Oakmaster Posted December 11, 2012 Share Posted December 11, 2012 Does ABS make it worse? I slid for about approximately 300 metres (or yards – if you prefer – approximately!) down our hill this morning on a layer of frost – I have a 110 Puma XS – the ABS was chuntering away but it didn’t seem to slow us up. (But we did go in a stright line) Normally I head for the verge and that slows me up just fine! - today I decided to see how far before I stopped Whilst I’m not a luddite, nor a great believer in old wives tales, I’m starting to wonder if the persistent rumours about ABS are true, and that in slippery conditions (Mud, ice, and snow) the ABS makes things worse! My previous 110 CSWs 300 Tdi and Td5 (Both W/O ABS) seemed to be better? Could this be true? I may have missed something obvious (and not for the first time!) If it were to be true, is there an easy way to turn the ABS on or off? Thanks Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted December 11, 2012 Share Posted December 11, 2012 Personally, I would rather still have it in slippery conditions, as you note you go in a straight line with it on, without it, and you catch a bit of tarmac WITH grip, the truck will lurch over to that side making a skid quite possible. I have driven non-ABS 90s and my RRC in the snow and ice (on the road), and I would rather have ABS every time, but then it may be down to personal preference Best thing is ofc not to get it going that quickly in the first place Quote Link to comment Share on other sites More sharing options...
elbekko Posted December 11, 2012 Share Posted December 11, 2012 I would pay good money to get my ABS to shut off below 5 km/h or so, the damn thing just kept on going instead of one wheel somewhere gripping and stopping me. Definitely very different with ABS compared to non-ABS. But that's probably because I'm used to non-ABS and know how it reacts, as opposed to this automagic thing with ABS. Quote Link to comment Share on other sites More sharing options...
Oakmaster Posted December 11, 2012 Author Share Posted December 11, 2012 Best thing is ofc not to get it going that quickly in the first place I should have clarifed - this was at less than 20 MPH Quote Link to comment Share on other sites More sharing options...
Orgasmic Farmer Posted December 11, 2012 Share Posted December 11, 2012 I too dislike it on ice. We have a long steep drive (1 in 4) to the farm which sometimes ices over. It is deep-set between 2 hedges with a deep ditch on one side. First time I drove it with ABS (on a Subaru) I gingerly braked at the top at the first ice patch. Next thing I know I am squirted out the bottom of the drive at about 60 mph. But at least I was able to avoid the ditch! Happened again on a back road where I hit ice (very slowly but downhill) and travelled many hundreds of metres before I was able to stop. The other side of the coin I have once needed the ABS to avoid a potential collision with a lorry which was cutting a corner and it allowed me to brake and turn on a slippery surface and get into the hedge. Possibly saved my live on that occasion. I too would like it to shut off at low speed! Quote Link to comment Share on other sites More sharing options...
simonr Posted December 11, 2012 Share Posted December 11, 2012 I think part of the problem is that people allow the ABS to take full responsibility for stopping you - i.e. all they do is push the brake pedal and hope! I would prefer to have ABS, even below 5mph - but still drive it as if it were not fitted. Cadence braking still works, steering still works, looking for a verge or a better place to crash you can still do! I watched someone this morning (in a Nissan Juke) slide on sheet ice (there were patches of tarmac in amongst the ice) straight in to a fence. You could see the ABS doing it's thing - but it was almost like at the point they started to slide, they just gave up trying to do anything about it until the fence stopped them! I navigated the same corner at about the same speed in a front wheel drive van. The ABS sounded like it was having a fit - or at least it was getting very excited! But with a bit of cadence, a bit of being gentle with the brakes and a bit of gentle steering it was fine! I knew it would under-steer a bit so started the corner early. It over-steered a little at the apex of the bend and I probably drifted sideways a few feet. The Nissan should have been able to do the same (or better) but just carried on in a straight-ish line into the fence. Front end was fairly mangled, drivers state of mind mangled but he was uninjured - so I left him to un-mangle his mind! There is probably a fuse you could pull to disable the traction control / ABS? Si Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted December 11, 2012 Share Posted December 11, 2012 it allowed me to brake and turn on a slippery surface and get into the hedge. Possibly saved my live on that occasion. And this is the main benefit of the ABS, it allows the steering wheels to still steer, locked wheels aren't turning so can't affect the direction of travel even slightly as much as a rotating wheel. Quote Link to comment Share on other sites More sharing options...
Guest Posted December 11, 2012 Share Posted December 11, 2012 Personally I think the ABS/TC is a great advantage on a Defender and I would not be without it, but as Si says it is also about driver inputs and basic physics if you just slam on the brakes on ice you are going to slide either way ABS or not until your tyres have regained friction on the road surface, ABS in the wet just allows the tyres to work and shift water regaining friction instead of just locking up. However on Ice the friction you need to achieve to overcome momentum is fairly large as you also have the weight of your truck to factor into things. In your example you are basically a passenger because the truck/tyres cannot achieve the friction required to overcome the momentum. If you know that you are getting into this sort of situation being able to drive out of it is the best option low box and a low gear still allowing the wheels to drive and giving you a better chance of achieving the friction required to overcome or at least reduce the forward momentum. If you don't know you are about to hit ice then cadence braking works in the same way allowing the wheels to turn and giving the tyres a better chance of achieving friction. Jason. Quote Link to comment Share on other sites More sharing options...
TFC Posted December 11, 2012 Share Posted December 11, 2012 I'm most familiar with anti-lock braking systems used on aircraft, but I understand a car system is similar. Maximum braking is achieved when the wheels are rotating about 15% slower than if the brakes were off. If the wheels rotate slower than 15% less the friction required for 'braking' is achieved between the tyre and the road - which is much less efficient than within the brake unit. So people’s perception that maximum braking is achieved with locked wheels is a fallacy. On ice or compacted snow the coefficient of friction is VERY low, so even if the ABS is doing its best, the ability to stop with ABS is not much different from that with no ABS. The advantage that ABS has, as has been mentioned, is that because the wheels are still rotating (almost at full speed) it is slightly easier to steer. The big BUT is that because of the extremely low friction coefficient of an ice covered road, speed is your biggest enemy – too fast and you are joined to another object with a helically inclined plane J Downhill on an icy road with ABS will help you steer but make little difference to your ability to convert your Kinetic Energy into heat. Brakes need to be ‘driven’ which is greatly reduced by a slippery surface. Cheers, Tony Quote Link to comment Share on other sites More sharing options...
UdderlyOffroad Posted December 11, 2012 Share Posted December 11, 2012 I’m not sure where this ABS-as-a-substitute-for-engaging-brain comes from – presumably marketing related from when ABS was first introduced. I remember on my driving theory test (10+ yrs ago now), there were questions pertaining to the fact that ABS was no substitute for proper braking. O/T alert: I had a day off yesterday, and during my lunch-break (no Landie progress sadly, house DIY) ‘Dave’ was showing an old Top Gear. They showed a young Finnish chap learning to drive, and he had to complete at least three lessons on a skid-pan, as well as night driving, motorways…etc. Would be better than bloody pass-plus!! Quote Link to comment Share on other sites More sharing options...
jeremy996 Posted December 12, 2012 Share Posted December 12, 2012 This is going to sound very much like swinging the lamp, but when I was taught to drive a 4x4 by the Army in 1981, we were expected to brake sufficiently on snow and pea gravel to build up a mound in front of the wheels. The "wedge" aided the stop and kept everything stable. ABS would make a mess of that idea, (the wedge would never form), so ABS was seen as a problem for snow, sand and small gravel. Now on ice that won't be possible, so ABS allowing you to steer is perhaps the most help. I remember one of the braking engineers for Land Rover giving a presentation at MIRA, explaining that the Terrain Response settings for ABS varied for surfaces but that braking on sheet ice was limited by the lack of friction. He also said that a well trained driver could out-brake the ABS on ice and loose surfaces, but that a bad or average driver was much, much safer and more consistent with ABS! Quote Link to comment Share on other sites More sharing options...
SteveG Posted December 13, 2012 Share Posted December 13, 2012 There is probably a fuse you could pull to disable the traction control / ABS? There is, I suspect it wouldn't be too difficult to modify circuit to put a switch in so that it could be turned off and n for off-road use. Quote Link to comment Share on other sites More sharing options...
elbekko Posted December 13, 2012 Share Posted December 13, 2012 From discussing this thread with a friend yesterday, it's very possible that I simply thought I had the grip to stop without ABS because of the ABS, because a car without ABS would've felt twitchy. Either way, I'll have to get used to it! Quote Link to comment Share on other sites More sharing options...
Maverik Posted December 13, 2012 Share Posted December 13, 2012 What an interesting read, all very valid points, if more people read this and understood what ABS was I'm sure they'd be better drivers for it. Mav Quote Link to comment Share on other sites More sharing options...
Orgasmic Farmer Posted December 13, 2012 Share Posted December 13, 2012 When i got my first car with ABS back in the mid 90's the very first thing I did was find and empty carpark with hardpacked snow and set up a couple of cones and practised avoiding the cones while braking hard. It really helps to experience just what is happening when it kicks in and just how much control you have if you actually continue to steer the car. I think that ABS would be of more benefit if everyone practised using it. I have asked a number of people of the years how they found their ABS systems. Most don't even know they have it. Perhaps that is a good thing or maybe I just drive too fast (too much rallying in my youth!). Another downside of ABS is that it makes handbrake turns impossible! Quote Link to comment Share on other sites More sharing options...
JeffR Posted December 13, 2012 Share Posted December 13, 2012 When i got my first car with ABS back in the mid 90's the very first thing I did was find and empty carpark with hardpacked snow and set up a couple of cones and practised avoiding the cones while braking hard. It really helps to experience just what is happening when it kicks in and just how much control you have if you actually continue to steer the car. I think that ABS would be of more benefit if everyone practised using it. I have asked a number of people of the years how they found their ABS systems. Most don't even know they have it. Perhaps that is a good thing or maybe I just drive too fast (too much rallying in my youth!). Another downside of ABS is that it makes handbrake turns impossible! Once, in my very distant youth, I tried to handbrake a 7.5t Merc flatbed (you could power slide the bugger ! and kick the back end out in bends)... broke my nose on the steering wheel- bloody air brake worked on all 4 corners, oh to be that age again and still running my 1558 8 port mini.......... Quote Link to comment Share on other sites More sharing options...
Snagger Posted December 15, 2012 Share Posted December 15, 2012 There is, I suspect it wouldn't be too difficult to modify circuit to put a switch in so that it could be turned off and n for off-road use. But try getting insurance with that mod! Quote Link to comment Share on other sites More sharing options...
Snagger Posted December 15, 2012 Share Posted December 15, 2012 What an interesting read, all very valid points, if more people read this and understood what ABS was I'm sure they'd be better drivers for it. Mav Couldn't agree more, but I'd extend that to all the vehicle systems. Undertsnding how they work helps you better predict and understand the vehicle's behaviour, so you can pre-empt or correct errors more swiftly and appropriately.My RRC ahs four-channel ABS and rear ETC and it's brilliant on snow and ice. An awful lot of that is down to being driven cautiosly in those conditions and having decent quality, normal spec size AT tyres (marked for mus and snow, as most decent ATs are) with plenty of tread on them. Oversize tyres, mud or summer road based patterns and poor driving will cause skids on even the best ABS systems. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted December 15, 2012 Share Posted December 15, 2012 Worth noting that ABS systems are not created equal - many cars have front-wheel only ABS, and the sophistication varies greatly. LR systems are (for their relative ages) pretty advanced and designed to cope with more than the average family hatchback system. There's a whole world of different ways to skin the same cat, if you were designing the ABS for a muppet-car like a Corsa* you might assume the driver is not going to do much more than stamp on the pedal and shut their eyes, whereas in a LR you might assume the driver would anticipate a bit more, try and correct, etc., and you might also assume the car may be used in much worse conditions due to the 4x4. For a Subaru or suchlike, it's unlikely to be towing a horsebox across a muddy field but it might well be heading for the armco at nurburgring, which means a different set of parameters in the ABS again. As with anything, it's well worth having some understanding of how the system works (AKA how it "thinks"), what it can & can't do, and the basic laws of physics which can't be cheated no matter how clever your car is. There's always some situation where driver aids can be fooled, or it's better not to wear a seatbelt, etc. but for 99.9% of the people 99.9% of the time it's a benefit, otherwise no-one would bother. * To any corsa drivers - tough, it's true, get over it. Quote Link to comment Share on other sites More sharing options...
Snagger Posted December 15, 2012 Share Posted December 15, 2012 I agree with you, Fridge - LR ABS is going to be better on slippery stuff than most because they're designed to cope in Arctic and muddy conditions or on wet grass, and of course are more expensive too. But, regardless of how well engineered a braking system is or how clever its ABS is, if you have no friction between the vehicle and the surface, you're not going to stop regardless, even if you use cadence braking. That's why tyre choice, condition and pressure and driver behaviour will always have vastly more effect than ABS, just as they have more influence than lockers, lifts kits, extreme articulation and so on off-road. Mud tyres are desperately bad on ice, as are low-profile performance tyres, so the original question of whether ABS makes it worse is rather moot, and comparisons between one vehicle and another, even of the same model, are misleading unless all the variables other than the fitment or omission of ABS are eliminated. Quote Link to comment Share on other sites More sharing options...
Escape Posted December 17, 2012 Share Posted December 17, 2012 There is, I suspect it wouldn't be too difficult to modify circuit to put a switch in so that it could be turned off and n for off-road use. In my Defender TD5 I had set up a relay that was activated at the same time as the compressor for the ARBs and cut power to the ABS-ECU (fuse 15 IIRC) to disable the TC. I know it shouldn't have been necessary, but found the TC acting quite erratic when using just one locker so decided to disable it to make life easier. This also disabled the ABS off course. Downside was that that the system wouldn't restart automatically when power was restored, you had to switch off the ignition to get the ABS-ECU to reboot. @orgasmic farmer, my Merc didn't have any problems with handbrake turns, despite having ABS. What did pose big problem (to the driver), was the fact that the parking brake is in fact a fourth pedal, making it quite difficult to get the timing just right AND use the clutch (RWD) at the same time. Filip Quote Link to comment Share on other sites More sharing options...
sean f Posted December 17, 2012 Share Posted December 17, 2012 Not looked to closely at the control module for the ABS on a Defender but I assume it will be basically the same module as on a P38. I have just finished (well nearly) rewiring a P38 for a replacement engine and had to bin the BECM. I wanted to retain the ABS and TC so had a good look at the unit, once you start looking it was surprisingly easy to rewire it and get it working complete with warning lights on the dash, there is even an output for a speedo which goes to the BECM which I just ignored. Not entirely sure now the BECM would have liked having the ABS off line and I expect it would throw up lots of errors and possible go to limp home mode since this was removed and sold not an issue for me. ABS and traction control are pretty much the same thing working in a different direction if that makes sense. ABS will release the brakes on a wheel it has detected is locked up, traction control will apply the brakes to a wheel it believes is spinning (think fiddle brakes). Obviously this is pretty simplistic and speed of reactions etc needs to be looked at to keep things working smoothly. For traction control to work there must be a means of having brake fluid pressure with out input from the brake pedal, normally an electronic pump, other than that it is just the software in the controller. I wouldn't be at all surprised if when an vehicle is availabe in standard form without TC and a premium version with TC it is the same set up but with the TC option either switched of in the software or disabled in some other way someone with sufficient knowledge could probable enable it in the standard vehicle. Quote Link to comment Share on other sites More sharing options...
Snagger Posted December 17, 2012 Share Posted December 17, 2012 ABS and traction control are pretty much the same thing working in a different direction if that makes sense. ABS will release the brakes on a wheel it has detected is locked up, traction control will apply the brakes to a wheel it believes is spinning (think fiddle brakes). Obviously this is pretty simplistic and speed of reactions etc needs to be looked at to keep things working smoothly. For traction control to work there must be a means of having brake fluid pressure with out input from the brake pedal, normally an electronic pump, other than that it is just the software in the controller. I wouldn't be at all surprised if when an vehicle is availabe in standard form without TC and a premium version with TC it is the same set up but with the TC option either switched of in the software or disabled in some other way someone with sufficient knowledge could probable enable it in the standard vehicle. That's also true in any ABS system - the brake pressure in the callipers is released on lock-up by isolating the feed circuit to the nrake unit and opening a return or depressirising line. Once traction is regained, the return valve closes and the feed line reopens to reapply pressure. That can only be done with fresh fluid pressure supplied by an accumulator (pumps are too slow, but are used to charge the accumulator). If you didn't have an accumulator (or if the accumulator isn't charged), then the ABS system will release the brakes once and that's all - you'd have to pump the pedal to get them back on.ETC is, as you said, just a different logic mode within the ECU that opens the feed valve from the accumulator to a spinning wheel's brake unit. Quote Link to comment Share on other sites More sharing options...
101sean Posted December 17, 2012 Share Posted December 17, 2012 The Defender uses a separate Wabco ECU. If you ever get shuttle switch failure on a Defender ABS modulator, the fix is same as Disco 2 Quote Link to comment Share on other sites More sharing options...
Escape Posted December 18, 2012 Share Posted December 18, 2012 The P38a can cope just fine with the ABS/TC disabled, without any problems or errors in the BECM, apart from a message on the dash. The key is to disable the system somewhere it expects, like a fuse. On the Defender (late TD5) fuse 11 (I thought it was 15, my mistake) is for the ABS-ECU only, so a perfect place to put a relay, as a fuse failure is something the system can definitely cope with. On the P38a, fuse 24 supplies power to both the ABS-ECU and EAS timer, so you need to do a bit more digging to disconnect only the ABS, but it is very possible. Again, when turning it off and back on again, the ECU will only reactivate after the ignition has been cycled. So far from ideal to use to disable the ABS in the rare situations when you'd want to, because you'd be left without ABS when you might need it back on the road and more importantly, you will expect it to be there as per usual. But it could be usefull for offroading. The pressure switch is hard wired to the relay for the ABS hydraulic pump, so you do have power assisted brakes even with the ABS-ECU disconnected. Filip Quote Link to comment Share on other sites More sharing options...
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