In true RU style .... an article on cornering.
Discussion
7db said:
Incidentally, I'm not sure I buy your explanation of power tightening the corner - I don't believe the slip angle changes - just that the drag component of the tyre's lateral force is killed off, making the available grip more usefully directed. Some people don't even believe that.
Presumably this effect is offset by rearward weight transfer from acceleration reducing the load on the front tyres, and presumably also it only applies below the speed at which understeer sets in. Is that right??But the experience described in Lady G's quotation (well found Sally) is much easier to demonstrate. Who here can experience and demonstrate the more power = tighter line phenomenon?
waremark said:
Who here can experience and demonstrate the more power = tighter line phenomenon?
It is very easy to demonstrate in a rwd car if you have enough power, but it is not something that always happens. It is untrue to say that applying more power in a rwd car will always result in it taking a tighter line. It IS true to say that under the right circumstances applying more power in a rwd car can result in it taking a tighter line. Edited by GreenV8S on Tuesday 4th September 09:34
GreenV8S said:
waremark said:
Who here can experience and demonstrate the more power = tighter line phenomenon?
It is very easy to demonstrate in a rwd car if you have enough power, but it is not something that always happens. It is untrue to say that applying more power in a rwd car will always result in it taking a tighter line. It IS true to say that under the right circumstances applying more power in a rwd car can result in it taking a tighter line. I find this quite marked in my rx-7 and, on longish bends at somewhere like Silverstone it can be really very interesting to play with the balance of the car.
waremark said:
Presumably this effect is offset by rearward weight transfer from acceleration reducing the load on the front tyres, and presumably also it only applies below the speed at which understeer sets in. Is that right??
We are only talking about a small amount of acceleration to kill off drag. Obviously with large (or sudden) acceleration you can develop terminal power understeer as the front wheels lose traction altogether. Properly alarming, although easily dealt with intuitively.It's a question of which is dominant physical effect.
GreenV8S said:
waremark said:
Who here can experience and demonstrate the more power = tighter line phenomenon?
It is very easy to demonstrate in a rwd car if you have enough power, but it is not something that always happens. It is untrue to say that applying more power in a rwd car will always result in it taking a tighter line. It IS true to say that under the right circumstances applying more power in a rwd car can result in it taking a tighter line. waremark said:
GreenV8S said:
waremark said:
Who here can experience and demonstrate the more power = tighter line phenomenon?
It is very easy to demonstrate in a rwd car if you have enough power, but it is not something that always happens. It is untrue to say that applying more power in a rwd car will always result in it taking a tighter line. It IS true to say that under the right circumstances applying more power in a rwd car can result in it taking a tighter line. Mainly because it's not oversteer. There are no changes in slip angle with the effect, so no change in the fundamental understeer/oversteer equation. At the risk of upsetting Reg, a brief description of what is happening:
When you corner, the tyres are forced to travel in a slightly different direction to the one in which they are pointing. The difference in angle between the two is called the slip angle. Now the cornering force produced by the tyre effectively is produced at 90 degrees to the direction in which the tyre is pointing. This force doesn't act towards the centre of the corner: In fact it points somewhere behind the centre, so that cornering force, relative to the car, is made up of a mixture of useful force (cornering the car) and drag. The fact that this drag is there means that you have to apply more power to maintain speed while cornering.
Now, lets imagine that we apply some power while cornering. The tractive force generated by the tyres splits in an opposite fashion to the cornering force - i.e. mainly forwards traction, but there is a, useful in this case, small component of cornering force. So if you just balance out the drag from cornering, you get a small but measureable amount of extra cornering grip. If you apply more power above and beyond what is necessary, then you get even more cornering force for the same amount of slip angle, at the driven wheels.
With big foot-fulls of extra power, then you start getting weight transfer coming into the act and this can swamp what is actually happening, but effectively, with more power applied in a corner you need slightly smaller slip angles, and hence less steering to maintain.
<war story mode> I spent the thick end of a decade investigating RTAs. One of the most common accidents was a loss of control on the exit of a corner - note exit, not entry. In most cases the cause was the driver getting back on the power reasonably gently having survived entry at a speed higher than he was able to control, causing the line to tighten because the drag was being balanced out and more cornering grip was instead occurring. The driver would then panic, lift off and weight transfer induced reductions in understeer (i.e. he'd steered too much for the chosen line, rather than oversteer per se) caused the final loss of control and scenery interaction</war story mode>
It's one of the reasons I've been known to tell clients that I've yet to see an accident caused by overconfidence, but I've seen plenty caused by it's sudden loss...
When you corner, the tyres are forced to travel in a slightly different direction to the one in which they are pointing. The difference in angle between the two is called the slip angle. Now the cornering force produced by the tyre effectively is produced at 90 degrees to the direction in which the tyre is pointing. This force doesn't act towards the centre of the corner: In fact it points somewhere behind the centre, so that cornering force, relative to the car, is made up of a mixture of useful force (cornering the car) and drag. The fact that this drag is there means that you have to apply more power to maintain speed while cornering.
Now, lets imagine that we apply some power while cornering. The tractive force generated by the tyres splits in an opposite fashion to the cornering force - i.e. mainly forwards traction, but there is a, useful in this case, small component of cornering force. So if you just balance out the drag from cornering, you get a small but measureable amount of extra cornering grip. If you apply more power above and beyond what is necessary, then you get even more cornering force for the same amount of slip angle, at the driven wheels.
With big foot-fulls of extra power, then you start getting weight transfer coming into the act and this can swamp what is actually happening, but effectively, with more power applied in a corner you need slightly smaller slip angles, and hence less steering to maintain.
<war story mode> I spent the thick end of a decade investigating RTAs. One of the most common accidents was a loss of control on the exit of a corner - note exit, not entry. In most cases the cause was the driver getting back on the power reasonably gently having survived entry at a speed higher than he was able to control, causing the line to tighten because the drag was being balanced out and more cornering grip was instead occurring. The driver would then panic, lift off and weight transfer induced reductions in understeer (i.e. he'd steered too much for the chosen line, rather than oversteer per se) caused the final loss of control and scenery interaction</war story mode>
It's one of the reasons I've been known to tell clients that I've yet to see an accident caused by overconfidence, but I've seen plenty caused by it's sudden loss...
I didn't want to drop into algebra to 'prove' my assertion, and I'm not sure that PH will suffer algebraic notation that well, but:
Slip Angle, Rear = (Sideslip velocity - distance from rear axle to c of g x yaw rate)/ Forward Speed
Slip Angle, Front = (Sideslip velocity + distance from front axle to c of g x yaw rate)/ Forward Speed - Steering Angle
The forward speed is normally >> sideslip velocity, so small variations in speed, i.e. acceleration or deceleration, result in neglible change in slip angle, and for that matter, yaw rate (rate of change of heading angle) hence the assertion.
This is just looking at the tyre contact patch. There's a whole heap of extra complexity when you start considering what's happening to the rubber bits in the suspension as the loadings change.
Slip Angle, Rear = (Sideslip velocity - distance from rear axle to c of g x yaw rate)/ Forward Speed
Slip Angle, Front = (Sideslip velocity + distance from front axle to c of g x yaw rate)/ Forward Speed - Steering Angle
The forward speed is normally >> sideslip velocity, so small variations in speed, i.e. acceleration or deceleration, result in neglible change in slip angle, and for that matter, yaw rate (rate of change of heading angle) hence the assertion.
This is just looking at the tyre contact patch. There's a whole heap of extra complexity when you start considering what's happening to the rubber bits in the suspension as the loadings change.
StressedDave said:
I didn't want to drop into algebra to 'prove' my assertion, and I'm not sure that PH will suffer algebraic notation that well, but:
Slip Angle, Rear = (Sideslip velocity - distance from rear axle to c of g x yaw rate)/ Forward Speed
Slip Angle, Front = (Sideslip velocity + distance from front axle to c of g x yaw rate)/ Forward Speed - Steering Angle
The forward speed is normally >> sideslip velocity, so small variations in speed, i.e. acceleration or deceleration, result in neglible change in slip angle, and for that matter, yaw rate (rate of change of heading angle) hence the assertion.
This is just looking at the tyre contact patch. There's a whole heap of extra complexity when you start considering what's happening to the rubber bits in the suspension as the loadings change.
You're trying to introduce a formula representing direction of travel, but there's no need. Simply define the slip angle as the angle between the direction the wheel points and the direction it travels. If you change the direction of travel (without changing the orientation of the wheel) you have changed the slip angle. The most likely reason for the direction of travel changing is that you've done something to change the magnitude or direction of the thrust vector, and that could be by changing the drive/brake torque, weight, camber, friction coefficient, whatever. These are all possible causes, but the consequence is that the direction of travel (and hence the slip angle) has changed.Slip Angle, Rear = (Sideslip velocity - distance from rear axle to c of g x yaw rate)/ Forward Speed
Slip Angle, Front = (Sideslip velocity + distance from front axle to c of g x yaw rate)/ Forward Speed - Steering Angle
The forward speed is normally >> sideslip velocity, so small variations in speed, i.e. acceleration or deceleration, result in neglible change in slip angle, and for that matter, yaw rate (rate of change of heading angle) hence the assertion.
This is just looking at the tyre contact patch. There's a whole heap of extra complexity when you start considering what's happening to the rubber bits in the suspension as the loadings change.
Good stuff this debate about what is going on during cornering.
Mathematical models, should tell us all we need to know?
Yet, we also know that and I'm talking on track, give a car, whatever the setup to two drivers and one will be faster.
Why is that?
Would that be the same if there was a headup display relaying such information as has been discussed here?
It is not simple when you consider the Human / machine interface.
Mathematical models, should tell us all we need to know?
Yet, we also know that and I'm talking on track, give a car, whatever the setup to two drivers and one will be faster.
Why is that?
Would that be the same if there was a headup display relaying such information as has been discussed here?
It is not simple when you consider the Human / machine interface.
GreenV8S said:
StressedDave said:
I didn't want to drop into algebra to 'prove' my assertion, and I'm not sure that PH will suffer algebraic notation that well, but:
Slip Angle, Rear = (Sideslip velocity - distance from rear axle to c of g x yaw rate)/ Forward Speed
Slip Angle, Front = (Sideslip velocity + distance from front axle to c of g x yaw rate)/ Forward Speed - Steering Angle
The forward speed is normally >> sideslip velocity, so small variations in speed, i.e. acceleration or deceleration, result in neglible change in slip angle, and for that matter, yaw rate (rate of change of heading angle) hence the assertion.
This is just looking at the tyre contact patch. There's a whole heap of extra complexity when you start considering what's happening to the rubber bits in the suspension as the loadings change.
You're trying to introduce a formula representing direction of travel, but there's no need. Simply define the slip angle as the angle between the direction the wheel points and the direction it travels. If you change the direction of travel (without changing the orientation of the wheel) you have changed the slip angle. The most likely reason for the direction of travel changing is that you've done something to change the magnitude or direction of the thrust vector, and that could be by changing the drive/brake torque, weight, camber, friction coefficient, whatever. These are all possible causes, but the consequence is that the direction of travel (and hence the slip angle) has changed.Slip Angle, Rear = (Sideslip velocity - distance from rear axle to c of g x yaw rate)/ Forward Speed
Slip Angle, Front = (Sideslip velocity + distance from front axle to c of g x yaw rate)/ Forward Speed - Steering Angle
The forward speed is normally >> sideslip velocity, so small variations in speed, i.e. acceleration or deceleration, result in neglible change in slip angle, and for that matter, yaw rate (rate of change of heading angle) hence the assertion.
This is just looking at the tyre contact patch. There's a whole heap of extra complexity when you start considering what's happening to the rubber bits in the suspension as the loadings change.
-all difference, and here we're talking about a few newtons not the application of loads.WhoseGeneration said:
Good stuff this debate about what is going on during cornering.
Mathematical models, should tell us all we need to know?
Yet, we also know that and I'm talking on track, give a car, whatever the setup to two drivers and one will be faster.
Why is that?
Would that be the same if there was a headup display relaying such information as has been discussed here?
It is not simple when you consider the Human / machine interface.
The information can be made available - I run a full telemetry system on my car which records all the necessary parameters, but by the time you could see and absorb it it's generally too late to do anything about it. The gifted drivers use force-feedback on the way into the bend as they are developing the minimum slip angles necessary for cornering. The less gifted work more on a positional based system.Mathematical models, should tell us all we need to know?
Yet, we also know that and I'm talking on track, give a car, whatever the setup to two drivers and one will be faster.
Why is that?
Would that be the same if there was a headup display relaying such information as has been discussed here?
It is not simple when you consider the Human / machine interface.
StressedDave said:
WhoseGeneration said:
The information can be made available - I run a full telemetry system on my car which records all the necessary parameters, but by the time you could see and absorb it it's generally too late to do anything about it. The gifted drivers use force-feedback on the way into the bend as they are developing the minimum slip angles necessary for cornering. The less gifted work more on a positional based system.
Those "gifted drivers", could they explain what they do, in your terms?That is surely the art of the Race Engineer, to interprate the feedback from the driver to utilise their engineering knowledge and theory to provide the driver with a setup that meets that driver's driving style.
It isn't simple.
StressedDave said:
WhoseGeneration said:
Good stuff this debate about what is going on during cornering.
Mathematical models, should tell us all we need to know?
Yet, we also know that and I'm talking on track, give a car, whatever the setup to two drivers and one will be faster.
Why is that?
Would that be the same if there was a headup display relaying such information as has been discussed here?
It is not simple when you consider the Human / machine interface.
The information can be made available - I run a full telemetry system on my car which records all the necessary parameters, but by the time you could see and absorb it it's generally too late to do anything about it. The gifted drivers use force-feedback on the way into the bend as they are developing the minimum slip angles necessary for cornering. The less gifted work more on a positional based system.Mathematical models, should tell us all we need to know?
Yet, we also know that and I'm talking on track, give a car, whatever the setup to two drivers and one will be faster.
Why is that?
Would that be the same if there was a headup display relaying such information as has been discussed here?
It is not simple when you consider the Human / machine interface.
Best wishes all,
Dave.
StressedDave said:
ProDrive refer to three regions of handling:
where nobody crashes (where TripleS likes to operate)
where some people crash (and that will range from the everage motorist to the stellar drivers like rally drivers)
where everybody crashes (the laws of physics taking over)
....but I still like the idea of folk having some fun, but keeping within reasonable bounds - and not discounting the possibility of something going wrong occasionally. There are no complete guarantees, so it's no use looking for one.where nobody crashes (where TripleS likes to operate)
where some people crash (and that will range from the everage motorist to the stellar drivers like rally drivers)
where everybody crashes (the laws of physics taking over)
Best wishes all,
Dave.
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