Hills, snow and ice

Strider590

It's not so simple, you need to be aware of which wheels do and don't have grip and bare in mind whether you are in a front or rear wheel drive car....

In FWD
Bad weather or none, if the front end loses grip you need come off the throttle... If the back end loses grip you need to hammer the throttle.

In RWD it's the opposite way around

skiddlydiddly

tomstickland wrote: »

With a lot of ice there then a two wheel drive vehicle can only generate half the total retardation force compared with all four wheels doing something.

In the dry I probably use too much engine braking; I see it as a challenge to control the speed mainly with gear selection rather than braking. I'm well aware of how it works. As I said a long while back, I'm talking about a descent down an icy hill. Conditions where some people refused to go any further because they said it was too dangerous.

That's assuming the rears are capable of giving the same amount of braking as the front, which they aren't.They don't receive as much pressure as fronts as the rear lifts up and the front squats down under braking, reducing rear grip and increasing front.More grip allows more braking effort.
On many cars the rear discs are also smaller with inferior calipers to the front, further reducing any potential braking they have.

If you drive as described in normal conditions, I don't understand why you'd switch to a style where you are in less control when the conditions worsen.
Driving down the hill in a lower gear, gives a much more predictable amount of grip than continually reacting to the gradient and ice, controlling your speed by braking.

skiddlydiddly

tomstickland wrote: »

Yes, and if that requires more force than the front wheels alone can generate then using the brakes will manage it when the front wheels alone wont.

This is what we've been saying......mostly control your speed with the lower gear, if thats not enough then use the brake.

skiddlydiddly

tomstickland wrote: »

My interest in this stems from descending a 1:10 hill near me where at 20mph in an old BMW E30 using engine braking the back wheels lost grip and the rear went into the bank on the side of the road. There's very little weight over the rear wheels in the E30. I managed to stop and got out and then realised that grip levels were very low.

Engine braking resulted in the rear of the car breaking free. So I descend the hill at walking speed in neutral using the brakes to control my speed.

You are comparing 20mph to walking pace which to me is 2-3 mph,Not very scientific .
You also say you didn' realise the grip levels were very low until you got out of the car?Maybe your driving isn't as good as you think it is if you cannot feel the conditions of the road from inside the car.

darich

skiddlydiddly wrote: »

You are comparing 20mph to walking pace which to me is 2-3 mph,Not very scientific .
You also say you didn' realise the grip levels were very low until you got out of the car?Maybe your driving isn't as good as you think it is if you cannot feel the conditions of the road from inside the car.

I'd add....that driving at 2-3mph in any conditions would necessitate use of clutch control - that speed is probably too slow for first gear.

If the conditions are genuinely so bad that it's quicker to walk (my walking pace is 4mph), then why take the car?

If the driver is unaware of the road conditions while in the car, then he shouldn't be driving eg driving down a steep hill in icy conditions at 20mph.

This whole "using neutral and brakes instead of gears is better" argument stems from one incident where he was driving too fast for the conditions, in a rear wheel drive car (minority of models) while not realising it was slippery.

skiddlydiddly

It makes me think that maybe he dropped it into too low a gear too quickly which would cause the rear to lock up on that car and cause the accident, a bit like pulling the handbrake on if you do it wrong.If you are already in the gear, controlling your speed the wheels won't lock up as they can just keep turning.Sure they will speed the engine up and you may need to go up a gear but you'd have ample warning of it.

cyclonebri1

darich wrote: »

I'd add....that driving at 2-3mph in any conditions would necessitate use of clutch control - that speed is probably too slow for first gear.

If the conditions are genuinely so bad that it's quicker to walk (my walking pace is 4mph), then why take the car?

If the driver is unaware of the road conditions while in the car, then he shouldn't be driving eg driving down a steep hill in icy conditions at 20mph.

This whole "using neutral and brakes instead of gears is better" argument stems from one incident where he was driving too fast for the conditions, in a rear wheel drive car (minority of models) while not realising it was slippery.

Not in neutral as the previous
poster stated

However TS has got it seriousley wrong here in his method of trying to slow the car, a rear wheel drive car. The engine breaking in low gear on a steep decent will very quickly overcome that applied through the pedal, or if the wheels grip will screw the engine,:eek:, no degree in anything needed to figure that

tomstickland

skiddlydiddly wrote: »

You are comparing 20mph to walking pace which to me is 2-3 mph,Not very scientific .
You also say you didn' realise the grip levels were very low until you got out of the car?Maybe your driving isn't as good as you think it is if you cannot feel the conditions of the road from inside the car.

The same forces are required to hold a steady speed regardless of the speed. Science allows anything to be compared.

It's not possible to feel the conditions until a response to an input is detected. Previous experience on the flat bits had shown that grip levels were low but not critically low. The hill first showed its low levels when the rear end went into the bank and stopping required using the bank as an aid. Getting out confirmed this.

tomstickland

darich wrote: »

If the conditions are genuinely so bad that it's quicker to walk (my walking pace is 4mph), then why take the car?

Because I was on the way home and conditions thus far had been acceptable.

If the driver is unaware of the road conditions while in the car, then he shouldn't be driving eg driving down a steep hill in icy conditions at 20mph.

Point being that conditions can be variable.

This whole "using neutral and brakes instead of gears is better" argument stems from one incident where he was driving too fast for the conditions, in a rear wheel drive car (minority of models) while not realising it was slippery.

However the situation arose, the journey had to be continued from where it had got to.

tomstickland

skiddlydiddly wrote: »

It makes me think that maybe he dropped it into too low a gear too quickly which would cause the rear to lock up on that car and cause the accident, a bit like pulling the handbrake on if you do it wrong.If you are already in the gear, controlling your speed the wheels won't lock up as they can just keep turning.Sure they will speed the engine up and you may need to go up a gear but you'd have ample warning of it.

The wheels will lock up if the forces acting to pull the vehicle down the hill exceed the braking forces that the engine is trying to apply.

I came over the brow of the hill in gear and travelling at about 20mph, travelled down the hill and the rear of the car broke away.