Why is it that the higher the performance, the slimmer the profile of the tyre becomes? I’ve seen performance car magazine bemoan low profile tyres because they destroy the ride of the car. So why have them, I thought grip and traction would depend more on the width of the tyre and not necessarily the profile 
I’m definitely not a car-whiz, but I’m going to guess that a low-profile tire is going to suffer less side-to-side flexing during cornering.
Exactly. Less horizontal flex = better cornering response. The other side of the coin is less vertical flex = harsher ride.
Lower profile tyres help, but only to a point. They were probably talking about people who put extremely low profile tyres on their cars, which are usually only for looks and give a very harsh ride. That’s because they are at a high pressure and also there’s hardly any sidewall to cushion bumps.
To a point. One thing wanna-be racers don’t seem to understand is that making your ride as stiff as possible is not the way to get your car to go around corners faster – otherwise racing suspension would be really simple, and race car tires would not be full of air. The right amount of sidewall flex will keep your tires from losing contact with the ground over uneven pavement at high speeds.
Are low profile tyres lighter than regular design tyres?
I know that for bicycles, narrower tires (and higher pressures) give less rolling resistance, but harsher ride. I imagine it works the same for cars, though I don’t think rolling resistance is very important at sports car speeds.
When I bought my car it had 17" rims with low profile tyres. I didn’t think about it much when I test drove it and have discovered since that driving on good roads the tyres are fantastic, driving on any other roads is like driving on random piles of house bricks, and the tyres cost twice as much.
There has been much discussion on this on cycling boards. The consensus seems to be that this is not really the case - at least the narrower tire bit. People have posted lots of data and theoretical treatise which ‘prove’ (I could never be bothered to read through them all) that, all else being equal and especially for a given pressure, a wider tire has the lower rolling resistance. The reason why narrow tires are preferred is that they are both lighter and can usually be inflated to a higher pressure without blowing off the rim, thus negating the above point.
That’s my understanding as well. Another important reason for wanting narrow tires is that narrow tires are more aerodynamic. At higher speeds, air resistance is much larger than rolling resistance, so reduction in air resistance will offset any small increase in rolling resistance.
Low profile tires also weigh much less for a given width. Less weight, prduces less angular momentum to overcome on breaking and accelleration. They are also a way of getting larger rim diameter tires into the wheelwell of a car.
IMO, I’d never get them, unless I moved to the warmer climates. New England roads do not treat low profile tires, nor the rims they are mounted to very well.
-Butler
Perhaps, but in most cases the weight of the larger rim (assuming you want to have the same overall diameter) will more than make up for any weight savings from the tire (tyre). In addition with a bigger rim the heaviest part (the outside) is father away from the center, increasing angular momentum (if I am using the term correctly).
I heard that the rim is lighter paer volume than the rubber of the tyre. If the tyres considered are of the same diameter then it is only the inner part of the tyre (the part that touches the rim not the road that is further away from the axis of rotation in a low profile tyre than a normal tyre of same diameter. I don’t know tyres that well, and can’t find a decent cross section on the web, but I thought that inner side of the tyre is not solid rubber but just forms an airtyte seal with the rim and so is made of light aluminium rather than heavy rubber.
I am not sure if I under stand what you are trying to say but the outer part of a rim clearly has the most mass. Browsing rims on tire rack and comparing identical rims of the same width it looks like, on average, a one inch larger rim is one-two pounds heavier.
Looking at a tire it is pretty clear the majority of the weight is at the tread, loosing an inch or two of sidewall should not make a significant difference. I did some quick checking at tire rack of listed tire weights and they seem to prove my point.
Brigestone potenza s-03 225/55R16 27LB (Radius 12.9")
Brigestone Potenza S-03 225/45R18 27LB (Radius 13.0")
Goodyear Eagle GS-D3 225/55R16 25LB (radius 12.9")
Goodyear Eagle GS-D3 225/50R17 26LB (radius 12.9") ??
Goodyear Eagle GS-D3 225/40R18 24LB (radius 12.5", the one pound weight savings is proabably due to the smaller overall diameter a 45 series is not available.)
If you want to compare tires of the same outside diameter with different rims this site is great http://www.miata.net/garage/tirecalc.html.
That’s what I was missing :smack: of course the side wall isn’t going to contribute much to the weight or moment of inertia.
The answer to “Why have them” is the same as to why I’m in downtown Vancouver and there’s a full-length, crew cab lifted pickup in the parking lot. 'cause people driving them think they look cool.
Normally I live in Edmonton, and was sad to see that some people are outfitting their SUVs and pickups with them. An SUV with a two foot circle of chrome and an elastic band for tires just looks silly IMHO.