Lift-off understeer

[Tdcist]

Could the issue be with weight/4WD?

Looking at those 2 lists, a couple jump at me...

911 C4S 4WD, better traction etc
911 C2S RWD, engine at back! No weight over front. Under steer? No driven front wheels, different steering feel...

Jag F type V6S, lighter engine up front
Jag F type V8S, heavier engine? Maybe too heavy... Plough in too quick... Under steer?

Panamera hybrid, battery location, lower centre Gravity etc
Panamera Diesel, heavier engine at front, higher CoG... Under steer?

I am not knowledgable on physics etc to any serious level, but that would be some things that jump at me straight away.

[fungus]

Could the steering sensitivity account for my wifes old Peugeot 306 with hydraulic power steering feeling more sure footed through bends than her Octavia, which, IIAC, has electronic power steering?

[zadocbrown]

Could the steering sensitivity account for my wifes old Peugeot 306 with hydraulic power steering feeling more sure footed through bends than her Octavia, which, IIAC, has electronic power steering?

More that the 306 was just a lovely handling car.

[5star]

991 or earlier?

991

I guess the difference between the naughty list and the nice list is not a particular difference in the amount of under steer present, but in steering sensitivity. All of them have a bigger initial gain, I.e. they appear to turn 'better' which you're interpreting as a loss of grip at the rear rather han 'more grip at the front than expected'.

That is interesting. In fact, the more a car tends to understeer, the easier I find it to judge available grip for turn-in (although once turned-in and balanced, I get on much better with cars that tend towards neutral/slight oversteer).

So I need to determine if it isn't so much the grip available that I'm sensing, but the difference in grip between front and rear. If this theory is correct, I then need to reassess how I'm judging grip feedback in such cars.

Go and see Hairy Don.

I've just seen his video "Interpreting feedback from tyres", and from what you've said, I think this is inevitable.

And thank you all for your comments so far.

[jont]

Go and see Hairy Don.

I've just seen his video "Interpreting feedback from tyres", and from what you've said, I think this is inevitable.

And thank you all for your comments so far.

Now is a good time of year. Hard frost or pissing rain strongly recommended.

[5star]

I've spent the day Googling the concepts you've described above. I'm beginning to see the light! Happily, the theory is matching the practical instruction of the respected tutors I've had. I'd always struggled to understand this before, because much of what I read was at odds with what was happening. The problem was, I was avoiding reading the scholarly articles, patents for yaw damping systems and books with algebra, preferring instead to read The Rest Of The Internet. When I discussed it with instructors, they tried to explain, but with limited time and my pre-conceived ideas, it never clicked before. I definitely owe some drinks.


A completely different question now.

Is there ever a situation where it is desirable to turn like this: Use little or no throttle, wait until as late as possible to turn the steering wheel, then turn the steering wheel quickly (to ramp up lateral g), but smoothly (to minimise body roll).

Turning like this, you feel it in the side bolster, and see a sharp, smooth curve on a lateral g-meter. Over-do it and the front washes out.

The reason I ask is, as I've been Googling, I've seen people (on other forums) say this is the way they've been instructed to take slower corners by professional instructors.

I've never been taught to drive like this, don't currently drive like this, but wonder - is this a tool I should have in the toolkit, and if so, when would it be appropriate to use it?

[5star]

5star, why are you still here? Why aren't you with Hairy Don?

Financial reasons. Q1 is not a good time of year in the budget department. And I only found out about him yesterday. I'm working on that.

So in the meantime... this forum still allows me to learn.

[Astraist]

Is there ever a situation where it is desirable to turn like this: Use little or no throttle, wait until as late as possible to turn the steering wheel, then turn the steering wheel quickly (to ramp up lateral g), but smoothly (to minimise body roll).

For sharp corners with very little visibility, I sometimes steer later and thus a tad more postively than strictly needed, Throttle position will vary.

As the required steering angle increases (and speed decreases), steering application can be more positive, without a destabilising effect. Many smooth drivers will be surprised if they actually looked how quickly they turn the steering for a tight corner in town.

[kfae8959]

Manchester.

Let's go for a drive. I neither drive nor coach anywhere near as well as StressedDave, but we could have some fun exploring.

David

[5star]

Let's go for a drive.

Will send PM when next available. Always up for a drive and coffee.

[5star]

OK, I've been through your posts and have a much clearer understanding of what is happening now.

When I turn, my aim is to set the body sideslip angle so that I have neutral steer. I adjust the body sideslip angle by using the throttle to manage the yaw moment balance. I'm able to feel when I have neutral steer as the front tyre slip angle required to maintain course is minimised.

With most road cars, obtaining neutral steer on a typical A road at an average speed of 60mph requires a slight reduction in speed before the turn (maybe -1mph), slight acceleration through the turn, resulting in a sligthly faster exit speed (maybe +1mph). The actual acceleration required through the turn will vary depending on load, car, radius and speed, but the point I'm making is that the required acceleration is manageable and achievable under normal road conditions.

The problem I have in the GT-R is that to achieve the necessary body slip angle for neutral steer, I need to be accelerating significantly. For typical A roads at 60mph, I need to accelerate at approximately +2mph per second. If a turn lasts 5 seconds, this is a difference between entry and exit speed of 10mph. On an empty country road this is fine, but in a procession of cars this is unmanageable - on entry I need to slow too much (cars behind run into me), and on exit I'm too fast (I'm now running into the car in front).

So I'm driving like a MORE ON, maintaining a constant speed, and using large tyre slip angles to make the turn. I know from experience, icy winter roads + large tyre slip angles = not good. So I'm tiptoeing around every corner slowly, in many cases far slower than other road users, generally feeling unconfident.

I'm sure you're thinking at this stage, I'm not accelerating enough. OK, let's look at what happens when I accelerate a bit. More understeer.

So I accelerate a bit more. Even more understeer.

Accelerate a LOT more. Even MORE understeer and I'm now approaching the limit of front grip, and rapidly approaching the car in front.

The solution, is to apply a LOT LOT LOT LOT more power. This works. This is why I don't have any trouble in faster corners, or when I'm Really Making Progress.

If using a LOT LOT LOT LOT more power isn't possible due to road conditions, and using just a bit more power makes things worse, what can I do to fix my problem?

[Astraist]

When I turn, my aim is to set the body sideslip angle so that I have neutral steer.

No, you aim at a little understeer. Neutrality is something you want to avoid.

For typical A roads at 60mph, I need to accelerate at approximately +2mph per second. If a turn lasts 5 seconds, this is a difference between entry and exit speed of 10mph. On an empty country road this is fine, but in a procession of cars this is unmanageable - on entry I need to slow too much (cars behind run into me), and on exit I'm too fast (I'm now running into the car in front).

Doing that will generate a good deal of power understeer.

If you slow down early enough I do not see how this could cause serious conflict with drivers behind. It's only a couple of miles per hour less.

Shunts typically follow a significant speed differential, like braking sharply or when you have pulled at the end of a queue and traffic behind hasn't. If any deceleration led to impact, driving would be impossible...

As for hitting the driver in front, slowing down before the bend gives you the needed space to accelerate coming out, given that you keep a sane following distance to begin with.

I'm sure you're thinking at this stage, I'm not accelerating enough. OK, let's look at what happens when I accelerate a bit. More understeer.

Nope. When you first start to accelerate you get less understeer (mainly due to improved front cornering stiffness), untill the increase of speed re-introduces it.

If you are gentle enough, and the corner is short enough, you get the reduced understeer all the way to the apex, and the power understeer on the exit, where it is desireable.

[jcochrane]

I'm thinking along the lines of Astraist. When I read your comments, 5star, what went through my head was it sounds as if entry speed is still too high. As Asraists says if the speed reductions is done as he suggests there should be no problem with following cars.

[waremark]

Why don't you just turn the steering wheel until the car is travelling where you want to go? At any speed that other cars can cope with, the electronics in the GTR will just take you wherever you steer. If you can detect the level of understeer which you may get you are obviously incredibly sensitive - but if you steer a little more the electronics will sort it out.

By the way, are you willing to share with us how come you are lucky enough to drive so many fantastic cars?

[Astraist]

the electronics in the GTR will just take you wherever you steer. If you can detect the level of understeer which you may get you are obviously incredibly sensitive - but if you steer a little more the electronics will sort it out.

Generally in most cars if you understeer, turning the wheel a bit more can help.

You will be increasing the front slip angle and thus the understeer, right enough. But, understeer is safe partially by dint of it diminishing on it's own.

The (usual) problem is excessive speed per the cornering radius. So you get understeer which wipes off speed and increases the radius until the car can grip again.

So, slightly increasing the understeer might make it diminish faster, without necessary making the car take an even wider line. You are generating more drag at the front which works to slow down the car, and once grip is restored, the angle is also suitable for the tighter radius needed to maintain the desired line.

Also, in cars with passive rear steering this can cause it to kick in and point the car in the right direction, and some stability control systems which struggle to identify a very slim skid, would benefit from the driver magnifying the slide, as you suggest.

With all that said, obviously drag is a poor way of reducing speed and reducing throttle or carefully braking is usually a better alternative for reducing understeer, with a small decrease in the steering angle accelerating the effect. Sometimes the steering has to be removed alltogether for a brieft moment!