Why is this race-car driver constantly jerking the steering wheel?
May 16, 2020 11:53 AM   Subscribe

I know nothing about auto racing, but I saw this video on Facebook. It surprises me that the driver is constantly jerking the steering wheel to and fro, but there is no obvious change in direction of the car. If I did that in my car, I think it would zig-zag.

I did some Googling, and I see explanations like this one, but I still don't fully understand the point of these rapid movements of the wheel, which seem to happen even on straightaways (at least in the video that I posted).

Can someone explain this to me like I'm five years old?
posted by alex1965 to Sports, Hobbies, & Recreation (11 answers total) 2 users marked this as a favorite
 
Ok, I read that explanation, lemme try:

The engine in the rear of the car is REALLY strong. So strong that it is capable of putting out SO MUCH PUSH that the friction on the front wheels starts to dig into the road, rather than just roll over it. If the front tires are doing more gripping than rolling, the rear tires want accelerate forward. But the car doesn’t flex that much to allow them to.

When this happens, the only place for the rear wheels to go is to the side and cause what I would call a “fishtail”, where the rear-end swings out to the side, possibly into a spin if it’s bad enough.

One thing you can do to fight this is back off the throttle, i.e. “put less PUSH into the wheels” so that it’s not causing a fishtail. But that kills your momentum, and this is a race.

The other option to control the car while maintaining momentum is to “oversteer”; if the rear wheels swing left, jerk the wheel left. and vice versa on the right. This turns the front wheels in the opposite direction of the rear-wheel slide. The net effect of this is to keep the car going forward rather than off course.

The cars are SO WELL engineered and so sensitive, the drivers can feel the slightest differences in how it is handling. Each of those jerks is a micro-adjustment at high-speed that keeps the car in a straight line when, if left to it’s own devices, the car would spin out of control.
posted by Pirate-Bartender-Zombie-Monkey at 12:09 PM on May 16 [18 favorites]


The video caption says that that Ferrari was built in 1964, and steering mechanisms are much different now. All that sawing in the straights is mostly accounting for looseness in the steering box and linkages—none of which have gotten tighter in the last 50+ years of spirited driving. (New-old-stock or refreshed steering boxes are often very hard to source parts such that even rich Ferrari racers might just live with a loose box.) I don't know much about that specific car but lock-to-lock could be 3 or 4 full rotations of the wheel, so sawing back and forth like that doesn't have much affect on direction. Also, I doubt that car has tons of aero downforce. I used to drive a 1965 Lincoln (a very different car that drove much differently!) that had floaty power steering. I had to saw the wheel like that to keep it straight, and I never took that car past 55 MPH.

An F1 car is a totally different beast in so many ways. Lock-to-lock is maybe 3/4 of a turn, so the steering is "twitchy". At the same time, the driver is always trying to ride the limit of the tires' traction, otherwise they're not braking, turning, or accelerating as hard as they could be. If they break traction, they have to quickly correct, so you might see them sawing the wheel through turns, but less so down straightaways than with that Ferrari and for different reasons.
posted by cyclopticgaze at 12:31 PM on May 16 [2 favorites]


So, here are the factors:

1: tyres - they are not racing slicks, these are relatively period correct treads although modern compounds. The car will move around A LOT on the tyres. It can tend to follow road imperfections and cambers too, so there is an element of that.

2: Suspension - it's a very old car, and so there is give and flex in the suspension joints and so the car wanders a lot, even on the straights. Even if they are 'new' bushes in them, the design is nowhere near as good as modern cars in generating stability.

3: The steering is not powered (I think), but either way there is a differently geared steering rack which means the wheel moves a lot before the wheels move as much as they would in a normal race car. Probably 50% or more turns lock to lock than your road car, so a set steering input has less effect on the angle of the wheels. In addition, even if it IS powered, there is play in it added to the factors above, so the first hand or two of movement (1/8 turn of the wheel?) is just 'taking up the slack' before it makes a positive change to road wheel angle.

4: The car is on the limit so is largely having it's trajectory determined by momentum. The driver is just keeping the car pointing in the same direction as his momentum is taking him. It is kind of similar to a light aircraft, if you have experience with that, lots of small corrections (that look big because of the wheel size and slack in the system) to keep the car pointing where it is going.

5: It's pretty well behaved on power down and exit but there is a lot of correction still, because the car is pretty powerful.

I've driven a much less powerful Ferrari (1977 308GT4) that is 15 years newer than this and even THAT was very, very busy when driving it at these kinds of speeds. I was also *cough* on the roads not a track, so bumps were worse but it was a huge workload to keep it under control. Fantastic fun, though. Everything moves around a lot with old cars and it's much more 'arms and elbows' driving style than modern cars.
posted by Brockles at 12:57 PM on May 16 [10 favorites]


Couple good answers. I'll add a few thoughts:

1. During hard acceleration (beginning, out of slow corners) you're applying so much suddenly high speed revolution that the engine actually creates torque (basically like a gyroscope ( and this actually causes the car to want to turn so much that the steering wheels do actually rotate. So you counter steer a bit to go straight. (Google torque steering, and you can try this yourself at a quiet stop sign: hold the wheel so delicately it would slide a bit and then accelerate pretty hard. You'll feel even a very modest car want to turn the wheels)

2. Steering input. As described above, around a continuous corner you are driving at or near the limit of friction. And there's not much traditional suspension in cars like this (suspension in your car's job is comfort. Suspension in that car's job is keep the wheels on the ground). So as you go around a corner a combination of weight shifting and bumps means micro losses of traction which you (literally most people to some extent) feel with your inner ears and your center of gravity (drivers usually refer to their butts as being sensitive). So as you feel a slight loss of traction you have to slightly lessen the radius of your turn (ie turn wider) or you'll spin. So you release your turn a little meaning steer OUT of the turn very momentarily.

3. Again as described above steering play. When you drive a car like this you instinctively move the week around so you can feel where the point is that the car will begin to rotate (fancy speed driving talk for turn). So you're constantly aware of what's looseness of components and what's actually changing your trajectory. This serves to visually amplify the steering input as he goes around a corner he is making millimeter or even sub millimeter adjustment but using a lot of motion to JUST touch the edge of the steering. Doing it at the limit of friction around a corner on race suspension makes it look a little flamboyant (and truthfully when driving on a track it feels flamboyant). Fyi you can do this one too. Just get going on some straight road and very gently move the wheel back and forth. Every car has SOME play. My truck I can probably move the week +)- 5 degrees without really impacting direction. Do that at 120mph into a hard braking turn and it would look like I was steering A LOT just to make the car barely change direction.

This is a great video btw. He's a pretty solid driver and is giving it the beans in a classic and amazing automobile.
posted by chasles at 1:17 PM on May 16 [5 favorites]


ELI5:

Driving a normal car on the road is easy and comfortable: The engine makes the front wheels pull the car down the road at the speed limit in a straight line until you need to slow down to turn onto a different road, and the car has springs and shock absorbers to make the ride soft and squishy. That way bumps don't hurt your butt and turning is smooth so you spill your drink.

Race car drivers want to go as fast as they can all the time! The engine has a lot more power and makes the back wheels push the car as fast as it can go. Racers also like the springs and shock absorbers on their cars to be much harder than a regular car, which makes them less comfortable but helps them drive faster because they can feel everything the car is doing through their butt and the steering wheel. Using what they feel through their body, they need to move their hands and feet a lot more to keep the car going in the right direction.

ELI3:

Think of a normal car like a riding tricycle - you can just pedal and go straight without having to worry about balancing. It's harder to turn sharp and slower, but that's okay because it is easy.

A race car is like riding a bike - while pedaling to move forward, you also need to steer and lean your body to keep from falling over. It's more complicated but you can turn sharper and go faster.
posted by hankscorpio83 at 2:24 PM on May 16 [2 favorites]


1. During hard acceleration (beginning, out of slow corners) you're applying so much suddenly high speed revolution that the engine actually creates torque (basically like a gyroscope ( and this actually causes the car to want to turn so much that the steering wheels do actually rotate.

This is only an effect of any real consequence in front wheel drive cars - the car in question is a rear wheel drive car and torque steer characteristics are not the issue here. The power does not affect the front wheels at all, and a 250GTO doesn't have all that much power by modern standards anyway - about 250-275Hp. With a rear wheel drive car and the ride kind of diff you *can* get a slightly off-centre sense of thrust as there is always a 'strong' side to the differential in older cars so you do get an uneven forward thrust between the two rear wheels, which may be what you are assuming is torque steer, but it tries to produce a yaw in the car (rotation around the centre of gravity when viewed from above) rather than a change in steering angle.

However: you're applying so much suddenly high speed revolution that the engine actually creates torque (basically like a gyroscope" This is very confusing and not explaining either effect. There is no 'sudden high speed revolutions', as the engine revs rise proportionally to the road wheel speed. Gyroscopic motion has no relation at all to either front wheel drive or rear wheel drive torque steer, and all engines produce torque, that's how they produce power.

Torque steer in a front wheel drive car is much more pronounced than unequal thrust in a rear wheel drive car and again a result of uneven power distribution through the differential (the gearing system that splits gearbox output from the engine (single shaft) into the two outputs to the wheels (assuming a 2 wheel drive car). As I said, there is always a 'strong' side of a diff and this means one of the front wheels tries to rotate faster and so pull that side of the car forward faster than the other, the mass of the car resists this, so the freedom of movement the stronger wheel has is in forcing that stronger wheel to turn. You can test this in any front wheel drive car with good power, more easily felt on a low grip surface. Accelerate hard with no hands on the wheel from rest and you will see the steering wheel turn. If you do the same thing again (aggressive start, as in) but hold the wheel still very firmly, you will feel the front of the car track left and right as the front wheels fight themselves.

Racers also like the springs and shock absorbers on their cars to be much harder than a regular car, which makes them less comfortable but helps them drive faster because they can feel everything the car is doing through their butt and the steering wheel.

This is so overly simplistic as to be wrong. That is not even close to why suspension on race cars are stiffer. It has nothing at all to do with the driver feel. None.
posted by Brockles at 2:52 PM on May 16 [3 favorites]


I just thought of another factor for the constant corrections - older suspension geometry design. With long wheel travels, like you have in a car as soft as the GTO, and older design suspension you get more bump steer in this travel - basically the wheel (front and sometimes rear) can change where it is pointing as it goes up and down its travel. So as the car is leaning (one side goes up, one goes down) the car wheels are changing where they are pointing by different amounts even before you turn the wheel. It is less noticeable on the straights, because usually both sides of the car are at even amounts of wheel travel through compressions so the bumpsteer largely cancels itself out.

For instance, a car on full compression may have 0.2 degrees of toe in (steering to the middle of the car - just using random numbers) when it is fully compressed (the car is low), but 0.3 degrees of toe out at full droop (wheels pointing out from the body when the car is high in the air with the wheels dropping down). So on compression in braking, the front of the car drops, the front wheels point a bit more towards each other but nothing major happens. However, with uneven bumps the car will follow that bump steer and in hard cornering (outside the the car compressed, inside wheel uncompressed) you get differing amounts of bump steer on each side of the car and as the car rolls and moves around the driver needs to chase the natural effect of each side of the car steering itself as its wheels go through their vertical travel.

Modern suspension design tries to use this effect to its best advantage and race cars try and reduce it (for the most part) to be as little as possible.
posted by Brockles at 3:02 PM on May 16 [4 favorites]


I watched that vid, thanks, great race, great car control. They are old racing cars, based on road-going 'GT' cars, with narrow tyres, unsophisticated suspensions. The engines will easily spin up the rear wheels, and that track has recently had rain on it, you can see the water lying in parts - so the track is probably 'low grip', compared to a nice sunny day.

Being a race, the cars are by definition, being driven on the limits of adhesion - braking, acceleration and cornering. These are pro or semi-pro drivers, with high skill levels, as you would expect to be racing cars each worth millions, or tens of millions, of dollars. They are responding to the subtle signals around loss of adhesion, to stop sideways movement before, or as, it starts. If they are slow to do this, the car will start to slide, or spin, and that will mean a major correction is needed, and that will slow them up, allowing the cars behind to catch and possibly pass them, and losing them time to the cars ahead.

As Brockles says, there are lots of technical things going on here which contribute to the magnitude and extent of the 'sawing', but the simple explanation is - racing old cars.
posted by GeeEmm at 4:04 PM on May 16


I don't think Brockles talks to many 5 year olds. ;)

Technical points about toe-in, camber, caster, weight transfer, steering racks, tire construction, suspension geometry, etc., and specifics about this particular driver in this particular car on this particular track in these particular conditions aren't necessary to convey the general idea.

I appreciate that you have plenty of technical knowledge to share, but an ELI5 is looking for metaphors and overly simplified explanations to convey the general idea, even at the expense of technical accuracy.
posted by hankscorpio83 at 4:39 PM on May 16 [3 favorites]


I agree with the above. A lot of those steering inputs are causing the front tires to slide, but imparting enough force to move the front of the car onto the desired track. I suspect there is some center play in the steering mechanism that would account for a fair amount of the movement of the steering wheel without necessarily doing much to what the front wheels are actually doing on the road surface.

I particularly enjoyed the beginning sequence when the driver is moving through fairly heavy traffic at high speed in a vintage Ferrari worth upwards of $45,000,000. Yes, that's forty-five million dollars.
posted by mygoditsbob at 5:23 AM on May 17


My simpler explanation is that older cars had a lot more steering wheel movement than newer ones do. That's basically what driving normal cars used to be like. You can see on the straights that he doesn't move it nearly as much.
posted by The_Vegetables at 10:27 AM on May 18 [1 favorite]


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