The Swedish testing report I linked to made a similar claim regarding stopping distance in very deep, loose snow and slush. However, I believe that if you are driving through gravel or snow deep enough that locking the wheels plows them down into the gravel or snow, directional control, not stopping distance, is likely your biggest problem. My experience driving cars in deep snow (I imagine gravel would be similar) is that the front wheels become rudders, and if you try turning on a "crowned" or tilting road surface, or fall off a road into a rut, once you start sliding in gravity's direction you will find it almost impossible to steer using your "rudders".
A stunt I used to do on my dirtbike: keep the power on and slowly apply the front brake until it locks. You can keep steering in deep gravel or snow.
Traction is not a simple quantity on loose surfaces, and it definitely isn't just a matter of Coulomb friction. Hell, even Coulomb friction isn't simple. Grip is a hugely complicated set of physical processes, involving hydrgen bonds, Van Der Waals forces, covalent and ionic bonds, and surface roughness to name probably too few. Top fuel dragsters are launching at 5 to 6 Gs with no aerodynamic downforce available, a condition you can't achieve with Coulomb friction, accomplished with massive amounts of sliding friction.
To see this manifest go watch a circle track, rally, or flat track race. Every contact patch is sliding at just about every point on the course. If static friction were the optimum condition these races would be run at a jogging pace. On loose surfaces it just ain't that simple.
Driving on loose surfaces is not a matter of avoiding sliding, it's a matter of managing sliding. Braking isn't a choice between locked wheels and the minimal braking you'd get without sliding, there's a continuum there. It's just one you can't explore with ABS on.
I use the e brake so I don't have to hit the pedal too hard. My experience has been that with very little weight in the rear, the backs will lock up immediately when hitting the pedal hard in the snow. The goal is to keep the backs from locking up and just slow them down and keep them rotating. Its a skill developed over many years and miles. This applies to disc fronts, drum backs, without ABS in snow. Most braking systems with front discs require very little pressure to make the discs do most of the work. On dry pavement, the backs don't lock up because of the traction. This also goes hand in hand with having your best tires on the rear (w/fwd) for driving in snow or rain for that matter to maintain directional control and braking.
Alls I can say is go out and try it in a large parking lot, it works.
I know of the bootleg turnaround. That's a whole different manuveur.
Yeah, that's a recipe for disaster. Drums already 'want' to lock up by the nature of their design, and with poor traction (snow) things only get worse. The e-brake tip is one of those I'll file away for safe-keeping: the opportunities I'll have to use it are pretty rare, but hey.
I guess you could accomplish something similar by messing around with an adjustable proportioning valve, to bias the brake line pressure to the front (?), but that's a lot more trouble than just using the e-brake.
Whenever I get around to hot-rodding my project vehicles, they are all getting four-wheel discs.
Why would you need to apply the emergency brake handle if you are also hitting the brake pedal? That pedal does operate all four brakes, you know. (at least, unless you've disconnected the rears).
BTW If you jam on the emergency brake to lock the rear wheels only on snow or ice, the rear end of the car will slowly come up front looking for something to do. It's the best way to do a 360/spin-erama in a FWD car (get some speed up, throw the wheel over carefully, and hit the brake lever!)
I use the e brake so I don't have to hit the pedal too hard. My experience has been that with very little weight in the rear, the backs will lock up immediately when hitting the pedal hard in the snow. The goal is to keep the backs from locking up and just slow them down and keep them rotating. Its a skill developed over many years and miles. This applies to disc fronts, drum backs, without ABS in snow. Most braking systems with front discs require very little pressure to make the discs do most of the work. On dry pavement, the backs don't lock up because of the traction. This also goes hand in hand with having your best tires on the rear (w/fwd) for driving in snow or rain for that matter to maintain directional control and braking.
Alls I can say is go out and try it in a large parking lot, it works.
I know of the bootleg turnaround. That's a whole different manuveur.
Why would you need to apply the emergency brake handle if you are also hitting the brake pedal? That pedal does operate all four brakes, you know. (at least, unless you've disconnected the rears).
BTW If you jam on the emergency brake to lock the rear wheels only on snow or ice, the rear end of the car will slowly come up front looking for something to do. It's the best way to do a 360/spin-erama in a FWD car (get some speed up, throw the wheel over carefully, and hit the brake lever!)
In a regular car you do it in reverse, AKA "A Rockford."
Only had ABS on rental cars so I never really put it to any tests.
But living in the land of ice and snow, one technique for safe, sure and controlled stopping in snow is to use the emergency brake in conjunction with the pedal, especially in a front wheel drive car. It will keep the back end from breaking loose and passing you by in a spin.
Of course, you need the type that has the lever in the middle and they must be properly adjusted, but you will stop in a straight line and in a hurry if needed.
Why would you need to apply the emergency brake handle if you are also hitting the brake pedal? That pedal does operate all four brakes, you know. (at least, unless you've disconnected the rears).
BTW If you jam on the emergency brake to lock the rear wheels only on snow or ice, the rear end of the car will slowly come up front looking for something to do. It's the best way to do a 360/spin-erama in a FWD car (get some speed up, throw the wheel over carefully, and hit the brake lever!)
Lazy8 wrote: Not sure what you're arguing with as the link is broken. Ian Law is probably wrong about stopping on snow and ice (certainly about ice, and at least about light accumulations of snow) but there are surfaces that ABS performs poorly on, especially gravel. The mechanism that produces the quickest stops on gravel is locking the wheels, which produces a "bow wave" and dissipates energy thru friction between the rocks over a large volume. Rolling smoothly to a stop will take about 30% farther. Link fixed.
The Swedish testing report I linked to made a similar claim regarding stopping distance in very deep, loose snow and slush. However, I believe that if you are driving through gravel or snow deep enough that locking the wheels plows them down into the gravel or snow, directional control, not stopping distance, is likely your biggest problem. My experience driving cars in deep snow (I imagine gravel would be similar) is that the front wheels become rudders, and if you try turning on a "crowned" or tilting road surface, or fall off a road into a rut, once you start sliding in gravity's direction you will find it almost impossible to steer using your "rudders".
Only had ABS on rental cars so I never really put it to any tests.
But living in the land of ice and snow, one technique for safe, sure and controlled stopping in snow is to use the emergency brake in conjunction with the pedal, especially in a front wheel drive car. It will keep the back end from breaking loose and passing you by in a spin.
Of course, you need the type that has the lever in the middle and they must be properly adjusted, but you will stop in a straight line and in a hurry if needed.
Using the emergency / parking brake is also a good way to avoid getting a speeding ticket. Your brake lights do not go on when you use it. When you are speeding in a group, when in doubt, the cop will key on the car that shows brake lights and pull it over. The brake lights are an admission of guilt.
Using the emergency brake when someone is tailgaiting you will also cause the tailgaiter to back off when all of a sudden they find themselves millimeters from your bumper in an unannounced brake check. When using this techique you must be ready to tromp on the gas to prevent an actual contact. Especially effective with tailgaiters who text while driving.
Only had ABS on rental cars so I never really put it to any tests.
But living in the land of ice and snow, one technique for safe, sure and controlled stopping in snow is to use the emergency brake in conjunction with the pedal, especially in a front wheel drive car. It will keep the back end from breaking loose and passing you by in a spin.
Of course, you need the type that has the lever in the middle and they must be properly adjusted, but you will stop in a straight line and in a hurry if needed.
Using the emergency / parking brake is also a good way to avoid getting a speeding ticket. Your brake lights do not go on when you use it. When you are speeding in a group, when in doubt, the cop will key on the car that shows brake lights and pull it over. The brake lights are an admission of guilt.
Using the emergency brake when someone is tailgaiting you will also cause the tailgaiter to back off when all of a sudden they find themselves millimeters from your bumper in an unannounced brake check. When using this techique you must be ready to tromp on the gas to prevent an actual contact. Especially effective with tailgaiters who text while driving.
Sure, ABS is not better in ALL cases, but in the vast majority of situations, ABS is better. But stopping distance is not necessarily the most important factor. ABS allows you to maintain CONTROL while braking, instead of skidding. In a real panic stop, you may not have enough distance to stop, period, with or without ABS. But if you stomp the pedal and start skidding, you lose the ability to steer off to the shoulder. With ABS, you may still be able to steer away from the impact.
But yeah, on gravel or other loose/bumpy surfaces, you're probably screwed regardless. But, on those surfaces, you're less likely to be driving at high speed, so there's that.
Lazy8 wrote: Not sure what you're arguing with as the link is broken. Ian Law is probably wrong about stopping on snow and ice (certainly about ice, and at least about light accumulations of snow) but there are surfaces that ABS performs poorly on, especially gravel. The mechanism that produces the quickest stops on gravel is locking the wheels, which produces a "bow wave" and dissipates energy thru friction between the rocks over a large volume. Rolling smoothly to a stop will take about 30% farther. Sure, ABS is not better in ALL cases, but in the vast majority of situations, ABS is better. But stopping distance is not necessarily the most important factor. ABS allows you to maintain CONTROL while braking, instead of skidding. In a real panic stop, you may not have enough distance to stop, period, with or without ABS. But if you stomp the pedal and start skidding, you lose the ability to steer off to the shoulder. With ABS, you may still be able to steer away from the impact.
But yeah, on gravel or other loose/bumpy surfaces, you're probably screwed regardless. But, on those surfaces, you're less likely to be driving at high speed, so there's that.
NEWS FLASH: Automotive writer Ian Law doesn't know the first thing about Newtonian mechanics, and has no business writing about automotive technical issues.
Here is a fact that catches a lot of motorists by surprise: if the vehicle we are driving is equipped with ABS brakes, our stopping distances on ice and snow will be longer than if our vehicle did not have ABS brakes. In older vehicles and less expensive vehicles, ABS can lengthen our stopping distances by up to 50 per cent compared to non-ABS.
(The above statement is demonstrably false. The reason: the coefficient of static friction is higher than the coefficient of kinetic friction)
Some common values of coefficients of kinetic and static friction (from Ben Townsend's website):
Surfaces
µ (static)
µ (kinetic)
Steel on steel
0.74
0.57
Glass on glass
0.94
0.40
Metal on Metal (lubricated)
0.15
0.06
Ice on ice
0.10
0.03
Teflon on Teflon
0.04
0.04
Tire on concrete
1.00
0.80
Tire on wet road
0.60
0.40
Tire on snow
0.30
0.20
These values are approximate.
Car and Driver set out to test the effectiveness of ABS when it first became widely available on passenger vehicles. The most effective way to stop a car, we know from physics, is to apply the brakes until lockup is imminent. Very few drivers are capable of doing this consistently. C&D corralled expert drivers, including race car drivers, and put them behind the wheel of cars equipped with disconnectable ABS in an attempt to beat or at least duplicate stopping distances produced using ABS. I don't think they succeeded. Their results have been duplicated. See
ABS produces shorter stopping distances regardless of the surface, (dry pavement, wet pavement, snow, ice, vaseline, etc.) because, although it does not achieve optimum braking, it gets closer than human drivers reliably can. Humans simply aren't capable of consistently braking at the point of lock-up at different speeds on different surfaces and in different vehicles. If you're on a car without ABS and need to stop in a straight path, your shortest stopping distance on average is produced by mashing on the brakes. In very slippery conditions, or when you need to turn and brake, you need to pump the pedal to allow some rolling for directional control (this is the technique everyone was advised to use before ABS, a sort of crude version of what ABS does).
NEWS FLASH: Automotive writer Ian Law doesn't know the first thing about Newtonian mechanics, and has no business writing about automotive technical issues.
Not sure what you're arguing with as the link is broken. Ian Law is probably wrong about stopping on snow and ice (certainly about ice, and at least about light accumulations of snow) but there are surfaces that ABS performs poorly on, especially gravel. The mechanism that produces the quickest stops on gravel is locking the wheels, which produces a "bow wave" and dissipates energy thru friction between the rocks over a large volume. Rolling smoothly to a stop will take about 30% farther.
NEWS FLASH: Automotive writer Ian Law doesn't know the first thing about Newtonian mechanics, and has no business writing about automotive technical issues.
Here is a fact that catches a lot of motorists by surprise: if the vehicle we are driving is equipped with ABS brakes, our stopping distances on ice and snow will be longer than if our vehicle did not have ABS brakes. In older vehicles and less expensive vehicles, ABS can lengthen our stopping distances by up to 50 per cent compared to non-ABS.
(The above statement is demonstrably false. The reason: the coefficient of static friction is higher than the coefficient of kinetic friction)
Some common values of coefficients of kinetic and static friction (from Ben Townsend's website):
Surfaces
µ (static)
µ (kinetic)
Steel on steel
0.74
0.57
Glass on glass
0.94
0.40
Metal on Metal (lubricated)
0.15
0.06
Ice on ice
0.10
0.03
Teflon on Teflon
0.04
0.04
Tire on concrete
1.00
0.80
Tire on wet road
0.60
0.40
Tire on snow
0.30
0.20
These values are approximate.
Car and Driver set out to test the effectiveness of ABS when it first became widely available on passenger vehicles. The most effective way to stop a car, we know from physics, is to apply the brakes until lockup is imminent. Very few drivers are capable of doing this consistently. C&D corralled expert drivers, including race car drivers, and put them behind the wheel of cars equipped with disconnectable ABS in an attempt to beat or at least duplicate stopping distances produced using ABS. I don't think they succeeded. Their results have been duplicated. See
ABS produces shorter stopping distances regardless of the surface, (dry pavement, wet pavement, snow, ice, vaseline, etc.) because, although it does not achieve optimum braking, it gets closer than human drivers reliably can. Humans simply aren't capable of consistently braking at the point of lock-up at different speeds on different surfaces and in different vehicles. If you're on a car without ABS and need to stop in a straight path, your shortest stopping distance on average is produced by mashing on the brakes. In very slippery conditions, or when you need to turn and brake, you need to pump the pedal to allow some rolling for directional control (this is the technique everyone was advised to use before ABS, a sort of crude version of what ABS does).
You've never been where I live, have you?
