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Old 10th May 2013, 07:28   #31
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Default Re: Who thinks wider tyres mean more tyre is in contact with the road?

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Originally Posted by FlatOut View Post
So I remembered my school and university physics equations. Pressure=Force/Area or rearranged to Area=Pressure/Force. Well the downwards force on the tyres is the vehicle's weight, the pressure in the tyres only alters with temperature since it's a trapped gas in a fixed volume.

From this it becomes clear that the amount of area of tyre touching the road will be constant if the car's weight and tyre pressures remain the same. Oh.
Isn't the "pressure" in the equation P=F/A different from air "pressure in the tyres" ? I'd think that the P in P=F/A stands for the pressure being exerted on the surface whereas air pressure in the tyre is the pressure being exerted by the air inside the tyre ON the tyre?

I may be wrong though...
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Old 10th May 2013, 08:36   #32
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Default Re: Who thinks wider tyres mean more tyre is in contact with the road?

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Originally Posted by FlatOut View Post
So I remembered my school and university physics equations. Pressure=Force/Area or rearranged to Area=Pressure/Force. Well the downwards force on the tyres is the vehicle's weight, the pressure in the tyres only alters with temperature since it's a trapped gas in a fixed volume.
Pressure is Force per unit Area. So, Area of contact will be = Force/ Pressure.

A narrow tyre will have a contact patch which is rectangular in shape. And as the width of the tyre goes up, it becomes squarer. And with varying load and camber, the square or over square shape can have less area of contact with the road below.

All this will again change when we introduce corners though. The square will have an advantage over the rectangle in that case.
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Old 10th May 2013, 08:44   #33
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Default Re: Who thinks wider tyres mean more tyre is in contact with the road?

Nice thread! Thanks for sharing.



What I understand is that in theory the contact patch of a narrow tyre and wide tyre remains the same if all other variables (weight pushing down on the tyre, air pressure, road surface etc...) are constant. But since the contact patch of the narrow tyre is long and narrow the sidewall has to flex more to get the contact patch on the road. As a result the deformation with a narrow tyre is more than the wider tyre. Deformation generates heat which is not so good for the rubber. Since wider tyres don't generate as much heat, it allows manufacturers to make them with softer rubber compounds which are more grippy.

So basically the higher amount of grip generated by wide tyres has more to do with better rubber compounds than the width itself. Also lower side profiles come into play when we talk of cornering ability.
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Old 10th May 2013, 09:06   #34
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Default Re: Who thinks wider tyres mean more tyre is in contact with the road?

Its only when you take corners you talk about understeer or oversteer, its one of the effects of tyres losing the contact patch on the tarmac because of the lateral forces (http://en.wikipedia.org/wiki/Cornering_force). The lateral forces push the contact patch of the tyre.In a narrow section of tyre, the inside wheel will lose contact with the road surface, you lose grip and you understeer. In a wider tyre, there is relatively more contact patch while taking a corner and the effect of understeer is controlled, you have the grip to take the corner fast.

I am not too familiar with the formulas in Physics, hence this crude explanation

read more here, http://www.f1technical.net/forum/vie...hp?f=6&t=12762

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Originally Posted by FlatOut View Post
A wider tyre means more rubber on the road. It's obvious, surely?
He might have been sipping his coffee too

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May I mention the design of car I was driving was first sold in 1934, and that the one in front was a Mercedes SLK, model year about 2002? You will now, of course, know I am quite mad!

Last edited by anachronix : 10th May 2013 at 09:14.
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Old 10th May 2013, 09:35   #35
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Default Re: Who thinks wider tyres mean more tyre is in contact with the road?

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Originally Posted by amitoj View Post
Isn't the "pressure" in the equation P=F/A different from air "pressure in the tyres" ? I'd think that the P in P=F/A stands for the pressure being exerted on the surface whereas air pressure in the tyre is the pressure being exerted by the air inside the tyre ON the tyre?

I may be wrong though...
You're indeed right! Tyre pressure is not related to the pressure on the road from the weight (Force) of car, wheels and tyres.

Also, through mathematically, A= F/P, Pressure is the dependent quantity here, i.e. Pressure is determined by Force acting on Unit area.

However, what the OP says about contact patch area is true. Since wider tyres have a wider contact patch that helps cornering and dry grip. Skinnier tyres have narrower patch, but longitudinally bigger, this gives better wet road grip.
Adding to that, one has to consider tyre tread. After all, its not the whole flat outer surface of the tyre which is in contact with the road - unless one has run the tyres bald beyond their useable life ;-)

Finally, tyre compound plays a huge role in grip as that affects the coefficient of friction etc.
So, the topic becomes multi-dimensional, not only 175mm vs 195mm!


Formula 1 teams are not mad to have those wide tyres :-) They do provide the grip required. And they have dry tyres for dry roads, slicks for wet conditions, and also intermediate tyres.

Last edited by lancer_rit : 10th May 2013 at 09:36.
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Old 10th May 2013, 09:56   #36
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Default Re: Who thinks wider tyres mean more tyre is in contact with the road?

By seat-of -the-pants-o-meter i definitely have felt positive difference in handling and grip after upgrading tyres in Gen 1 Scorpio to 295/50R15, Gen 1 Swift to 205/50R15, Figo to 185/65R14. But i felt no much difference after upgrading my M800 to 155/70R12 except the Michelin being more silent than stock MRF.

I have used the above vehicles extensively before and after tyre upsize & wider tyres definitely made higher speed cornering (public roads/not in track) less nervous. It must be because of wider contact patch.
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Old 10th May 2013, 11:02   #37
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Default Re: Who thinks wider tyres mean more tyre is in contact with the road?

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Originally Posted by FlatOut View Post
A wider tyre means more rubber on the road. It's obvious, surely?
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Originally Posted by condor View Post
There was this brilliant video (BBC ?) that showed the effects of width of tyre, and how much the car would under-steer / over-steer.
Flatout,

Could you please explain this video??
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Old 10th May 2013, 11:16   #38
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Default Re: Who thinks wider tyres mean more tyre is in contact with the road?

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Originally Posted by Skyline GT-R View Post
By seat-of -the-pants-o-meter i definitely have felt positive difference in handling and grip after upgrading tyres
I have myself upsized my Ikon tyres from 175 to 185. While the OE was Bridgestone, the replacements are Yoko A-drives. And there is a goood difference.
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Old 10th May 2013, 11:30   #39
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Default Re: Who thinks wider tyres mean more tyre is in contact with the road?

my understanding too was what Santoshbhat said.
in practical, I can feel the difference of wider tyre's grip esp in cornering.
(don't know, I might theoretically wrong)
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Old 10th May 2013, 19:05   #40
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Default Re: Who thinks wider tyres mean more tyre is in contact with the road?

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Originally Posted by dhanushs View Post
Flatout,
Could you please explain this video??
Unless you have a rear wheel drive and a limited slip diff you cant drift like that. And when you cant drift like that, there is no point going for narrower tyres.

But the logic is correct. Wider tyres = More contact = More sliding friction = Better Braking & Traction.

But once you reach the optimum level, upsizing further gives no significant benefit.
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Old 10th May 2013, 19:20   #41
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Default Re: Who thinks wider tyres mean more tyre is in contact with the road?

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... upsizing further gives no significant benefit.
Correct, Law of diminishing returns! Increased rolling resistance > lesser fuel efficiency > more fuel consumption.
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Old 10th May 2013, 20:04   #42
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Default Re: Who thinks wider tyres mean more tyre is in contact with the road?

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Originally Posted by FlatOut View Post
I did a little more crude experimentation as above and began to wonder if a wide tyre's contact was actually bigger. It looked as if it may not be. Must be my crude expermentation, I thought.
So I remembered my school and university physics equations. Pressure=Force/Area or rearranged to Area=Pressure/Force. Well the downwards force on the tyres is the vehicle's weight, the pressure in the tyres only alters with temperature since it's a trapped gas in a fixed volume.

From this it becomes clear that the amount of area of tyre touching the road will be constant if the car's weight and tyre pressures remain the same. Oh.
I think you meant to derive Area=Force/Pressure :P
Really topics such as this make for an interesting read, But people have got to stop quoting stuff from high-school Physics. Those books contain information from the Newtonian era. Have you not noticed that there are several more parameters one has to consider in the real world thus altering equations? On a winding surface, at high rolling speeds, with many resultant forces in other directions and considering the fact that each tyre in effect creates several small contact patches due to the type of tread, such an equation will simply not work.

Last edited by IshaanIan : 10th May 2013 at 20:10.
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Old 10th May 2013, 20:10   #43
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Default Re: Who thinks wider tyres mean more tyre is in contact with the road?

@Flatout, are you sure you are not mixing up area and weight ?

Wider vs narrower tyre = does contact area change ?
You are also saying Pressure = Force/Area

but where are you connecting the two sets of points ? The two sets of points are discussing different parameters.
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Old 11th May 2013, 01:49   #44
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Default Re: Who thinks wider tyres mean more tyre is in contact with the road?

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Originally Posted by dhanushs View Post
Flatout,

Could you please explain this video??
Explain how a 480hp car can go round a track with completely the wrong tyres on? Explain how it went so well? Explain the point the journalist was trying to get over?

Note he mentioned the tyre pressures were 60psi, so unless everything I have been saying is gibberish, the contact patches were way smaller than for the bigger tyres. I wonder how the car would have gone with the standard tyres at that pressure? Probably better than the tiny ones becuase they are not tyres made for occasional, emergency use with everything that implies, but I doubt the handling would have been anywhere near as good as at 30psi, or whatever they were.

I think Harris was quietly trying to suggest that many wide tyres are ideal for tracks and race days but not for everyday on the road. He started out by saying the car appeared under-tyred (with the originals on), [supposedly] compared with similar output cars. Then showed how well it went, even on a track.

By being ridiculous, he was trying to show that by going to extremes, you make a fool of yourself. Maybe some boy-racers wouldn't quite have the ability to see that they, with their cheap cars but lowered suspension and much wider (than standard) tyres, are doing exactly what Harris did, just the other way round.




Quote:
Originally Posted by Santoshbhat View Post
Nice thread! Thanks for sharing.

What I understand is that in theory the contact patch of a narrow tyre and wide tyre remains the same if all other variables (weight pushing down on the tyre, air pressure, road surface etc...) are constant. But since the contact patch of the narrow tyre is long and narrow the sidewall has to flex more to get the contact patch on the road. As a result the deformation with a narrow tyre is more than the wider tyre. Deformation generates heat which is not so good for the rubber. Since wider tyres don't generate as much heat, it allows manufacturers to make them with softer rubber compounds which are more grippy.

So basically the higher amount of grip generated by wide tyres has more to do with better rubber compounds than the width itself. Also lower side profiles come into play when we talk of cornering ability.

I think that what you, Santoshbhat, wrote encapsulated in a beautifully succinct manner everything that is pertinent to this discussion. Spot on!!



Quote:
Originally Posted by oxyzen View Post
But the logic is correct. Wider tyres = More contact = More sliding friction = Better Braking & Traction.

But once you reach the optimum level, upsizing further gives no significant benefit.

Think what you will, but at least you mention that there is some optimum to be had. And a little either side of this will bring about different qualities in tyres. Wider, and there is more positive cornering, sharper response, more sudden break-away - and poorer steering and tracking, poorer wet grip, more susceptibility to losing all grip standing water, more air resistance, more rolling resistance, less directional stability. Narrower and there is the opposite of the above.



Quote:
Originally Posted by IshaanIan View Post
I think you meant to derive Area=Force/Pressure :P
Really topics such as this make for an interesting read, But people have got to stop quoting stuff from high-school Physics. Those books contain information from the Newtonian era. Have you not noticed that there are several more parameters one has to consider in the real world thus altering equations? On a winding surface, at high rolling speeds, with many resultant forces in other directions and considering the fact that each tyre in effect creates several small contact patches due to the type of tread, such an equation will simply not work.
I'm glad someone noticed my deliberate error :P !!

I do agree with you IshannIan, but you have to start somewhere with this sort of understanding - it's tricky enough to begin with without all the other parameters and subtle complexities. Not least mentioning suspension rates, suspension layouts and the dreaded anti-roll bar!



Quote:
Originally Posted by anachronix View Post
Its only when you take corners you talk about understeer or oversteer, its one of the effects of tyres losing the contact patch on the tarmac because of the lateral forces (http://en.wikipedia.org/wiki/Cornering_force). The lateral forces push the contact patch of the tyre.In a narrow section of tyre, the inside wheel will lose contact with the road surface, you lose grip and you understeer. In a wider tyre, there is relatively more contact patch while taking a corner and the effect of understeer is controlled, you have the grip to take the corner fast.

He might have been sipping his coffee too
Sipping his coffee - definitely not, the be-suited driver was trying hard to keep his car from mis-behaving.

Understeer and oversteer are most definitely not products of tyre width. They are to do with car balance and setup. Unless you are talking about driving around in a very tight circle on a slippery surface, at low speeds. Then the greater slip angle sections of a narrower tyre will work most obviously work against it.




I'm realy pleased so many of you have read this thread, and so many have bothered to reply. I find the whole idea that tyre width isn't somehow directly proportional to contact patch size fascinating - it would seem so obvious and was something I just asumed for years and years.

It was my ability to push on a fairly hard-driven modern, quick Mercedes on a winding road with high profile (82) 165 (albeit Michelin X) tyres. Sure, he didn't have the skills of a racing driver, but he wasn't fearful either. On a racetrack I wouldn't have had a chance of even keeping up, but how many of those do we use regularly?

Also see this article which describes how an ancient French peasant's car with tyres narrow enough to be almost invisible from head on managed to surprise quite a few people when it repeatedly outbraked and outhandled VW's biggest selling European car under controlled conditions. http://bit.ly/ZUvMjb

If tyre width had much to do with grip levels/tyre contact area, then neither what I experienced nor what is mentioned in the link above could have happened.
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Old 7th June 2013, 12:01   #45
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Default Re: Wide Tyres - More Contact? More Grip? or Overrated?

The question occurred to me some days ago, but I have been unable to convince myself either way, or find any relevant answers from books or the internet.

My question is:
With respect to temperature build-up in a tyre when travelling long distances at high speeds, is it the narrower tyre that will heat up more, or the wider tyre? Or is it that there can be an optimum width for the given weight (and engine power) of a vehicle, and anything narrower or wider generates more heat than the optimum?

Arguments for the narrower tyre heating up more:
At high speeds, especially when running over minor bumps and imperfections on the road, the narrower tyre is likely to lose some grip and 'skid' on the road surface while rotating. Also, the narrower tyre suffers heavier loading per unit area when braking or accelerating. Therefore, there is more heat buildup.

Arguments for the wider tyre heating up more:
Primarily, a wider tyre has more rolling resistance - more the resistance, more the heat generated. Can we say... More grip = more heat?

Look forward to your opinions.
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