Help settle an argument please

[Wayn0r]

yea, the physics of pressure has to be involved somewhere.

simple explanation is a smaller surface area exerts more pressure than a large surface area.

example: rally cars run wide tyres on tarmac so they get more grip, and thinner tyres on ice, with spikes to cut through the top layer and get to the grip. (obviously thinner tyres with spikes = exerting more pressure.

 

[Jonny69]

Dragsters have wide tall soft tyres so that on launch they rise and form a very long thin contact patch to launch the car off the start line.

Wrong way round. On launch they are squashed out really wide for loads of grip, then at speed they grow up really tall and narrow to reduce rolling friction and in effect work like another gear for top speed.

 

[Jonnycoupe]

If you are correct, why do dragsters have such large tyres?

Absorb shock loads better so they hook up.

Store elastic energy from initial load up and slowly release it like a coiled up spring.

They grow with speed effectivley lengthening the gears but without compromising the low speed acceleration.

 

[[huzeeee]]

It will deffinatley give more grip as more surface area means more grip, thus why f1 use as wider wheels as possible and ice skates are a sharp as possible. Also going on more surface area = no better grip then surley a slick provides no advantage over a treaded tyre? If his car is standard then he is a **** but if he has modified it to go faster (not with stipes) then fair enough.

 

[Entai]

It will deffinatley give more grip as more surface area means more grip, thus why f1 use as wider wheels as possible and ice skates are a sharp as possible. Also going on more surface area = no better grip then surley a slick provides no advantage over a treaded tyre? If his car is standard then he is a **** but if he has modified it to go faster (not with stipes) then fair enough.

F1 have big wide tyres to help them go round corners fast, wide tyres do not help in a straight line at all.
Look at Thrust 2 the wheels were only 6 inches wide on that and it did mach 1, but it would never go round a corner at any speed.

Again in a straight line you are perfectly correct a slick tyre does not offer any advantage at all over a treaded one, but in a corner it helps tremendously, that is why F1 now use treaded (read grooved) tyres so that the corner speeds are vastly reduced compared to what they would be if they were running true slick tyres.

 

[Bear]

It will deffinatley give more grip as more surface area means more grip, thus why f1 use as wider wheels as possible and ice skates are a sharp as possible. Also going on more surface area = no better grip then surley a slick provides no advantage over a treaded tyre?

If the wider tyres are of the same rolling radius as the standard ones then there is no more surface area, you just change the shape of the contact patch from a long thin one to a short wide one.

If he was to not care about rolling radius and went for a wide and high aspect ratio with soft sidewalls then yes you would get more grip.

 

[NicktheNorse]

F = mu * N

where N is the force normal to the contact patch, mu the coefficient of friction (static or dynamic) and F the retardation force. The area of the contact patch does not figure into it.

But it can't be that simple. The amount of grip has a lot more to do with the compound of the rubber and how much elastic deformation it is allowed to go through.

It's a good question, actually.

 

[robbiemc]

F1 have big wide tyres to help them go round corners fast, wide tyres do not help in a straight line at all.
Look at Thrust 2 the wheels were only 6 inches wide on that and it did mach 1, but it would never go round a corner at any speed.

But that has nothing to do with the original question though does it. Thrust 2 was designed for maximum top speed, not maximum acceleration from stand-still. Don't forget that Thrust 2 was powered by jet engines that were not driving through the wheels (such as in a car).

It's obviously an interesting question, but surely if wide tyres help a car with cornering speeds, then surely it's the same thing as pulling away from a stand-still i.e grip.

 

[Dogbreath]

If you look at it purely from a physics point of view, assuming perfect materials it shouldn't make any difference. A larger contact patch will be balanced out by the lower force per unit area, so frictional force should remain constant.

In practice materials such as car tyres and road surfaces don't behave in such a predictable and linear fashion. For a tyre, the coefficient of friction actually reduces as pressure (i.e. force per unit area) goes up, so a larger contact patch is better if it moves the tyre out of this non-linear region.

Probably the biggest effect is that when larger wheel are fitted, usually a more performance orientated tyre is fitted with them, which of course gives more grip.

 

[Ev0]

F1 have big wide tyres to help them go round corners fast, wide tyres do not help in a straight line at all.
Look at Thrust 2 the wheels were only 6 inches wide on that and it did mach 1, but it would never go round a corner at any speed.

But those wheels are being "pushed" not driven. When you pull off quickly and break traction you don't skid the rears do you? Nope they just roll along I'd have thought that would make a difference?

 

[InvaderGIR]

Simple way or sorting it.

Get an impartial third party to rip the poop out of it off a line with the current wheels, and then get them to do it again with the ones he wants to put on it.

InvG

 

[Entai]

But that has nothing to do with the original question though does it. Thrust 2 was designed for maximum top speed, not maximum acceleration from stand-still. Don't forget that Thrust 2 was powered by jet engines that were not driving through the wheels (such as in a car).

It's obviously an interesting question, but surely if wide tyres help a car with cornering speeds, then surely it's the same thing as pulling away from a stand-still i.e grip.

But those wheels are being "pushed" not driven. When you pull off quickly and break traction you don't skid the rears do you? Nope they just roll along I'd have thought that would make a difference?

Ok, Ok, maybe Thrust was the wrong example.

What I was trying to say is that wide tyres and more importantly slick tyres are on racing cars to help them go round corners fast, they do not help with straight line speed. The tyres are wide and slick to generate lateral grip not longitudinal. The benefits of grip (if there are any) are far outweighed by the negatives in regard to drag and rolling resistance.

In fact and I am sure NicktheNorse will help out here the huge wide rear tyres on an F1 are a hinderance to high speed because of the drag they impart to the vehicle. I would be fairly sure that if an F1 car was designed just to go in a straight line, then the tyres would not be as wide as they are now.

 

[robbiemc]

In fact and I am sure NicktheNorse will help out here the huge wide rear tyres on an F1 are a hinderance to high speed because of the drag they impart to the vehicle. I would be fairly sure that if an F1 car was designed just to go in a straight line, then the tyres would not be as wide as they are now.

I have no doubt that wide tyres have a detrimental affect on top speed, but going back to the original question; isn't it about getting grip from a standing start?

US muscle cars seem to be a good example of having huge rear tyres to channel massive torque to the road, these cars certainly weren't designed with going around corners quickly.
Surely if you put, say, 195 section tyres on one of these the wheels would just spin...surely!

 

[robbiemc]

Hmm, this thread certainly has got me interested.
I found an excellent discussion over at PH about this very subject.

When you fit wider tyres, what you're doing is making the contact patch wider and shorter for the same tyre pressure. This means you get a more abrupt breakaway but more grip right on the limit. The disadvantage is more expensive tyres, more tramlining and steering kickback, more wind and rolling resistance and noise, less grip in slippery conditions, a more abrupt breakaway to catch out the unwary driver and less warning through the steering about how close the tyres are to breaking away.

This probably explains why manufacturers tend to put wide tyres on high performance cars and narrower ones on ordinary family saloons.

Very interesting..more here

 

[thefullcollapse]

ah i was asked this in a maths lesson, i never found the answer

the tires do give more grip, though they dont have more friction, theres another factor involved

 

[Ev0]

Would it be something along the lines of spreading the force out over a larger area thus reducing the chance of losing friction? If that makes sense :/

 

[Jonny69]

F1 have big wide tyres to help them go round corners fast, wide tyres do not help in a straight line at all.
Look at Thrust 2 the wheels were only 6 inches wide on that and it did mach 1, but it would never go round a corner at any speed.

Again in a straight line you are perfectly correct a slick tyre does not offer any advantage at all over a treaded one, but in a corner it helps tremendously, that is why F1 now use treaded (read grooved) tyres so that the corner speeds are vastly reduced compared to what they would be if they were running true slick tyres.

Slicks do have an advantage in a straight line. Firstly more rubber on the road for the same width tyre and second no tread blocks to roll over so a slick will grip better in a straight line and in bends.

 

[Entai]

Slicks do have an advantage in a straight line. Firstly more rubber on the road for the same width tyre and second no tread blocks to roll over so a slick will grip better in a straight line and in bends.

As NicktheNorse said F=mu*N, the area of rubber in contact with the road plays no part in that equation.
So extra wide slick tyres makes no difference to the amount of friction(grip) compared to thin treaded tyres, when both are made from the same compound of rubber, and have the same constuction techniques employed, because the size of contact patch has no relation to the coefficient of friction between the two materials.

I think really there are way to many other variables involved here to get a straight yes or no answer, it would be great to have the resources to test it out properly, because I think many people woould be very surprised at the results.

 

[NicktheNorse]

As NicktheNorse said F=mu*N, the area of rubber in contact with the road plays no part in that equation.

That equation applies only to "normal" (whatever that may be) cases involving closed system forces. I don't think it can be applied to the case of the rubber contact patch, particularly because it is viscous and deforms.

I'll ask someone at work who might know more about it (I'll see if I can trap Pat Symonds in the cafeteria, he always loves babbling on about tyres!)

 

[comp builder]

Hi all, here is a good one for you, a guy at work, wants to get wider wheels and tyres so that at traffic light races he will get better traction, and a better launch, with less wheel spin.

I said, most likely that will not happen, if anything you will be worse off I said. As the friction is still the same between the tyres and the road surface, no matter how big the tyres.

My reasoning is, that surely the size of the surface area of a contact patch between tyre and road, has no bearing on the friction coefficient of that contact.
The friction coefficient is only determined by the types of material that the friction is occuring between, (tyre rubber and road tarmac) and to some extent the load applied to those materials.

So in this example, the contact patch is still between the same two materials, and if anything, the load on the contact patch will be less than he already has (he is changing from steelies to alloys as well, so lighter wheels), and getting wider tyres so the contact patch is larger spreading the load more. Therefore by my reckoning in a straight line he will possibly have less traction than before, but in cornering he will be much better off.

He still insits that bigger tyres equals more rubber on the road so it has to be more grip.

So who is right??

i thought bigger surface area= more grip


To answer someone else's question i THINK the drag racers have large back wheels and small front wheels is to give them better speed. I think it works like gear ratio's only with tyres lol

i race rc cars (cause im not old enough to drive, and they're fun) and i read that a smaller wheel gives more acceleration but a lower to speed and visa versa, wether it's true for full size cars i don't know.