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Old 7th May 2013, 18:35   #466
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Default re: The ABS discussion thread

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... I'm talking about the off-road situations caused by vehicles running off the road in accident situations and I'm not talking about ...
There is no difference between intentional and unintentional off-roading. If you have gone off road anyhow, the rules are different. No, I am not talking of "hang on for dear life", but "steer car to safety, even if it means crashing into the nearest bush or tree that will stop your car".

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... ABS increases braking distance to provide you steerability/control ...
The "Increases Braking distance" part is NOT true in all cases. Gravel and snow are the only ones where ABS many times results in longer stopping distances (compared to locked brakes / no ABS). ABS doesn't increase it by telling the car "Hey, why are you stopping so early?" - in reality it is an interplay between ABS, tyres treads and surface, and wherever the car is ploughing through, that results in a certain braking distance.

ABS achieves steerability by not allowing the wheel to lock-up and slide. If the wheel slides, the car cannot roll in the desired direction with the momentum pushing it in another. There is no link between steerability and braking distance as you seem to make it out to be. Braking distance depends on Mu - gravel (on hard surface) and ice are close to 0.

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Originally Posted by Ketan View Post
... <<< seems to be incorrect. With ABS the deceleration is slightly greater on such surface and hence increased braking distance. We are not talking about wet roads here, ABS is useful on wet roads for sure. ...
ABS or no ABS, braking distance is governed by Mu of the surface on which the car is. Wet roads have greater Mu than Icy road, which is close to 0. Lesser the Mu, greater the braking distance, independent of ABS. ABS just prevents wheel lockup.

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... that confirms what I have read is correct. ...
But, it doesn't confirm that you have understood it! Bit of physics will correct it. Try.

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... I'd love to learn the new technology you are talking about. ...
I don't think I talked about new tech, I thought you were trying to. I am just trying to make you understand technology which hasn't changed in 30 years. And no, Internet and Wikipedia cannot replicate test track experiences.

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... we are planning to go next level ...
Sure. In which organization?

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... 'brake assist', 'traction control system', 'emergency brake assist', 'brake distribution system' and finally ESP. I consider all of them as an extension to ABS. Lets not go by the name ABS but consider it to be 'enhanced braking systems' ...
A very nice but simplistic abstraction. Real systems don't work on abstraction, only human mind uses abstraction to understand it (standard B-school funda). Wrong usage of abstraction kills all understanding.

Each of these is an INDEPENDENT control system, even though the method of delivery is through the same valves and piping used by ABS. There is NO overlap of functionality of these control systems. 'Functionality' is not the same as 'Delivery Method', as you seem to infer wrongly.

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... Now we use more sensors compared to conventional ABS systems, ...
Namely, which? Please quote actual devices, not indirect inferences based on the names of the control systems.

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... - Not sure which off-road situation you are comparing with the bad road situation here (JeepThrills or run-off-road situation during crashes). Either ways they are different categories ...
<Sigh> From the control systems p-o-v they aren't different at all. If a wheel is not in contact with the ground, it will invariably lock when braked. No difference if the wheel lifted due to a pothole, rut, stone or ... you going off the road.

At least the real OTR guys are in control of their senses in an OTR drive, and that matters the most. The guy who got ran off the road probably is at panic stations. And the frustrated guy who is driving fast on a bad potholed road is in a wrong state of mind anyhow!

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... internals == how to pump brakes == good driving habits!! ...
HUH? Noooo! I am sure you didn't mean that!
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Old 7th May 2013, 19:35   #467
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Default re: The ABS discussion thread

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HUH? Noooo! I am sure you didn't mean that!
OOps, there are hardly a thing where I look to be in agreement here. You are talking about so many things at the same time that is confusing to me, my points are very specific and may be simpler. Thats alright. We dont have to be. We are all unique
I shall probably try some other time or may not even find time to clarify my points more than this over a discussion group like this, may be a personal interaction would surely help. Wikipedia and research documents are based on tons of practical tests, if you think you have a different pov, you will have to prove it by researching on it. I adopted the easier way to produce the research already done
Anyways, it was a good discussion, wish we can meet up during some t-bhp meet to carry this forward if none of our experts helps us get to the right information.
Have a good day!
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Old 7th May 2013, 19:46   #468
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Default re: The ABS discussion thread

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Originally Posted by Ketan View Post
OOps, there are hardly a thing where I look to be in agreement here. ...
No hard feelings, but... it is not about agreement here. Engineering cannot be seen at 50 thousand feet level zoom-out level, one has to come down to low level processes, principles, algorithms and data. Assumptions and generalizations are killers of understanding. Perhaps you have only read the subject at a very high level and understood it by abstraction. You are not on the wrong track as far as the information is concerned, just that you are at a bit too high a level to relate to the actual implementation. Given time and further digging, I am sure you will understand it like anyone else - there is nothing to prevent or preclude it.
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Old 7th May 2013, 20:26   #469
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Default re: The ABS discussion thread

Hi All

One question

How efficient a car with ABS/ESP/EBD and Traction Control.If So how can we differentiate between these terminologies.

Still a grey area for many(including me )
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Old 7th May 2013, 21:16   #470
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Originally Posted by BinFord View Post
Hi All

One question

How efficient a car with ABS/ESP/EBD and Traction Control.If So how can we differentiate between these terminologies.

Still a grey area for many(including me )
What do you mean by efficient?
As far add the terminologies, they are quite different in what they are, the ones you mentioned above. Wiki it. That'll give you an understanding of at least what they do.
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Old 7th May 2013, 22:13   #471
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Originally Posted by BinFord View Post
... How efficient a car with ABS/ESP/EBD and Traction Control.If So how can we differentiate ...
It is difficult to understand 'efficiency' in the context of your question. The obvious relationship of 'efficiency' is with fuel consumption.

A car with ABS is safer than without one, specifically in case of controllability in hard braking situation. Each of the other systems incrementally adds to safety in specific situations.

In tandem, a car with all the 4 systems is a substantially safer car than one without. Of course, one has to remember that the efficacy of these systems is limited by the driver's driving behaviour. In the hands of a bad driver, such a car is no better than a car without any safety system!
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Old 7th May 2013, 22:22   #472
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Default re: The ABS discussion thread

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Originally Posted by DerAlte View Post
ABS or no ABS, braking distance is governed by Mu of the surface on which the car is. Wet roads have greater Mu than Icy road, which is close to 0. Lesser the Mu, greater the braking distance, independent of ABS. ABS just prevents wheel lockup.
Dada, wouldn't braking distances in sand improve significantly without ABS, due to the 'wheel-lock-and-gouge-in' effect?
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Old 7th May 2013, 22:44   #473
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Originally Posted by SS-Traveller View Post
Dada, wouldn't braking distances in sand improve significantly without ABS, due to the 'wheel-lock-and-gouge-in' effect?
It would, same as gravel, but only if the underlying surface is soft enough to support that. Sand or gravel on tarmac / concrete it is the same low Mu as wet surface - same lubricating behaviour approximately.
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Old 7th May 2013, 22:58   #474
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Default re: The ABS discussion thread

Quote:
Originally Posted by BinFord View Post
One question

How efficient a car with ABS/ESP/EBD and Traction Control.If So how can we differentiate between these terminologies.

Still a grey area for many(including me )
Let me guess that the question is in terms of braking/safety efficiency?.

If so, yes, ALL the above mentioned electronic add-on's make a normal passenger car considerably safer than the rest.
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Originally Posted by SS-Traveller View Post
Dada, wouldn't braking distances in sand improve significantly without ABS, due to the 'wheel-lock-and-gouge-in' effect?
I guess what DerAlte meant was the not just Mu, but Mu X Area upon which Mu acts, which is the main differentiator when its a question between ABS/NO ABS.

Last edited by dhanushs : 7th May 2013 at 23:01.
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Old 8th May 2013, 05:34   #475
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Default re: The ABS discussion thread

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Originally Posted by SS-Traveller View Post
Dada, wouldn't braking distances in sand improve significantly without ABS, due to the 'wheel-lock-and-gouge-in' effect?

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Originally Posted by DerAlte View Post
It would, same as gravel, but only if the underlying surface is soft enough to support that. Sand or gravel on tarmac / concrete it is the same low Mu as wet surface - same lubricating behaviour approximately.
We are entering a fascinating world of fluid dynamics here. I think DerAlte's reply is quite particular to this 'gouge-in' remark. This term in itself implies a deep layer of gravel or sand and that the wheel embeds itself more deeply into it the longer it's locked up, using the tyre sidewalls as friction and developing such a deep wedge of gravel or sand that it becomes a high wall of resistance.

In reality, this isn't always the case - certainly unless I go beach driving, this is never the case for me. If gravel or snow is so deep you can 'gouge-in' as you brake, the chances are you will have more trouble maintaining any speed than slowing down.

It is the intermediate state which is of interest in this matter, when the underlying surface is reached quickly when braking. In which case, DerAlte's supposition is wrong - the tyre may reach the underlying tarmac quickly when a wheel brakes, but it is the wedge effect of a build-up of sand, gravel or snow in front of the tyre which often performs most retardation.

'Gravel' encompasses stones from 4mm to 64mm. So this is a very difficult situation to categorize - 10mm gravel even in a thin layer may well prevent the tyre from gripping a layer of tarmac, especially if it rounded, whereas inch and a half, or 38mm gravels would most likely allow a tyre of a conventionally-sized wheel to grip the tarmac under braking. What happens when this gravel is rounded as opposed to sharp-edged, what happens if this gravel is of various sizes and shapes?

So concentrating our minds on sand and snow (I will pass over gravel because of its never-ending permutations, although I hope you all consider it effects under braking - most usually I encounter it after heavy rainfall, strewn across a minor road. One gets used to local roads and their dangers) which are more easily categorized (although still varying widely depending on locality and conditions) it is quite likely that although the tyre quickly reaches the underlying tarmac under braking, it is the 'wedge effect' of the build up of material in front of the tyre which has the bigger slowing effect, since the small size of snow and sand particles act as a huge lubricant between rubber and road.

This wedge effect is what causes aquaplaning in water which is too deep for the tyre to clear - like a noisy speedboat, the wedge creates a force which is sufficient to raise the suspension up, then the entire vehicle mass to plane over the water. With most sand and all snow, the friction of particles is sufficient to prevent this planing effect and the opposite happens - the wedge creates much more friction than the contact patch of the tyre on the 'ground'. If the layer is very thin, build up of the wedge may be insufficient to create much braking, but over a certain depth this will slow the vehicle much more effectively than the tyre's contact patch. It is the friction of a certain surface area of sand on sand under pressure, same for snow, as well as the wall of material at the front of the wedge which slows you down.

What becomes clear is how, although careful theoretical mechanical analysis of this hazard is beneficial, it is something which may be different from one mile to the next. I live in a valley which is reached only by steep hills, and almost every year these inclines are made interesting with strewn gravels and sands after heavy rain as well as snow in winter. I have learnt never to expect a guaranteed reaction of my cars in these conditions - different cars with different wheels, suspension, mass distribution and braking systems all react differently to the same condtions. And these same conditions never exist, snow alters from one day to the next, the same goes for ice, gravel and stones are always different, even if always in the same place on a slope - and so you use your brain.

Sometimes ABS works best, sometimes it makes sense to switch it off and let the wheels lock. Sometimes I wish I had huge diameter wheels, sometimes I wish they were tiny. Same for tyre width. But I usually prefer a deepish sidewall, if only to prevent the suspension (or my backside) from having to absorb every little corrugation. In an age where people think technology and science can provide every answer, it is still the individual human brain which works best, when used.
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Old 8th May 2013, 10:12   #476
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Default re: The ABS discussion thread

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We are entering a fascinating world of fluid dynamics here.
A very detailed explanation, an eye-opener. Fluid dynamics was one chapter that I had not considered too deeply in the event of braking on gravel/sand.

I am minimally experienced in driving on snow. I wonder if the dynamics of snow if / when it melts under tyres when brakes are applied & locked (higher pressure, friction) may produce any improvement/deterioration of braking performance when compared to ABS-equipped vehicle tyres that refuse to lock.

Would look forward to a similar detailed explanation. Thanks a ton for the previous one!
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Old 8th May 2013, 11:33   #477
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Default re: The ABS discussion thread

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Originally Posted by dhanushs View Post
... I guess what DerAlte meant was the not just Mu, but Mu X Area ...
No, I meant for a particular car (unique make+model), the primary dependency is Mu, since Area (tyre footprint) will be constant in all tests / comparisons. Ignoring Area (actually assuming Area constant), one can say braking distance is proportional to Mu. Engineering language, not precise unambiguous mathematical equation - which would be the long form including wheel camber, toe, moisture content of surface, contaminants etc. etc. In a crazily inhomogenous world, engineering makes assumptions to stay sane.

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Originally Posted by FlatOut View Post
... using the tyre sidewalls as friction and developing such a deep wedge of gravel or sand that it becomes a high wall of resistance. ...
Actually we meant resistance due to a material build-up transverse to the car, not longitudinal. The material build-up is due to the pushing of loose sand much like a bulldozer would. Sidewalls do contribute to braking, but since they are not exerting much force against the sides of the channel, that is not significant. Unless one angles the wheels, that is.

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Originally Posted by FlatOut View Post
... If gravel or snow is so deep you can 'gouge-in' as you brake, the chances are you will have more trouble maintaining any speed than slowing down. ...
By "trouble maintaining any speed" do you mean control over the car? The objective in this situation is to slow down by hook or by crook. And slow down it does, very similar to snow-boarders and skiers turning while stopping, to enable the larger area presented by board / skis in building up snow in front. 'Gouge in' as expressed by @ss-traveller meant the same, not longitudinal gouging.

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Originally Posted by FlatOut View Post
... the tyre may reach the underlying tarmac quickly when a wheel brakes, but it is the wedge effect of a build-up of sand, gravel or snow in front of the tyre which often performs most retardation ...
Misinterpretation - I didn't make supposition here. If the underlying surface is hard, sand / gravel / snow acts as a lubricant, deteriorating braking. Snow is even worse - it melts and then water reduces the Mu further. On black ice, the front tyres make the situation worse for the rear tyres. Reduced Mu = reduced retardation = less reduction in momentum, which increases the chances of the tyres simply sliding over whatever wedge was built up.

On a soft surface (obviously the same material going down deeper), this wouldn't happen as the transverse wedge will build-up faster than Mu reduction.

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Originally Posted by FlatOut View Post
... 'Gravel' encompasses stones from 4mm to 64mm. ...
In India, gravel is coarse river sand (usually reddish or yellowish brown) with particle size 0.5-2mm! Sand is finer, and funnily not the color of gravel - it is usually grey in North India. In South India, gravel and sand are both the same color, with gravel being the coarse particles seived out of the river sand.

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... What happens when this gravel is rounded as opposed to sharp-edged, what happens if this gravel is of various sizes and shapes? ...
Unless the stones have something to grip into, they all roll no matter angled or rounded. In cities like Mumbai, where sloping surfaces like on overpasses are a nightmare in the rainy season, the road maintaining agencies embed 'sized stones' (that's what they are called in English here; in Hindi it is 'roDi' or 'roDa' depending on size) 10-15mm dia into the tarmac to increase Mu.

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... This wedge effect is what causes aquaplaning ...
The main difference is 'how much' material is there between the tyre surface and a surface that can cause planar separation in the material. The harder the substrate, the tougher it is for wedge buildup (and the easier for the material to act like liquid / lubricant). In deep enough water, planar separation doesn't occur causing the bow-wave buildup = wedge. If sand / gravel / snow is deep enough, the same will happen. That's what I expressed earlier.

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... What becomes clear is how, although careful theoretical mechanical analysis of this hazard is beneficial, ...
Correct. In informal discussion we tend to be empirical.

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... sometimes it makes sense to switch it off and let the wheels lock. ...
For cars where an ABS override is provided intentionally (most cars in India don't have that), the owner / driver is usually instructed at the time of purchase of the car why it is provided and under what circumstances should one use it. One wouldn't have the presence of mind to switch ABS off in mid-slide, so forewarned is forearmed.

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... In an age where people think technology and science can provide every answer, it is still the individual human brain which works best, when used.
+10^6!

Last edited by Eddy : 11th May 2013 at 01:28. Reason: Extra smiley
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Old 8th May 2013, 15:27   #478
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Default re: The ABS discussion thread

There is nothing more hazardous than a layer of gravel across a road, in my experience. A car seems to gather speed rapidly in whatever direction the laws of physics dictate and there is little you can do other than wait to hit the end of it. (DerAlte, I used the official definition of gravel - to me gravel is about 2mm to 25mm diameter. Smaller than that I would call grit and sand, larger than that pebbles then small stones. I guess this will alter according to where you are in the world and what type of gravel you encounter.)

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Originally Posted by SS-Traveller View Post

I am minimally experienced in driving on snow. I wonder if the dynamics of snow if / when it melts under tyres when brakes are applied & locked (higher pressure, friction) may produce any improvement/deterioration of braking performance when compared to ABS-equipped vehicle tyres that refuse to lock.

Would look forward to a similar detailed explanation. Thanks a ton for the previous one!
Snow comes in scores of different forms, as any Eskimo would tell you - they even have many different names for it. As well as this, its temperatures, ambient temperature, road temperature and other factors affect how it behaves under you tyres.

When compressed sufficiently it often turns to ice, if your wheels spin then a layer of ice usually builds up. It would take pages to do justice to driving on snow - so I will simply say that it is rarely the same twice! Snow tyres are the answer, without them you go nowhere fast if there are any hills, four wheel drive or not.

Drifting snow occurs when the snow is powdery and the wind blows it into the air - it drops back to the ground where the windspeed drops - often behind hedges and walls, creating beautiful but hazardous drifts.

The West of Britain experienced some freak snow a few weeks ago - there's a picture below of a car stuck in a big drift. It was very unusual, especially in late March. It feels very balmy now we have hot sunshine and 20C!
Attached Images
  
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Old 8th May 2013, 20:24   #479
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Default re: The ABS discussion thread

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Originally Posted by FlatOut View Post
A car will stop a little more quickly with all four wheel locked up on dry tarmac than with ABS deployed.
Interesting. Any explanation as to why this should be so.

Regards
Sutripta
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Old 9th May 2013, 04:29   #480
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Default re: The ABS discussion thread

No definitive explanation, Sutripta, but it's the case as far as I am aware - a friend and myself did back-to-back tests a few years ago on three different cars and there are other similar results to confirm my findings.

The thoughts we had at the time were that although a locked wheel may not provide quite as much retardation as one which is at the point of locking (which from memory is 80-90% of the speed it would be doing if not beginning to slide) the ABS system is not able to hold the tyre at that point - instead it is pulsing between the lock up point and rotating at normal speed, so on average the braking effort isn't quite as high as the potential maximum and in reality this is a little lower than when the tyres are locked. There is quite a lot of fore and aft movement of the front wheels with most cars, which is a deliberate ploy to try to prevent a harsh ride with cheap suspension design such as the MacPherson strut coupled with front drive. This compliance, delivered with rubber bushing, is something which the ABS has to deal with and may slow the effective rate at which ABS works.

Another thought was that as the rubber slides, it heats up and becomes more sticky. But all three cars were conclusively quicker to stop without ABS.

However, I would never be without this massive safety feature - although I generally fit a cut-out switch to my cars since we usually have snow in this closed-off valley.

As a matter of complete non-interest to most motorists, but which may intrigue those who are interested in such intimate details, my Citroen CX with no ABS would stop significantly more quickly than the same car with ABS, when its ABS was switched off, using the technique Jeroen described. (This did not involve locking the wheels, just slowing them to a gentle howl. The Citroen braking system and mechanical elements of the suspension allow this very easily even when the surface friction changes, in part due to steel bearings in the suspension rather than cheap rubber bushes.)

Both cars stopped more quickly than a BMW M5, in all circumstances. Similarly a seventy-year old design with very skinny tyres , a Citroen 2cv (http://www.lowtechmagazine.com/2008/06/citroen-2cv.html), has been demonstrated to stop more quickly than a modern VW Golf http://www.cats-citroen.net/citroen_...ingsafety.html

The laws of physics are immutable and quality engineering will always shine through.
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