ABS Demonstration
Discussion
I know every biker I speak to is a riding god, and never has a lapse of concentration so ABS is just unnecessary weight, but i'd quite like it...
http://www.youtube.com/watch?v=-Zv3Sacl7JQ&NR=...
It just doesn't seem to be fitted to any bikes I want. The clip is hardly conclusive. It seems to show that even with both wheels locked, which is theoretically a fairly efficient way of stopping, ABS still stops quicker. I quite fancy those outriggers, would be a spectacular way to stop at the lights, sliding backwards
http://www.youtube.com/watch?v=-Zv3Sacl7JQ&NR=...
It just doesn't seem to be fitted to any bikes I want. The clip is hardly conclusive. It seems to show that even with both wheels locked, which is theoretically a fairly efficient way of stopping, ABS still stops quicker. I quite fancy those outriggers, would be a spectacular way to stop at the lights, sliding backwards
Locking the wheels is not the most efficient way of stopping. The test would have been better if the rider hadn't locked up or had at least released and reapplied the brakes when he did. I'm sure ABS would help in some circumstances (as would traction control) but I don't think novices should use an ABS equiped bike until they've learnt some survival skills. Most bikes don't have ABS and could you imagine what would happen when they slam the brakes on expecting the bike to sort it out?
AlexHancock said:
Locking the wheels is not the most efficient way of stopping. The test would have been better if the rider hadn't locked up or had at least released and reapplied the brakes when he did. I'm sure ABS would help in some circumstances (as would traction control) but I don't think novices should use an ABS equiped bike until they've learnt some survival skills. Most bikes don't have ABS and could you imagine what would happen when they slam the brakes on expecting the bike to sort it out?
I did not claim that locking was the most efficient way of stopping, just a fairly efficient way. I thought around 10% tyre slip was the most efficient way of stopping? Trying to apply just the right amount of pressure with the tire on the edge of slip is very hard in anything less then perfect conditions (any camber makes it interesting!). So locking actually achieves pretty good results (assuming you dont want to change direction!). Obviously, this is theoretical, as you can't lock both wheels on a motorcycle and stay upright! People often talk about cadence braking improving stopping distance in a straight line, surely it's only beneficial when you need to change direction? I'm no expert in this field and am happy to be corrected.It is true that it would have been interesting to see what would happen with the non-abs rider trying to stop as quick as possible without locking. Does the fact Honda did not show this suggest they thought it might ruin the abs demo? Dunno...
Edited by doc3 on Tuesday 29th January 20:17
You can't read anything about braking distances into that because a locked wheel has far less grip than a rolling one, and the bike slewed round putting weight onto the castor wheel which was unbraked. All that demo shows is that for bikes as for cars, it's easier to stay in control if you avoid locking up.
GreenV8S said:
You can't read anything about braking distances into that because a locked wheel has far less grip than a rolling one
I had always thought that until my IAM observer told me the difference was not that great, and the Roadcraft book backed him up. It only becomes an issue when changing direction. Is there any quantified results showing the stopping difference between a locked and a close to locking wheel? It comes up quite a lot when talking to people about braking. "Just because everyone knows it is better" isn't good enough for me. I'm an awkward sodHyperion said:
My next bike will definitely have ABS...It’s a life saver. Practising emergency stops is easy because you know it's going to happen. But performing a real emergency stop is scary. Especially if you're cold and tired.
That's my feeling. I've never needed it. I might need it one time in a million. But if i ever do need it, and it makes the difference between getting up and ever walking again, or just ever getting up, i'll take it. I suppose it's the reason i also use ATGATT, including back protector. Some would sneer, i couldn't care less. I realise many people have ridden for decades without it and survived. People rode with drum brakes for decades and survived, doesn't mean disc brakes aren't a good idea! (my ancient bike still has a rear drum!). On road, i really think it makes a lot of sense. I have ridden old bikes with abs, and a new 12GSA with, just the other day. Modern ABS is a world apart from the early systems!Edited by doc3 on Tuesday 29th January 21:22
doc3 said:
GreenV8S said:
You can't read anything about braking distances into that because a locked wheel has far less grip than a rolling one
I had always thought that until my IAM observer told me the difference was not that great, and the Roadcraft book backed him up. It only becomes an issue when changing direction. Is there any quantified results showing the stopping difference between a locked and a close to locking wheel? It comes up quite a lot when talking to people about braking. "Just because everyone knows it is better" isn't good enough for me. I'm an awkward sodFor cars the main advantage of ABS is that you stay in control. For bikes the main advantage I can see is that you stay on the bike. I don't think it's going to stop very well once it's on its side.
GreenV8S said:
doc3 said:
GreenV8S said:
You can't read anything about braking distances into that because a locked wheel has far less grip than a rolling one
I had always thought that until my IAM observer told me the difference was not that great, and the Roadcraft book backed him up. It only becomes an issue when changing direction. Is there any quantified results showing the stopping difference between a locked and a close to locking wheel? It comes up quite a lot when talking to people about braking. "Just because everyone knows it is better" isn't good enough for me. I'm an awkward sodFor cars the main advantage of ABS is that you stay in control. For bikes the main advantage I can see is that you stay on the bike. I don't think it's going to stop very well once it's on its side.
The reason you take longer to stop locked up over rolling is that a locked wheel doesn't keep the same kinetic coeficient of friction.
At the beginning of an emergency stop, you hit the brakes. Your rolling friction provides the resistance to your momentum and the car or bike slows down. As you keep applying more brake pressure you get to the point of locking up. At this point it becomes 'easier' for the wheel to lock up than keep rolling. (Excuse the poor terminology, but it's the simplest way of explaining it.) This point is known as starting friction, or sometimes known as stiction. Once this point has passed we move to kinetic friction, which has a lower coefficient than starting friction.
This can be demonstrated when doing something like pulling an old fencepost from the ground. The effort to get it initially moving is large, but once moving less effort is required to keep it moving.
This can be seen in a car/bike by releasing the brakes just a little after locking up to find that rather than change back to rolling, you're still sliding.
Or for anyone familiar with wheelspinning/burnouts, once you've got it spinning, you don't need as much gas to keep it there.
In terms of the tyre, friction drops off when sliding due to massive contact point over heating (smoke) and the tyre melting and almost lubricating itself. Plus, a fair amount of your rolling resistance comes from the continual tyre deformation that rolling produces. It is this deformation that heats your tyres on trackdays, not the tyre sliding on the ground.
Please note much of the above is based on physics I heven't used for about 15 years. Any physicists out there may want to correct some of it. But I think the general gist is okay.
At the beginning of an emergency stop, you hit the brakes. Your rolling friction provides the resistance to your momentum and the car or bike slows down. As you keep applying more brake pressure you get to the point of locking up. At this point it becomes 'easier' for the wheel to lock up than keep rolling. (Excuse the poor terminology, but it's the simplest way of explaining it.) This point is known as starting friction, or sometimes known as stiction. Once this point has passed we move to kinetic friction, which has a lower coefficient than starting friction.
This can be demonstrated when doing something like pulling an old fencepost from the ground. The effort to get it initially moving is large, but once moving less effort is required to keep it moving.
This can be seen in a car/bike by releasing the brakes just a little after locking up to find that rather than change back to rolling, you're still sliding.
Or for anyone familiar with wheelspinning/burnouts, once you've got it spinning, you don't need as much gas to keep it there.
In terms of the tyre, friction drops off when sliding due to massive contact point over heating (smoke) and the tyre melting and almost lubricating itself. Plus, a fair amount of your rolling resistance comes from the continual tyre deformation that rolling produces. It is this deformation that heats your tyres on trackdays, not the tyre sliding on the ground.
Please note much of the above is based on physics I heven't used for about 15 years. Any physicists out there may want to correct some of it. But I think the general gist is okay.
doc3 said:
Thanks for the reply. 20% is quite substantial! Is there any data that can be viewed? I'd been told it was <10% but once again there was no data to back it up.
Racelogic published some sample data here but don't say where it comes from:http://www.racelogic.co.uk/?show=Traction_Control-...
I've seen similar data in one of the Bosch handbooks and maybe that's where they got this from. These figures show a 25% drop, which is slightly more than I suggested but it depends on all sorts of things such as how hot the contact patch gets. If you grab a wheel under braking in a road car you can feel it pull to the side, lock both wheels you can feel the grip drop off dramatically, similarly you can feel the acceleration drop off sharply if you break traction under acceleration. This is all for road cars but I would expect to find road bikes broadly similar.
I'd repeat though: the main benefit of ABS is not that you stop quicker, it's that you stay in control.
Edited by GreenV8S on Tuesday 29th January 23:19
carlosvalderrama said:
The reason you take longer to stop locked up over rolling is that a locked wheel doesn't keep the same kinetic coeficient of friction.
At the beginning of an emergency stop, you hit the brakes. Your rolling friction provides the resistance to your momentum and the car or bike slows down. As you keep applying more brake pressure you get to the point of locking up. At this point it becomes 'easier' for the wheel to lock up than keep rolling. (Excuse the poor terminology, but it's the simplest way of explaining it.) This point is known as starting friction, or sometimes known as stiction. Once this point has passed we move to kinetic friction, which has a lower coefficient than starting friction.
This can be demonstrated when doing something like pulling an old fencepost from the ground. The effort to get it initially moving is large, but once moving less effort is required to keep it moving.
This can be seen in a car/bike by releasing the brakes just a little after locking up to find that rather than change back to rolling, you're still sliding.
Or for anyone familiar with wheelspinning/burnouts, once you've got it spinning, you don't need as much gas to keep it there.
In terms of the tyre, friction drops off when sliding due to massive contact point over heating (smoke) and the tyre melting and almost lubricating itself. Plus, a fair amount of your rolling resistance comes from the continual tyre deformation that rolling produces. It is this deformation that heats your tyres on trackdays, not the tyre sliding on the ground.
Please note much of the above is based on physics I heven't used for about 15 years. Any physicists out there may want to correct some of it. But I think the general gist is okay.
This makes some sense. But what are the coefficients for stiction and kinetic friction? I'm interested in what the differential between, say 10% tyre slip, and lock would be. I'm too stoopid to work out the formulaeAt the beginning of an emergency stop, you hit the brakes. Your rolling friction provides the resistance to your momentum and the car or bike slows down. As you keep applying more brake pressure you get to the point of locking up. At this point it becomes 'easier' for the wheel to lock up than keep rolling. (Excuse the poor terminology, but it's the simplest way of explaining it.) This point is known as starting friction, or sometimes known as stiction. Once this point has passed we move to kinetic friction, which has a lower coefficient than starting friction.
This can be demonstrated when doing something like pulling an old fencepost from the ground. The effort to get it initially moving is large, but once moving less effort is required to keep it moving.
This can be seen in a car/bike by releasing the brakes just a little after locking up to find that rather than change back to rolling, you're still sliding.
Or for anyone familiar with wheelspinning/burnouts, once you've got it spinning, you don't need as much gas to keep it there.
In terms of the tyre, friction drops off when sliding due to massive contact point over heating (smoke) and the tyre melting and almost lubricating itself. Plus, a fair amount of your rolling resistance comes from the continual tyre deformation that rolling produces. It is this deformation that heats your tyres on trackdays, not the tyre sliding on the ground.
Please note much of the above is based on physics I heven't used for about 15 years. Any physicists out there may want to correct some of it. But I think the general gist is okay.
Has anyone done real world examples, bike or car?GreenV8S said:
doc3 said:
Thanks for the reply. 20% is quite substantial! Is there any data that can be viewed? I'd been told it was <10% but once again there was no data to back it up.
Racelogic published some sample data here but don't say where it comes from:http://www.racelogic.co.uk/?show=Traction_Control-...
I've seen similar data in one of the Bosch handbooks and maybe that's where they got this from. These figures show a 25% drop, which is slightly more than I suggested but it depends on all sorts of things such as how hot the contact patch gets. If you grab a wheel under braking in a road car you can feel it pull to the side, lock both wheels you can feel the grip drop off dramatically, similarly you can feel the acceleration drop off sharply if you break traction under acceleration. This is all for road cars but I would expect to find road bikes broadly similar.
GreenV8S said:
I'd repeat though: the main benefit of ABS is not that you stop quicker, it's that you stay in control.
I'd agree with that. The critical element when you're on a bike! Most of the physics is academic.
What matters is how you apply the brakes and how much pressure you use.
And under emergency conditions i.e. milf in the 4x4 pull out from side street just how do you react in the 0.2sec
This is really where ABS comes into its own.
Happened to me twice, once i was able to stop without locking the wheel, nice dry day etc, other time the front locked up (winter greasy roads) i ended up in hospital.
If I had ABS the second time I would not have come off my bike.
If I had It the first time I think I would still have been able to stop in time. I doubt I am good enough to out brake ABS.
Pretty sure one of the bike mags did a test on this and the ABS bike consistently out braked the non ABS bike even when a top racer was doing the braking.
What matters is how you apply the brakes and how much pressure you use.
And under emergency conditions i.e. milf in the 4x4 pull out from side street just how do you react in the 0.2sec
This is really where ABS comes into its own.
Happened to me twice, once i was able to stop without locking the wheel, nice dry day etc, other time the front locked up (winter greasy roads) i ended up in hospital.
If I had ABS the second time I would not have come off my bike.
If I had It the first time I think I would still have been able to stop in time. I doubt I am good enough to out brake ABS.
Pretty sure one of the bike mags did a test on this and the ABS bike consistently out braked the non ABS bike even when a top racer was doing the braking.
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