ABS and Slippery but Dry Roads
Discussion
Hi Chaps,
Since having moved over to Greece I have encountered some excellent driving roads but there is a mojor problem with the road surface and lack of grip (the Greek Drivers are also a problem but best saved for another topic!). It appears that that they crush marble into the stuff resulting in shiny and very slippery surface.
In some ways this fun. The prospect of me downgrading from a BMW 330i to a 1.4 Clio almost had me in tears, but with the lack of grip here, even the mighty 98bhp at my disposal can seem too much as it is so easily be wasted through wheelspin. Also I haven't had this much overteer action, even when I had a RWD car!!
However, there are some serious safety issues(!) with this sort of tarmac, particulary with stopping distances. Now as far as I know, ABS is supposed to reduce stopping distances and help keep you in control of the car, in particular allowing you to steer the car even when you have applied maximum pressure on the pedal. On these roads the ABS triggers very easily (alot tlike when you drive on ice) and de-acceleration seems to stop for a moment before slowing again.
My question is: Is ABS doing more harm than good on these sorts of roads??
Or is the ABS system on a basic car like my 2002 Clio just plain shite??
Since having moved over to Greece I have encountered some excellent driving roads but there is a mojor problem with the road surface and lack of grip (the Greek Drivers are also a problem but best saved for another topic!). It appears that that they crush marble into the stuff resulting in shiny and very slippery surface.
In some ways this fun. The prospect of me downgrading from a BMW 330i to a 1.4 Clio almost had me in tears, but with the lack of grip here, even the mighty 98bhp at my disposal can seem too much as it is so easily be wasted through wheelspin. Also I haven't had this much overteer action, even when I had a RWD car!!
However, there are some serious safety issues(!) with this sort of tarmac, particulary with stopping distances. Now as far as I know, ABS is supposed to reduce stopping distances and help keep you in control of the car, in particular allowing you to steer the car even when you have applied maximum pressure on the pedal. On these roads the ABS triggers very easily (alot tlike when you drive on ice) and de-acceleration seems to stop for a moment before slowing again.
My question is: Is ABS doing more harm than good on these sorts of roads??
Or is the ABS system on a basic car like my 2002 Clio just plain shite??
It could be argued that ABS in general is plain shite... certainly, ABS does NOT reduce stopping distances - that's a myth promoted by the manufacturers. What it does do is to maintain steering and stability if you lock the wheels by incompetent 'panic' braking.
That's perhaps a little harsh, but you've got to remember that it operates by locking and unlocking the wheels very rapidly (that's the pulsing you can feel through the pedal when it cuts in). What this means is that, basically, 50% of the time it is doing no braking at all, but you have grip to steer the car should you so wish, whilst the other 50% of the time the wheels are cycling through lock-up, hence braking, but not as efficiently as they could be (optimum braking efficiency being achieved by holding the braking effort just below the point where the wheels lock).
So... if you expect to be able to brake by standing on the brake pedal and letting the ABS sort it out, you'll find that your stopping distances increase dramatically.
However... the ABS won't cut in in the first place unless you have already locked the wheels (so you were braking too hard for the road surface) and will cut out again if you reduce the pedal pressure to the point where the wheels aren't quite locked.
If you are driving correctly, the ABS should never really cut in... maybe a few pulses as you find the locking point of the wheels when you're really driving hard, but that's about it.
ABS is a safety net for people with poor car control - it isn't a miracle cure!
That's perhaps a little harsh, but you've got to remember that it operates by locking and unlocking the wheels very rapidly (that's the pulsing you can feel through the pedal when it cuts in). What this means is that, basically, 50% of the time it is doing no braking at all, but you have grip to steer the car should you so wish, whilst the other 50% of the time the wheels are cycling through lock-up, hence braking, but not as efficiently as they could be (optimum braking efficiency being achieved by holding the braking effort just below the point where the wheels lock).
So... if you expect to be able to brake by standing on the brake pedal and letting the ABS sort it out, you'll find that your stopping distances increase dramatically.
However... the ABS won't cut in in the first place unless you have already locked the wheels (so you were braking too hard for the road surface) and will cut out again if you reduce the pedal pressure to the point where the wheels aren't quite locked.
If you are driving correctly, the ABS should never really cut in... maybe a few pulses as you find the locking point of the wheels when you're really driving hard, but that's about it.
ABS is a safety net for people with poor car control - it isn't a miracle cure!
Sam, what you said makes perfect sense. Indeed, when out on a hoon the ABS doesn't bother me and usully just kicks in a little when I have braked a liitle too hard and easily remidied by a slight reduction in brake pressure until the wheels grip again.
However, when caught unawares in traffic by an errant driver and I need to stop in hurry the ABS on one occasion got me worried with what I percieved as retarded stopping power. Unfortunately, in Athens the sort of panic braking that causes this problem occors all too often.
In the handbook for the car it says that when the abs intervenes I should apply maximum pressure to the pedal for the best braking effect . I have tested this on a quiet, slippery road and was shocked at how long the car took to stop using the abs as opposed to my own judgement with the pedal pressure.
This got me thinking that either the abs on this basic model car is shite or that abs in general is not that great on slippery surfaces. I never had the ABS kick in whilst I was in UK with my previous cars (except on ice).
Would I be right in thinking that, on a slippery surface, a car without abs, with locked up wheels will stop quicker than a car whose driver has activated the abs by applying maximum pressure?
However, when caught unawares in traffic by an errant driver and I need to stop in hurry the ABS on one occasion got me worried with what I percieved as retarded stopping power. Unfortunately, in Athens the sort of panic braking that causes this problem occors all too often.
In the handbook for the car it says that when the abs intervenes I should apply maximum pressure to the pedal for the best braking effect . I have tested this on a quiet, slippery road and was shocked at how long the car took to stop using the abs as opposed to my own judgement with the pedal pressure.
This got me thinking that either the abs on this basic model car is shite or that abs in general is not that great on slippery surfaces. I never had the ABS kick in whilst I was in UK with my previous cars (except on ice).
Would I be right in thinking that, on a slippery surface, a car without abs, with locked up wheels will stop quicker than a car whose driver has activated the abs by applying maximum pressure?
Dino D said:
Would I be right in thinking that, on a slippery surface, a car without abs, with locked up wheels will stop quicker than a car whose driver has activated the abs by applying maximum pressure?
On a very slippery surface (eg. compacted snow or very icy tarmac), yes, that's absolutely correct. In extreme low-grip conditions, though, the fact that you retain some steering control under braking is probably worth more than the reduced stopping distance. Some people will argue that retention of steering control is more importance, anyway, but I think most of us are so heavily programmed to do all the hard braking in a straight line that it is of limited value under most circumstances.
might be overkill on a 1.4 but there are two ways really to improve braking if the brakes are up to the job of coping with the heat generated. Better suspension to improve weight transfer under braking and better tyres. Due to your summer weather a good set of Yoko AO48's would work nicely
Avocet said:
Not sure there's anything you can do with the suspension to reduce weight transfer - I thought it was ONLY a function of the centre of gravity height.
True enough, broadly speaking. At least a function of the CoG and the wheelbase.Lowered suspension will, of course, lower the centre of gravity, however, hence will also reduce weight transfer (albeit not by a massive amount)... whether lowered suspension equates to Batfink's 'better' suspension on rough Greek tarmac is another discussion, of course!
Better dampers, properly adjusted, will allow the tyres to stay in more consistent contact with the road, hence offer better grip, but don't effect overall weight transfer and in any case I'm not sure that modifying a 1.4 Clio is the way to go... surely more sensible to simply trade it in on a Clio 182, which as been developed by Renault already - rather competently - to give better grip, handling and braking!
Sam_68 said:
basically, 50% of the time it is doing no braking at all, but you have grip to steer the car should you so wish, whilst the other 50% of the time the wheels are cycling through lock-up, hence braking, but not as efficiently as they could be (optimum braking efficiency being achieved by holding the braking effort just below the point where the wheels lock).
I don't think it's a bad as you're making out. If the ABS system is working properly the wheel speed should be cycling up and down around the target in a sort of saw-tooth, alternating between slightly too little and too much slip. You don't stop getting braking just because the ABS has taken the pressure off and is letting the wheels spin up.The problem in this situation is, how much slip should the ABS system be aiming for? In order to keep part of the grip circle available for lateral grip it has to be some way below the optimum slip for maximum braking, and that is something that will vary depending on the state of the tyres, how grippy the road is and so on. The nett result is that the ABS may be slaving away to maintain a slip amount which is actually miles away from the optimum for minimum stopping distances.
GreenV8S said:
I don't think it's a bad as you're making out. If the ABS system is working properly the wheel speed should be cycling up and down around the target in a sort of saw-tooth, alternating between slightly too little and too much slip. You don't stop getting braking just because the ABS has taken the pressure off and is letting the wheels spin up.
Yes, you're right... I was exagerating when I said 'no braking at all'. Never the less;as you said:
In order to keep part of the grip circle available for lateral grip it has to be some way below the optimum slip for maximum braking...
...and to be able to offer enough of the lateral part of the grip circle to enable worthwhile steering control, the braking effort during the 'unlocked' part of the cycle has to be substantially below maximum.Also, the ABS can't sense the state of the tyres, how grippy the road surface is, etc. All it can do is back off the braking pressure to a (relatively small) percentage of the pressure at which it senses brake lock-up.
So...
as you also said:
The nett result is that the ABS may be slaving away to maintain a slip amount which is actually miles away from the optimum for minimum stopping distances
In fact, I'd be inclined to substitute the word will for the word may in the above sentence... if the ABS is activated, it will always be offering braking effort which is considerably below the optimum 'wheels just about to lock' braking condition.Edited by Sam_68 on Wednesday 23 May 12:40
Is that true though? Surely, if you're stopping in a straight line, it will try to dish out as much braking force as each tyre can manage - so the state of the tyres and the tarmac are irrelevant because it will just let them grip as much as they can on whatever surface and then back off a tad when lockup occurs? If you then turn the wheel whilst braking at the limit, you will obviously go beyond what the tyres can manage so they'll lock up more readily and the ABS system will unlock them again. I guess what I'm trying to say is that if you ask for a steering input as well as a braking input, the system will end up not delivering as much braking retardation as it could have done in a straight line but it won't just be "optimised" on the assumption that you MIGHT want to steer? surely???
Avocet said:
Is that true though? Surely, if you're stopping in a straight line, it will try to dish out as much braking force as each tyre can manage - so the state of the tyres and the tarmac are irrelevant because it will just let them grip as much as they can on whatever surface and then back off a tad when lockup occurs?
There may be ABS systems that do this, but it's not how they used to work, I don't know if any are that clever these days or whether the OP was about one that is.An interesting footnot to add to the ABS debate,
in the early ABS days, the BIB or PLOD class one driving instructors proved inconclusively that a highly trained and experienced driver could out brake and out manoever a non ABS Granada Scorpio 4x4 versus a standard ABS equiped jobbie, off the back of this research Ford produced a batch of non ABS Granadas for the motorway patrol guys, which they duly stuffed over a period of time, many into motorway bridges.
The lesson gleaned from this exercise was: ABS is a constant, a human being isn't, the ABS doesn't get exited or carried away and unlike a human, it doesnt panic.
Therefore, an ABS car in general is a better place to be when the way ahead becomes, unexpectedly fraught!!
Yuo'll probably find that your clio is equiped with the hardest,least compliant and adhesive tyres known to man, and they have dried out in the heat too, also your suspension is likely to be clapped out as well( aged budget motor on low rent roads) check that every thing else is tip top before cusing the abs
in the early ABS days, the BIB or PLOD class one driving instructors proved inconclusively that a highly trained and experienced driver could out brake and out manoever a non ABS Granada Scorpio 4x4 versus a standard ABS equiped jobbie, off the back of this research Ford produced a batch of non ABS Granadas for the motorway patrol guys, which they duly stuffed over a period of time, many into motorway bridges.
The lesson gleaned from this exercise was: ABS is a constant, a human being isn't, the ABS doesn't get exited or carried away and unlike a human, it doesnt panic.
Therefore, an ABS car in general is a better place to be when the way ahead becomes, unexpectedly fraught!!
Yuo'll probably find that your clio is equiped with the hardest,least compliant and adhesive tyres known to man, and they have dried out in the heat too, also your suspension is likely to be clapped out as well( aged budget motor on low rent roads) check that every thing else is tip top before cusing the abs
ELAN+2 said:
in the early ABS days, the BIB or PLOD class one driving instructors proved inconclusively that a highly trained and experienced driver could out brake and out manoever a non ABS Granada Scorpio 4x4 versus a standard ABS equiped jobbie...The lesson gleaned from this exercise was: ABS is a constant, a human being isn't, the ABS doesn't get excited or carried away and unlike a human, it doesnt panic
I assume you mean 'conclusively', not inconclusively?I did some testing with a Rover 800 (don't laugh!) a few years back, doing exactly the same thing. In terms of straightline stopping distances, the difference was dramatic on both wet and dry tarmac... with ABS the car took tens of metres further to stop from high speed. And I wouldn't consider myself a 'highly trained and experienced' driver by any means.
The big advantage of ABS is that you retain steering control. I suspect that the accidents were mainly caused by people in an emergency braking situation suddenly thinking 'I'm not going to stop in time!' and swerving to avoid an obstacle, but panicking and forgetting that to do so they need to come off the brakes, at least momentarily. The result in a non-ABS equipped car is, more than likely, a very messy spin.
Maybe it's just a personal thing, but I'm fairly sure that I'm so heavily conditioned not to steer whilst braking that I'd suffer the opposite problem... even with an ABS equipped car, it would never even occur to me that steering to avoid a collision whilst braking hard was actaully an option!
I'm not anti-ABS by any means. It doesn't bother me to drive an ABS equipped car because if it cuts in and stays activated for more than a fraction of a second, I'd know that I'd made a huge error of judgement in the first place. It's just that I think we should recognise it for what it is... a safety net, not a miracle that can defy the laws of physics!
Thanks for the interesting comments guys. I have been checking the braking distances and best mnethods on these slippery roads and have come to some conclusions about my braking and the abs.
Bearing in mind the car has nice new Toyo rubber (albeit only 185/14in) and the shocks aare bit worn:
On slippery dry tarmac (I mean so slippery that this meagre 98bhp car cannot find traction all the way through first and most of second on a hard pull away) activating the abs increases stopping distances. According to the instruction manual one should apply maximum force to the pedal for best effect. Doing this reults in rather jerky braking as tha abs cuts in and out very abruptly resulting in the car actually pitching back and forth and a little 'side to side' when one wheel is braked/released and the other is not.
Conversley, braking hard without activating the abs results in shorter (a few meters at 60km/h but I can't be accurate) and smoother, more controlled braking.
The abs is not a problem when out on a hoon as I am braking withing the limits so the abs rarely kicks in except for a major surface change whist braking.
The abs becomes a problem in city driving and low speed emergency stops. In Athens, the drivers are very erratic. I leave plenty of stopping distance but every now on then I find myself in situation where an immediate stomp of the brakes is required. It is in these circumstances that the abs feels couter productive as when it activates, the car stops slowing altogether for a while.
However, the benefit of having steering control is handy as if I can't stop at least I might have a chance of steering past the deranged scooter driver!
I am practising 'stomping' on the pedal (what I mean is appplying as much force as possible, as fast as possible without triggering the abs) and still stopping sharpish. Pretty much what you would do in a non abs equipped car (gone are the days eh?). I can't help thinking that in these low speed emergency stops locked wheels will do a better job as the distance you lose when the abs kicks in is not regained in such short stops. Thats my theory anyway-If I have the time I might just pop the abs fuse out and test this theory out and measure the distances (But with the lovely weather we having I'll probably just take a drive over the moutain on my favourite roads and go to the beach for the day...!)
It is very likely that this car just has a very basic abs system. On my BMW 330 sport (which had 225in tyres on front and 255 on the back, stiff sports suspension, 4 discs etc) the braking was always great and I don't remeber triggering the abs. The same with my Honda Prelude (except in snow and ice of course). However, this was all back in the UK where the roads have far better traction so my experience with those cars may not really apply here. In fact today I witnessed a new Jeep Grand Cherokee lurch to stop halfway accross the pelican crossing. I was standing in the side waiting for him to stop. The surface was very slippery and I could hear the tyres squealing but when he hit the paint you could see the wheels being unbraked and look as if it the speeded up.
On the up side-this little basic clio on these slippery roads is very involving indeed even at the posted speed limits. Makes a big change from the more sorted cars that require big speeds to push the envelope.
Bearing in mind the car has nice new Toyo rubber (albeit only 185/14in) and the shocks aare bit worn:
On slippery dry tarmac (I mean so slippery that this meagre 98bhp car cannot find traction all the way through first and most of second on a hard pull away) activating the abs increases stopping distances. According to the instruction manual one should apply maximum force to the pedal for best effect. Doing this reults in rather jerky braking as tha abs cuts in and out very abruptly resulting in the car actually pitching back and forth and a little 'side to side' when one wheel is braked/released and the other is not.
Conversley, braking hard without activating the abs results in shorter (a few meters at 60km/h but I can't be accurate) and smoother, more controlled braking.
The abs is not a problem when out on a hoon as I am braking withing the limits so the abs rarely kicks in except for a major surface change whist braking.
The abs becomes a problem in city driving and low speed emergency stops. In Athens, the drivers are very erratic. I leave plenty of stopping distance but every now on then I find myself in situation where an immediate stomp of the brakes is required. It is in these circumstances that the abs feels couter productive as when it activates, the car stops slowing altogether for a while.
However, the benefit of having steering control is handy as if I can't stop at least I might have a chance of steering past the deranged scooter driver!
I am practising 'stomping' on the pedal (what I mean is appplying as much force as possible, as fast as possible without triggering the abs) and still stopping sharpish. Pretty much what you would do in a non abs equipped car (gone are the days eh?). I can't help thinking that in these low speed emergency stops locked wheels will do a better job as the distance you lose when the abs kicks in is not regained in such short stops. Thats my theory anyway-If I have the time I might just pop the abs fuse out and test this theory out and measure the distances (But with the lovely weather we having I'll probably just take a drive over the moutain on my favourite roads and go to the beach for the day...!)
It is very likely that this car just has a very basic abs system. On my BMW 330 sport (which had 225in tyres on front and 255 on the back, stiff sports suspension, 4 discs etc) the braking was always great and I don't remeber triggering the abs. The same with my Honda Prelude (except in snow and ice of course). However, this was all back in the UK where the roads have far better traction so my experience with those cars may not really apply here. In fact today I witnessed a new Jeep Grand Cherokee lurch to stop halfway accross the pelican crossing. I was standing in the side waiting for him to stop. The surface was very slippery and I could hear the tyres squealing but when he hit the paint you could see the wheels being unbraked and look as if it the speeded up.
On the up side-this little basic clio on these slippery roads is very involving indeed even at the posted speed limits. Makes a big change from the more sorted cars that require big speeds to push the envelope.
I was taught "cadence braking" on a skid pan with the IAM immediately after passing my test (mum didnt fancy me creaming her car) and skid control techniques.
At the Millbrook proving ground (was an employee there for a while) I had additional skid/braking training. With practice I could stop the car in a shorter distance with out the abs, using cadence braking also I could swerve and stop in a shorter distance than with an abs equipped car.
If a suitably trained/skilled/experienced driver is out driving rapidly, ie concentrating and there fore prepared for a "suprise", then ABS could be a hinderance. However the chances are, the evasion techniques wouldnt be required any way as the driver would anticipate the situation. Where ABS comes into its own is when you are driving home after a shitty day, on the phone to 'er indoorsd explaining your lateness (hands free of course) whilst mentally preparing tomorrows schedule, its raining, almost dark, the twits coming the other way all seem to be on full beam, then a kid runs out in front of you. This is the situation that ABS and other electronic driver aids are supreme in.
As a human being we are flawed, we can be distracted, and we can make errors and panick/freeze. I know I have and I know I will in the future, its the nature of the beast. I'm glad that my daily driver has ABS and Traction control, although i haven't activated either for several months. I am also glad that my Lotus hasn't got these aids, for basically the same reasons!!
Mark
P.S. I'm not trying to make out that I'm a particularly good driver, Iam acutely aware of my limitations and try not to play to them
At the Millbrook proving ground (was an employee there for a while) I had additional skid/braking training. With practice I could stop the car in a shorter distance with out the abs, using cadence braking also I could swerve and stop in a shorter distance than with an abs equipped car.
If a suitably trained/skilled/experienced driver is out driving rapidly, ie concentrating and there fore prepared for a "suprise", then ABS could be a hinderance. However the chances are, the evasion techniques wouldnt be required any way as the driver would anticipate the situation. Where ABS comes into its own is when you are driving home after a shitty day, on the phone to 'er indoorsd explaining your lateness (hands free of course) whilst mentally preparing tomorrows schedule, its raining, almost dark, the twits coming the other way all seem to be on full beam, then a kid runs out in front of you. This is the situation that ABS and other electronic driver aids are supreme in.
As a human being we are flawed, we can be distracted, and we can make errors and panick/freeze. I know I have and I know I will in the future, its the nature of the beast. I'm glad that my daily driver has ABS and Traction control, although i haven't activated either for several months. I am also glad that my Lotus hasn't got these aids, for basically the same reasons!!
Mark
P.S. I'm not trying to make out that I'm a particularly good driver, Iam acutely aware of my limitations and try not to play to them
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