Left foot braking in a tt?
Discussion
Was just reading an article on left foot braking and using it to kill understeer. Those track fiends among us are probably all in 2WD porkers and may or may not use left foot braking for the benefits of forward weight transfer while cornering or to keep the engine (and turbo if appropriate) spooled up ready to nail it on the way out.
I was debating the effects of using it on a 4WD tt and whether it risks having any deleterious consequences for the front/rear diff? On tight curves the tendency of the tt to understeer is very marked - a quick lift-off tightens the line and allows rebootage but also lets the boost levels drop. Left foot braking might be the ideal way to tighten the line while keeping the horses ready for tyre shreddage - has anyone here given this a try? When I sober up I might go out on a quiet road and try and train some sensitivity into my left foot.
I was debating the effects of using it on a 4WD tt and whether it risks having any deleterious consequences for the front/rear diff? On tight curves the tendency of the tt to understeer is very marked - a quick lift-off tightens the line and allows rebootage but also lets the boost levels drop. Left foot braking might be the ideal way to tighten the line while keeping the horses ready for tyre shreddage - has anyone here given this a try? When I sober up I might go out on a quiet road and try and train some sensitivity into my left foot.
Ignoring the technicalities of your actual question (sorry), but I think you'll find any attempt at left foot braking in a modern VAG product an "interesting" experience. If you are going to try it, check your rearview mirror first.
I spoke to their product manager about this feature and the offical line is "it's to prevent brake fade and, besides, it's not something you'd be doing in the normal course of driving".
Just an aside...
I spoke to their product manager about this feature and the offical line is "it's to prevent brake fade and, besides, it's not something you'd be doing in the normal course of driving".
Just an aside...
I think 'tt' here means a Porsche turbo , not an Audi (VAG) 'tt'...
The theoretical answer for the porsche is probably dependent on the electronics that are active , the practical and pragmatic answer would be to experiment (on the empty festive season roads perhaps ?)
The person most likely to know ??? I'd shortlist Don Palmer and Andrew Walsh , you could post at www.carlimits.com for latter
The theoretical answer for the porsche is probably dependent on the electronics that are active , the practical and pragmatic answer would be to experiment (on the empty festive season roads perhaps ?)
The person most likely to know ??? I'd shortlist Don Palmer and Andrew Walsh , you could post at www.carlimits.com for latter
I have a suspicion modern Porsches don't allow you to do it in a pure fashion.
Not being an expert on left foot braking myself, but I do get the impression the electronics will try to kill the revs if you brake and accelerate at the same time (and this was with a non-PSM Carrera 2, so with a PSM 4wd TT, I assume it holds even truer).
Anyone care to correct me?
Not being an expert on left foot braking myself, but I do get the impression the electronics will try to kill the revs if you brake and accelerate at the same time (and this was with a non-PSM Carrera 2, so with a PSM 4wd TT, I assume it holds even truer).
Anyone care to correct me?
oldtimer said:
I think 'tt' here means a Porsche turbo , not an Audi (VAG) 'tt'...
Ooops! Sorry. Just read 4wd and jumped to the wrong conclusion. Should have realised we weren't talking Audi when the "keeping the horses ready for tyre shreddage" comment came up!
>> Edited by dxg999 on Sunday 26th December 13:11
I tried it once in a boxster and got the distinct feeling that it cut the accelerator automatically - as in the Audi TT as mentioned above (you can't heel/toe in any VAG car).Sorry - I was imprecise - I do of course mean a 993tt. This doesn't have the PSM system of the 996tt, so I don't think that the brain would automatically cut the throttle on braking. As far as I know, the throttle is a purely mechanical linkage, so it shouldn't be able to!
The sort of situation that I'm thinking of is zipping round a tight little roundabout. There isn't enough room to allow much understeer, so powering through it to provoke the back out isn't an option. Here a dab of brakes to throw the back out while the right foot keeps the turbos spinning might just do the trick. Sometimes really regret having 4WD as it dampens my hooliganacious, RWD pleasure.
Anyway, will report back once I've played with it.
The sort of situation that I'm thinking of is zipping round a tight little roundabout. There isn't enough room to allow much understeer, so powering through it to provoke the back out isn't an option. Here a dab of brakes to throw the back out while the right foot keeps the turbos spinning might just do the trick. Sometimes really regret having 4WD as it dampens my hooliganacious, RWD pleasure.
Anyway, will report back once I've played with it.
Not sure I'd want to try it - I have a 993 but not 4wd so this may be irrelevant...
Left foot braking has worked for me in the past with front wheel drive cars (hot hatches such as mk2 Golf GTi and 205 GTi 1.9). The Golf really benefited from a quick dab of brakes whilst keeping the power on to tighten a line. The 205 had lairy lift-off oversteer as standard, so LFB was a touch dodgy but since your throttle foot was still on the pedal, you could always power out of any unexpected tailslides.
With this in mind (and a heavy rear end on 911s), I'd be really nervous of trying it on greasy, tight bends. After all, the idea with LFB is that you can destabilise the back end, but with the safety net of still having throttle control....
In the 911, let's say you pitch into a tight, slippery bend and it understeers. Bit of left foot braking, and the back end breaks free and tightens your line. What next? You can't nail the throttle like in a FWD to pull you straight: hard on the power in any 911 with the tail wagging will likely throw you off the road. Lifting off won't help as you've already unsettled the back through forward weight transfer. Only option (for driving non-gods) is to lean on the ABS and hope you don't hit the scenery before you stop.
I'd be more inclined to use power to tighten your line in these cases.
Or, of course, you should avoid these silly 4wd contraptions and get a RWD 911 like god intended
DISCLAIMER: I am not a driving god. And, however much I want a 993tt, I have never driven one
Also, I have no loose-surface experience where LFB is mainly used... interestingly though, the only other racing I've heard of LFB being common is the UK touring cars which are FWD...
Left foot braking has worked for me in the past with front wheel drive cars (hot hatches such as mk2 Golf GTi and 205 GTi 1.9). The Golf really benefited from a quick dab of brakes whilst keeping the power on to tighten a line. The 205 had lairy lift-off oversteer as standard, so LFB was a touch dodgy but since your throttle foot was still on the pedal, you could always power out of any unexpected tailslides.
With this in mind (and a heavy rear end on 911s), I'd be really nervous of trying it on greasy, tight bends. After all, the idea with LFB is that you can destabilise the back end, but with the safety net of still having throttle control....
In the 911, let's say you pitch into a tight, slippery bend and it understeers. Bit of left foot braking, and the back end breaks free and tightens your line. What next? You can't nail the throttle like in a FWD to pull you straight: hard on the power in any 911 with the tail wagging will likely throw you off the road. Lifting off won't help as you've already unsettled the back through forward weight transfer. Only option (for driving non-gods) is to lean on the ABS and hope you don't hit the scenery before you stop.
I'd be more inclined to use power to tighten your line in these cases.
Or, of course, you should avoid these silly 4wd contraptions and get a RWD 911 like god intended
DISCLAIMER: I am not a driving god. And, however much I want a 993tt, I have never driven one
Also, I have no loose-surface experience where LFB is mainly used... interestingly though, the only other racing I've heard of LFB being common is the UK touring cars which are FWD...IMO Cyberface has it spot on.
You can LFB in a 911 and it will kill understeer and rotate the car; The thing is, how much will it rotate?
Skillfully done with a delicate touch on the brakes and gentle re-application of the throttle getting the balance "just so" and you can drift round the corner like a driving god. Get it a bit wrong and the high polar moment of inertia means you'll complete your corner backwards.
IIRC the centre diff is electronic using the ABS sensors and I'm not sure it is going to like shifting torque about if the ABS is operating ( which it will if the rear starts to drift under braking )
You can LFB in a 911 and it will kill understeer and rotate the car; The thing is, how much will it rotate?
Skillfully done with a delicate touch on the brakes and gentle re-application of the throttle getting the balance "just so" and you can drift round the corner like a driving god. Get it a bit wrong and the high polar moment of inertia means you'll complete your corner backwards.
IIRC the centre diff is electronic using the ABS sensors and I'm not sure it is going to like shifting torque about if the ABS is operating ( which it will if the rear starts to drift under braking )
Maybe you guys are right and I admit I hadn't thought of what the ABS and the ABD would make of such antics. And maybe it would take a driving god, or at least an awful lot of familiarity to control the resulting pendulum. I'll make sure that I only try it somewhere with plenty of room. 
At the last VMax I was really giving the car some stick round the bends and the back just would not step out under power. In fact, though I'm sure the 993tt has no PSM system (other than the ABD and that only operates up to about 40 mph), everytime the back was about to start to powerslide it felt like some electronics took over, and redistributed the power such that the power oversteer didn't happen.
I've always been a keen drifter of RWD cars but had to admit myself flummoxed on the day - the only way I could get the back to step out was braking deep into the corner so that the weight transfer did the trick, and even then re-application of the horses didn't prolong the slide. Most frustrating. Maybe I've simply bought an excessively competent machine that is designed to do it's job brilliantly without the drama...
At the last VMax I was really giving the car some stick round the bends and the back just would not step out under power. In fact, though I'm sure the 993tt has no PSM system (other than the ABD and that only operates up to about 40 mph), everytime the back was about to start to powerslide it felt like some electronics took over, and redistributed the power such that the power oversteer didn't happen.
I've always been a keen drifter of RWD cars but had to admit myself flummoxed on the day - the only way I could get the back to step out was braking deep into the corner so that the weight transfer did the trick, and even then re-application of the horses didn't prolong the slide. Most frustrating. Maybe I've simply bought an excessively competent machine that is designed to do it's job brilliantly without the drama...
nel said:
At the last VMax I was really giving the car some stick round the bends and the back just would not step out under power. In fact, though I'm sure the 993tt has no PSM system (other than the ABD and that only operates up to about 40 mph), everytime the back was about to start to powerslide it felt like some electronics took over, and redistributed the power such that the power oversteer didn't happen.
That'll be excess power being redirected from the rear axle to the front axle (ie what the 4WD is designed to do). The extra grunt through the front tyres effectively pulling the car around the corner.
DAZ
Have to disagree with the last few coments. At Bedford I'm usually the first to go off the track (backwards) due to excessive arse hanging out!
I find my TT perfectly balanced and the arse is always nice and willing to play (only on track), either going into a corner excessively fast and braking a little longer into the corner (be ready to get back on the power!) or simply lift off for a split second and then reaply excessively and out she pops!
I did have problems with excessive understeer when my front tyres were set at 30psi cold. 36psi soon restored their bite. I don't know why you'd want to provoke the car on the roads though. Do you have a death wish? Far too much to hit!
I find my TT perfectly balanced and the arse is always nice and willing to play (only on track), either going into a corner excessively fast and braking a little longer into the corner (be ready to get back on the power!) or simply lift off for a split second and then reaply excessively and out she pops!
I did have problems with excessive understeer when my front tyres were set at 30psi cold. 36psi soon restored their bite. I don't know why you'd want to provoke the car on the roads though. Do you have a death wish? Far too much to hit!
Daz - I thought the torque split front:rear on the 993tt was limited to 20:80, so it could't send all the oomph up front. Anyway, it was a very strange feeling at the limit as though the engine was bridled for second until all possibility of powering out the back had gone. Will look into it - my car's from 98, so in the last year of production - maybe they added more elctronic wizardery.
Sounds like I'm not trying hard enough then - some track time needed to explore further I suppose. I don't have a deathwish and don't normally come anywhere the car's limits on the public road, there's just a couple of choice roundabouts that are very tempting when there's nobody about! I just want some damned tail happy action now and then....
I don't know the absolute details of the 993tt but assumed they were similar to the 996tt, where the power is normally split 95% rear and 5% front, but upto 40% can be sent to the front if slippage on the rear axle is detected.
DAZ
Edited due to Don's subsequent comment indicating that I was talking nonsense.
>> Edited by dazren on Monday 27th December 12:51
DAZ
Edited due to Don's subsequent comment indicating that I was talking nonsense.
>> Edited by dazren on Monday 27th December 12:51
Don said:
Didn't pre PSM cars have Traction Control? i.e. control over the throttle when the abs sensors detected slip?
I don't know. Does anyone with a 993tt car to comment?
If booting it leads to slippage on the rear tyres, the car then sends more power to the front wheels, what happens if there is too much power for the front wheels top cope with? Does the car override the throttle pedal, or do you get wheelspin all over the place?
DAZ
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