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Re: ABS, slipping and sliding and so...


Hello all

On  Tue, 9 Sep 1997 20:03:37, Heiko Schwerdt wrote:
.
> ABS WILL NOT SHORTEN YOUR STOPPING DISTANCE!
> The purpose of ABS is to keep the vehicle under control i.e. be able
> to steer while applying the full brake force. 
> Under certain circumstances the stopping distance will be longer than
> without ABS.

This is true to a certain extent. Compared to a vehicle without ABS 
where one or more wheels may lock under emergency braking, a vehicle 
equipped with ABS will stop in a shorter distance.

> Without ABS (ie. on all Type 3s) the following applies:
> Independent of road surface (Bitumen, gravel, sand, ice...) or 
> wether condition (dry, rain, snow...) the shortest way to stop your
> car is with four locked wheels.

I disagree totally! Friction generated by the brakes combined with the 
adhesion of the tyres to the road surface cause a vehicle to stop. 
The distance it takes to stop is influenced by the power applied by 
the brakes in the first place, and the amount of adhesion that is 
possible between the tyres and road surface. This adhesion is 
influenced by many aspects like, tread depth, rubber compound, 
inflation pressure, tyre temperature, physical road surface (dry/wet 
bitumen, gravel, snow, ice, etc.), weight transfer during braking to 
name but a few. Friction generated between the tyres and the road 
surface alone is not sufficient to stop a vehicle quickly

> I have done a safety training at the ADAC (german counterpart of AAA)
> and it was really impressive how much you actually have to hammer
> the brakes on a dry road.
> Ok you cannot steer your car anymore and the car may start spinning
> but you keep on going in the direction that you were going before 
> the braking (This is a law of physics).

Sir, I do not hold your standards of safety training in high regard 
anymore. The important issue here is to remain in control over your 
vehicle. That means keeping all the wheels rotating, the rear end in 
line, and above all to be able to steer the car away from obstacles, 
whist stopping in the shortest possible time and distance

One never sees Formula One drivers lock all four wheels when braking 
from 200 mph to take a corner or to out-brake another driver in 
advance to a corner. Why should we then do that?

> When people tell about cars breaking out and *jumping* off the road
> they may have loosened the brake pedal as they recognized that 
> the car started spinning. But the car, already being at an angle to 
> the previous direction, will suddenly grab the road again and head
> in the new direction.

It is possible to counteract a skid by briefly steering the car in 
the opposite direction and it is impossible to do that  with locked 
wheels. 

 

Regards

Adriaan Loedolff
adriaan@norton.ctech.ac.za
'69 Variant Automatic (200 000 miles + and still cruisin' after all of these years!)


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