Dabbing your brakes when you haven't got a LSD
Discussion
I seem to remember hearing many years ago that you can sometimes stop a wheel from spinning on ice by dabbing your brakes with your left foot while still on the gas with your right. You only do it for a split second and it's supposed to stop the spinning wheel in the hope that both the driving wheels can try to start again.
Is there any truth in it or was it just national service talk from my old dad.(He was a driver in the RAF 1948/1950)
Is there any truth in it or was it just national service talk from my old dad.(He was a driver in the RAF 1948/1950)
If you have a RWD car with an open diff, you can put the handbrake on slightly which can help.
As for FWD cars and dabbing the brakes. Well i guess in theory it would work, but modern brakes are so heavily servo'd you'd have to have an extremely sensitive left foot, so i'm not sure if you'd actually be able to do it?
Basically with an open diff, if one wheel has no traction, all the torque goes there and it spins. If you put the handbrake on, it causes resistance on the other wheel, so some torque is sent there too. Thats a very basic way of explaining it, but I'm sure someone with a better understanding will elaborate.
As for FWD cars and dabbing the brakes. Well i guess in theory it would work, but modern brakes are so heavily servo'd you'd have to have an extremely sensitive left foot, so i'm not sure if you'd actually be able to do it?
Basically with an open diff, if one wheel has no traction, all the torque goes there and it spins. If you put the handbrake on, it causes resistance on the other wheel, so some torque is sent there too. Thats a very basic way of explaining it, but I'm sure someone with a better understanding will elaborate.
Edited by reggie82 on Friday 8th January 21:15
james_gt3rs said:
Very interesting, thanks.Most new cars have a throttle cut when you press the brakes and throttle together, but it doesnt usually get in the way untill quite a bit of brake is on. So you might be able to do it.
Its the same technique thats needed if you have a Torsen differential and one wheel is off the ground.
Its the same technique thats needed if you have a Torsen differential and one wheel is off the ground.
james_gt3rs said:
I was going to link that exact same video! 
, you appear to have beaten me to it sir .loomx said:
Most new cars have a throttle cut when you press the brakes and throttle together, but it doesnt usually get in the way untill quite a bit of brake is on. So you might be able to do it.
If, as indicated above, this technique is mainly for use with rear wheel drive cars, then because they're RWD they'll be driver's cars (I'm including BMW and Mercedes in that), ergo they won't have the brake/throttle cut out.I hate them too.
Only reasons I can think of are that it stops throttle cables getting stuck though, an means you can suspposedly increase throttle responce with a sport button, although if you drive any car like this you will see that it doesnt do that, it just makes it so 10% throttle is more like 50% throttle.
The other reasons is on a bumpy road if you foot wiggles on the pedel it can cancle out the changes in the throttle so you dont kangroo all over the place...
Also traction control systems can then adjust the throttle against what you request and so on.
Only reasons I can think of are that it stops throttle cables getting stuck though, an means you can suspposedly increase throttle responce with a sport button, although if you drive any car like this you will see that it doesnt do that, it just makes it so 10% throttle is more like 50% throttle.
The other reasons is on a bumpy road if you foot wiggles on the pedel it can cancle out the changes in the throttle so you dont kangroo all over the place...
Also traction control systems can then adjust the throttle against what you request and so on.
Edited by loomx on Wednesday 13th January 14:13
loomx said:
I hate them too.
Only reasons I can think of are that it stops throttle cables getting stuck though, an means you can suspposedly increase throttle responce with a sport button, although if you drive any car like this you will see that it doesnt do that, it just makes it so 10% throttle is more like 50% throttle.
The other reasons is on a bumpy road if you foot wiggles on the pedel it can cancle out the changes in the throttle so you dont kangroo all over the place...
Also traction control systems can then adjust the throttle against what you request and so on.
Rather stupid invention in my opinion then!Only reasons I can think of are that it stops throttle cables getting stuck though, an means you can suspposedly increase throttle responce with a sport button, although if you drive any car like this you will see that it doesnt do that, it just makes it so 10% throttle is more like 50% throttle.
The other reasons is on a bumpy road if you foot wiggles on the pedel it can cancle out the changes in the throttle so you dont kangroo all over the place...
Also traction control systems can then adjust the throttle against what you request and so on.
Edited by loomx on Wednesday 13th January 14:13
Why you would want to transform the profile of your throttle pedal in a *sport* mode is beyond me. I would much rather have a cable throttle and be 100% aware of how my actions with my right foot on the loud pedal will equate to speed and or control over the car.
IMO pressing the sports button and making 10% more like 50% is just an absolute recipe for disaster for people who have no idea how to control their car, especially in a situation where the *sport* button would be pressed, hinting at increased cornering speed used etc.
loomx said:
Wrong, pretty much any car with drive by wire has it, be it, BMW, Audi, Mini and so on.
Remaps usually remove it though
Its not an instant throttle cut, but if you put your foot on the brake and pedel for x ammount of time it will cut the throttle.
No need to be so smug and rude. Firstly, Audi and Mini build front wheel drive boring cars, not rear wheel drive performance cars. Read my post again; I was referring only to RWD cars.Remaps usually remove it though
Its not an instant throttle cut, but if you put your foot on the brake and pedel for x ammount of time it will cut the throttle.
Secondly, how long does one need to operate the brake and accelerator together for, and what's the threshold time where it'll cut the power? I've got a DBW equipped BMW and I know it'll take dabs of brake <1s whilst on the throttle (tried for fun) and the other way round (heel and toe). Given the low speed of this wheel slip scenario, I don't expect someone will be off the clutch for that long would they?
Thirdly, such DBW cut out devices don't operate on the handbrake do they? Wouldn't that be the main source of braking at the driven wheels in a RWD car? Given the low braking force needed to get this effect to work, low steering input but requirement for clutch use, I'd have thought the handbrake would be ideally fit for purpose.
loomx said:
I agree, in cars with sport buttons I just have to turn it on all the time, can get used to having to press the throttle so far for anything to happen.
I totally agree. Bring back cable throttles, there was never anything wrong with them. Sport buttons are just paper on the cracks opened by the introduction of DBW.Edited by RobM77 on Wednesday 13th January 14:46
It is rather an irritating feature in my car (clio). The fact its fly by wire means that 65% throttle yields near enough what full throttle does, so not only when your foot hits the floor when you are expecting more go, disappointingly the car is less easy to control as the progression of the throttle is somewhat sporadic.
Could such throttle mapping be employed to try and mask a small engine? For example, many people just using it as a shopping car, or as something to pootle around in will be much less inclined to give it full throttle, therefore giving the illusion that the car has more power to give if you press the loud pedal more.
Could such throttle mapping be employed to try and mask a small engine? For example, many people just using it as a shopping car, or as something to pootle around in will be much less inclined to give it full throttle, therefore giving the illusion that the car has more power to give if you press the loud pedal more.
Edited by doodles19 on Wednesday 13th January 14:50
Most likely, I have to say that some DBW cars are fine, My S4 feels just like a cable throttle, responce is instant and progressive, its perfect. But all new cars I have driven are terrible, if you stamp on and off the throttle (full to 0) the revs barley move.
My S4 has had quite a bit done to it though, and the throttle map has been changed along with engine map.
My S4 has had quite a bit done to it though, and the throttle map has been changed along with engine map.
When I drove my friends cars for a few days, abarth scicento (or however its spelt 
) and a classic cooper sportspack, the throttle response on both were much more pleasing, so much more responsive to the full progression of the pedal. I honestly don't know what companies such as renault were thinking when they thought that putting a fbw throttle on a little city car would be a good idea, surely just added to the cost of the car whilst also making it a less pleasurable experience to drive.
(The cooper sportspack btw, HUGE FUN! Not as fast in a straight line on the track as a modern car (just). More than capable in the corners however, and im sure I had much more fun in the cooper, though... ride is pretty shocking on the road... only let down of the day)
Also, in a fwd car, does anyone think that using the principal of slightly brake application whilst pulling off, would A) ever be possible with a manual. and B) whether it would work.
) and a classic cooper sportspack, the throttle response on both were much more pleasing, so much more responsive to the full progression of the pedal. I honestly don't know what companies such as renault were thinking when they thought that putting a fbw throttle on a little city car would be a good idea, surely just added to the cost of the car whilst also making it a less pleasurable experience to drive.(The cooper sportspack btw, HUGE FUN! Not as fast in a straight line on the track as a modern car (just). More than capable in the corners however, and im sure I had much more fun in the cooper
, though... ride is pretty shocking on the road... only let down of the day)Also, in a fwd car, does anyone think that using the principal of slightly brake application whilst pulling off, would A) ever be possible with a manual. and B) whether it would work.
Edited by doodles19 on Wednesday 13th January 15:03
Edited by doodles19 on Wednesday 13th January 15:16
doodles19 said:
It is rather an irritating feature in my car (clio). The fact its fly by wire means that 65% throttle yields near enough what full throttle does, so not only when your foot hits the floor when you are expecting more go, disappointingly the car is less easy to control as the progression of the throttle is somewhat sporadic.
Could such throttle mapping be employed to try and mask a small engine? For example, many people just using it as a shopping car, or as something to pootle around in will be much less inclined to give it full throttle, therefore giving the illusion that the car has more power to give if you press the loud pedal more.
Could such throttle mapping be employed to try and mask a small engine? For example, many people just using it as a shopping car, or as something to pootle around in will be much less inclined to give it full throttle, therefore giving the illusion that the car has more power to give if you press the loud pedal more.
Edited by doodles19 on Wednesday 13th January 14:50
Many DBW systems interpret what you ask of the engine, rather than just controlling the throttles. In a modern Porsche your right foot controls torque, not throttle opening. You know those moments with a real throttle pedal at low speed where you get more acceleration from 50% throttle than overfuelling it at 100%? They're not present in a modern Porsche; it's a complete disconnection.doodles19 said:
Also, in a fwd car, does anyone think that using the principal of slightly brake application whilst pulling off, would A) ever be possible with a manual. and B) whether it would work.
Yes and yes. I proved this point this afternoon by moronically driving downhill into a small yard covered with virgin snow and then, strangely enough, finding that I couldn't drive uphill out of the yard. I thought I might do better by reversing, and whilst that helped a bit it wasn't quite enough. Thankfully my trusty Mondeo has a fairly effective idle control system that will maintain the engine idle speed against a mostly-engaged clutch, leaving right-foot free to modulate the brake. It worked a-treat and I escaped from the trap. In my younger days I used to do production car trials in my Mini. A common trick was to do the same technique, albeit increasing the idle speed with the choke.
On another topic, the principal benefit of FBW throttle is as Rob says; to allow the ECU to alter the throttle independently of the drivers command; for instance a wide-open throttle does not necessarily produce the best performance and careful mapping of the throttle position during engine development can give big benefits. I don't suppose this applies to most Vauxhall Corsas, though.
And on the other topic, I once had a 2006 Ford Focus as a courtesy car. I thought it would be good but hated everything about it, but especially the daft brake/throttle intollerance. A very quick prod of the throttle whilst braking would be ok, but a more progressive heel 'n' toe would result in the engine cutting out for a few seconds. Utter pile of crap.
Edited by RT106 on Wednesday 13th January 17:29
RT106 said:
On another topic, the principal benefit of FBW throttle is as Rob says; to allow the ECU to alter the throttle independently of the drivers command; for instance a wide-open throttle does not necessarily produce the best performance and careful mapping of the throttle position during engine development can give big benefits. I don't suppose this applies to most Vauxhall Corsas, though.
I don't really see it as a benefit though, just another layer of chinese whispers between control input and car output. Even if for some people this interpretation of their commands is of use, the benefits to those people are surely more than outweighed by the main disadvantage, which is the lag that the system gives. The car I race or my Elise (both cable throttles) are far easier and more natural to drive. When I've driven the BMW all week I jump in the Elise and drive it naturally. Conversely, When I've spent a week in the Elise I jump in the BMW and have to re-learn all of my throttle and clutch control, and I never quite achieve the smoothness of operation that the Elise gives me.Gassing Station | Advanced Driving | Top of Page | What's New | My Stuff