Approaching junctions - Gear / Clutch

Approaching junctions - Gear / Clutch

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Discussion

woodyTVR

Original Poster:

622 posts

245 months

Thursday 26th February 2015
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What's the advanced method for stopping at a junction in say a 60mph limit?

My car has six gears, assuming I'm in anything above 4th I will drop to 4th when approaching a junction - If I stayed higher the engine would complain when I started to brake - see below. If I dropped to 3rd the engine would be reving quite high and would turn an calm drive into something else at every junction.

I brake for the junction and if I have to come to a complete halt (a stop sign) I have to put the clutch in at least two car lengths before the junction otherwise the engine revs up (a diesel) and drives the car against the brakes and tries to speed up.

I'm guessing this is the right way to do it as you wouldn't want to come off the brakes drop to second and start breaking again.

So is this coasting the accepted approach? How much coasting time is acceptable?


Dave Hedgehog

14,541 posts

203 months

Thursday 26th February 2015
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chase down the box whilst pressing hard on the brakes with a constant pressure

if you get it right you will stop a couple of inches before the line with your hazards activated but no ABS engagement

R_U_LOCAL

2,676 posts

207 months

Thursday 26th February 2015
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If you're driving to the Roadcraft system, the accepted method is just to leave it in whatever gear you are in whilst you brake to a stop and then dip the clutch just as the engine reaches tickover speed.

It isn't "coasting" in the accepted sense and allows you to keep your options open (by, for instance, coming off the brakes and taking 2nd gear whilst still moving if your view improves) whilst minimising drivetrain wear.

LordGrover

33,531 posts

211 months

Thursday 26th February 2015
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This Roadcraft malarky is all well and good. If only there were a decent, well written, less formal guide for PHers. scratchchin

woodyTVR

Original Poster:

622 posts

245 months

Thursday 26th February 2015
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R_U_LOCAL said:
If you're driving to the Roadcraft system, the accepted method is just to leave it in whatever gear you are in whilst you brake to a stop and then dip the clutch just as the engine reaches tickover speed.

It isn't "coasting" in the accepted sense and allows you to keep your options open (by, for instance, coming off the brakes and taking 2nd gear whilst still moving if your view improves) whilst minimising drivetrain wear.
Nice one, that's what I figured but it seemed like a good chunk of distance to have the clutch in, more so if you're going slower in the first place as the % of speed drop is less harsh, you reach a speed much sooner where the clutch needs to go in.

titian

55 posts

118 months

Thursday 26th February 2015
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Standard procedure on approaching a Stop sign is one phase of braking, declutch and stop at the line. Select an appropriate gear to move off when clear. OK, having said that diesel engines by and large, don't like that approach at the speed you mention so, it's acceptable to take a lower gear to prevent judder/fighting the brakes.

However BGOL ought to be avoided where possible (Brake, Gear, Overlap) - so brake down to a speed where 3rd is acceptabe and where its selection once the clutch is re-engaged, will not cause the engine revs to rise, release the clutch and in a second phase of braking, approach the stop line disengaging the clutch before the car complains, stop. Engage the appropriate gear to move off.

If you were delivering a commentary at the time you would explain that the intermediate gear was both for better car control and mechanical sympathy.

R_U_LOCAL

2,676 posts

207 months

Thursday 26th February 2015
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LordGrover said:
This Roadcraft malarky is all well and good. If only there were a decent, well written, less formal guide for PHers. scratchchin
Now there's a thought!

SK425

1,034 posts

148 months

Thursday 26th February 2015
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woodyTVR said:
Nice one, that's what I figured but it seemed like a good chunk of distance to have the clutch in, more so if you're going slower in the first place as the % of speed drop is less harsh, you reach a speed much sooner where the clutch needs to go in.
So what? smile

Personally it doesn't really bother me. I just put the clutch down when I need to put the clutch down. But if it bothers you, you've already identified a solution (and it's one that's often suggested): take a lower gear before you start braking. Job done smile

Bigends

5,412 posts

127 months

Thursday 26th February 2015
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R_U_LOCAL said:
If you're driving to the Roadcraft system, the accepted method is just to leave it in whatever gear you are in whilst you brake to a stop and then dip the clutch just as the engine reaches tickover speed.

It isn't "coasting" in the accepted sense and allows you to keep your options open (by, for instance, coming off the brakes and taking 2nd gear whilst still moving if your view improves) whilst minimising drivetrain wear.
Exactly this - dont touch the gears until you know you can move off. Same for red lights- stay in whatever gear you are in, dip the clutch just prior to stall, brake to a gentle stop, handbrake, neutral - easy! If cars start to move as you approach, judge their speeds, brake to suit their speed - select the right gear and follow them off.

waremark

3,241 posts

212 months

Sunday 1st March 2015
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titian said:
Standard procedure on approaching a Stop sign is one phase of braking, declutch and stop at the line. Select an appropriate gear to move off when clear. OK, having said that diesel engines by and large, don't like that approach at the speed you mention so, it's acceptable to take a lower gear to prevent judder/fighting the brakes.

However BGOL ought to be avoided where possible (Brake, Gear, Overlap) - so brake down to a speed where 3rd is acceptabe and where its selection once the clutch is re-engaged, will not cause the engine revs to rise, release the clutch and in a second phase of braking, approach the stop line disengaging the clutch before the car complains, stop. Engage the appropriate gear to move off.

If you were delivering a commentary at the time you would explain that the intermediate gear was both for better car control and mechanical sympathy.
I dislike that 'on brakes, off brakes, on brakes' again approach. More processes, more work, less smooth for passengers and following vehicles, requires starting the braking earlier.

Personally I would remain in whichever gear I happened to be in, brake as required, and declutch before the engine laboured or the anti stall kicked in to push against the brakes. If this results in declutching at 30 that is no problem. The change into 4th before starting to brake as suggested in an earlier post is also an option.

titian

55 posts

118 months

Monday 2nd March 2015
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I understand your point Waremark and would wholly agree if I was driving a petrol engined vehicle which is much more tolerant of low speeds in higher gears. However, in a diesel engined car I hate travelling for an extended distance with my left foot flat to the floor on the clutch and my right foot on the brake - it feels unnatural and out of control.

If it were possible using acceleration sense to allow the diesel vehicle to slow down to the lower speed appropriate for say 3rd, so much the better, then one phase of braking to the junction.

SK425

1,034 posts

148 months

Monday 2nd March 2015
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titian said:
I understand your point Waremark and would wholly agree if I was driving a petrol engined vehicle which is much more tolerant of low speeds in higher gears. However, in a diesel engined car I hate travelling for an extended distance with my left foot flat to the floor on the clutch and my right foot on the brake - it feels unnatural and out of control.
That's interesting. Two hands on the steering wheel, a positive decision that this is a braking phase and will continue to be a braking phase and only a braking phase until the speed is where I want it, clutch disengaged so there is no chance of any juddering or anti-stall interfering with what I'm doing, deceleration being applied to all of the wheels, knowledge that I won't need to move either of my hands or either of my feet to anywhere else during this entire braking phase - all of that stuff makes me feel very, very, very in control.

I know that you are by no means alone in feeling differently about it though.

davepoth

29,395 posts

198 months

Monday 2nd March 2015
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It's doubly odd because there's almost no engine braking on a diesel engine - you might as well install a freewheel really.

Bigends

5,412 posts

127 months

Monday 2nd March 2015
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davepoth said:
It's doubly odd because there's almost no engine braking on a diesel engine - you might as well install a freewheel really.
Use brakes for braking - my instructors always emphasised brakes are cheaper than clutches

woodyTVR

Original Poster:

622 posts

245 months

Tuesday 3rd March 2015
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SK425 said:
So what? smile

Personally it doesn't really bother me. I just put the clutch down when I need to put the clutch down. But if it bothers you, you've already identified a solution (and it's one that's often suggested): take a lower gear before you start braking. Job done smile
I went through the whole roadcraft thing when I first started to drive and like to think I have a good grasp of it. However I don't think it's the be all and end all of driving. I have my own interpretation of it and perhaps a more relaxed approach to it's use. However after reading the thread R_U_Local I happened to drive home that night consciously thinking roadcraft and what would an observer make of my driving - I'd like to think there wouldn't be much they could say. However on approaching a junction in 60 that I pass through several times a week when I was conscious of my actions (rather than naturally driving) I wondered how it would be seen in the eyes of an 'expert'. From my point of view my way is perfectly safe and I would think from a normal passengers point of view they wouldn't have any feelings about it either way, I was just curious as to whether it's the 'right' way. Had there been a more appropriate solution I'd have given some consideration but it seems there isn't.

RobM77

35,349 posts

233 months

Friday 13th March 2015
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In my opinion (and it is just that) this is where Roadcraft starts to fall apart, because as far as I understand it, Roadcraft gives you two choices:

1) Slow in the gear you were in and declutch before the engine triggers anti-stall or labours. In my BMW 3 series this is about 38mph in 6th.

2) Come off the brakes before the engine reaches the aforementioned low revs, rev match a gear change to a lower gear, then start braking again.

1 involves coasting (and I'm really not comfortable with coasting from over 30mph) and 2 involves changing your speed profile too much, as well described by Waremark above (I'd add to that the brake lights going on and off for drivers behind sending mixed signals too).

If you now imagine that the junction is a steep downhill, 2 gets ruled out due to the car speeding up too much between gearchanges, so you're left with option 1. Now imagine a bend before the junction and 1 starts to look a bit dodgy as you'd be coasting around a bend at 30mph, or if you choose to slow at 10mph with a queue of frustrated drivers behind you.

My solution to the above is to heel and toe into a lower gear/s, because then I'm braking smoothly and constantly, keeping the car stable and sending a consistent message to those behind me, I'm avoiding coasting so the car is in gear ready for anything and stable, and I'm avoiding non rev-matched gearchanges. This isn't compatible with Roadcraft though, and it's one of a few reasons why I'm not either!

Needless to say, in a car with an automatic gearbox, double clutch or roboticised manual, this problem goes away.

waremark

3,241 posts

212 months

Sunday 15th March 2015
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RobM77 said:
If you now imagine that the junction is a steep downhill, 2 gets ruled out due to the car speeding up too much between gearchanges, so you're left with option 1. Now imagine a bend before the junction and 1 starts to look a bit dodgy as you'd be coasting around a bend at 30mph, or if you choose to slow at 10mph with a queue of frustrated drivers behind you.

My solution to the above is to heel and toe into a lower gear/s, because then I'm braking smoothly and constantly, keeping the car stable and sending a consistent message to those behind me, I'm avoiding coasting so the car is in gear ready for anything and stable, and I'm avoiding non rev-matched gearchanges. This isn't compatible with Roadcraft though, and it's one of a few reasons why I'm not either!

Needless to say, in a car with an automatic gearbox, double clutch or roboticised manual, this problem goes away.
Don't know why you think that is not compatible with Roadcraft Rob. Your downhill 30 mph bend is a separate hazard for which a gear change is appropriate, and preparing for a downhill bend is an example given by Roadcraft of a situation for which BGOL is appropriate. With your skill use of H & T is ideal. Without your skill an occasional downchange into an intermediate gear at relatively low revs without rev matching is not a problem.

Back on the flat, what is wrong with declutching at 38? (My previous example of 30 is comfortable for 6th in the V12V)

GravelBen

15,654 posts

229 months

Sunday 15th March 2015
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davepoth said:
It's doubly odd because there's almost no engine braking on a diesel engine - you might as well install a freewheel really.
Since when? Every manual diesel I've driven has had more engine braking than an equivalent petrol thanks to the higher compression.

ohtari

805 posts

143 months

Sunday 15th March 2015
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GravelBen said:
davepoth said:
It's doubly odd because there's almost no engine braking on a diesel engine - you might as well install a freewheel really.
Since when? Every manual diesel I've driven has had more engine braking than an equivalent petrol thanks to the higher compression.
Someone will be along to explain why you're wrong very shortly

RobM77

35,349 posts

233 months

Sunday 15th March 2015
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waremark said:
RobM77 said:
If you now imagine that the junction is a steep downhill, 2 gets ruled out due to the car speeding up too much between gearchanges, so you're left with option 1. Now imagine a bend before the junction and 1 starts to look a bit dodgy as you'd be coasting around a bend at 30mph, or if you choose to slow at 10mph with a queue of frustrated drivers behind you.

My solution to the above is to heel and toe into a lower gear/s, because then I'm braking smoothly and constantly, keeping the car stable and sending a consistent message to those behind me, I'm avoiding coasting so the car is in gear ready for anything and stable, and I'm avoiding non rev-matched gearchanges. This isn't compatible with Roadcraft though, and it's one of a few reasons why I'm not either!

Needless to say, in a car with an automatic gearbox, double clutch or roboticised manual, this problem goes away.
Don't know why you think that is not compatible with Roadcraft Rob. Your downhill 30 mph bend is a separate hazard for which a gear change is appropriate, and preparing for a downhill bend is an example given by Roadcraft of a situation for which BGOL is appropriate. With your skill use of H & T is ideal. Without your skill an occasional downchange into an intermediate gear at relatively low revs without rev matching is not a problem.

Back on the flat, what is wrong with declutching at 38? (My previous example of 30 is comfortable for 6th in the V12V)
That's great if H&T is compatible with Roadcraft if required (e.g. entry to downhill bends), I've heard different from others, but it's really good to hear it from someone as experienced as you. Regarding declutching at 38mph, I personally wouldn't want to coast from such a speed in an ideal world, but I'll be the first to admit it's not really much of a problem in most situations if we look at the risks and benefits sensibly.