Left foot braking for the road with a manual transmission

[BertBert]

Steve H said:

I’m with Panamax here. How would a car be generating boost off throttle?

Anything with a throttle body will snap straight to vacuum as soon as it shuts and anything without a throttle body would not be utilising the manifold for it’s servo vacuum anyway, there would be a separate pump.

You've conflated two parts of the debate. The first is on the merits of LFB. The second is about using the throttle (or other means) to keep a turbo spooled up.

In the latter case there can't be any vacuum

[Steve H]

Didn’t mean to conflate . Just pointing out the impossibility of what was being suggested.


But if it helps, lfb is a waste of time and generally produces worse driving not better, and if you need lfb to keep your turbo spooled then you should get a car that was built in the last 30 years - they spool fine all on their own

[Panamax]

732NM said:

There is no vacuum when on throttle or off throttle when there is boost.

I see what you mean although I can't help thinking it would take a pretty unusual road driving style to have a car "on boost" all the time. If it's a genuine problem then a separate pump seems the obvious answer.

[732NM]

Steve H said:

I’m with Panamax here. How would a car be generating boost off throttle?

Anything with a throttle body will snap straight to vacuum as soon as it shuts and anything without a throttle body would not be utilising the manifold for it’s servo vacuum anyway, there would be a separate pump.

I've already explained how. Early manual drive by cable systems use aditional air valves to bypass the throttle body or use a throttle jack strategy where the throttle butterfly is left jacked open, later drive by wire just keep the throttle open whilst you are off the pedal, both then use a combination of ignition cut and retard and fuel to generate no torque but still fire a spark to energise the turbo. You can have full boost off throttle if you want. Thats used on every turbo rally car running ALS, i can have my road car using this.

Using launch control also generates boost when sat stationary with the throttle open, i have mine set at 1BAR as any more fries the clutch as its still an organic type, i can dial in 2BAR if i wanted to.

Then you have systems like the rocket, that are effectively a mini jet engine in the pre turbo exhaust pipe, that run without any need for engine strategy intervention, which drives the turbo generating full boost at idle. Prodrive utilised that on the WRC Subaru until it was banned. That was available as an aftermarket product for a while called zero lag.



Then you have flat foot shifting where you keep the throttle wide open during gear shifts, the engine strategy cuts ignition, retards the ignition and reduces fuel to kill torque, but air is still passing through and some fuel burn is keeping the turbo spooled, so when the gear shift is finished you have instant full torque, the engine never saw a vacuum during the shift.

Even without ALS if you are doing a lot of LFB with throttle and brake crossover, you will not generate any vacuum.

[732NM]

Panamax said:

I see what you mean although I can't help thinking it would take a pretty unusual road driving style to have a car "on boost" all the time. If it's a genuine problem then a separate pump seems the obvious answer.

It doesn't take long to exhaust a vacuum, the issue is also consistency of assistance, you want the same assistance every application. A vacuum pump will get around the issue. Competition cars you simply remove the servo and if allowed in the rules, change the pedal ratio and cylinder sizes to suit.

[PhilAsia]

ecsrobin said:

PhilAsia said:

The main reason is a 0.3 sec (ish) quicker reaction time. That can be a few centimeters, or many car lengths in overall stopping distance. Pointless?

But when every other car around you is not doing that and have a slower reaction time it’s a good way to increase the chances of being rear ended when you stop quicker than those around you. Can’t really think of anytime where I’ve thought I’d need to stop quicker than I have.

I encourage constant reevaluation when driving, and would consider that those wishing to become better on the road to do the same.

You are correct in stating that the chances of being rear-ended increase, that is built into my drive. To avoid such an occurrence I:

a) increase the distance to the vehicle ahead, and

b) am able to brake possibly 0.3 ish seconds earlier, possibly more gently, and to show the brake lights earlier to those following, thereby enabling them to brake earlier.

"...Can’t really think of any time where I’ve thought I’d need to stop quicker than I have..." Well done!!

[CheesecakeRunner]

PhilAsia said:

I LFB in both manual and auto, mainly for following reasons:

...0.3ish faster response time

If you find yourself needing an extra 0.3 seconds reaction time, you need to work on your observation, not which foot you’re pressing the brake pedal with.

[ecsrobin]

PhilAsia said:

I encourage constant reevaluation when driving, and would consider that those wishing to become better on the road to do the same.

You are correct in stating that the chances of being rear-ended increase, that is built into my drive. To avoid such an occurrence I:

a) increase the distance to the vehicle ahead, and

b) am able to brake possibly 0.3 ish seconds earlier, possibly more gently, and to show the brake lights earlier to those following, thereby enabling them to brake earlier.

"...Can’t really think of any time where I’ve thought I’d need to stop quicker than I have..." Well done!!

I’d say you’re not giving a big enough distance to the vehicle ahead if you need 0.3 seconds extra braking time.

[Pica-Pica]

CheesecakeRunner said:

PhilAsia said:

I LFB in both manual and auto, mainly for following reasons:

...0.3ish faster response time

If you find yourself needing an extra 0.3 seconds reaction time, you need to work on your observation, not which foot you’re pressing the brake pedal with.

If he has to stamp on the brake, he will soon become Phil latterly.

[PhilAsia]

CheesecakeRunner said:

PhilAsia said:

I LFB in both manual and auto, mainly for following reasons:

...0.3ish faster response time

If you find yourself needing an extra 0.3 seconds reaction time, you need to work on your observation, not which foot you’re pressing the brake pedal with.

I continually do work on my observation. I have activated the ABS once, for approximately 2 seconds, in the twenty years I have been driving in Metro Manila and worldwide. The ABS would have been activated for 2.3 seconds - or (definitely) longer, as I would have been later on the brakes - and probably (definitely) closer to hitting to the lovely person that decided to accelerate hard from a side road, across two lanes causing a collision, and straight across my bow.

I will admit to thinking that no sane person would move at the point they did...and should have known better. But, the proximity of the vehicles on the opposing carriageway was so close that, when the insane person did "GO!!", they caused a number of collisions.

I did avoid the vehicle with a comfortable buffer, but I was thankful for peripheral vision and gave myself a good telling off. Philippines is a great training ground.

[Steve H]

732NM said:

Steve H said:

I’m with Panamax here. How would a car be generating boost off throttle?

Anything with a throttle body will snap straight to vacuum as soon as it shuts and anything without a throttle body would not be utilising the manifold for it’s servo vacuum anyway, there would be a separate pump.

I've already explained how. Early manual drive by cable systems use aditional air valves to bypass the throttle body or use a throttle jack strategy where the throttle butterfly is left jacked open, later drive by wire just keep the throttle open whilst you are off the pedal, both then use a combination of ignition cut and retard and fuel to generate no torque but still fire a spark to energise the turbo. You can have full boost off throttle if you want. Thats used on every turbo rally car running ALS, i can have my road car using this.

Using launch control also generates boost when sat stationary with the throttle open, i have mine set at 1BAR as any more fries the clutch as its still an organic type, i can dial in 2BAR if i wanted to.

Then you have systems like the rocket, that are effectively a mini jet engine in the pre turbo exhaust pipe, that run without any need for engine strategy intervention, which drives the turbo generating full boost at idle. Prodrive utilised that on the WRC Subaru until it was banned. That was available as an aftermarket product for a while called zero lag.



Then you have flat foot shifting where you keep the throttle wide open during gear shifts, the engine strategy cuts ignition, retards the ignition and reduces fuel to kill torque, but air is still passing through and some fuel burn is keeping the turbo spooled, so when the gear shift is finished you have instant full torque, the engine never saw a vacuum during the shift.

Even without ALS if you are doing a lot of LFB with throttle and brake crossover, you will not generate any vacuum.

The thread is about road driving not WRC or weird aftermarket mods so you may well be right about all that but I’m not seeing how it’s really relevant.

[PhilAsia]

ecsrobin said:

PhilAsia said:

I encourage constant reevaluation when driving, and would consider that those wishing to become better on the road to do the same.

You are correct in stating that the chances of being rear-ended increase, that is built into my drive. To avoid such an occurrence I:

a) increase the distance to the vehicle ahead, and

b) am able to brake possibly 0.3 ish seconds earlier, possibly more gently, and to show the brake lights earlier to those following, thereby enabling them to brake earlier.

"...Can’t really think of any time where I’ve thought I’d need to stop quicker than I have..." Well done!!

I’d say you’re not giving a big enough distance to the vehicle ahead if you need 0.3 seconds extra braking time.

You would be wrong...

[PhilAsia]

Pica-Pica said:

CheesecakeRunner said:

PhilAsia said:

I LFB in both manual and auto, mainly for following reasons:

...0.3ish faster response time

If you find yourself needing an extra 0.3 seconds reaction time, you need to work on your observation, not which foot you’re pressing the brake pedal with.

If he has to stamp on the brake, he will soon become Phil latterly.

I would attempt a first class stamp...

[732NM]

Steve H said:

The thread is about road driving not WRC or weird aftermarket mods so you may well be right about all that but I’m not seeing how it’s really relevant.

I covered all types of driving, if you can't understand the information i can't do more to help.

[Steve H]

I appreciate you trying to help but as you ignored the thread title and didn’t cover the 99%+ of manual road cars where your examples didn’t apply, I am inclined to agree that you aren’t able to .

[732NM]

Steve H said:

I appreciate you trying to help but as you ignored the thread title and didn’t cover the 99%+ of manual road cars where your examples didn’t apply, I am inclined to agree that you aren’t able to .

I covered the basic road car, i expanded on it further.

[mko9]

PhilAsia said:

I LFB in both manual and auto, mainly for following reasons:

...0.3ish faster response time

How did you measure a 0.3sec difference in brake reaction time? Honestly, I don't really see how there can be much of any difference between picking your left foot up off the floor and putting it on the brake vs picking your right foot up off the throttle and putting it on the brake. Maybe if you are driving around with your left foot hovering over the brake pedal at all times, but that is incredibly tiresome.

[PhilAsia]

mko9 said:

PhilAsia said:

I LFB in both manual and auto, mainly for following reasons:

...0.3ish faster response time

How did you measure a 0.3sec difference in brake reaction time?

Not my figures, industry generated figures of 0.3ish seconds on average.

mko9 said:

Honestly, I don't really see how there can be much of any difference between picking your left foot up off the floor and putting it on the brake vs picking your right foot up off the throttle and putting it on the brake.

I do not do that.

mko9 said:

Maybe if you are driving around with your left foot hovering over the brake pedal at all times, but that is incredibly tiresome.

Yes, that is exactly what I do. Where there is no hazard I use the footrest. Where there is a possibility of a potential hazard, or an actual hazard, my left foot is hovering. I do not find it in the least bit tiring, but then I have been doing it for almost 50 years, with some breaks for shopping, socialising and sleeping, etc.

Edited by PhilAsia on Sunday 12th May 11:39