[kpzen]

^^ Please define "poor performance".

[VCheng]

Originally Posted by vina

It does.

More questions now:

How does sidewall help in cornering? I would think higher sidewall will flex more = poor performance. OTOH lower sidewall may generate so much force, the tread may "peel off" - again poor performance.

The danger of "peeling off" is related to tire pressure and the matching of the width of the wheel and the tire. A tire, mounted properly on the specified width wheel, and inflated at the proper pressure, will not peel off with any amount of cornering force generated by a vehicle, under routine operating conditions.

The amount of side wall flex is what determines the cornering feel. The major determinant is the height of the sidewall, but other factors like tire pressure, material of the sidewall reinforcing belts and their orientation, and the suspension geometry settings also play important roles.

[vina]

Originally Posted by kpzen

^^ Please define "poor performance"

first time - I meant a feeling of (perhaps actually happening) understeer and glide.

second time - I meant actual trouble of losing traction

[kpzen]

Originally Posted by vina

first time - I meant a feeling of (perhaps actually happening) understeer and glide.

second time - I meant actual trouble of losing traction

The above mentioned behaviour of a car would depend on lot of factors like suspension setup, steering setup, car's weight balance, COG and the wheels (tires+rims)
Tire alone doesn't make a car understeer, glide or lose traction.

Also, the sidewall construction of a passenger car tire and SUV tire is different.

[rajanprash]

Originally Posted by vina

It does.

More questions now:

How does sidewall help in cornering? I would think higher sidewall will flex more = poor performance. OTOH lower sidewall may generate so much force, the tread may "peel off" - again poor performance.

AFAIK there is a semi-rigid srtucture ( made up of steel wires ) inside the tire ( steel wire mesh is sandwiched between layers of rubber ) which balances the load which is applied at a particular point while cornering. so the pressure is evenly distributed.

A low profile tire is like a thin mattress which will be suitable for a smooth and even floor ( marble or granite like ). A high profile tire is like a thick mattress , so even if there are small uneven patches on the floor, nothing will be felt on the other side )

[vina]

Originally Posted by kpzen

...
Also, the sidewall construction of a passenger car tire and SUV tire is different.

can you elaborate on this one?

[AbhiJ]

Purely commenting on Sidewall Height.

Less Sidewall : Better Handling, More Feedback to the Steering Wheel.

More Sidewall : Better Ride, Comfort, Safery for Rim.

[Chewbacca]

Originally Posted by vina

How does the sidewall height of a tyre help/hurt performance, comfort ....

50% of the shock absorbing is done by the tyre sidewalls but the average car owner does not know thisYour question really boils down to comparing tubed tyres (higher profile) v/s tubeless (lower profile)

Advantage to car manufacturers:
Tubeless tyres = lower profile = less sidewall, less rubber, thinner sidewall, no tube = much lighter and cheaper tyre = lighter car = more milage (did you see the recent ad on TV - "kitna deti hai?" - that what matters in India)

Advantage to user:
Thinner sidewall = looks chic = less body roll = tighter cornering

But Indian road conditions need higher sidewalls which the tubeless can't offer. The sidewall of any tubeless tyre is thin and bulges easily with laden weight, thus greater the risk of a tear and losing control at higher speeds.

My car's stock tyres were tube-type 175/80/R13 on 13 inch stock alloys. The profile of 80 is approx 4.5 inches of side wall; this is the highest for a car tyre and gives me a complaint ride on a comparatively stiffer suspension of the Lancer. When I went shopping for new tyres I could not easily find the same size because tubed tyres are passe and nowadays everyone is ga-ga for tubeless but nobody makes tubeless in that size. The closest match was 185/70/R13 from Michellin and that's what I purchased - a big mistake. Rest of the story is at http://www.team-bhp.com/forum/techni...bed-tyres.html

[vina]

Originally Posted by Chewbacca

50% of the shock absorbing is done by the tyre sidewalls but the average car owner does not know thisYour question really boils down to comparing tubed tyres (higher profile) v/s tubeless (lower profile)

Actually sir - 100% of the high frequency (more than about 10Hz) shocks and almost 0% of low frequency shocks (less than about 1Hz) are absorbed by the tyres.

Since on a straight road at a decent speed (40+) you'll have minute undulations all over the place we can safely say that close to 100% shock absorption is done by tyres

No offence - just (stupidly) nitpicking




Regarding tubeless/tubed - you comments are welcome but I'm not sure whether all high profile tyres are tubed - thanks for explaining stuff below anyway.

Originally Posted by Chewbacca

Advantage to car manufacturers:
Tubeless tyres = lower profile = less sidewall, less rubber, thinner sidewall, no tube = much lighter and cheaper tyre = lighter car = more milage (did you see the recent ad on TV - "kitna deti hai?" - that what matters in India)

Advantage to user:
Thinner sidewall = looks chic = less body roll = tighter cornering

But Indian road conditions need higher sidewalls which the tubeless can't offer. The sidewall of any tubeless tyre is thin and bulges easily with laden weight, thus greater the risk of a tear and losing control at higher speeds.

My car's stock tyres were tube-type 175/80/R13 on 13 inch stock alloys. The profile of 80 is approx 4.5 inches of side wall; this is the highest for a car tyre and gives me a complaint ride on a comparatively stiffer suspension of the Lancer. When I went shopping for new tyres I could not easily find the same size because tubed tyres are passe and nowadays everyone is ga-ga for tubeless but nobody makes tubeless in that size. The closest match was 185/70/R13 from Michellin and that's what I purchased - a big mistake. Rest of the story is at http://www.team-bhp.com/forum/techni...bed-tyres.html

I went through your thread, there is some information there (quite a bit actually, but it is mostly specific, apart form the rant/opinion posts)

My question is:

Does a shorter sidewall always guarantee less body roll? I think when you say there is a higher risk of losing control you are onto something - how do shorter sidewall tyres lose control?

Also I'm not sure tubeless will reduce weight so much that mileage will have a significant effect - I mean given my muscle definition if I can lift two tyres at a time there is hardly any load at all

[Chewbacca]

Originally Posted by vina

100% of the high frequency (more than about 10Hz) shocks and almost 0% of low frequency shocks (less than about 1Hz) are absorbed by the tyres.

Appreciate your granular logic

Originally Posted by vina

I'm not sure whether all high profile tyres are tubed

We don't have a choice with tubed tyres. A conventional tubed tyre has a "normal" profile. On tubeless they cannot maintain the same; could be some engineering challenges like air escaping through the rim edges or whatever but they have to keep it lower than normal. With rim upgrades the profile becomes really "low" so as to maintain the same overall diameter. With all new cars being clad with tubeless, the "normal" tubed tyres now seem to be "high profile"

Originally Posted by vina

Does a shorter sidewall always guarantee less body roll?

Not always but it helps. On soft suspension cars you may not notice any difference.

Originally Posted by vina

I think when you say there is a higher risk of losing control you are onto something - how do shorter sidewall tyres lose control?

Here again the shorter sidewall is possible only with tubeless tyres. The wall thickness is less on tubeless and rips off easily. You must have seen road edges protruding with sharp stones that were left exposed or the road edges where layer of tar/concrete is approx. 5 inches thick and is almost vertical (does not taper off like it should). When the left side wheels go off the paved surface you can imagine how the sidewall takes a beating. Also the rim might scrape since they much closer to the ground. When this happens there is either a knee-jerk reaction from the driver (over-steer) or loss of control due to a ruptured tyre. I have seen many accidental cars in scrap yards with a ruptured sidewall.

Originally Posted by vina

Also I'm not sure tubeless will reduce weight so much that mileage will have a significant effect

The butyl rubber tube is 1 Kg + the tyre itself is heavier (Bridgestone / MRF) so that goes upto10 Kgs extra overall weight of the car!!
Visit this link to understand what I mean...
Maruti’s 1 component 1 gram initiative – better than Tata's Nano strategy?

[1self]

Vina,

To answer your original query.....here goes:

When you turn the steering wheel, the rubber on the tyre tread deflects by an amount proportional to speed of the vehicle at the time & magnitude of the steering wheel movement. This deflection is transmitted via the sidewall to the alloy & thence to the rack, which is where you get the sensation of the car following the direction you originally pointed it at.

Now the above sequence of events takes time...however miniscule that may be. At higher speeds this becomes perceptable.

Also, when turning the steering wheel by a certain angle, does not cause the vehicle to turn by the same angle at all. This is due to the tyre deflection being different on different surfaces (coefficient of friction). When the sidewall height is greater, more steering input is needed to turn by the same angle, compared to a low profile tyre, due to more rubber on the sidewall requiring more movement to deflect.
Also, the weight transfer o the vehicle causes more tyre deflection, further complicating things & leading to a wallowy ride.

So, a low profile tyre takes less steering input & less time to turn by the same angle than a higher profile tyre. Hence the percieved performance gains.

[SS-Traveller]

Originally Posted by vina

Pure technical question:
How does the sidewall height of a tyre help/hurt performance, comfort ....

@vina: I think you can answer that question pretty well yourself, and all of us would like to hear about it!

Originally Posted by vina

I searched on the internet as well as TBHP and went through general tyre threads also. Nothing specific turned up regarding tyre sidewall height - though people do talk about tyre width.

Hence the question. If Moderators feel this has been answered elsewhere - please delete the thread and PM me the search terms to use.

Another thread discussed this topic a little a long time ago, and I'd suggest mods merge your thread with that one, to keep things in the same place.

To take the quest for knowledge further, I'm also putting in a question here, which I'd like other members to answer:
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?

[Chewbacca]

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?

Bike tyre profile goes upto 90
On LMVs, LCVs and trucks it goes upto 80

30 years ago there was no tubeless technology. With tubes you have to keep it as round as possible within the tyre and that won't be possible within a low profile tyre.

[vina]

Originally Posted by 1self

Vina,

To answer your original query.....here goes:

When you turn the steering wheel, the rubber on the tyre tread deflects by an amount proportional to speed of the vehicle at the time & magnitude of the steering wheel movement. This deflection is transmitted via the sidewall to the alloy & thence to the rack, which is where you get the sensation of the car following the direction you originally pointed it at.

Now the above sequence of events takes time...however miniscule that may be. At higher speeds this becomes perceptable.

Also, when turning the steering wheel by a certain angle, does not cause the vehicle to turn by the same angle at all. This is due to the tyre deflection being different on different surfaces (coefficient of friction). When the sidewall height is greater, more steering input is needed to turn by the same angle, compared to a low profile tyre, due to more rubber on the sidewall requiring more movement to deflect.
Also, the weight transfer o the vehicle causes more tyre deflection, further complicating things & leading to a wallowy ride.

So, a low profile tyre takes less steering input & less time to turn by the same angle than a higher profile tyre. Hence the percieved performance gains.

Let us say one is travelling at 80kmph and turns the steering. How much time wold it typically take for the turn to fully transfer the turn in the rim to tread in the contact patch - if you have numbers - for a high vs. low profile tyre? While the time may be enough to be perceptible to race car drivers, I'm not sure in normal driving (on road cars) it will be perceptible - but then most normal road car users are buying the low profile tyres because "somebody told me they are better - and/or I want to make all my friends look like yokels by my empty talk"

Your comment makes me think in another direction too - taller sidewall will allow more flex, this can lead to a bigger difference in the yaw angle between the tyre contact patch on ground (actual direction of tyre travel) and the yaw angle of the rim - thus causing more over/under-steer

I think the second effect can be siginficant and perceptible by experienced, even average, drivers of even normal road cars (depending on how compliant is the sidewall)

Originally Posted by SS-Traveller

[/b] @vina: I think you can answer that question pretty well yourself, and all of us would like to hear about it!


Another thread discussed this topic a little a long time ago, and I'd suggest mods merge your thread with that one, to keep things in the same place.

To take the quest for knowledge further, I'm also putting in a question here, which I'd like other members to answer:
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?

Sir,

I shall look into details on the internet and if I do find something I will post that here. My daughter has to go to sleep before I do that.

Unfortunately one of the most important (if not the most important) components of a vehicle doesn't find much mention in most discussions - the only time sidewall etc. is mentioned is in the context of upsizing and as has been pointed out earlier most such discussions have little to do with technical aspects of things.

Also the nature of the internet is such, if you already know a little bit, it becomes easier to find more (you know better search terms etc.) That is one place where BHPiams such as you, @1self above, and Sutripta sir come very very helpful


I think I had seen the thread you had mentioned (not sure - went through a lot of threads to see if any had some tech info in this matter) - but that was a more generic one (not really related to sidewall and nothing tech except sidewall height calculation - not really something I wanted to discuss).

Anyway now that mods have merged the two - can they move the thread to the technical section - that'll be more appropriate IMHO.

[SS-Traveller]

Originally Posted by vina

...taller sidewall will allow more flex...

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

Originally Posted by vina

...the only time sidewall etc. is mentioned is in the context of upsizing...

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?