Afternoon All,

 

I know this is ca can of worms but I would like to understand why there is a need for complete brake gear overlap (BGOL) in general driving. I realise in assessment drives you can use BGOL on safety grounds or when going down hill etc. but I don't understand why you'd want to do it at all other than perhaps on poor road conditions.

 

Here is a great description of how to avoid BGOL in practice, and the acceptable situations where you may choose to avoid it.

 

Ben Colins How To Drive - Gear Change pretty much sums up my view of BGOL.

 

Ok, I understand avoiding overlapping sharp cornering and dropping down gears. Generally you should be at the lowest speed before you enter the corner as braking forces can upset car balance and give you too many things to do when you may also need to control any unpredicted slips or unseen hazards as you move around a blind bend.

 

Isn't it excessive to take a dim view on braking and changing down as the engine aproaches idle revs, or block changing while decelerating to the gear you want to use after the hazard while still braking. I'm not even advocating engine braking here.

 

For me I'd rarely go down the box a gear at a time but could see making changes before idle engine speed means you'll have a benefit if you have to emergency stop (as engine revs are higher and will help brakes initially) or get out of a bad situation quickly (idle in 6th on a 2.0 TDI CR is about 35-40, the car will not be happy about/will not acellerate or provide torque to help change direction really quick if the throttle is applied).

Edited 27 November, 201510 yr by WesBrooks

I actually agree with you that changing down just to get engine braking is a bad thing, but with modern cars you can (even do) find yourself dropping engine speed below "pull away revs" if you're braking from a highway cruise to junction or hairpin bend speeds without changing down.

Yeah that's in line with the way I drive. If pulling up to something that I suspect may be a stop I'll drop the revs right down. If however I suspect that the hazard either doens't require a complete stop, or it will clear (like a red light on a duel carridge way with no one in the queue) I'll change down to keep in gears that I'd be comfortable accelerating in.

 

What doesn't seem to fit in with the Advanced Driving guides I've seen so far is that the gear changes are made while I'm braking. As far as I understand it I couldn't get through the current IAM or ROADAR assessments doing this?

 

On ice it makes sense as you don't want sudden variations in torque to the wheels - engine braking just being a negative torque. Brakes are far more controllable than the engine braking in this case. I've pitched a diesel Mondeo into a salom like skid on a straight road just by lifting off the throttle too sudenly when unbeknown to me I was on black ice.

 

I often use engine braking when going down long hills, but it's more using the engine to stop the car accelerating rather than changing down the box to get the car to below 15 or so without brakes.

I know exactly where you're coming from. From my understanding it's also about separating sections of 'The System' and not rushing to get everything done, before the corner. It can also aid smoothness of the drive.

 

Using Position, Speed, Gear, Acceleration means you'll have got your speed correct, before selecting the gear. Following that Roadcraft approach, you'll then avoid BGOL.

 

I try to remove it as much as possible and find that there aren't that many instances where BGOL is required on safety grounds.