Safe Speed Forums

The campaign for genuine road safety
It is currently Mon Nov 19, 2018 02:50

All times are UTC [ DST ]




Post new topic Reply to topic  [ 28 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: 30 seconds to impact....
PostPosted: Wed Dec 22, 2010 14:05 
Offline
Friend of Safe Speed
Friend of Safe Speed

Joined: Sat Mar 06, 2004 12:01
Posts: 4813
Location: Essex
I was coming to the top of a hill that 20 minutes ago I'd sailed up with good traction (Market Hill in Maldon Essex if anyone knows it).

I was not well and needed to get home, so when I negotiated the mini-roundabout at the top I gave a dab of loud pedal, just as the rest of my brain told me that it had snowed since I came up. That was me "gone". I was doing perhaps 15 mph and realised - too late - I should be doing 2 - 3 mph at the top of the descent about 100 yards ahead of me, and no chance of scrubbing any speed off worth speaking of.

I told June - calmly - that we were in trouble. I did that roughly every three or four seconds. I kept gently trying to brake between very subtle and gentle steering corrections to keep the car facing forward. I might now be down to 10 mph - but just entering descent (from flat). The nearest car ahead heading the same way as me is now... 10 seconds away at the speeds we were both moving at. He doing just under walking pace and a good distance behind cars, sensibly spaced, all doing that speed. I'm going 2 - 3 times as fast. I have no escape lanes to left or right - simply going too fast to stand any chance of adequate traction to be able to get any of them without risk of hitting walls/spikes/pedestrians/houses... It got to 5 seconds to impact. I have lost a little speed by the repeated search for optimum (very low) brake force. There are cars coming up the hill - with a little slithering. Both the up and down traffic is a good couple of feet away from the kerb due to piled-up snow boulders.

I decided to thread the needle to buy time and gently steered the car and straightened up. I am now alongside the one I'd have biffed if I'd not deviated - with only a few inches either side to spare. Provided everyone else keeps their nerve. I can cope with this for a little while, but I know it gets steeper soon. People did keep their nerve, but I now have a new hazard - a Keep-Left bollard on a well-raised centre island at what once was a junction I think (may even still be, but I've now lost ANY side-off options). Back to 5 seconds to impact. Then....... virgin snow. Car stopped about a car length from the island. The two cars I'd offsided in this save slipped back past my nearside, and I filtered in behind them - the last carriage in the long train, now at their speed.

Safely home - and lesson learned. The lesson? Don't take to the road in bad weather when you're bursting for a s**t.


Top
 Profile  
 
PostPosted: Wed Dec 22, 2010 14:58 
Offline
Gold Member
Gold Member
User avatar

Joined: Wed Dec 08, 2004 14:26
Posts: 4364
Location: Hampshire/Wiltshire Border
A fortunate result but could you have scrubbed off speed by driving at the piled-up snow at the roadsides which you mentioned?

_________________
Malcolm W.
The views expressed in this post are personal opinions and do not represent the views of Safespeed.


Top
 Profile  
 
PostPosted: Wed Dec 22, 2010 15:31 
Offline
Friend of Safe Speed
Friend of Safe Speed

Joined: Sat Mar 06, 2004 12:01
Posts: 4813
Location: Essex
malcolmw wrote:
A fortunate result but could you have scrubbed off speed by driving at the piled-up snow at the roadsides which you mentioned?


Yes - but I'd have taken pedestrians with me if I'd mounted the kerb, and may also have bounced back into the oncoming traffic.

Nothing about this was good until the end. I was calm (insofar as in full control of faculties and making correct logical decisions) but extremely worried at the likely outcome.

If I'd just plumped for biffing the next carriage in the train up the back, it could so easily have been a 15-vehicle pile up. Inevitably one of them would have slewed across the road and involved traffic coming up the hill. If either of the two I "overtook" had panicked, or the one coming the other way who I managed to miss (the uphill train was much better spaced out) had slewwed and clipped me into making a canon, it could have been extremely serious.

Once the oncoming car was passed, I breathed slightly easier, with a strong chance that our car would be the only casualty (umless of course another plonker had come at the hill too fast, when I would have been a sitting duck).

I guess the joking apart lesson to share here is to always keep evaluating options. The keep-left island was what I'd resigned to - and I was actually doing the sums in my mind for replacement spoilers and sump guards (really...) when the car came to a fairly abrupt but very safe and damage-free full stop.

Who knows what might have happened if any of the adjacent others had panicked.


Top
 Profile  
 
PostPosted: Wed Dec 22, 2010 17:35 
Offline
Site Admin
User avatar

Joined: Tue Oct 12, 2004 02:17
Posts: 7354
Location: Highlands
Sorry to hear this.
Why did you decide to dab the pedal ? Was it a traction test ? On a roundabout it would neigh always encourage oversteer - or are you in a FWD or 4WD these days ?

I am with Malcolm with using the snow banks at the road side and honking.
Honking though if you had carried on would have encouraged others to react and you absolutely didn't want that - unless it would have had them able to stop and you might then have got back in before said island.
A difficult situation and good that you held your nerve and kept trying.

What about using the handbrake too? With modern cars the various 'aids' might have been hindering braking effort too - although it might help when slipping ... perhaps turning those features off might have helped too ? (If you have them?)
How many peds were about ? You mention that the oncoming were well spaced - no 'chance' (not ideal) of going across the road into that snow-bank if your pavement was busy ?
Any other poles or furnishing to run into ? Even a run off into an empty garden ?

Definitely a case for the 'drop anchor' SOS brake !
What if you had thrown it into reverse ? (help to straighten up the car - although you said it was straightened twice - is that, that is slide again ?)
The only other action I might have gone for is to allow the rear end to side into the snowbank - honking a lot as I go to ensure peds are aware prior to my clear route. And I would have hit the hazards - unless I needed to use an indicator to help ...
Well I hope I would have been so capable anyway ! :)

V pleased that you are both safe and relieved now!

_________________
Safe Speed for Intelligent Road Safety through proper research, experience & guidance.


Top
 Profile  
 
PostPosted: Wed Dec 22, 2010 18:28 
Offline
Friend of Safe Speed
Friend of Safe Speed

Joined: Sat Mar 06, 2004 12:01
Posts: 4813
Location: Essex
Front wheel drive CVT automatic - almost the worst combination for any form of predictable transmission effects to control handling!

I dabbed the loud pedal to pick up speed. I was in a hurry. That dab - and it was only a small dab, I'd already straightened up from the roundabout - 15mph remember and probably doing 10 mph as I went around the roudabout) - not a roaring plunge to the carpet - and failing to realise I should have slowed instead of sped up and dab the antidote pedal before I was too late - was my moment of madness. I had simply blocked out of my mind that just a few seconds further along the road, there was no grit or grip (20 minutes before hand the grip was good on the very road I was now about to become a sled upon).

At no time was the car violent in any torsional moves in any axis - and nearly all of the suggestions above, whilst probable speed scrubbers, are certainly going to damage something on the car, put me further in to the lap of the Gods with instability in at least one and probably two axes, and going to put others at risk. The only thing I'm not sure about is the horn. I did think of it once or twice, but (despite it all happening in slow motion), I had too much else on my mind to hoot (though the chap coming up the hill gave a nice angry blast for me - forgot to mention that earlier ;-).

I am mighty proud of my recovery here (although the last bit was luck), but all that is paled WAY into insignificance by my self-castigation for the poor anticipation of what was to come 30 seconds before it finished.

I won't do it again - lesson learned.


Top
 Profile  
 
PostPosted: Wed Dec 22, 2010 19:40 
Offline
Member
Member

Joined: Fri Oct 26, 2007 19:08
Posts: 3428
I had something similar but not so scary ,a couple of weeks ago. It was a sunday evening, where it had been snowing most of the weekend and that night I was returning from a friends house, through a set of large traffic lights that i use almost daily, where the approach is down a slight incline. The road leading up to the lights was fine on the flat approach but the down hill last bit, was icy ,so my (too late) braking was doing nothing and I wanted to turn left but it just wasn't going to happen.

I had three alternatives, try and handbrake round and risk spinning in the middle of a large but not busy junction and looking a pratt, carrying straight on and entering a college grounds and everyone thinking, "where's that pratt going?", third option, in the end I managed to (by going straight on towards the college), lose enough speed/gain enough traction to make a gentle right turn....I wonder how many people noticed and queeried why I was indicating left though...;-)

_________________
My views do not represent Safespeed but those of a driver who has driven for 39 yrs, in all conditions, at all times of the day & night on every type of road and covered well over a million miles, so knows a bit about what makes for safety on the road,what is really dangerous and needs to be observed when driving and quite frankly, the speedo is way down on my list of things to observe to negotiate Britain's roads safely, but I don't expect some fool who sits behind a desk all day to appreciate that.


Top
 Profile  
 
PostPosted: Wed Dec 22, 2010 19:57 
Offline
Friend of Safe Speed
Friend of Safe Speed

Joined: Sat Mar 06, 2004 12:01
Posts: 4813
Location: Essex
graball wrote:
I had something similar but not so scary ,a couple of weeks ago. It was a sunday evening, where it had been snowing most of the weekend and that night I was returning from a friends house, through a set of large traffic lights that i use almost daily, where the approach is down a slight incline. The road leading up to the lights was fine on the flat approach but the down hill last bit, was icy ,so my (too late) braking was doing nothing and I wanted to turn left but it just wasn't going to happen.

I had three alternatives, try and handbrake round and risk spinning in the middle of a large but not busy junction and looking a pratt, carrying straight on and entering a college grounds and everyone thinking, "where's that pratt going?", third option, in the end I managed to (by going straight on towards the college), lose enough speed/gain enough traction to make a gentle right turn....I wonder how many people noticed and queeried why I was indicating left though...;-)


A red light would have given your one an extra dimension; at least I never had lights to contend with!


Top
 Profile  
 
PostPosted: Wed Dec 22, 2010 20:46 
Offline
Member
Member

Joined: Fri Oct 26, 2007 19:08
Posts: 3428
No, i had actually passed the green light, at the point that i realised that a left turn wasn't on the cards but if someone had been turning right, out of the college grounds (by assuming I was actually going left), that could have been a problem.
It's actually a tricky junction in this weather because the slope doesn't actually start until you have passed the lights, so if you try and beat the lights (on the flat) you then find yourself on a slope going faster than you should be if it's icy (my fault for trying to beat the lights and assuming the traction wasn't going to change in the last few yards)

_________________
My views do not represent Safespeed but those of a driver who has driven for 39 yrs, in all conditions, at all times of the day & night on every type of road and covered well over a million miles, so knows a bit about what makes for safety on the road,what is really dangerous and needs to be observed when driving and quite frankly, the speedo is way down on my list of things to observe to negotiate Britain's roads safely, but I don't expect some fool who sits behind a desk all day to appreciate that.


Top
 Profile  
 
PostPosted: Thu Dec 23, 2010 16:44 
Offline
Gold Member
Gold Member
User avatar

Joined: Mon Mar 26, 2007 16:34
Posts: 4923
Location: Somewhere between a rock and a hard place
Glad you’re okay too Roger.

If there’s one thing that’ll take the edge off any Christmas it’s a prang just before it. I’m not sure if the lesson here is to let the s~~t hit your underpants instead of the fan?

I’ve sort of done that but I was busting for a wee instead. It felt like I was trying to hold gallon in a pint pot. Luckily no-one was with me in the van. (It was when I was doing a delivery job for a friend and I was stuck on a motorway).

Even the willie-grabbing us men can do to allay the feeling didn't work; well not after about 15 minutes it didn't. I’m still not clear on some legal thing I was told about where you are allowed to get out and pee on your nearside rear wheel, or something like that? If that’s right how would it work for women? Is it only for a number 1 or can you leave a Richard III there?

I have more questions than answers today :D

_________________
The views expressed in this post are personal opinions and do not necessarily represent the views of Safe Speed.
You will be branded a threat to society by going over a speed limit where it is safe to do so, and suffer the consequences of your actions in a way criminals do not, more so than someone who is a real threat to our society.


Top
 Profile  
 
PostPosted: Thu Dec 23, 2010 23:11 
Offline
Member
Member

Joined: Wed Feb 16, 2005 18:54
Posts: 4036
Location: Cumbria
Yeah, I've been far more scared going down hills than up them in this weather. And unfortunately, they're something of a fact of life round here!

Did the car have electronic stability control? My preferred option (I think!) would have been to keep the middle pedal planted and leave the ABS and other electronics to work on it. I say that, and I know its much easier to say than to do, but when your foot is planted, each wheel will do as much braking as it can, and the ESC should prevent it from swapping ends. When you feel a wheel lock or the car start to not go the way you point it and lift off the brakes, you remove the braking effect from ALL wheels simultaneously. I think that would waste valuable retardation from the ones that weren't locked.


Top
 Profile  
 
PostPosted: Fri Dec 24, 2010 00:19 
Offline
Friend of Safe Speed
Friend of Safe Speed

Joined: Sat Mar 06, 2004 12:01
Posts: 4813
Location: Essex
Mole wrote:
Yeah, I've been far more scared going down hills than up them in this weather. And unfortunately, they're something of a fact of life round here!

Did the car have electronic stability control? My preferred option (I think!) would have been to keep the middle pedal planted and leave the ABS and other electronics to work on it. I say that, and I know its much easier to say than to do, but when your foot is planted, each wheel will do as much braking as it can, and the ESC should prevent it from swapping ends. When you feel a wheel lock or the car start to not go the way you point it and lift off the brakes, you remove the braking effect from ALL wheels simultaneously. I think that would waste valuable retardation from the ones that weren't locked.

Yes the Civic IMA has top of the range electronic stability control - and I did try leaving my foot planted for 3 or 4 seconds a couple of times, but decided manual release and re-application more gently was best. It *might* have been worthwhile to do as you suggest - and indeed it was as it hit virgin snow. However, I believe it needed full wheel rotation (ie no "slip" to be able to then brake for best effect). Unlike on dry roads (when a certain percentage of skid is more effective for early arrest than not quite locked), on ice, once the wheel is slipping at all, it is likely to add a microscopic layer of water in front and be worse than not quite locked (it's amazing how much physics etc you can recall when out of control in slowmo!).

Also - and this was a real concern - I was worried about the ABS running out of puff. In a dry panic stop, it's all over (even if coming down from 120) in about 5 - 8 seconds. I went on for almost ever - the kickback reservoir can only hold so much!


Top
 Profile  
 
PostPosted: Sat Dec 25, 2010 19:50 
Offline
Member
Member

Joined: Wed Feb 16, 2005 18:54
Posts: 4036
Location: Cumbria
Interesting. First of all, you needn't worry about it running out of puff. The pump keeps making more as required. It uses a fair amount of power too. When the ABS pump kicks in on my wife's car, I can see the headlights dim momentarily!

As for whether it was better or not with your foot planted, well, you tried it, and that's the bottom line! Although I can see (on paper!) how leaving the ABS to sort it all out ought to be better, I too find it very hard to "delegate" that responsibility! I'm sure all cars will be subtly different in how they decide to cope with extremely low friction surfaces. Yes, the film of water will build up in front of a locked wheel, but I sometimes wonder whether the simple fact that the wheel is repeatedly rotating and locking (even with no grip at all) still means that some energy is being taken from the moving car and turned into something else. The bottom line is that I simply don't know enough about it to be sure. Conventional wisdom says that virgin snow is one of the few situations where the locked wheel will stop QUICKER (because of the wedge of snow that builds up in front of the tyre). There's also the possibility that the ABS doesn't work below certain speeds (some cars don't) and you were below that speed. The intervention that you felt might simply have been the ESC trying to keep it pointing the right way rather than the ABS trying to stop it. Too many unknowns really, but glad you're here to tell the tale - must have been a pretty trouser-browning moment!

Incidentally, whilst generally hugely impressed with Mrs. M's Nissan X-Trail, I had a bit of a "moment" myself the other day. I passed a van on a fairly steep snowy hill and he wasn't going anywhere. Being a decent chap, I thought I'd stop and help. I stopped some way in front of him, applied the handbrake, and went to get out, but as soon as I took my foot off the footbrake, it started sliding back down towards the van with it's back wheels locked! I got back in (pretty sharp-ish!) and re-applied the footbake - whereupon it stopped. Now the dilema! It was fine if left in gear or with my foot on the footbrake. Being a 4x4, it has sufficient traction to climb slippy slopes that it's own handbrake then can't hold it on! Obviously, if it was a "proper" 4x4, it would have a transmission handbrake that worked on all 4 wheels. Needless to say, I wasn't in a position to offer him a tow, and even setting off again myself was a bit tricky!


Top
 Profile  
 
PostPosted: Sat Dec 25, 2010 21:50 
Offline
Friend of Safe Speed
Friend of Safe Speed

Joined: Sat Mar 06, 2004 12:01
Posts: 4813
Location: Essex
Mole wrote:
Interesting. First of all, you needn't worry about it running out of puff. The pump keeps making more as required. It uses a fair amount of power too. When the ABS pump kicks in on my wife's car, I can see the headlights dim momentarily!

On earlier generation ABS cars, the kick-back pressure was built up with an electric pump, but the rate of replenishment did not match that of continuous use (I think it held about fifteen kick-backs from memory, then took a minute or two to build back up). You're likely right though that these days they're wise to that.

Mole wrote:
I'm sure all cars will be subtly different in how they decide to cope with extremely low friction surfaces. Yes, the film of water will build up in front of a locked wheel, but I sometimes wonder whether the simple fact that the wheel is repeatedly rotating and locking (even with no grip at all) still means that some energy is being taken from the moving car and turned into something else. The bottom line is that I simply don't know enough about it to be sure.
Nor me - though the calculational processes in parallel in my brain were doing their damndest to work out the best course.
Mole wrote:
Conventional wisdom says that virgin snow is one of the few situations where the locked wheel will stop QUICKER (because of the wedge of snow that builds up in front of the tyre).
:yesyes: definitely.
Mole wrote:
There's also the possibility that the ABS doesn't work below certain speeds (some cars don't) and you were below that speed. The intervention that you felt might simply have been the ESC trying to keep it pointing the right way rather than the ABS trying to stop it.
That'#s also possible - and one aspect I'd not considered. However, I *was* getting pedal kick-bak. I think (but am not sure) that ABS takes priority over ESC - when the brake pedal is touched.
Mole]Too many unknowns really, but glad you're here to tell the tale - must have been a pretty trouser-browning moment![/quote] ;-)

[quote="Mole wrote:
Incidentally, whilst generally hugely impressed with Mrs. M's Nissan X-Trail, I had a bit of a "moment" myself the other day. I passed a van on a fairly steep snowy hill and he wasn't going anywhere. Being a decent chap, I thought I'd stop and help. I stopped some way in front of him, applied the handbrake, and went to get out, but as soon as I took my foot off the footbrake, it started sliding back down towards the van with it's back wheels locked! I got back in (pretty sharp-ish!) and re-applied the footbake - whereupon it stopped. Now the dilema! It was fine if left in gear or with my foot on the footbrake. Being a 4x4, it has sufficient traction to climb slippy slopes that it's own handbrake then can't hold it on! Obviously, if it was a "proper" 4x4, it would have a transmission handbrake that worked on all 4 wheels. Needless to say, I wasn't in a position to offer him a tow, and even setting off again myself was a bit tricky!

I have to confess the only time I came acrosss someone coming back at me (trying to go forward) on an uphill stretch, I went past it and kept going. That was years ago.


Top
 Profile  
 
PostPosted: Sun Dec 26, 2010 06:25 
Offline
Member
Member

Joined: Fri Oct 26, 2007 19:08
Posts: 3428
I must admit that the worst thing that I find about driving on snow, is that ABS brakes seem to cause more problems than they solve on snow, I've often thought about removing the fuse at this time of year.

_________________
My views do not represent Safespeed but those of a driver who has driven for 39 yrs, in all conditions, at all times of the day & night on every type of road and covered well over a million miles, so knows a bit about what makes for safety on the road,what is really dangerous and needs to be observed when driving and quite frankly, the speedo is way down on my list of things to observe to negotiate Britain's roads safely, but I don't expect some fool who sits behind a desk all day to appreciate that.


Top
 Profile  
 
PostPosted: Sun Dec 26, 2010 06:58 
Offline
Friend of Safe Speed
Friend of Safe Speed

Joined: Sat Mar 06, 2004 12:01
Posts: 4813
Location: Essex
graball wrote:
I must admit that the worst thing that I find about driving on snow, is that ABS brakes seem to cause more problems than they solve on snow, I've often thought about removing the fuse at this time of year.

The problem with that is that, unlike on non ABS cars, these days they don't fit a brake balancer - so if you do, the back will lock when you brake hard - not recommended, unless you also disconnect the back brakes (or fit a limiter made for the non-abs version of the model).

if you do the back dis - you'll need to put it back for mot (and in any case will be illegal, but safe except when reversing quickly).


Top
 Profile  
 
PostPosted: Sun Dec 26, 2010 09:16 
Offline
Member
Member

Joined: Wed Feb 16, 2005 18:54
Posts: 4036
Location: Cumbria
One of the many advantages claimed for ABS (and it's associated whistles and bells) is Electronic Brake Force Distribution. This, as Roger says, replaces the old brake pressure limiter / proportioning valve that limited the line pressure to the rear brakes. These were incredibly crude devices that simply limited the pressure to the rear wheels to prevent them locking under any possible circumstances. Later, they got a bit cleverer and had them sensitive (to a point!) to the level of deceleration the car was undergoing, but they were still no match for an electronic system - especially the more recent ones that could limit the pressure to each rear wheel individually. In consequence, modern (not the first generation 3-channel systems) cars with ABS are supposed to be able to stop quicker because their rear wheels are doing a bigger proportion of the braking than the could ever have done with a simple hydraulic valve.

What I don't know (we need Ed back!) is what happens when there is an ABS system failure. My (20+year old!) car has ABS but it ALSO has a brake valve for the rear brakes - presumably a fail-safe. Modern ones don't. I guess that;s why it tells you to "proceed to your nearest dealer carefully" when the light comes on!


Top
 Profile  
 
PostPosted: Sun Dec 26, 2010 09:21 
Offline
Member
Member

Joined: Wed Feb 16, 2005 18:54
Posts: 4036
Location: Cumbria
Roger wrote:
Mole wrote:
There's also the possibility that the ABS doesn't work below certain speeds (some cars don't) and you were below that speed. The intervention that you felt might simply have been the ESC trying to keep it pointing the right way rather than the ABS trying to stop it.
That'#s also possible - and one aspect I'd not considered. However, I *was* getting pedal kick-bak. I think (but am not sure) that ABS takes priority over ESC - when the brake pedal is touched. [
;-)

You can still get pedal kick-back with ESC - it still uses the ABS pump to lock / unlock whatever wheel is appropriate to what it's trying to achieve. The first time I took Mrs Mole's previous car (something a bit sportier!) out for a gratuitous hoon in the snow, I was surprised to hear the pump cut in when I pulled the handbrake on - without touching the brake pedal. It did a spectacularly good job of preventing me from enjoying a handbrake turn! Fortunately, it still had a switch to turn the ESC off, but I really was quite impressed with how it prevented the car from oversteering when I had my foot on the throttle and was pulling the handbrake on whilst winding on an armful of lock!


Top
 Profile  
 
PostPosted: Sun Dec 26, 2010 10:40 
Offline
Friend of Safe Speed
Friend of Safe Speed

Joined: Sat Mar 06, 2004 12:01
Posts: 4813
Location: Essex
Mole wrote:
You can still get pedal kick-back with ESC - it still uses the ABS pump to lock / unlock whatever wheel is appropriate to what it's trying to achieve.
Unless they have got very sophisticated of late, the ESC applies brake forces to wheels that are losing drive (on the driven axis) and to an imperceptible extent to cause weight redistribution or (very momentary) loss of traction on the wheel(s) on the passive axis. By definition, when the ESC lets go, unless you have the brake pedal planted, it will let go of the wheel(s) it had braked and allow it/them to spin freely again.

Mole wrote:
The first time I took Mrs Mole's previous car (something a bit sportier!) out for a gratuitous hoon in the snow, I was surprised to hear the pump cut in when I pulled the handbrake on - without touching the brake pedal.
That would have been it trying to compensate for what you'd done. If this was in a rear drive car, if one of the rears had locked/semi-locked as a result of your handbrake tug, it would have thought that that was the one getting traction and applied brakes to the other one to even up the score. If it was a front drive car, it would have also removed/backed off the power as it would have thought that it was front wheel spin.

Mole wrote:
It did a spectacularly good job of preventing me from enjoying a handbrake turn!
It should not have done that. Or was it a grey import? Vehicles approved for use on English roads must have an independent and un electronically-interfereable means for the emergency brake. It could have applied brakes to other wheels, but should under no circumstances have kicked you off the handbrake. The kick-back works the hydraulics - the handbrake should wither work on auxiliary pads/shoes (disk braked cars usually do this as it's easier, and often they are in board from the wheel on a stub axle), or, on drummed rears, a separate mechanical cam that applies the brakes irrespective of what the hydraulics are doing.

Mole wrote:
Fortunately, it still had a switch to turn the ESC off, but I really was quite impressed with how it prevented the car from oversteering when I had my foot on the throttle and was pulling the handbrake on whilst winding on an armful of lock!

I still do handbrake about faces in the snow when I'm facing the wrong way - for efficiency rather than effect. And I don't turn the ESC off.


Top
 Profile  
 
PostPosted: Sun Dec 26, 2010 13:17 
Offline
Member
Member

Joined: Fri Oct 26, 2007 19:08
Posts: 3428
Quote:
graball wrote:I must admit that the worst thing that I find about driving on snow, is that ABS brakes seem to cause more problems than they solve on snow, I've often thought about removing the fuse at this time of year.


The problem with that is that, unlike on non ABS cars, these days they don't fit a brake balancer - so if you do, the back will lock when you brake hard - not recommended, unless you also disconnect the back brakes (or fit a limiter made for the non-abs version of the model).

if you do the back dis - you'll need to put it back for mot (and in any case will be illegal, but safe except when reversing quickly).


New postby Mole on Sun Dec 26, 2010 8:16 am
One of the many advantages claimed for ABS (and it's associated whistles and bells) is Electronic Brake Force Distribution. This, as Roger says, replaces the old brake pressure limiter / proportioning valve that limited the line pressure to the rear brakes. These were incredibly crude devices that simply limited the pressure to the rear wheels to prevent them locking under any possible circumstances. Later, they got a bit cleverer and had them sensitive (to a point!) to the level of deceleration the car was undergoing, but they were still no match for an electronic system - especially the more recent ones that could limit the pressure to each rear wheel individually. In consequence, modern (not the first generation 3-channel systems) cars with ABS are supposed to be able to stop quicker because their rear wheels are doing a bigger proportion of the braking than the could ever have done with a simple hydraulic valve.

What I don't know (we need Ed back!) is what happens when there is an ABS system failure. My (20+year old!) car has ABS but it ALSO has a brake valve for the rear brakes - presumably a fail-safe. Modern ones don't. I guess that;s why it tells you to "proceed to your nearest dealer carefully" when the light comes on!


Top


Thanks for the advice, guys, I never realised that ABS failure, or whatever, may result in braking unbalance. I must admit this Old Omega Estate, that I was thinking about disabling the ABS on, does have the ABS warning light come on occasionally for short periods and then it will diappear just as quick. Mind you, at the moment the roads round us don't appear to have been gritted for days, so everywhere that I am travelling at the moment, my braking is minimal,using engine braking to slow me alot more than I normally would.

_________________
My views do not represent Safespeed but those of a driver who has driven for 39 yrs, in all conditions, at all times of the day & night on every type of road and covered well over a million miles, so knows a bit about what makes for safety on the road,what is really dangerous and needs to be observed when driving and quite frankly, the speedo is way down on my list of things to observe to negotiate Britain's roads safely, but I don't expect some fool who sits behind a desk all day to appreciate that.


Top
 Profile  
 
PostPosted: Sun Dec 26, 2010 13:46 
Offline
Friend of Safe Speed
Friend of Safe Speed

Joined: Sat Mar 06, 2004 12:01
Posts: 4813
Location: Essex
Assuming a conventional manual gearbox, engine braking is "digital" - watch it. Better to keep it in a high gear and use the brake pedal gently than the gears.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 28 posts ]  Go to page 1, 2  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 3 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group
[ Time : 0.310s | 14 Queries | GZIP : Off ]