Low rolling resistance, high grip.. How??????
Discussion
I know nothing about tyres, but given that nobody's responded yet I'm going to have a guess that rolling resistance is a subtley different thing to grip. For a start, lateral grip is very different to a tyre rolling along its intended longitudinal axis, but even longitudinal grip is different if you think about it - the sheer properties of the tyre for instance are relevant to it's coefficient of friction, but not involved in rolling resistance.
quick blast at explanation - I'm far from expert though
when a tyre rolls, the surface in contact with the road sticks to it a little - how much it can stick is how much grip you have. The carcass of the tyre stretches like a rubber band to accomodate this - the lateral stretching when cornering is referred to as the slip angle. That stretching takes energy, and most (probably all) of that energy is lost, this is AFAIK the main source of rolling resistance. So a tyre that stretches less, takes less energy to stretch, or returns more of its energy into rotation (if that's possible), will have lower rolling resistance for the same grip. So no, they're not incompatible, but they tend to be - in the same way that power and economy are not strictly incompatible, but often are.
when a tyre rolls, the surface in contact with the road sticks to it a little - how much it can stick is how much grip you have. The carcass of the tyre stretches like a rubber band to accomodate this - the lateral stretching when cornering is referred to as the slip angle. That stretching takes energy, and most (probably all) of that energy is lost, this is AFAIK the main source of rolling resistance. So a tyre that stretches less, takes less energy to stretch, or returns more of its energy into rotation (if that's possible), will have lower rolling resistance for the same grip. So no, they're not incompatible, but they tend to be - in the same way that power and economy are not strictly incompatible, but often are.
kambites said:
One is resistance to sliding, the other is resistance to rolling, I don't see why they would be directly related.
That's essentially what I meant in my post 
Bear in mind that car tyres shouldn't be thought of like a wooden wheel on the floor or a bicycle tyre - car tyres actually have a slip angle during cornering (and even in a straight line due to toe), and certainly when providing grip, so as you rightly say, a tyre that's gripping is actually sliding somewhat.I saw a demo on this yesterday involving 2 rubber balls, I'm going to be honest I was working on something at the time so didn't pay enough attention to tell you why, however:
1 ball was fairly hard, the other ball a bit softer and felt like a grippier compound.
The guy dropped the balls from a height. The harder of the two balls barely bounced at all, it absorbed the energy from the fall. The more elastic ball bounced.
The lesson was showing how the harder ball was absorbing energy into the compound, so the softer gripper ball had both a lower rolling resistance and more grip.
I tried to ask exactly the same question at the end of the demo, asking if a hard tyre would inherently be low rolling resistance but apparently it isn't that way. Unfortunately there was a language barrier and we were being moved on so I didn't get a conclusion.
1 ball was fairly hard, the other ball a bit softer and felt like a grippier compound.
The guy dropped the balls from a height. The harder of the two balls barely bounced at all, it absorbed the energy from the fall. The more elastic ball bounced.
The lesson was showing how the harder ball was absorbing energy into the compound, so the softer gripper ball had both a lower rolling resistance and more grip.
I tried to ask exactly the same question at the end of the demo, asking if a hard tyre would inherently be low rolling resistance but apparently it isn't that way. Unfortunately there was a language barrier and we were being moved on so I didn't get a conclusion.
OK.
Which has more rolling resistance - a wet road or a dry road? (I can think of arguments for both)
A wet road will have more 'lubrication' so to speak but then again, a wet road will also cause some resistance (think of driving through a puddle and the resultant 'pull' on the steering).
Which has more rolling resistance - a wet road or a dry road? (I can think of arguments for both)
A wet road will have more 'lubrication' so to speak but then again, a wet road will also cause some resistance (think of driving through a puddle and the resultant 'pull' on the steering).
doogz said:
Not really the same, is it.
In a rack and pinion, friction is pretty much irrelevant, compared to a tyre on a piece of tarmac.
We don't drive about on star shaped tyres on zig zag roads.
As I understand it, that's not far off what friction is at a molecular level. In a rack and pinion, friction is pretty much irrelevant, compared to a tyre on a piece of tarmac.
We don't drive about on star shaped tyres on zig zag roads.
Anyway, I don't really understand why people think the two should be related at all? grip is due to coefficient of friction, rolling resistance (in a straight line) is due to deformation causing energy to be lost as heat.
Says the person who says "I couldn't be f
ked". If you couldn't be bothered, why start in to the discussion in the first place? Especially when you haven't grasped the analogy in the post you're responding to?
Anyway, have a good weekend, must be nice slacking off before 3 on a Friday.
ked". If you couldn't be bothered, why start in to the discussion in the first place? Especially when you haven't grasped the analogy in the post you're responding to?Anyway, have a good weekend, must be nice slacking off before 3 on a Friday.
More silica in the tyre compound is the main way they are providing both, the disadvantage is cost to the tyre production.
Dont confuse friction with resistance they are not absolutely directly related. The rolling resistance of a tyre has a number of factors, the stiffeness of the steel radial belts is one of the main contributors though.
Of coure by limiting deformation you effect the hysteria of the tyres which by definition is required for a squishy thing to grip something rough and bumpy like a road surface hence the trade is difficult.
Dont confuse friction with resistance they are not absolutely directly related. The rolling resistance of a tyre has a number of factors, the stiffeness of the steel radial belts is one of the main contributors though.
Of coure by limiting deformation you effect the hysteria of the tyres which by definition is required for a squishy thing to grip something rough and bumpy like a road surface hence the trade is difficult.
Not many tyres get hysterical 
Streetrod said:
I think I'm more confused than when I posted the question, thats the joy of PH.
So in conclusion can we just put it down to Witch Craft?
Kambites explained it well in simple terms. Rolling resistance and grip are just different things. One is the resistance to a tyre rolling freely, and the other is resistance to a tyre dragging or sliding, to put it very simply. Obviously, (I presume! I'm no tyre expert) a tyre with any toe will be sliding as it rolls, but still - the rolling component is rolling resistance and the sliding component is sliding resistance and they remain different.So in conclusion can we just put it down to Witch Craft?
That's what I understand by this anyway - feel free to correct me!
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