Braking

[legion]

In my '85 S10 that had no rear brakes, I used to downshift while braking. By playing with the brake pedal and clutch pedal, it gave me control over how much stopping power was going to the front verses rear tires. Kinda a poor-man's bias valve.

[singpilot]

Originally posted by VaSteve
Add the threshhold braking and the engine braking and you should stop in shorter distance than the middle pedal alone.

ABS actually increases your stopping distance. The grab-release-grab-release ABS effect increases the braking distance during the release. True threshold braking is before the ABS comes on.

Panic stops and track driving are two different things however.

Unfortunately Steve, There is an error in your thinking.

The brakes in any vehicle should be more than powerful enough to lock each wheel (on their own). If you are panic braking (the question that was originally asked), you should be either in ABS (shortest distance to stop) or without the clear and undeniable advantage of ABS, modulating the brakes to near locked wheel state. If you were to ADD MORE LOCKING CAPABILITY TO AN ALREADY ALMOST LOCKED WHEEL (by downshifting), You would in fact, lock the wheel, DECREASING it's coefficient of friction to the pavement (meaning LESS STOPPING/LONGER STOPPING DISTANCE).

The only way to prevent the locked wheel from downshifting (and the classic 911 end-swap) would be to release enough brake (in all 4 wheels) to get the one (or two in a locking diff) driven wheels to rotate again (or... HEY! Push the clutch in.... ). All of this happening while panic stopping, steering, downshifting, and uttering the two most famous words in the driver's language.

No one is going to be able to do that in a panic stop. No one.

Fact is, panic stop, both pedals (clutch and brake) to the floor (with ABS) or without ABS work the brake to get almost locked wheel braking. Steer to avoid the collision. Average driver will have his hands full doing only just that.

I have seen this discussion mix the question up several times. The question was Panic stop. Both pedals to the floor.

[VaSteve]

I agree. There should be no downshifting. In a panic, you stay in the gear you're in. But I disagree on the clutch in, for the reasons I said. Granted in the last little bit, then you hit the clutch to keep from stalling so you can skeedaddle when the semi behind you is bearing down.

[stuartj]

Originally posted by VaSteve
I agree. There should be no downshifting. In a panic, you stay in the gear you're in. But I disagree on the clutch in, for the reasons I said. Granted in the last little bit, then you hit the clutch to keep from stalling so you can skeedaddle when the semi behind you is bearing down.

Steve- I think i wasnt clear. The engine connected to the driving wheels- as long as the engine is running, there is direct mechanical relationalship that is turning the wheels *forward*.

What you say is quite correct, take your foot of the throttle and the engine braking effect will retard the car. However, the engine is turning, the mechanical relationship is still there, and the engine is still turning the wheels *forward*, albeit at slower speed than the present road speed of the wheel, hence the retardation.

But when retardation via braking exceeds the retardation via the engine, and it easily does in a hard stop, the engine is now acting against the brakes. While the brakes are trying to stop the wheel, the engine is trying to turn the wheel forward.

Proably doesnt mean much in real life because the brakes will win over the engine- the important thing, as you say, is to keep the engine running so as to be able to drive away form the next problem.

Cheers

Stuart

[Victor]

Unless someone has already mentioned it, do yourselves a favour and invest $14,93 in Vic Elford's “Porsche High Performance Driving” book.

There is an entire section dedicated to those who seek clarity on what this double clutching business is about also. Seems to be hotly debated here about once a month or so.

Order now:

BUY THE DAMN BOOK

[stuartj]

Originally posted by Victor
Unless someone has already mentioned it, do yourselves a favour and invest $14,93 in Vic Elford's “Porsche High Performance Driving” book.

There is an entire section dedicated to those who seek clarity on what this double clutching business is about also. Seems to be hotly debated here about once a month or so.

Order now:

BUY THE DAMN BOOK

Going all euro on us? $14,93

[dad911]

In a panic stop, the limiting factor is the contact of the tire to the road. In any modern car, the brakes are strong enough to 'lock up the tires' therefore engine braking is not necessary.

However, try going down a 3 mile descent in a tow vehicle with a full trailer, like the hill into town from Watkins Glen. Brakes alone, and they will be smoking & glowing by the bottom. However, shift into a lower gear, and you will hardly need the brakes at all.

[greglepore]

Originally posted by singpilot


No one is going to be able to do that in a panic stop. No one.

Fact is, panic stop, both pedals (clutch and brake) to the floor (with ABS) or without ABS work the brake to get almost locked wheel braking. Steer to avoid the collision. Average driver will have his hands full doing only just that.

I have seen this discussion mix the question up several times. The question was Panic stop. Both pedals to the floor. [/B]

Spot on.

I posted in another thread, but I'll do so again here. My 9 yr old daughter may well owe her well-being to ABS. I was left-turned on a 4 lane road while going about 55 in my M5 from maybe 100-150 ft. I was able to STOMP on the brake pedal and simultaneously turn right (left would have put me headon into the car following her, going straight and straight would have reduced my travel distance such as to ensure a collision), such that I increased the available distance to stop and was able to come to rest behind her (thank god the right lane was empty). Now, I've spent loads of time theshold braking during hillclimbs and a/x's, but there was no freaking way I would have been able to do that under these circumstances, plus the turn would have taken the tires out of the friction circle faster than I could accomodate.

Yes, on a racetrack ABS is slower if you are fresh. In the real world, both feet in and steer.