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PostPosted: Sun Dec 26, 2010 14:09 
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Yes, i would agrre to some extent but think it depends on how much you want to slow down and to what extent. If the slow down is long and straight, I would use gentle change downs using enginge braking to the last moment before gentle braking but it the braking was down to someone puling out in front of you, on a long straight, from a junction, I would agree that gentle braking would be better than a suddden downchange.
I had a ten mile drive along very narrow country lanes to see an old mate on fri night. The roads where he lived were, for the most part, still white over with compacted snow/ice and about minus 10 outside and they hadn't been gritted at all. Made for some great driving technique with anything over twenty mPH being tricky and wheel slip when taking off even on the flat...;-)

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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.


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PostPosted: Sun Dec 26, 2010 21:00 
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Roger wrote:
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.

Pretty certain it can do more than that on most modern cars. It certainly does what you suggest, but I think it will also brake a wheel on the non-driven axle if it wants to degrade the grip at that end instead. Part of the problem is that there isn't a standard for many of these "whistles and bells" as yet, so each manufacturer does their own thing and has their own terminology. I know there's a lot of regulatory work going on right now to try and develop standards / regulations for these systems.

Roger wrote:
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.

No it's smarter than that. It was a front wheel drive - an Alfa 156. It knew I had my foot on the throttle and that both front wheels were turning but that the rears had stopped. However, I'm pretty certain that it takes an input from the handbrake warning light switch too, so it knew the rear wheels had stopped because the handbrake was on, rather than the fronts were spinning and the car stationary. I think it also had a yaw sensor which told it that the vehicle was starting to spin. It then thwarted my efforts by shutting the throttle and braking the "outside" front wheel so as to straighten the car up (albeit at the expense of a short 4-wheel drift before it scrubbed off its speed and stopped).

Roger wrote:
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.

For "English" read "EC" these days! Yes, it was purely mechanical and no, nothing interfered with it. As you suggest, it had no means by which to do so - so it just messed about with the other end of the car to spoil my fun! The handbrake was still on as I came to a stop and didn't do anything peculiar. As stated above, I'm pretty certain it just braked the front wheel on the outside of the curve in which the car was travelling, to degrade its grip and straighten me up.

Roger wrote:
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.

Yeah, that's the thing. Everyone's magic system works slightly differently at present. To be honest, I like finding out about each new vehicle's little quirks, but I'm sure the regulators will kill that pleasure off in the next few years. The "General Safety Regulation" which comes into force (starting) in (I think) 2014 will demand that all passenger cars are fitted with ESC (among other things). Mrs. M's current X-Trail is another example. In the wide, snowy entrance to our lane, I've been sticking it in 4-wheel drive and booting it as I come round the bend. Sometimes, I can get a half-decent amount of oversteer before the little yellow "you're-having-too-much-fun" light starts flashing and it straightens me up. Other times I've actually bottled-out and lifted off because I've thought I was going to spin before it comes on! Not sure why, but it's quite unnerving. You start to trust it and about every fourth or fifth time, it lets you get well and truly out of line before cutting in. I'm assuming it's the "teach-you-a-lesson" algorithm in the software :wink:


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PostPosted: Sun Dec 26, 2010 23:06 
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*sigh*

Yes it is all wrapped up in one system with various confusing acronyms.

What roger describes as ESC sounds to me like traction control, and in this case brake intervention to stop a spinning wheel across the diff on a driven axle. If both driven wheels are spinning typically you'd just get engine intervention to back off the throttle.
What mole describes on the alfa sounds like ESC (stability control), again brake intervention on one wheel which is about generating yaw moment in the right direction. Engine intervention is also an option for stability control to restore grip on driven wheels. As a bonus, both interventions act to slow the vehicle which also generally helps with regaining grip.
Understanding what effect has triggered the intervention is not always straightforward with the overlap, if you're dealing with the system as a black box & don't have the algorithms to hand.

Obviously (?) preventing excessive wheelslip takes priority whether it's driver demanded from the pedal or driven directly from ESC.

As to the stability control tune, it varies from system to system but also between customers and even marques. I've had alot of fun in sweden with very loose tunes, some even allowing the back end to come out quite alot but being damn well ready to catch the eventual overshoot. I also recall driving an alpha tuned extremely cautiously, so that may well be part of their target for the brand.
It's all very well enjoying it on a track, but I'd take the cautious tune on an unpredictable open road 9 times out of 10.

What else ? oh yes rear proportioning.... No doubt this just uses the same isolation valves that come as part of the ABS, could be triggered by any variety of things pressure/decel. I recall graphs of adhesion utilisation for braking regs, ie the rears must never lock before the fronts, but don't know if they allow for ABS and/or system failure.
(whereas I know ECE13 has different decel & force requirements for powered system & failed systems)

And finally.... regs say handrakes must be capable of holding the vehicle at GVW on an 18% slope if i recall correctly.
You must also have a secondary emergency braking system which must be independantly actuated from the service brakes, usually this happens to be the handbrake! But the only requirement on this secondary system is being capable of decel of 0.15g from 30kph to zero! which really isn't very much at all, oh and i think that allows for up to 400N at the handbrake lever, which took me two hands the last & only time i had to do the test.


For what its worth i'm in the middle camp on what to do... sure let the system do its job but it helps if you're doing yours too, reacting, countersteering, backing off the throttle. Even with ABS to an extent i'll apply until i get (continuous) pedal feedback and dont usually press any harder as there's not much point, let the ABS do its thing, if the pedal feedback stops i know ive got some more grip and can apply more pressure.

[merry christmas & happy new year!]


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PostPosted: Sun Dec 26, 2010 23:40 
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Wow!

I am learning lots here.

My (and June's) Hondas have what is acronysed as VFD. There is a press-button to disconnect - and I only did it once. I thought the engine was missing - but I realised rapidly that it was backing off keeping me straight!


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PostPosted: Mon Dec 27, 2010 12:57 
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It is all very educational ...
I had my car once slide after getting out (plus dog) - funnily enough Christmas day 05 (or was it 04 ?), taking a dog to a vets (puppies being born!) anyway, the roads were not gritted at all and they were totally icy. I tried parking on the only location available very gently and I was shocked when it moved - happily though it only moved and inch or so then stopped. I shut the door really gently and locked it very gently and then got to the vets up the hill over much ice worrying how was I ever going to reverse up the hill! I hoped that the engine and car warmth might heat the ground a little.
(Happily when I left I was OK and it reversed ok - at least I had LSD but that was all - scary though!) :)

I am not sure that I have tried any of the modern systems - ABS now but I don't want that certainly don't need it.
I want ALL systems available to be turned OFF if I choose. I think reliance on them is a grave mistake.
We must never loose sight of driver / rider education to enable proper responsibility.

As a matter of interest what systems are on Swedish and Norwegian vehicles ? Do they demand all these gadgets when on ice?

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PostPosted: Mon Dec 27, 2010 13:11 
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SafeSpeedv2 wrote:
I had my car once slide after getting out (plus dog)
[...]
(Happily when I left I was OK and it reversed ok - at least I had LSD but that was all - scary though!) :)

Obviously a rewarding trip ;-)


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PostPosted: Mon Dec 27, 2010 18:54 
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SafeSpeedv2 wrote:
...I am not sure that I have tried any of the modern systems - ABS now but I don't want that certainly don't need it.
I want ALL systems available to be turned OFF if I choose...

The trouble with ABS is that when the occasion arises where you DO want it, you wouldn't be in any position to switch it back on quickly enough!
SafeSpeedv2 wrote:
I think reliance on them is a grave mistake.
We must never loose sight of driver / rider education to enable proper responsibility.

Naturally, I'd like to agree. But there are techniques to getting the best out of these electronic aids that are also (I feel) valuable driving skills in their own right. In much the same way as double-declutching was once essential, or hand-cranking a car to start it, the technology has now made these skills redundant. Naturally, I don't rely on my ABS every time I brake - it would cost a fortune in tyres and make my passengers sick! However, I DO rely on (in fact actively use) it on occasions. The most common one is where I'm going downhill on a single track road and someone comes the other way round a bend - usually too fast. I'm in the "give way" position, and I end up with the two nearside wheels on the grass. Under these conditions, I can brake and the car will prevent the two nearside wheels from locking whilst still allowing useful braking from the two offside wheels. If I was in a non-ABS car, I'd have to make the choice betwen lifting off and not stopping as quickly, or keeping my foot on the brakes and risking a spin as the two on the grass locked up. With ABS I can have the best of both worlds, and I've never yet met the driver who could replicate that! In fact, when they're getting type apporved (the ECE Reg. 13 that Ed mentioned) cars with ABS have EXTRA tests to do on split-friction surfaces (half slippy, half grippy) that they don't make non-ABS cars do, simply because a non-ABS car would just spin.
SafeSpeedv2 wrote:
As a matter of interest what systems are on Swedish and Norwegian vehicles ? Do they demand all these gadgets when on ice?

They're global players just like most other manufacturers. I'm not aware of Saab / Volvo having any significantly different system architecture to anybody else (notwithstanding the slight differences that have become apparent between marques in this thread). To be honest, most major manufacturers seem to use Bosch technology in this respect anyway. Over there, they use winter tyres more - and even studded tyres in the really icy areas, but I think that just ups the level of grip all roud. The "toys" still work on the same principle. Anyway, surely your Beamer has ABS?!


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PostPosted: Mon Dec 27, 2010 19:52 
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My X5 has all the three letter acronyms you can imagine fitted and... it works pretty well in the snow but you have "tickle" the controls as you might imagine. However, the one important rule to remember is that while you have traction to get going, you can't stop like it's dry tarmac.

You don't need to switch all the electronic aids on and off, just be very cautious with grip when wanting to slow. Where I live there is a 50 yard gentle slope down to a T junction which I approach in first gear at a crawl. I have slid out of this at about 1mph due to the lack of grip and am now wise to this type of hazard.

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