Hinting the steering
Discussion
Pebbles167 said:
Definitely, my last track car was a Peugeot 406 V6, stiffened springs but still fairly wafty. Driving on track would be nothing but understeer if you didn't use this technique.
Also useful in my Fiesta when driving briskly, especially in the wet. I didn't know this was named technique as such, it just feels natural to do this to keep the car balanced.
Oddly reminds me of conversations about how Imprezas would understeer all of the time and telling people mine didn't, unless I wanted it to. I did do a day with Don in my Impreza and hinting was something that was covered, possibly why mine didn't understeer? Also useful in my Fiesta when driving briskly, especially in the wet. I didn't know this was named technique as such, it just feels natural to do this to keep the car balanced.
S. Gonzales Esq. said:
When I first read about ‘hinting’ I took it to mean a separate steering input before the main one, but that’s not it at all.
The way I describe it now is a gradual build-up of the steering input on the way into a corner, so that the car responds accurately when you need it to.
By ‘starting to steer’ a certain distance before the corner, you load up all the components of the system from the pads of your fingers to the tyre tread blocks.
At the point where the car actually needs to turn, it should only require minimal further input.
As mentioned above, it works wonders when driving something big, heavy and soft. Combine with more active weight transfer techniques for sharper bends.
Never realised steering a car was so complex. But happy to learn from experts on this forum The way I describe it now is a gradual build-up of the steering input on the way into a corner, so that the car responds accurately when you need it to.
By ‘starting to steer’ a certain distance before the corner, you load up all the components of the system from the pads of your fingers to the tyre tread blocks.
At the point where the car actually needs to turn, it should only require minimal further input.
As mentioned above, it works wonders when driving something big, heavy and soft. Combine with more active weight transfer techniques for sharper bends.
Kawasicki said:
Some cars have weak yaw damping. These benefit from a very slow rate of initial steer.
Some cars have strong yaw damping. Here, the rate of initial steer to get a fast lap time might be a lot faster than most would expect.
How are you defining weak or strong yaw damping? Do you mean yaw gain? How is a very slow rate of initial steer beneficial? Some cars have strong yaw damping. Here, the rate of initial steer to get a fast lap time might be a lot faster than most would expect.
LaurasOtherHalf said:
underwhelmist said:
LaurasOtherHalf said:
I heard ( I can't recall who now but I'm guessing it was Jenson Button) someone say it was more about using centrifugal force to put more pressure in the tyre sidewall.
Eh?bigothunter said:
How are you defining weak or strong yaw damping? Do you mean yaw gain? How is a very slow rate of initial steer beneficial?
Both earlier and slower, think of it as you acting like a PID controller trying to get the tyre to stabilise at a certain angle in an optimum time.Toltec said:
bigothunter said:
How are you defining weak or strong yaw damping? Do you mean yaw gain? How is a very slow rate of initial steer beneficial?
Both earlier and slower, think of it as you acting like a PID controller trying to get the tyre to stabilise at a certain angle in an optimum time. What is the optimum yaw response time? What are optimum frequencies of yaw resonance and cut-off? What role do stability margins play?Can you elucidate further please?
Does this erudite statement help?
From a controls standpoint, yaw damping can be easily calculated using the axle cornering stiffness derivatives. In a nutshell, the effective damping coefficient is the sum of the load normalized cornering stiffness reciprocals over their product. Keep in mind that vehicle dynamics is NOT a 2nd order pendulum or a spring mass damper. There is a lead term in the numerator that is proportional to input velocity. Sideslip (and of course lateral acceleration, has both a lead term and a 3rd order term in the numerator. These terms dominate the responses of race cars. That's why 'smooth' drivers (i.e one's who control with low steer velocity) do better than jerky ones. Jerks have high steer velocity, get it?
ref: https://www.eng-tips.com/viewthread.cfm?qid=303491
From a controls standpoint, yaw damping can be easily calculated using the axle cornering stiffness derivatives. In a nutshell, the effective damping coefficient is the sum of the load normalized cornering stiffness reciprocals over their product. Keep in mind that vehicle dynamics is NOT a 2nd order pendulum or a spring mass damper. There is a lead term in the numerator that is proportional to input velocity. Sideslip (and of course lateral acceleration, has both a lead term and a 3rd order term in the numerator. These terms dominate the responses of race cars. That's why 'smooth' drivers (i.e one's who control with low steer velocity) do better than jerky ones. Jerks have high steer velocity, get it?
ref: https://www.eng-tips.com/viewthread.cfm?qid=303491
bigothunter said:
Toltec said:
bigothunter said:
How are you defining weak or strong yaw damping? Do you mean yaw gain? How is a very slow rate of initial steer beneficial?
Both earlier and slower, think of it as you acting like a PID controller trying to get the tyre to stabilise at a certain angle in an optimum time. What is the optimum yaw response time? What are optimum frequencies of yaw resonance and cut-off? What role do stability margins play?Can you elucidate further please?
As you know vehicle dynamics are much more complicated than damped spring, I was just using it as an illustration as to why the rate of turn is important. While automotive engineers will use actual figures as drivers we are using our senses or maybe a stopwatch or telemetry as well for racing. As I said earlier the concept of the hint is more as a coaching aid to make a driver consider how they are using the steering wheel and feel the differences in the way the car reacts to those inputs.
bigothunter said:
Kawasicki said:
Some cars have weak yaw damping. These benefit from a very slow rate of initial steer.
Some cars have strong yaw damping. Here, the rate of initial steer to get a fast lap time might be a lot faster than most would expect.
How are you defining weak or strong yaw damping? Do you mean yaw gain? How is a very slow rate of initial steer beneficial? Some cars have strong yaw damping. Here, the rate of initial steer to get a fast lap time might be a lot faster than most would expect.
Yaw damping is something that happens in a transient state and it is, unscientifically speaking, the ratio of the peak to the steady state yaw velocity. When you turn the steering wheel the yaw rate climbs/overshoots to a peak, then drops back down (or even overshoots on the negative side) to the yaw rate that is required to simply go round a constant bend. Yaw damping is the ratio of the peak to the steady state yaw rate (or velocity).
Why does the yaw rate overshoot? It overshoots because the rear wheels need the whole body of the car to rotate in yaw before they can run at a slip angle and therefore generate a cornering force. Without a cornering force at the front and the rear you won't corner.
The body has a mass, and a mass in motion has inertia. If the yaw damping is weak, then it's better to not overly excite the system, so steering slowly means reduced yaw overshoot, and the overshoot can (at least at the limit) get you into trouble. The steady state yaw velocity is obviously not dependent on how quickly you turned into a corner, only the peak and the overshoot is.
With a rear wheel steer system the rear tyres can generate a cornering force without having to wait for the whole body to rotate.
That is only scratching the surface... but it gives you an idea. If you have an ounce of feel in your body, someone could show you this stuff in 30 minutes. If you then focus on it for a few months, every single car you drive becomes much more interesting.... if, and only if, you're the analytical type. Otherwise it's boring as sh!t and just gets in the way of a good blast.
If you spot any crap up above, or if I wasn't clear...please pull me up on it.
An introduction phase that is made earlier and more slowly than the main steering input (but still part of a single movement) has two distinct advantages at ordinary road speeds;
- it alerts the driver to low grip conditions when he / she still has time to do something about it;
- it settles the vehicle gradually rather than suddenly.
That’s it (for road driving). I was taught this way as a teenager by my police instructor uncle and use it even for motorway lane changes. It has saved me innumerable embarrassments since then on black ice especially.
- it alerts the driver to low grip conditions when he / she still has time to do something about it;
- it settles the vehicle gradually rather than suddenly.
That’s it (for road driving). I was taught this way as a teenager by my police instructor uncle and use it even for motorway lane changes. It has saved me innumerable embarrassments since then on black ice especially.
Bweber said:
An introduction phase that is made earlier and more slowly than the main steering input (but still part of a single movement) has two distinct advantages at ordinary road speeds;
- it alerts the driver to low grip conditions when he / she still has time to do something about it;
- it settles the vehicle gradually rather than suddenly.
That’s it (for road driving). I was taught this way as a teenager by my police instructor uncle and use it even for motorway lane changes. It has saved me innumerable embarrassments since then on black ice especially.
Weird, my check for low grip surfaces is to brake hard, or turn in early, and aggressively. If the car grips, then grip is high. If it doesn’t, grip is low.- it alerts the driver to low grip conditions when he / she still has time to do something about it;
- it settles the vehicle gradually rather than suddenly.
That’s it (for road driving). I was taught this way as a teenager by my police instructor uncle and use it even for motorway lane changes. It has saved me innumerable embarrassments since then on black ice especially.
Still trying to digest what is being discussed,
To me this appears to be a combination of smooth gradual inputs and not overworking the front (steered) tyre particularly in the entry to a corner (extreme example is being very heavy on the brakes and then steering leads to loss of front grip, one scenario ABS was designed to help overcome ) , combined with a consideration for the sidewall loading you get transitioning from a straight line to turning to prevent/reduce understeer on corner entry.
Have I missed anything ?
What about consideration for loading the rear tyre ?
To me this appears to be a combination of smooth gradual inputs and not overworking the front (steered) tyre particularly in the entry to a corner (extreme example is being very heavy on the brakes and then steering leads to loss of front grip, one scenario ABS was designed to help overcome ) , combined with a consideration for the sidewall loading you get transitioning from a straight line to turning to prevent/reduce understeer on corner entry.
Have I missed anything ?
What about consideration for loading the rear tyre ?
Edited by NGRhodes on Wednesday 17th February 19:59
Kawasicki said:
Yaw velocity gain is a a steady state measurement it's the ratio of the yaw velocity to the steer angle. It's interesting, but not what I was referring to.
Yaw damping is something that happens in a transient state and it is, unscientifically speaking, the ratio of the peak to the steady state yaw velocity. When you turn the steering wheel the yaw rate climbs/overshoots to a peak, then drops back down (or even overshoots on the negative side) to the yaw rate that is required to simply go round a constant bend. Yaw damping is the ratio of the peak to the steady state yaw rate (or velocity).
Why does the yaw rate overshoot? It overshoots because the rear wheels need the whole body of the car to rotate in yaw before they can run at a slip angle and therefore generate a cornering force. Without a cornering force at the front and the rear you won't corner.
The body has a mass, and a mass in motion has inertia. If the yaw damping is weak, then it's better to not overly excite the system, so steering slowly means reduced yaw overshoot, and the overshoot can (at least at the limit) get you into trouble. The steady state yaw velocity is obviously not dependent on how quickly you turned into a corner, only the peak and the overshoot is.
With a rear wheel steer system the rear tyres can generate a cornering force without having to wait for the whole body to rotate.
That is only scratching the surface... but it gives you an idea. If you have an ounce of feel in your body, someone could show you this stuff in 30 minutes. If you then focus on it for a few months, every single car you drive becomes much more interesting.... if, and only if, you're the analytical type. Otherwise it's boring as sh!t and just gets in the way of a good blast.
If you spot any crap up above, or if I wasn't clear...please pull me up on it.
Thanks for your detailed and informative reply Yaw damping is something that happens in a transient state and it is, unscientifically speaking, the ratio of the peak to the steady state yaw velocity. When you turn the steering wheel the yaw rate climbs/overshoots to a peak, then drops back down (or even overshoots on the negative side) to the yaw rate that is required to simply go round a constant bend. Yaw damping is the ratio of the peak to the steady state yaw rate (or velocity).
Why does the yaw rate overshoot? It overshoots because the rear wheels need the whole body of the car to rotate in yaw before they can run at a slip angle and therefore generate a cornering force. Without a cornering force at the front and the rear you won't corner.
The body has a mass, and a mass in motion has inertia. If the yaw damping is weak, then it's better to not overly excite the system, so steering slowly means reduced yaw overshoot, and the overshoot can (at least at the limit) get you into trouble. The steady state yaw velocity is obviously not dependent on how quickly you turned into a corner, only the peak and the overshoot is.
With a rear wheel steer system the rear tyres can generate a cornering force without having to wait for the whole body to rotate.
That is only scratching the surface... but it gives you an idea. If you have an ounce of feel in your body, someone could show you this stuff in 30 minutes. If you then focus on it for a few months, every single car you drive becomes much more interesting.... if, and only if, you're the analytical type. Otherwise it's boring as sh!t and just gets in the way of a good blast.
If you spot any crap up above, or if I wasn't clear...please pull me up on it.
A few points where your comments would be appreciated (as emboldened above). How does yaw rate overshoot relate to frequency of steering input (below cut-off) ?
Does out-of-control body rotational oscillation (aka tank slapper) occur at yaw resonant frequency?
My understanding is that rear wheel steering alters the effective polar inertia. Turning in the same direction as front wheels improves yaw response whereas turning rear wheels outwards slows yaw response. Additional rear suspension links such as fitted to later Mazda MX5s, intentionally dull yaw response by steering outwards, making it acceptable to the average driver. Is this your understanding?
aponting389 said:
I’ve heard this too, in saloon car racing usually. You have to “ask the car to turn in” was the phrase!
Closely related to vehicle inertia in pitch and yaw. Or in other words, how quickly the vehicle can respond to driver inputs from brakes, steering and throttle. I suspect this "hinting the steering" is swamped by the effects of dynamic weight transfer between front and rear 'axles' during accel and decel (but happy to be proved wrong).Toltec said:
..the concept of the hint is more as a coaching aid to make a driver consider how they are using the steering wheel and feel the differences in the way the car reacts to those inputs.
In context of this thread, your statement above captures significance of 'hinting the steering' extremely well bigothunter said:
Thanks for your detailed and informative reply A few points where your comments would be appreciated (as emboldened above).
No problem A few points where your comments would be appreciated (as emboldened above). bigothunter said:
How does yaw rate overshoot relate to frequency of steering input (below cut-off) ?
There is a clear relation, but it's not easy to give a definitive statement. Cars have too many non-linear processes operating simultaneously. The tyre for example has load dependent cornering stiffness and lateral stiffness... which are also related, but not fully, to a tyre parameter called relaxation length. The relaxation length is how far the tyre needs to roll before it once again runs at a steady state. All these are also dependent on the vertical load acting on that tyre in that moment, and also under what condition that tyre is operating (camber for example) also in that moment. EVERYONE struggles to understand the complexity, whether they accept that or not.bigothunter said:
Does out-of-control body rotational oscillation (aka tank slapper) occur at yaw resonant frequency?
No, not necessarily.There are many kinds of tank-slapper. That is pretty much the answer to your question. Just the weight of the drivers hands on the rim of the steering wheel changes the natural frequency of the steering system. I often do hands off tests. I tweak the wheel to one side at various speeds and then let the car oscillate hands free. Some cars at some speeds resonate constantly. Others have rock solid damping. In vehicles yaw doesn't work "on it's own", it's fairly clearly related to roll too. If the resonant frequency of roll and yaw are matched, it's not good.
bigothunter said:
My understanding is that rear wheel steering alters the effective polar inertia. Turning in the same direction as front wheels improves yaw response whereas turning rear wheels outwards slows yaw response. Additional rear suspension links such as fitted to later Mazda MX5s, intentionally dull yaw response by steering outwards, making it acceptable to the average driver. Is this your understanding?
I wouldn't say rear wheel steering alters the effective polar inertia. Mass is mass. Inertia is inertia. Turning the rear wheels in the same direction of the front reduces the peak of the yaw... obviously the steady state yaw remains the same. It does this by reducing how far the body needs to swing outwards...because the rear wheels are "fed" a suitable slip angle, instead of having to wait for it. This is a classical good vehicle dynamic property. Low time delay and low overshoot as the car turns. Crisp lateral acceleration build up. Very, very controllable. Very precise. Criticised for being boring. Hmm.When you steer the rear wheels opposite to the front, well the opposite happens. Now you have to wait not just for the normal body slip angle to develop, but also for the angle of the rear tyres. So the car really develops a big yaw rate overshoot, and the buildup of lateral acceleration is slow. At low speeds you have the advantage of small turning circle. At higher speeds tricky to control.
There is a whole pile of junk written about the way cars are set up for the average/crap driver. I can say, when it comes to the linear zone of vehicle dynamics, say 0-0.7g lateral in the dry, what is good for a bad driver is also good for an expert. Don't believe the oft repeated truisms. Think for yourself.
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