raymondu999]

Cheers Z - that helped a bunch (the graph)

[mx_tifoso]

Changing the rolling resistance characteristics will not have a significant impact on grip? For some reason I doubt it.

[amouzouris]

Changing the rolling resistance characteristics will have not have a significant impact on grip? For some reason I doubt it.

i agree...generally tyres are a very hard thing to engineer...if you try to improve one aspect it is going to have a negative impact on the other aspects of the tyre's characteristics...but in this case because of the use of different materials to improve rolling resistance the trade of might not be that big of a deal