Hills, snow and ice

tomstickland

darich wrote: »

This is backed up by the comment you made on the video of the idiot driving on the hard shoulder and you reckoned his spin was caused by changing lane too quickly!?!?!?

Oh dear.

Can you tell me what you disagree with in my statement that "his spin was caused by changing lane too quickly"?

tomstickland

darich wrote: »

No, the allegation was that having all the brains in the world doesn't automatically make you a good driver.

It does tend to help with discussing with what is happening in terms of the forces acting on a vehicle in a special and rare situation though.

The highway code advises that keeping the car in a low gear helps to prevent speed building up and therefore reduce the chance of losing control of the car.

If the grip levels are too low to sustain the forces needed to do this then the driver will lose control. Engine speed control is fine for most situations, but a steep hill with sheet ice on can fall outside this situation.

By selecting neutral, you're removing a method of control - a method of braking and therefore increasing the chance of losing control and skidding.

If the grip levels are so low that the forces required to maintain a steady speed are more than two wheels can generate then there will be a loss of control.

Using the brakes could generate up to twice as much force to counteract the proprotion of gravity trying to accelerate the car down the hill.

If you genuinely believe that being in neutral on a steep hill gives you more control then you're entitled to think that. But it's not the advice in the highway code, it's not taught in lessons and it's probably not taught for the advanced driving test. That just might indicate that perhaps it's not the best method.

It's not an advisable method for most driving situations. But in abnormal conditions where the grip levels are very low then what the highway code and lessons teach might not be relevant.

From a physics point of view, no one can argue that 4 wheels give better stopping/reducing power than simple engine braking. That's not debated. But what must be remembered is that when the wheels are connected to the engine in gear, then they're turning. When you select neutral and coast, then with very low friction between tyre and road, it's VERY easy to lock up - keeping speed down ABS deactivates at a few mph so at 5mph you may find you have no ABS - and locked wheels.

Yes, it's easy to lock up. It's very important to feather the brakes and let them off and then back on if a slide develops.

However with the engine connected, the wheels are turning, keeping the speed down (as do the brakes when coasting) but the big difference is that in gear the wheels will never lock meaning you always have steering and maintain control of the car.

If the front wheels cannot generate the force required to keep the speed down then they will start to slide. If the driver puts foot on clutch and off brake momentarily then the wheels will adjust their speed to match the rate which the ground is going by and steering can be regained. Then back on the brakes.


I did look back through this thread and see that I wrote something about "coasting with the brakes on". Bad used of language there, I agree.

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.

tomstickland

Of course, avoiding the need to travel down a hill in situations where there isn't enough grip for engine braking to work is probably the best solution.

Funnily enough, someone at work who was telling me "low gear is the way to do it" crashed into a wall on an icy hill last month. He said "I don't know why I went that way. It was too steep really".

darich

tomstickland wrote: »

Can you tell me what you disagree with in my statement that "his spin was caused by changing lane too quickly"?

I don't think the driver intended to change lane.
I believe he spun because he had his nearside wheels in snow/ice and his offside wheels in a relatively clear lane.
Much more friction on one side of the car compared to the other caused the spin.

I think this is backed up by him going back into the same lane after spinning. If he was intending to change lane, then after the spin, he'd have gone into the lane he was changing into......not the one he spun from.

darich

tomstickland wrote: »

It does tend to help with discussing with what is happening in terms of the forces acting on a vehicle in a special and rare situation though.
If the grip levels are too low to sustain the forces needed to do this then the driver will lose control. Engine speed control is fine for most situations, but a steep hill with sheet ice on can fall outside this situation.

If the grip levels are so low that the forces required to maintain a steady speed are more than two wheels can generate then there will be a loss of control.

Using the brakes could generate up to twice as much force to counteract the proprotion of gravity trying to accelerate the car down the hill.


It's not an advisable method for most driving situations. But in abnormal conditions where the grip levels are very low then what the highway code and lessons teach might not be relevant.

Yes, it's easy to lock up. It's very important to feather the brakes and let them off and then back on if a slide develops.

If the front wheels cannot generate the force required to keep the speed down then they will start to slide. If the driver puts foot on clutch and off brake momentarily then the wheels will adjust their speed to match the rate which the ground is going by and steering can be regained. Then back on the brakes.


I did look back through this thread and see that I wrote something about "coasting with the brakes on". Bad used of language there, I agree.

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.

Maybe you should advise the Department for Transport of your improved control going downhill, so the highway code can be re-written?
Think you could get a job at RED driving school teaching learners your superior methods of control?
Given that no where will ever teach you to coast in neutral then either everyone at the IAM is behind you in driving ability.....or you're wrong.

I can't prove the first point and you won't accept any argument proving neutral is wrong meaning further posts on the subject are a waste of time.

mikey72

tomstickland wrote: »

Blah blah blah, no common sense, too clever for their own good, think they know everything. All the qualifications but no idea about real life.

Keep going with your lazy stereotypes. These guys are not like that; they're practial people who get things done and also happen to know a lot about maths and analytical thinking, ditching preconceptions and building arguments from first principles.

tomstickland wrote: »

Of course, avoiding the need to travel down a hill in situations where there isn't enough grip for engine braking to work is probably the best solution.

Funnily enough, someone at work who was telling me "low gear is the way to do it" crashed into a wall on an icy hill last month. He said "I don't know why I went that way. It was too steep really".

Hopefully not the same person.

tomstickland

darich wrote: »

I don't think the driver intended to change lane.
I believe he spun because he had his nearside wheels in snow/ice and his offside wheels in a relatively clear lane.
Much more friction on one side of the car compared to the other caused the spin.

I think this is backed up by him going back into the same lane after spinning. If he was intending to change lane, then after the spin, he'd have gone into the lane he was changing into......not the one he spun from.

I can't be arsed to watch it again now.
My understanding was that he changed lanes to come out round some traffic that was moving more slowly than him and he tried to turn to turn too quickly.

tomstickland

darich wrote: »

I can't prove the first point and you won't accept any argument proving neutral is wrong meaning further posts on the subject are a waste of time.

What first point?

I've never disagreed that engine braking is the correct procedure for most situations. I think it's pretty simple really - I've described a situation that's rare and that should be avoided. A situation where grip levels are so low that "being in control" is something to aspire to rather than expect to have.

If you weren't so quick to go for the ad hominem then I'd be less inclined to agitate.

tomstickland

mikey72 wrote: »

Hopefully not the same person.

No. Wall crasher was Mr "1st gear no brakes".
He did say "I shouldn't have gone that way really".
Which is back to the point I was trying to make in a spirit of conciliation.

tomstickland

darich wrote: »

Maybe you should advise the Department for Transport of your improved control going downhill, so the highway code can be re-written?
Think you could get a job at RED driving school teaching learners your superior methods of control?
Given that no where will ever teach you to coast in neutral then either everyone at the IAM is behind you in driving ability.....or you're wrong.

Have you read what I wrote tonight?

I said my original post with "coasting in neutral" was badly worded and gave the wrong idea.

The highway code and driving schools are going to start with the most common solution to the most common problem. Which is the well understood selection of gear to control speed.

Next, good practice in poor conditions is to avoid steep hills.

Best practice for icy hills is low gear and no brakes.

If a skid develops then clutch down to regain steering control. Then use brakes on and off to try and control speed.

Now, this is where it gets different.
If driving down the hill under the control of the engine that is acting on two wheels causes the driven wheels to slide then you have a problem.

The driving school would avise you to park the car and walk home.

I'd say that you should try using all 4 wheels to slow you down. ie: Gently apply the brakes and let go of them if you feel a slide starting. It's risky. If all the wheels are locked then control will be quickly lost.

I've been there and done it and it worked.