Does heel/toe cause any extra wear on any parts of the car?

[RobM77]

7db said:

RobM77 said:

The only time I've ever heard of anyone accelerating round a corner is in rally driving where a drift is being maintained on the power.

Hmmm. Going round a corner *is* accelerating. And given that it's unlikely that the force is exactly directed towards the centre of the bend, then some acceleration or deceleration is likely.

You know what I mean! I think you're overcomplicating (or perhaps just mis-understanding) what is, for the purposes of this discussion, quite a basic principle.

7db said:

In a road corner limited by vision, not grip, why not accelerate in the curved phase once the vision starts to open up irrevocably to start that accelerating straight earlier?

Acceleration (yes...longitudinal!) in a car causes understeer, and should only be performed with an accompanying lessening of the steering lock to compensate after the apex in the exit phase of a bend. The only exception to this is when the car has sufficient power to overcome the grip at the rear and slide.

[StressedDave]

RobM77 said:

7db said:

In a road corner limited by vision, not grip, why not accelerate in the curved phase once the vision starts to open up irrevocably to start that accelerating straight earlier?

Acceleration (yes...longitudinal!) in a car causes understeer, and should only be performed with an accompanying lessening of the steering lock to compensate after the apex in the exit phase of a bend. The only exception to this is when the car has sufficient power to overcome the grip at the rear and slide.

True for large levels of longitudinal acceleration, but untrue for lesser levels... There's also the issue that most road bends are relatively short duration, so you don't reach a steady-state where that truism is more true.

[GreenV8S]

RobM77 said:

Acceleration (yes...longitudinal!) in a car causes understeer, and should only be performed with an accompanying lessening of the steering lock to compensate after the apex in the exit phase of a bend. The only exception to this is when the car has sufficient power to overcome the grip at the rear and slide.

It strikes me as a sweeping generalisation that more power always results in understeer, it is not nearly as black and white as that.

I also don't understand why you say that you should take off lock as understeer increases. Rather than compensating, surely the reduced lock would reinforce the tendency to follow a wider line?

[7db]

RobM77 said:

Acceleration (yes...longitudinal!) in a car causes understeer, and should only be performed with an accompanying lessening of the steering lock to compensate after the apex in the exit phase of a bend. The only exception to this is when the car has sufficient power to overcome the grip at the rear and slide.

Even if your supposition were true (and it's not, as Dave says - mild doses of long acc help the car to tuck in) as the forces are orthogonal to the tyre track, not its heading) - then it doesn't follow that you don't want to increase speed towards the apex. It depends on how your vision of the corner develops.

If you are going slower than you need to on entry, then you can accelerate hard than you otherwise would through the mid-corner to the apex and beyond.

[Vaux]

RobM77 said:

Vaux said:

accompanied by some gentle acceleration to maintain speed round the bend.

eh? If you're accelerating how can you be maintaining your speed?

Well, if you don't apply acceleration, you slow down. Something to do with physics or maths and vectors. You don't want to be slowing down for no good reason.

[Vaux]

p1esk said:

RobM77 said:

Vaux said:

accompanied by some gentle acceleration to maintain speed round the bend.

eh? If you're accelerating how can you be maintaining your speed?

I've noticed these misleading descriptions before.

Maintaining (a constant) speed through a bend (unless it's downhill) means no acceleration; it does mean applying some accelerator pedal, or throttle opening. Some people seem to be talking about accelerating when they really mean applying a bit of throttle.

Best wishes all,
Dave.

And I thought I was pedantic........

[RobM77]

GreenV8S said:

RobM77 said:

Acceleration (yes...longitudinal!) in a car causes understeer, and should only be performed with an accompanying lessening of the steering lock to compensate after the apex in the exit phase of a bend. The only exception to this is when the car has sufficient power to overcome the grip at the rear and slide.

It strikes me as a sweeping generalisation that more power always results in understeer, it is not nearly as black and white as that.

But that's not what I said was it? If you read what I said again, I mentioned the case where power overcomes grip and causes oversteer. There are other small effects; power stabilies in some situations for instance. For the purposes of this discussion though, we can think of power as applying a tendancy to understeer and lack of power applying a tendancy oversteer. The idea in a bend is to achieve neither state.

GreenV8S said:

I also don't understand why you say that you should take off lock as understeer increases. Rather than compensating, surely the reduced lock would reinforce the tendency to follow a wider line?

When a tyre's given all it can give, there's no point throwing more lock at it.

In an attempt to understand what Stressed Dave is saying to explain his unusual driving style (and I still don't understand all this acceleration through corners business!!!), I've been reading through an old book today that I'd recommend to anyone interested in the Physics and Maths of how cars react in corners. It's called "The Racing Driver" by Denis Jenkinson, and covers all this sort of thing in great depth. Getting on a bit now, but with the wonders of the interweb it should be possible to find a copy. "Drive to Win" is also good. That's a more recent book. Both cover track driving, but examine the physics in entirity.

Stressed Dave: if you could explain what you mean by acceleration being a good thing in a corner, as shown in your video, it would help greatly! I saw your post briefly before I went out earlier and I've been scanning the books and they all just seem to confirm what I've been saying. I've even discussed it with a couple of fellow Physics grads who are also into motor racing. I can't find any reference at all to accelerating round corners being a good thing, other than a mention in the Jenks book of acceleration being a stabilising force in a FWD car, and also at very high speed (even for a track) in a rear drive car. So far everything I've read just confirms the standard technique: turn in the car to a balanced state, keep a steady throttle to the apex to maintain the balance and then accelerate out as you unwind lock. Accelerating from the turn in just seems like a nice way to increase your chances of crashing?!

[GreenV8S]

RobM77 said:

GreenV8S said:

I also don't understand why you say that you should take off lock as understeer increases. Rather than compensating, surely the reduced lock would reinforce the tendency to follow a wider line?

When a tyre's given all it can give, there's no point throwing more lock at it.

I assumed that was a typo in your post. You genuinely do mean that taking lock off counteracts understeer?

[StressedDave]

RobM77 said:

In an attempt to understand what Stressed Dave is saying to explain his unusual driving style (and I still don't understand all this acceleration through corners business!!!), I've been reading through an old book today that I'd recommend to anyone interested in the Physics and Maths of how cars react in corners. It's called "The Racing Driver" by Denis Jenkinson, and covers all this sort of thing in great depth. Getting on a bit now, but with the wonders of the interweb it should be possible to find a copy. "Drive to Win" is also good. That's a more recent book. Both cover track driving, but examine the physics in entirity.

If you think that those books examine the 'physics' of vehicle dynamics in suitable depth, I'm afraid you're somewhat mistaken. Jenks' book was written by a journo and was written quite some years before the advent of vehicle dynamics as a serious subject. Smith's book is indeed very good, but again limits itself to what it thinks drivers should know rather than what is necessarily happening. Serious students of the subject rely on the 'bibles' of 'Race Car Vehicle Dynamics' by Milliken and Milliken and 'Tire and Vehicle Dynamics' by Pacejka. The latter is particularly good on the effect of driveline torque on the behaviour of the car. BTW, neither is 'Vehicle Dynamics for Dummies' - you'll need a good understanding of algebra and advanced maths such as calculus, Laplace Transforms and partial differential equations. They aren't cheap to buy either...

RobM77 said:

Stressed Dave: if you could explain what you mean by acceleration being a good thing in a corner, as shown in your video, it would help greatly! I saw your post briefly before I went out earlier and I've been scanning the books and they all just seem to confirm what I've been saying. I've even discussed it with a couple of fellow Physics grads who are also into motor racing. I can't find any reference at all to accelerating round corners being a good thing, other than a mention in the Jenks book of acceleration being a stabilising force in a FWD car, and also at very high speed (even for a track) in a rear drive car. So far everything I've read just confirms the standard technique: turn in the car to a balanced state, keep a steady throttle to the apex to maintain the balance and then accelerate out as you unwind lock. Accelerating from the turn in just seems like a nice way to increase your chances of crashing?!

You're spending too much time considering the limit handling case. I'm talking about road driving in the linear region of the tyre (up to around 0.4g). Brief explanation:

1) In this region cornering force is proportional to slip angle. This force is produced perpendicular to the slip angle, effectively point to a point behind the centre of rotation.

2) The cornering force produces a component of drag, so some is wasted and acts to slow you down.

3) Traction forces are produced parallel to the slip angle, so some of that traction force acts to counter the drag force produced - that's why you're told you need more power in a corner to maintain speed. A small component of the force acts towards the centre of rotation - traction is providing a small cornering force.

4) Now, if you consider the state where you've actually added a little more power than that required. Firstly the car does start increasing speed, so you would imagine the car would start to follow a widening radius. But you're getting even more cornering force, so the effect is countered. Careful manipulation of throttle can have a significant effect on cornering beyond the obvious maintenance of stability.

In long duration corners (of which you don't get many on the roads I like to drive, but you get plenty of on track) the technique will not work, because you do end up increasing speed to the point where the extra cornering force produced by traction isn't enough to keep the car on line. Most road corners are short duration and there's very little steady-state, even less if you follow Smith's advice about selection of cornering line.

[7db]

StressedDave said:

Serious students of the subject rely on the 'bibles' of 'Race Car Vehicle Dynamics' by Milliken and Milliken and 'Tire and Vehicle Dynamics' by Pacejka...you'll need a good understanding of algebra and advanced maths such as calculus, Laplace Transforms and partial differential equations.

It's worth nothing that you'll also need a caffeine habit that would make Hunter S Thopmson blush to stay awake if you read these at bedtime. Although even if you only make it as far as chapter one of Milliken and Milliken then you'll have a better feel for the difference between dynamic and terminal oversteer and understeer.

StressedDave said:

1) In this region cornering force is proportional to slip angle. This force is produced perpendicular to the slip angle

Tsk. That angle has got direction and magnitude? Perpendicular to track. (which is what RobM77 spend a lot of his time doing )

[p1esk]

Vaux said:

p1esk said:

RobM77 said:

Vaux said:

accompanied by some gentle acceleration to maintain speed round the bend.

eh? If you're accelerating how can you be maintaining your speed?

I've noticed these misleading descriptions before.

Maintaining (a constant) speed through a bend (unless it's downhill) means no acceleration; it does mean applying some accelerator pedal, or throttle opening. Some people seem to be talking about accelerating when they really mean applying a bit of throttle.

Best wishes all,
Dave.

And I thought I was pedantic........

I thought you knew I invented the term. :laugh.

In fact I still feel there was a degree of confusion there so I thought it might be helpful - to some, at least - to mention it.

Best wishes all,
Dave.

[p1esk]

GreenV8S said:

RobM77 said:

GreenV8S said:

I also don't understand why you say that you should take off lock as understeer increases. Rather than compensating, surely the reduced lock would reinforce the tendency to follow a wider line?

When a tyre's given all it can give, there's no point throwing more lock at it.

I assumed that was a typo in your post. You genuinely do mean that taking lock off counteracts understeer?

Rightly or wrongly I've gained the impression that it can do in some circumstances, but that's only from what I've read, and not from personal experience on the road.

Best wishes all,
Dave.

[StressedDave]

p1esk said:

Rightly or wrongly I've gained the impression that it can do in some circumstances, but that's only from what I've read, and not from personal experience on the road.

It's more of a limit technique, so only likely to occur on the road in low grip conditions. From my description on the previous page, you can have so much slip angle that effectively you've gone over peak cornering force and over the other side - i.e. you;re wasting the cornering grip in drag. Taking steering off at this point means that climb back up the curve and get more grip.

Anyone who has been on a skid pan and got into a terminal understeer situation can accept what happens when you take lock off and also how hard it is to program the brain to do so!

[7db]

Of course we've only really discussed the first order / steady state effects here. We could also consider the effect of transients in the system...

[Vaux]

p1esk said:

In fact I still feel there was a degree of confusion there so I thought it might be helpful - to some, at least - to mention it.

Do you like Dave's wording:

StressedDave said:

I'm talking about road driving in the linear region of the tyre (up to around 0.4g). Brief explanation:

1) In this region cornering force is proportional to slip angle. This force is produced perpendicular to the slip angle, effectively point to a point behind the centre of rotation.

2) The cornering force produces a component of drag, so some is wasted and acts to slow you down.

3) Traction forces are produced parallel to the slip angle, so some of that traction force acts to counter the drag force produced - that's why you're told you need more power in a corner to maintain speed. A small component of the force acts towards the centre of rotation - traction is providing a small cornering force.

4) Now, if you consider the state where you've actually added a little more power than that required. Firstly the car does start increasing speed, so you would imagine the car would start to follow a widening radius. But you're getting even more cornering force, so the effect is countered. Careful manipulation of throttle can have a significant effect on cornering beyond the obvious maintenance of stability.

All I know is it feels better to be "driving" round a corner.

As every one's talking about books, I'm off to read "Going Faster - Mastering the art of race driving" - it's got simple pictures!

[StressedDave]

For simplicity, I do still prefer Carroll Smith's 'Drive to Win' - it does explain the dynamics better.

[p1esk]

StressedDave said:

p1esk said:

Rightly or wrongly I've gained the impression that it can do in some circumstances, but that's only from what I've read, and not from personal experience on the road.

It's more of a limit technique, so only likely to occur on the road in low grip conditions. From my description on the previous page, you can have so much slip angle that effectively you've gone over peak cornering force and over the other side - i.e. you;re wasting the cornering grip in drag. Taking steering off at this point means that climb back up the curve and get more grip.

Anyone who has been on a skid pan and got into a terminal understeer situation can accept what happens when you take lock off and also how hard it is to program the brain to do so!

OK, thanks. In that case I'm still surprised at what Peter (GreenV8S) said, especially as he does some competition driving. Maybe he'll come back and comment further.

Best wishes all,
Dave.

[RobM77]

7db said:

StressedDave said:

Serious students of the subject rely on the 'bibles' of 'Race Car Vehicle Dynamics' by Milliken and Milliken and 'Tire and Vehicle Dynamics' by Pacejka...you'll need a good understanding of algebra and advanced maths such as calculus, Laplace Transforms and partial differential equations.

It's worth nothing that you'll also need a caffeine habit that would make Hunter S Thopmson blush to stay awake if you read these at bedtime. Although even if you only make it as far as chapter one of Milliken and Milliken then you'll have a better feel for the difference between dynamic and terminal oversteer and understeer.

StressedDave said:

1) In this region cornering force is proportional to slip angle. This force is produced perpendicular to the slip angle

Tsk. That angle has got direction and magnitude? Perpendicular to track. (which is what RobM77 spend a lot of his time doing )

I've read Race Car Vehicle Dynamics in its entirity actually. I was just recommending books to people that are a good read.

Without wishing to be too arrogant here (moreso to re-enforce what I'm saying), I have both a degree in Physics and have been racing for 8 years with only two spins, have a full trophy cabinet and still have a number of lap records to my name. I'm not just spouting rubbish!

Edited by RobM77 on Sunday 8th June 21:30

[RobM77]

Vaux said:

p1esk said:

In fact I still feel there was a degree of confusion there so I thought it might be helpful - to some, at least - to mention it.

Do you like Dave's wording:

StressedDave said:

I'm talking about road driving in the linear region of the tyre (up to around 0.4g). Brief explanation:

1) In this region cornering force is proportional to slip angle. This force is produced perpendicular to the slip angle, effectively point to a point behind the centre of rotation.

2) The cornering force produces a component of drag, so some is wasted and acts to slow you down.

3) Traction forces are produced parallel to the slip angle, so some of that traction force acts to counter the drag force produced - that's why you're told you need more power in a corner to maintain speed. A small component of the force acts towards the centre of rotation - traction is providing a small cornering force.

4) Now, if you consider the state where you've actually added a little more power than that required. Firstly the car does start increasing speed, so you would imagine the car would start to follow a widening radius. But you're getting even more cornering force, so the effect is countered. Careful manipulation of throttle can have a significant effect on cornering beyond the obvious maintenance of stability.

All I know is it feels better to be "driving" round a corner.

As every one's talking about books, I'm off to read "Going Faster - Mastering the art of race driving" - it's got simple pictures!

Interestingly, to me it just feels plain wrong to be accelerating round a corner. It feels like understeer is building. I always corner with the car poised in a balanced state.

I follow your analysis Dave, but what about weight transfer? Surely under acceleration the weight comes off the front and onto the rear, thus increasing rear traction and decreasing front traction, i.e. understeer. If you accelerate in a bend whilst keeping the steering wheel still then it will widen its radius, and if you back off then it tightens its radius. When I corner I simply balance these two out so the car is holding a steady line. I realise that this isn't just weight transfer, but nevertheless that's what happens in a car - in fact that's how I drive; I tend to just steer to guide the car, the throttle has just as much of an effect, no matter what speed I'm doing.

Regarding needing power to corner, of course, yes, a cornering car produces a slip angle which creates drag and needs power to counter it. We must be careful to draw a distinction between power and acceleration though. If I open the windows of my car then I need more power to maintain my speed - I'm not accelerating though - acceleration is change of speed with respect to time.

[7db]

RobM77 said:

7db said:

StressedDave said:

Serious students of the subject rely on the 'bibles' of 'Race Car Vehicle Dynamics' by Milliken and Milliken and 'Tire and Vehicle Dynamics' by Pacejka...you'll need a good understanding of algebra and advanced maths such as calculus, Laplace Transforms and partial differential equations.

It's worth nothing that you'll also need a caffeine habit that would make Hunter S Thopmson blush to stay awake if you read these at bedtime. Although even if you only make it as far as chapter one of Milliken and Milliken then you'll have a better feel for the difference between dynamic and terminal oversteer and understeer.

StressedDave said:

1) In this region cornering force is proportional to slip angle. This force is produced perpendicular to the slip angle

Tsk. That angle has got direction and magnitude? Perpendicular to track. (which is what RobM77 spend a lot of his time doing )

I've read Race Car Vehicle Dynamics in its entirity actually. I was just recommending books to people that are a good read.

Without wishing to be too arrogant here (moreso to re-enforce what I'm saying), I have both a degree in Physics and have been racing for 8 years with only two spins, have a full trophy cabinet and still have a number of lap records to my name. I'm not just spouting rubbish!

Rob -- you could be Albert Einstein mixed with Lewis Hamilton (and my cat has read Pacejka cover to cover) your claims of grandeur add no weight to your words that they cannot carry themselves.

I suggest you should open your mind a little to what SD is saying. This is the physics of the road, not Southampton Poly, and there's a noticable effect where the line tightens under gentle power before it runs wider from increasing speed. Try it next time you are out and about.

I think there are other good reasons for this technique on the road, but let's start with the physics and work up from there.