Other Ideas on Tyres

Submitted: Thursday, May 12, 2005 at 19:28
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Remembering to when I studied the co-efficient of friction I would like to add a scientific angle to the new tyre buying debate. Here are some para phrased friciton rules which I hope some people here have real life experiance with proving they are true.

1. If the weight of the car does not change, the width of the tyre (excpet in mud and other heavy off road terrain) is irrelevant to grip. (water on the road can cause a car to aqua plane with wide tyres but this effect is a seperate issue when speaking of friction.)

2. The Type of rubber used will change the type of grip levels from tyres.

3. Therefore F1 tyres are not wide to add grip levels, because even a skinny tyre will give the same grip. They are wide to give more wear time and less tyre changing.

4. Completly bald tyres are better in the dry (onroad) than brand new tyres.

Q: Does anyone think that wide tyres get more k's? because from this point of view, the only advantage to wider tyres is a longer wear time, there is no theoretical advantage in grip etc...

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Reply By: Rosco - Bris. - Thursday, May 12, 2005 at 19:34

Thursday, May 12, 2005 at 19:34
Cobber

You've lost me a tad on the width aspect. Seems to me friction is entirely dependent upon contact area. Width or length ?? So what, you will still end up with a relatively small contact area. As friction is directly proportional to contact area it matters not one wit whether it's wider or longer. Having said that I have to say I'm not a great believer in the fat tyre syndrome ... ;-))

Cheers
AnswerID: 111047

Reply By: Utemad - Thursday, May 12, 2005 at 19:43

Thursday, May 12, 2005 at 19:43
What are you talking about? I thought people only got wider tyres because they look cool LOL.

I had 205/75 16s and got 40k out of each set. Then I got 70k out of 225/75 16 and they still have about 10-20k in them I reckon. Now swapped to 31x10.5.

The 225s were BFG KOs and the 205s where Bridgstone A/Ts. Not sure why the difference in kms but maybe the extra 20mm width is part of it plus they are a little bit taller.
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Reply By: F4Phantom - Thursday, May 12, 2005 at 19:54

Thursday, May 12, 2005 at 19:54
A small clarification, as you increase the surface area of the tyre, you also decrease the load on any give part of the contact area, if you do the maths you will find as the load per unit area decreases and the area increases, your new grip level is the same, this is provided the weight on the tyre does not change. If you increase the weight of the vehicle the grip level increases. Remember all this is actually theory based on lab experiments. To prove it yourself, get a block of timber and a spring Newton metre, drag the block on a small surface area size and measure the newtons, then drag it on a large surface area, the newtons should be the same to pull the block irrelivent of the surface area. Transform this test into tyres and your wide tyres dont give better grip, but much better wear.
AnswerID: 111054

Reply By: Bob of KAOS - Thursday, May 12, 2005 at 20:02

Thursday, May 12, 2005 at 20:02
Wide tyres: with twice the area of road swept by inflated rubber the chance of puncture doubles.
AnswerID: 111056

Reply By: Exploder - Thursday, May 12, 2005 at 20:07

Thursday, May 12, 2005 at 20:07
Theory and out in the field are to different thing’s.

1.Therefore F1 tyres are not wide to add grip levels, because even a skinny tyre will give the same grip. They are wide to give more wear time and less tyre changing.=

NO, NO, NO. Forget the theory. The more rubber you have touching the ground the higher the grip. Put a set of 175”s on a 260KW XR8 and see how much traction you get off the mark and around corners. If skinny’s gave the same grip the F1's would use them think of the extra weight and drag caused buy wide tyres

4. Completely bald tyres are better in the dry (on road) than brand new tyres.= Yes but only if the tyre is warm and the road is clean ( No sand, water) otherwise grip is Shi*

2. The Type of rubber used will change the type of grip levels from tyres.= Yes hard/ soft compound also silica.

Just my figuring

AnswerID: 111060

Follow Up By: F4Phantom - Thursday, May 12, 2005 at 20:13

Thursday, May 12, 2005 at 20:13
my prob here is that I love science, but i agree with this cause i have seen it myself.

Put a set of 175”s on a 260KW XR8 and see how much traction you get off the mark and around corners. If skinny’s gave the same grip the F1's would use them think of the extra weight and drag caused buy wide tyres

This leaves one more quesiton from the lab to real life to be disputed - tyre wear - i would still like to think wider ones wear better.
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Follow Up By: Member - Jeff M (WA) - Friday, May 13, 2005 at 18:44

Friday, May 13, 2005 at 18:44
I'm sure truckster will have some comment on this. What would you prefer on the back of your high powred sports bike? A skinny tyre or a wide tyre?

BZZZZ!

That's correct, a wide tyre is the answer!

Why?

Who care's, but you wouldn't catch me riding a fireblade 900 with a CB250 tyre on it. EVER!
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Reply By: F4Phantom - Thursday, May 12, 2005 at 20:17

Thursday, May 12, 2005 at 20:17
and another thing, the reason wide tyres SEEM to grip better is because of some other factor not included in this discussion, because we dont really know what we are on about, i bet the co-efficient of friction is exactly like i say it (was taught it), it's just much more complex in real life.
AnswerID: 111067

Follow Up By: Scubaroo - Thursday, May 12, 2005 at 22:01

Thursday, May 12, 2005 at 22:01
Ya reckon torque might have something to do with it? The engine is applying force to the tyres as well, not just vehicle weight.
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Reply By: ianmc - Thursday, May 12, 2005 at 21:36

Thursday, May 12, 2005 at 21:36
Proven it several times that 30x9.5 tyres on my ute give much improved steering response & cornering compared to 205X16s. Also last a lot longer.
Wide tyres may increase aquaplaning risk depending on treads ability to shed water.Dont see the super cars changing to skinnies in the wet, just softer compounds.
Found that wider tyres certainly increase fuel consumption to a noticeable degree even with same rolling diameter.
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Reply By: robak (QLD) - Friday, May 13, 2005 at 10:08

Friday, May 13, 2005 at 10:08
F4Phantom,

You've raised an interesting point. I think you're missing some part of the equation. Perhaps this is a question for link Dr Karl. I thin k he is on the air right now.

R.
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Reply By: Member - Hugh (WA) - Friday, May 13, 2005 at 15:42

Friday, May 13, 2005 at 15:42
Hi F4Phantom,

A pilot by chance? I like the name.

To expand upon the science, there is rolling friction and sliding friction. With respect to rolling friction, you also need to factor in torque and rolling diameter. Rolling friction is the ratio of torque applied at the centre of a wheel to the load on the wheel, as required to roll the wheel at a steady speed. Assuming a vehicle at steady speed, then your comments re weight apply, however not so for transient torque as in vehicle acceleration.

F1 cars have heaps of torque, as do XR8s and other cars discussed above. We've probably all tried it too in our younger days - put on a set of small OD skinny tyres and burn-outs are easy. Performance cars have wide tyres so that the torque can be transmitted into traction without wheel spin, hence improving acceleration performance.

Hope this adds another dimension to the puzzle.

Hugh

AnswerID: 111191

Follow Up By: robak (QLD) - Friday, May 13, 2005 at 17:02

Friday, May 13, 2005 at 17:02
So.... F4phantom theory would only be correct if in your car you locked your wheels and screeched to a halt. sliding friction? Then it wouldn't matter if you've got fat or skinny tyres?

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Follow Up By: F4Phantom - Friday, May 13, 2005 at 17:30

Friday, May 13, 2005 at 17:30
I wish i were a pilot, i am not just yet. The F4 is one of the best tho. Anyway I understand the difference between sliding and static friction. Sliding friction (when your wheels are in a skid) is less than Static friction (when you are driving at any speed). What you are saying is that under acceleration or deceleration a larger surface area provides more friction. I dont see how this makes any sense though, because the only difference acceleration could make is an additional force on the wheel, trying to induce sliding friction. This means the same law applies, the surface area of a wide tyre is larger, the load on the surface area is increased due to some change in front to rear weight proportions when the suspension allows movement. But all proportions are still the same irrevelant of tyre width - therefore surface area. The co-efficient of friction is constant for a certain material. With the XR6 example, the coefficient of friction for the tyre, wether large or small surface area is the same. You can only have one of the following two situations.

1. Large surface area where the total friction amounts to the nominal figure 100, each surface area unit is 10, and a total of 10 surface area units.

2. Small surface area. Total friction amounts to 100. Each surface area unit is 20, and there are only 5 surface area units.

This means i can only pin point the XR6 wider tyre example where it skidds less under acceleration with the wider tyres to the fact that it's because the tyres are a better more sticky rubber compund with a different co-efficient of friction value. perhaps a surface area unit would be 20 for a total of 200.
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Follow Up By: Member - Jeff M (WA) - Friday, May 13, 2005 at 18:50

Friday, May 13, 2005 at 18:50
Why is it then that when I ride my mountain bike with big chucky wide tyres on it it's majorly hard to do 40km/hr but on my mates racer with skinny tyres it's a peice of bleep ? Gearing is the same, wheel size is the same, only real difference is the width of the tyre...
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Follow Up By: Exploder - Friday, May 13, 2005 at 21:27

Friday, May 13, 2005 at 21:27
Arr HA, now F4 you been reading conceptual Physics (Ninth edition) haven’t you.) (There is a good photo of a BFG all Terrane)

I think we are missing a important peace of the puzzle hear and I can’t remember enough physics to comment accurately, Wider tyres have to give you more traction due to surface area contacting the road!!

I spoke to a friend who was a bit of a physics buff (a bit rusty now thou) and he agrees a wider tyre will give better traction than a skinny tyre, In terms of best traction a low profile wide tyre is the best.

P.S My favourite military aircraft it the Lockheed S-R 71 Black bird

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Follow Up By: F4Phantom - Saturday, May 14, 2005 at 17:30

Saturday, May 14, 2005 at 17:30
I hear you, i am not trying to make a nusance of myself but i do like logical answers. Jeff M the reason your mountain bike tyres are slower then racers would be because of wind resistance and rolling resistance not because of the static friction on the ground. Over 25km/h wind resistance becomes a massive problem. Also racers have a lot less rolling resistance builty into every part and component of the bike.
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Reply By: TomV - Saturday, May 14, 2005 at 07:06

Saturday, May 14, 2005 at 07:06
F4Phantom. The answer is that the sliding resistance is not just due to friction. There is also a significant amount of mechanical interlock between the surfaces. This is type of keying effect, and does increase with surface area. It is dependent on surface roughness and shape, and not coefficient of friction. There is a complex interaction between the two surfaces in real life. Your analysis is correct for perfectly flat surfaces, which of course roads are not. Velcro is an extreme example of the effect that I am talking about. More surface area, more grip, even with no contact pressure. regards Tom
AnswerID: 111249

Follow Up By: F4Phantom - Saturday, May 14, 2005 at 17:24

Saturday, May 14, 2005 at 17:24
NOW THAT, makes a bit of sense! I actually thought that the coefficient of friction IS the mechanical interlocking on a very small scale, some areas lots of it, some areas not much but over all an even effect (value) for a given material - except the velcro thing means that on a much larger scale its all surface area and weight does not make a difference at all. But then we are not actually talking about velco so i dont think this is the same effect.
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Reply By: Pezza - Saturday, May 14, 2005 at 23:05

Saturday, May 14, 2005 at 23:05
Hi F4 phantom,

I don't know jack about the co-effient of friction, but if what you are saying is true then the drag racing guys like Vic Bray should be able to do the same et's with 4inch skinny's on the rear!! Somehow I can't see that happening.

Avagoodn
Pezza
AnswerID: 111298

Follow Up By: robak (QLD) - Monday, May 16, 2005 at 14:15

Monday, May 16, 2005 at 14:15
Just to summerise

The "grip" of the tyre to the road is the same on both fat and skinny tyres - but the forces within the tyre are smaller on a fat tyre and greater on a a skinny tyre. So a skinny tyre breaks up sooner and makes your wheels spin.

R.
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Follow Up By: robak (QLD) - Monday, May 16, 2005 at 14:17

Monday, May 16, 2005 at 14:17
oh bugger - replied to the wrong one

Ignore that.

R.
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Reply By: robak (QLD) - Monday, May 16, 2005 at 10:41

Monday, May 16, 2005 at 10:41
F4phantom

I've been thinking about this puzzle over the weekend and I think I may have a piece of the puzzle. The interlocking of the two surfaces I think is also on the right path therefore the softer the tyre the more grip you get.

I think it may actually have something to do with the wear of the tyre. If you can imagine that your tyre is covered with small spikes that dig into the ground they drive on. Like on running shoes. If you had about 10 spikes in contact with the ground at any one time the total torque of the rotating wheel would be evenly spread across those ten spikes in pushing the car foraward ( or sideway for some). If you increase the torque on the wheel, and therefore on the spikes at a certain point they will start breaking off as the force becomes too great.

Now, if you double the width of your tyre, you double the amount of spikes to 20 and half the pressure on each individual one. Therefore you could double the torque before they broke. It might be the same thing with rubber on asphalt. The grip is not so much about the coeficient of friction between the tyre and the road, but about tyre wear. At a cetain amount of torque the tyre will begin to loose a small area that is in contact with the road. That's why wider tyres last longer they can withstand greater forces.

R.
AnswerID: 111420

Follow Up By: F4Phantom - Monday, May 16, 2005 at 11:20

Monday, May 16, 2005 at 11:20
I recon you are making a lot of sense here. What you are saying is when you put the tyre and asphalt under a microscope, you see tiny spikes protruding out and locking into the grooves in the asphalt. I agree with you - however is this not the co-efficient? If you get any two materials and slide them together, measure the force and you get a figure, this is it. So that means apart from what is going on at the molecular or slightly larger level, in practice you are actually sliding the two surfaces, and recieveing a figure. Therefore not matter if the tyre has parts breaking off, or not breaking off the figure from practise is a co-efficient. So if there is less weight on each surface unit, but more surface in contact, - mate i will stop here i need to think about this a bit more + i will try to get through to Dr Karl on thursday morning at 10:00am in Melbourne. I will ask him, all i know is that i have done the experiment and it does work, but in real life with tyres it goes against the experiment. And i am out of ideas. Tune in for an answer.
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Follow Up By: robak (QLD) - Monday, May 16, 2005 at 14:07

Monday, May 16, 2005 at 14:07
I don't really remember back to high school physics but I don't think you should sacrifice a material in the coeficient of friction.

Like writing with chalk on a blackboard. The friction between the chalk and the board is greater then the force holding the chalk together - so it crumbles.

If the tyre is wearing down, I think it means that the friction exerted on the tyre/road is greater then what the actual tyre rubber is able to withstand and therefore crumbles way. So you spin or slide your tyres not because of loss of grip but because of the crumbling away of your tyres.

Now - that would explain why fat tyre last much longer. A tyre of double width will not only last double the distance but infact much much longer. The forces indside will be halfed so it will very rarely reach the point where the tyre begins to crumble away.

Something to think about anyway.

R.
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Follow Up By: robak (QLD) - Monday, May 16, 2005 at 14:15

Monday, May 16, 2005 at 14:15
Just to summerise

The "grip" of the tyre to the road is the same on both fat and skinny tyres - but the forces within the tyre are smaller on a fat tyre and greater on a a skinny tyre. So a skinny tyre breaks up sooner and makes your wheels spin.

R
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Reply By: Member - Ross H (QLD) - Monday, May 16, 2005 at 14:27

Monday, May 16, 2005 at 14:27
I think you guys need to get out a bit more

regards ross
AnswerID: 111450

Follow Up By: Exploder - Monday, May 16, 2005 at 21:36

Monday, May 16, 2005 at 21:36
Good point Ross

Welcome to the exciting world of 4Wding

F4 put the physics book down tell the wife/girlfriend that you have to go and do some field experiments in the 4by in the name of science. That should keep the where the hell are you going questions to a minimum
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Follow Up By: F4Phantom - Monday, May 16, 2005 at 23:17

Monday, May 16, 2005 at 23:17
Hey Robak, again this chaulk thing makes a lot of sense, so basicly a tyre with MORE material will take longer to wear given the same set of conditions, becuase there is more material to wear down and under less stress. This is sensible. I am still going to try to get onto Karl tho, he may have a few answers, plus all the smarties who go on his board to help answer the questions we have. Also Exploder and Ross, i agree, there is nothing like the real thing (in the name of science) and i regulary put real dents in my 4x4 in the real world. My wife dosent mind me leaving her for a weekend but refuses to accompany me, she hates the smell of diesel and dirt in the morning.
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Reply By: Member - Hugh (WA) - Monday, May 16, 2005 at 23:03

Monday, May 16, 2005 at 23:03
Hi F4,

Further to my reply above and your comments.

I think my comments re transient torque still apply i.e. if there is more torque than required for constant velocity then motion will occur and if that torque is high enough then slippage can occur. Also, static friction refers to force to get surfaces to move, sliding friction is force necessary to maintain slippage, whereas rolling friction is that generated by a surface rotating about another (theoretically no slip for perfect rolling).

Anyhow, I guess your original question was about rolling friction, which we agree is when there shouldn't be any sliding occuring. The comments re surface interaction are part of the picture (similar to surface finish in a cylinder, with bumps known as asperities). There is also the effect of tyre deformation, influenced by tyre profile, construction, pressure, etc. I found the attached link that may give you some more points to continue your understanding.

physics - rolling friction

I hope this helps,
Hugh
AnswerID: 111552

Reply By: Member - Hugh (WA) - Monday, May 16, 2005 at 23:10

Monday, May 16, 2005 at 23:10
Another link..........

rolling friction

Regards,
Hugh
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Follow Up By: F4Phantom - Monday, May 16, 2005 at 23:26

Monday, May 16, 2005 at 23:26
cool, now we can all go out and dazzle people with our "higher" undertsnading of tyres and friction and a little thing called co-efficient. When (and they surley will) they ask further questions as to our knowledge of such things we will inevitably give a full and complete surmon and an account of the history of tyres wearing down, wide and narrow and all manner of compunds. This will illuminate their minds bring peace to their and their family's lives. I hope this makes you all feel good about our important discussion - not a waste of time, but a time to plant seeds, a time for the future, for surley, children are our future.
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