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Originally Posted by dhanushs |
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.
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Originally Posted by Santoshbhat 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!!
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Originally Posted by oxyzen 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.
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Originally Posted by IshaanIan 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!
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Originally Posted by anachronix 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.