[vina]

Originally Posted by SS-Traveller

Right. Now can we consider the difference in flexibility of a cross-ply tyre vs. a radial tyre?

So why does an off-roader come with 80-profile tyres and a sports car come with 20-profile tyres? OTOH, what is the profile of a F-1 car tyre, and why?

Regarding off-roaders:

I was going to write this later (with more info - and nobody had asked earlier about this). This is what I read on the internet:

off-roader often go in muddy/sandy/watery conditions - higher profile allows them to "dig" into the terrain. Also sidewalls do provide some traction is such terrains.

Flex causing understeer/oversteer is not that big a problem, but losing traction just because tyres can not flex can perhaps mean trouble - no-flex may induce tyre slipping in certain conditions resulting in complete loss of grip.




For a "sporty car" (the sales guy at Maruti told me Swift looks "sporty" - I asked him what he meant - I'm sure a lot of people who think some road cars look sporty will have the same answer as he did - none at all) looks are usually more important than anything else. I think that is a reason you already mentioned. But also, if my guess about flex resulting in understeer is correct - there you go.




Regarding F1 - I was going to search more thoroughly later, but this is one of the good articles I have found so far:

Tyre use in Formula One - F1technical.net


Some of the information is relevant on this thread too http://www.team-bhp.com/forum/techni...ml#post2441184

(I'll be posting there also)

Originally Posted by http://www.f1technical.net/articles/1

A dry-weather racing tyre in Formula One generally operates at an optimal temperature of around 100° C. In contrast, intermediate spec tyres are operate at between 40°C to 100°C, depending on the wetness of the track, while full wets approximate 30°C to 50°C. All heat that is created due to the tyre's friction with the surface should, in theory, be ideally distributed between the outside, the centre and the inside of the tyre tread (a bad distribution is often adapted to by changing camber). This temperature should also be identical from left to right, and from the front to the rear of the car. Too much heat at the front tyres will cause understeer while non-optimal temperatures in the rear tyres will result in oversteering.

[kpzen]

Originally Posted by SS-Traveller

Why is it that we don't see 100% (or even 90%) profile tyres today, but >30 years ago we didn't see low sidewall height at all?

Wouldn't a 100% profile make a square tire ?

Originally Posted by vina

can you elaborate on this one?

Originally Posted by SS-Traveller

So why does an off-roader come with 80-profile tyres and a sports car come with 20-profile tyres?

Off-road SUV tires have higher sidewalls
1. For extra reinforcement to absorb the vehicle's huge gross weight.
2. Highly stiff sidewall to absorb the shocks.
3. For High ground clearance.
4. To make it over loose sand, mud or rocks.

Originally Posted by SS-Traveller

OTOH, what is the profile of a F-1 car tyre, and why?

Front 270/55 R13
Rear 325/45 R13

Why ?
1. F1 regulations.
2. Less unsprung weight for better acceleration.
3. Suspension has very less travel so partly does the job of a suspension.

[vina]

Originally Posted by kpzen

...

Off-road SUV tires have higher sidewalls
1. For extra reinforcement to absorb the vehicle's huge gross weight.
2. Highly stiff sidewall to absorb the shocks.


...

1. -> if I "imagine" the sidewall to be cut up in sections (horizontal cuts) then you have several layers stacked vertically. Each section supports the weight of the one above - taller sidewall will have no advantage simply due to its size in terms of vertical force supported.

On lateral force, it can flex more - so I'm not clear either way - perhaps more flex allows more upward force on the sidewall (due to increased flex area) and hence more weight can be supported at the same pneumatic pressure. But I'm merely guessing can you please tell mehow it works, or point me to some material that has the answers?

2. -> Perhaps you meant "more compliant sidewall to absorb the shocks" rather than more stiff sidewall. Otherwise your comment doesn't make sense to me - how would a stiffer tyre absorb more shocks and also how would a taller sidewall be stiffer than a shorter sidewall (assuming thickness remains same) - can you please elaborate a little more.

[Chewbacca]

Originally Posted by vina

On lateral force, it can flex more ......
....Perhaps you meant "more compliant sidewall to absorb the shocks" rather than more stiff sidewall.

The flex or stiffness would depend on the ply rating and the cord type used (steel, nylon or fabric)

I pulled this from www.thediagrams.com and www.cdxetextbook.com", should help the discussion.

This particular tire is a four-ply/four-ply rating. Note width in relation to height, indicating a very low profile design.

[thoma]

Originally Posted by Vid6639

14" to 15" is basically one inch of rubber in the tire lost and one inch gain the in the wheel so lesser sidewall rubber to absorb the bumps hence stiffer ride.

Ok, so these manufacturers are loosing ride quality (and normal braking?) over alloys and handling for their top variant cars. Thanks, I just searched and found this thread for the topic and I will continue here.

Does the difference in sidewall height between tires also attribute to better / worse (moderate) braking? As with any mild flexing of the tire towards the rear as a whole, while braking? Lesser flexing means that the contact patch remains more or less the same. Why I'm asking this is that I felt the braking to be a wee bit better with the demo car shod on higher profile tires on 14" wheel. And this was not hard emergency braking. May be it is my mind.

Quoting some good information on the topic.

Originally Posted by hydrashok

The lower profile tyres have stronger sidewalls that don't flex during hard cornering.

Originally Posted by Ricky_63

The taller the tyre wall height the more comfortable the ride because of better absorption of shocks on a bad road etc, lesser the chance of damage to the rim.

Originally Posted by Rehaan

They have superior sidewall stability under braking (eg. mistu lancer with stock "high profile" tires, everyone complains about the car wandering a bit under hard braking)

Another post with the picture of flexion.

[Vid6639]

Originally Posted by thoma

Ok, so these manufacturers are loosing ride quality (and normal braking?) over alloys and handling for their top variant cars. Thanks, I just searched and found this thread for the topic and I will continue here.

Does the difference in sidewall height between tires also attribute to better / worse (moderate) braking? As with any mild flexing of the tire towards the rear as a whole, while braking? Lesser flexing means that the contact patch remains more or less the same. Why I'm asking this is that I felt the braking to be a wee bit better with the demo car shod on higher profile tires on 14" wheel. And this was not hard emergency braking. May be it is my mind.

Braking will be better with low profile tyres by a small margin because of less flex. But braking is more proportional to tyre width. A 195 width tyre will have better braking that 185 due to additional contact patch and resultant friction.