Low Profile Tyres. Why?

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Horse
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Re: Low Profile Tyres. Why?

Postby Horse » Wed Apr 13, 2016 12:29 pm

akirk wrote: I have owned a number or range rovers and they were initially designed with tall skinny wheels / tyres to cut through mud and find grip, now they look like racing cars...


I think you'd need to explain 'driving in mud' to the majority of recent RR owners ;)
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Re: Low Profile Tyres. Why?

Postby Gareth » Wed Apr 13, 2016 12:44 pm

Silk wrote:is it inherently unsafe to have, for example, a 200BHP hot hatch on 16" wheels?

FWIW the Sierra Cosworth was shod with 205/50R15, the Alfa 75 Cloverleaf came with 195/60R14 and, I think, the Ford Capri 2.8i had 205/60R13.
Last edited by Gareth on Wed Apr 13, 2016 1:02 pm, edited 1 time in total.
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devonutopia
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Re: Low Profile Tyres. Why?

Postby devonutopia » Wed Apr 13, 2016 12:52 pm

Silk wrote:
StressedDave wrote:Ignoring the marketing reasons (which probably add to the 'how many inches' have I got argument, the main reason for Low profile tyres is that higher profile tyres won't work within the necessary parameters today.


I'm trying to follow the science as best I can, but what I'd really like to know is, are there any real advantages in having lower profile tyres on a road car and is it inherently unsafe to have, for example, a 200BHP hot hatch on 16" wheels?


I would love to see a test with a car like a new Renault Clio 200 on same track, same driver, same weather conditions, same rubber brand, but with laps on say 205/55 R15 and then on 205/40 R17 (and same weight of wheel/tyre combination to rule out unsprung weight argument), and see if any noteable difference in times - I would expect more feedback would come from the driver and how the car feels rather than necessarily in the lap times?

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Re: Low Profile Tyres. Why?

Postby Gareth » Wed Apr 13, 2016 1:25 pm

devonutopia wrote:I would love to see a test with a car like a new Renault Clio 200 on same track, same driver, same weather conditions, same rubber brand, but with laps on say 205/55 R15 and then on 205/40 R17 (and same weight of wheel/tyre combination to rule out unsprung weight argument), and see if any noteable difference in times

Not what you're asking, but Car and Driver magazine conducted a test with different wheel/tyre sizes on a Golf.
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sussex2
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Re: Low Profile Tyres. Why?

Postby sussex2 » Wed Apr 13, 2016 3:13 pm

There may well be some technical issues but I feel certain that much of it is to do with marketing and the bling factor. The size of engines seems to vary as well, according to the market and it seems we Brits do like a bit of flash. It is, perhaps, also something to do with the UK having a very large fleet market and the percieved status that goes with it.
The 2.0 litre version of the latest MX5 is, I believe, only for U.K. and U.S. consumption; other markets make do with the (in my opinion preferable) 1.5 around which the car was designed.
I've driven both and the smaller engine/wheel version is to my mind by far the better of the two.

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Re: Low Profile Tyres. Why?

Postby Horse » Wed Apr 13, 2016 4:16 pm

devonutopia wrote:
Silk wrote:
StressedDave wrote:Ignoring the marketing reasons (which probably add to the 'how many inches' have I got argument, the main reason for Low profile tyres is that higher profile tyres won't work within the necessary parameters today.


I'm trying to follow the science as best I can, but what I'd really like to know is, are there any real advantages in having lower profile tyres on a road car and is it inherently unsafe to have, for example, a 200BHP hot hatch on 16" wheels?


I would love to see a test with a car like a new Renault Clio 200 on same track, same driver, same weather conditions, same rubber brand, but with laps on say 205/55 R15 and then on 205/40 R17 (and same weight of wheel/tyre combination to rule out unsprung weight argument), and see if any noteable difference in times - I would expect more feedback would come from the driver and how the car feels rather than necessarily in the lap times?


Top Gear did an episode where they tried to get a Renault . . . err . . . thing (the two-door executive saloon jobbie, 'Avatar', 'Avantine', 'Avaniceday' or summat) to go faster around their track.

IIRC most of what they did slowed it down, including 'better' wheels and tyres.
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michael769
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Re: Low Profile Tyres. Why?

Postby michael769 » Thu Apr 14, 2016 8:02 am

Gareth wrote:
michael769 wrote:Modern alloys mean that the rims can be much lighter than the tyres - hence you want bigger rims and smaller tyres.

I'm wondering why you think this - have you weighed any wheels and tyres to check?



Have you weighed racing wheels? :-) On a track racing car you don't really need your rims to survive 100,000+ miles of potholed roads so you have options that are not available to the manufacturers of rims intended for road use.

The composites and alloys used in racing wheels can have densities of 80% of that of tyre rubber (and I've heard of composites in the pipeline that can get down to 60%). Furthermore there are more opportunities on a wheel to reduce the weight further (thinner metal, narrower spokes etc) that you cannot do to tyres.

That is very different to what you will experience on a road going car - the most common alloys used are around twice a dense as tyre rubber, and the aforementioned need for them to survive on the public roads means you need considerably more material on them.

Road car rims are 80-90% cosmetic - they just need to look sporty - not be sporty.

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Re: Low Profile Tyres. Why?

Postby StressedDave » Thu Apr 14, 2016 9:03 am

Horse wrote:Top Gear did an episode where they tried to get a Renault . . . err . . . thing (the two-door executive saloon jobbie, 'Avatar', 'Avantine', 'Avaniceday' or summat) to go faster around their track.

IIRC most of what they did slowed it down, including 'better' wheels and tyres.

I think you mean the Renault AvenalaffthinkingthatarseonaroadcarwillsellmorethantenandthosetoblinddriversandJohnBarrowman.

The only way to get a better lap time with the same amount of power is stickier tyres and the suspension optimised for those stickier tyres.
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Re: Low Profile Tyres. Why?

Postby Gareth » Thu Apr 14, 2016 9:08 am

michael769 wrote:The composites and alloys used in racing wheels can have densities of 80% of that of tyre rubber

Density doesn't tell us enough to be useful; it might be that less dense alloys are less strong, so more material would be needed ...

I've found a website with some tyre weights ... according to this, a couple of Vredestein Quatrac 5 tyres that are close enough to be a reasonable comparison are:
  • 195/70TR14 weighs 7.76 kg
  • 195/65HR15 weighs 7.67 kg
According to a tyre calculator, the diameter of 15" tyre is 5 mm larger, (0.79%).

Just need the weights of two wheels now, (and then we have some statistically insignificant data).
Last edited by Gareth on Thu Apr 14, 2016 9:40 am, edited 1 time in total.
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Re: Low Profile Tyres. Why?

Postby Gareth » Thu Apr 14, 2016 9:12 am

StressedDave wrote:The only way to get a better lap time with the same amount of power is stickier tyres and the suspension optimised for those stickier tyres.

Not a lighter wheel/tyre combination?
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