Hills, snow and ice

Strider590

expertlinguist wrote: »

I do believe in dangerous drivers killing themselves on good roads!:A

They rarely kill just themselves......

cyclonebri1

Strider590 wrote: »

They rarely kill just themselves......

That is so sadly true. In any accident, be it through dangereous, or just careless driving, there is usually an innocent party, and so often they come off the worst:mad:

tomstickland

I brought this question up at work today.
Bear in mind that my work colleagues are pretty clever...most people where I work are physics or engineeering graduates with 1st class degrees and several years thinking about and solving difficult questions.

I just said "what about descending a steep hill on ice and engine braking?".
Straight away one said to me "brakes work on 4 wheels, engine on 2". None of them were shocked by the idea of using the brakes to control speed, for the above reason. Rear wheel drive was discussed, lack of weight over driven wheels means that they are even worse on engine braking on steep hills. This is what I discovered with my old BMW E30 (3 series). Trucks were discussed, possibility of less control of their brakes due to load factor of trailer and that a car can't jack knife.

Discussion went on for quite a long time. There was no really obvious conclusion. It was very much a case of quite a lot to think about.

Now, for a subtle point that we are going to ponder for a bit longer.

Take a car where the brakes only operated on the front wheels. If you descended a hill on the brakes only and used them to follow a certain speed profile then a certain force would be acting on the tyres at any moment. If you then did the same with the car in gear and used the brakes to control the speed to follow the same speed profile then the forces acting on the car at any moment would have to be same as they were before.

Hence in this example the engine braking could not be adding to the braking force...rather the brakes would be acting on the road and also acting on the engine to slow it. In which case having the car in gear would make no difference at all. ie: in this example engine braking plus brakes has the same effect as just braking. In which case being in gear would be no issue.

tomstickland

skiddlydiddly wrote: »

Tom- you don't really go down 2 mile hills in neutral on ice do you?You are not in full control of your car and risk boiling the brake fluid.If you are constantly on the brakes it doesn't give them time to cool down, even in cold weather.
I'm not really sure what kind of skid control training would advocate you being in neutral, surely better to be in gear and put the clutch in.It achieves the same thing and you are still in control.

How can you say that I was not in full control of the car when I clearly controlled it all of the way down the hill?
I didn't come off the road at any point and I could stop at any moment provided there was enough distance to bring the speed right down.

At less than walking speed in freezing temperatures the chances of the fluid boiling was clearly very low. I had to release the brakes as soon as the car showed any sign of slipping.

Inactive

tomstickland wrote: »

I brought this question up at work today.
Bear in mind that my work colleagues are pretty clever...most people where I work are physics or engineeering graduates with 1st class degrees and several years thinking about and solving difficult questions.

But are often amongst the worst drivers out there.;)

darich

tomstickland wrote: »

Bear in mind that my work colleagues are pretty clever...most people where I work are physics or engineeering graduates with 1st class degrees and several years thinking about and solving difficult questions.

Since when did a first class degree in physics make someone a good driver?
Last I heard you had to have lessons, sit a test, gain experience and perhaps even sit an advanced test.

And those with degrees can still be stupid and wrong.

Strider590

darich wrote: »

And those with degrees can still be stupid and wrong.

They can have this wealth of knowledge and still be utterly stupid! Maybe a degree in common sense would be more useful? :rotfl:

darich

Strider590 wrote: »

They can have this wealth of knowledge and still be utterly stupid! Maybe a degree in common sense would be more useful? :rotfl:

They'd fail!! :rotfl:

Lum

Reminds me of my dad's mate with an electrical engineering degree. His wife had to show him how to wire a plug!

skiddlydiddly

tomstickland wrote: »

How can you say that I was not in full control of the car when I clearly controlled it all of the way down the hill?
I didn't come off the road at any point and I could stop at any moment provided there was enough distance to bring the speed right down.

At less than walking speed in freezing temperatures the chances of the fluid boiling was clearly very low. I had to release the brakes as soon as the car showed any sign of slipping.

Is that a joke question?If you aren't in gear you aren't in full control of the vehicle.See what a traffic offficer or driving instructor says about coasting.IN fact see what the highway code says about it too.I used to do no handers on my bike down big hills when I was a kid and didn't come off, it didn't mean I was in control, it means I was lucky.

As you mention engineers it has some relevance to your brake temperature and fluid boiling.There is only a small amount of flui in the calipers, a few tablespoons.The heat generated by a car stopping can be measured in energy and I've seen figures where not particularly high speeds(think it was around 60mph) to a standstill generate enough heat to boil a kettle full of water.Thats just stopping once.If you don't believe me just touch your disc after an emergency stop and kiss goodbye to your fingerprints.
Now your lower speed wouldn't generate that kind of energy from stopping but its sustained braking if you are using the brakes to control your speed down a 2 mile hill so the brakes don't get chance to cool again, the fluid heats up, gases build up on the discs and the brakes lose effectiveness.
Its not like a radiator on a car where water in constantly circulating, the fluid more or less stays where it is so doesn't get chance to cool with constant use, hence larger discs/calipers and extra cooling ducts on race cars and in some cases water cooling for them to get the temps down.

Finally, have you ever seen the steep gradient signs on the road which tell you to use a low gear?They don't don't tell you to put the car in neutral and freewheel for a very good reason.