Avoiding BGOL around town

[sussex2]

Which has reminded me to disable the daft 'gear change indicator' on our van.
The van being a Citroen (brilliant to drive and truly superb brakes) it'll probably take twenty minutes of pushing the most unlikely buttons

[kfae8959]

Please bear in mind I live in Liverpool

You're very welcome to drop me a line and we'll arrange a drive: it's often easier to explore these things in practice!

David

[TheInsanity1234]

I have this issue with our Yeti.

What I tend to do is on approach, I'll change down to about 2nd (3k rpm at 30), and then slow down.

The engine doesn't actually inject fuel into the cylinders when you're off the throttle, which means even 4000 rpm doesn't make much noise when slowing.

I used to be afraid of going over 2500 rpm which made things like this very difficult, but after moaning for a bit on here, I got the advice to just ignore the noise/vibration and just drive the thing, and now I'm happy to accelerate to 4500 rpm at times...

[fungus]

I still struggle to se what all the fuss is about BGOL. It's often smoother, and as long as the driver is not compressing the system, and has the vehicle unde fullr control, travelling at the correct speed and in the correct position for the hazard to be negotiated, then I see no issue. IMHO, this all goes back to the days of crash gear boxes when the driver had to double-de-clutch.

Opens a can of worms. Oh dear, I'm beginning to sound like Silk.

[Rainmaker]

Thanks for the input everyone. Some contradictory stuff, but overall I get the gist. Out of interest (I'm a bit anal like that) I drew up a pro forma and took out my long suffering wife, who filled it in as I read out the numbers. At 30mph I noted the cruising speed on neutral throttle, and then slowed the car down until it began to shudder and threaten to stall. This is how things look across the box:

4th gear
Steady throttle - 1,450rpm
Shudder begins - 800rpm
Speed at shudder start - 27mph

3rd gear
Steady throttle - 1,750rpm
Shudder begins - 800rpm
Speed at shudder start - 15mph

2nd gear
Steady throttle - 2,750rpm
Shudder begins - 800rpm
Speed at shudder start - 10mph

So quite surprising to actually see written down, especially 4th gear basically losing just ~3mph before threatening to stall (despite there being a 650rpm change in engine speed). Third gear slowing to 15mph would still necessitate 2nd gear unless I rev matched high in 1st and changed up again quickly (pointless). The big shocker (not really) was how much better 4th was for economy in town. I normally get mid 30s MPG for mostly town with some A road or short motorway work. Trying it Mark's way (using 4th more but changing down to a more flexible gear as soon as I spot hazards ahead, to allow me to carry on through System) I ended up with 48mpg this evening after an hour out.

Trying it the way everyone else recommended (using primarily 3rd and 2nd only) I lost some mpg, but now I am more concrete on the shift points, stall points etc I found I'm better able to balance the engine speed v road speed without BGOL even being a consideration. For example I can happily be in 4th where I can see it's worthwhile, but dropping early to 2nd or 3rd for hazardous areas anticipated ahead. Because I now know exactly when the engine would begin to struggle I was able to make a snap decision.

I can now see that previously I'd be in too a high gear for the conditions (whether 3rd or 4th), and would thus end up clutching in for what I now understand was most of the speed phase (until I'd gotta to a suitable speed to finally select a gear). Tonight I was able to be more proactive with more revs to play with, and an understanding of where the slowing would leave me in the power band versus what gear I'd be selecting (earlier than before, with no danger of BGOL). It 'felt' a lot cleaner and I didn't end up overlapping as any time I ended up approaching 1,000rpm I was already at the end of the speed phase and slotting into the next suitable gear to accelerate away.

I apologise if I've bored anyone but I definitely learnt something new about my car (and applying System). TBH with a DSG gearbox on the incoming car I was keen to iron out my knowledge so I always had it in future (instead of always having that niggling feeling of there being a sizeable gap in my knowledge I couldn't work on in real life). Thanks again to everyone, and sorry to anyone I bored.

Please bear in mind I live in Liverpool

You're very welcome to drop me a line and we'll arrange a drive: it's often easier to explore these things in practice!

David

Nice to hear from you again David. I'll drop you a PM in a moment.

[waremark]

Good stuff from Rainmaker. I tend to declutch at around 1k rpm, which in my manual diesel is about 40 in 6th. I am happy to hold the clutch down as I continue braking. I don't generally take my hand off the wheel to change gear until after I have the speed for the hazard and I virtually never change to an intermediate gear. I don't experience a problem of not being ready to go.

Except - at other times and particularly when driving in a more spirited fashion I like to overlap with heel and toe.

[Gareth]

It's often smoother

It the gear changed is rev-matched, then it should be smooth irrespective of anything else.

and as long as the driver is not compressing the system

Isn't BGOL, by definition, compressing the system?

[sussex2]

The bottom line is not compromising the control of the vehicle.

At low speeds in town,especially a very hilly town like Brighton, you are going to be hard pushed not to brake and change gear; unless you want to make a damned nuisance of yourself and probably frighten a few people
This low speed work is completely distinct from faster driving where the balance of the vehicle is more critical.

Likewise depressing the clutch in sufficient time to allow a smooth full stop such as at traffic lights, in no way compromises the stability of the vehicle; nor does changing to an intermediate gear to keep the vehicle driveable.

[Mr Cholmondeley-Warner]

Loads of stuff including ...

4th gear
Steady throttle - 1,450rpm
Shudder begins - 800rpm
Speed at shudder start - 27mph

So you've proved what you and most of us suspected all along - 4th is not a flexible gear at 30 mph. At 800 rpm you're probably hitting an anti-stall mechanism that's causing the engine to fight the car trying to drive it at below its idle speed, hence the shudder.

The 600 rpm probably doesn't equate to only 3 mph; inaccuracies in the instruments, and your observation of them, probably fudge the value somewhat. If the 1450 rpm is true for steady state at 30, 600 rpm is about 12 mph. There's probably a difference between light throttle to maintain the 30 mph, and no throttle at all, to allow the speed to fall such that rpm=800. A bit like slack in a thread - the first bit of turn achieves nothing other than taking up the slack.

[Speary]

The only time you are performing BGOL is if you select a gear whilst braking
To be honest around town when it's busy it can be preferable to BGOL to avoid confusion and to aid progress, a point the IAM have realised lately