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Today, we're talking about one of the most important
functions of a vehicle, right up there with
going and not going.
Steering!
(distorted music)
If we didn't have steering, we'd all just
go in a straight line, and never be able to turn,
and that might work if the earth is flat.
But, it's not flat you dummy!
Steering covers a whole world of stuff,
and there's no way I could fit everything
there is to know about steering into one of these episodes.
Even if I used my secret blinking code,
which I know none of you have figured out,
'cause I still haven't been rescued.
So, we're gonna focus on rack and pinion steering system,
and then take a look at steering angles.
If y'all behave, we might have a very special guest.
(racecar engine)
Alright, special guest is Dai Yoshihara.
Alright, rack and pinion steering
gets mentioned all the time,
but, nobody talks about what it is.
Well, 'cause it's not really that special.
I mean, it's how cars turn.
But, it sure sounds cool, huh?
All it really means is there's a rack that gets moved
by a pinion gear, that's it.
It's a pretty simple mechanism
used to convert rotation into linear motion.
It really took off in the seventies when
Arthur Ernest Bishop developed
a variable-ratio rack and pinion system.
A rack and pinion gear set is enclosed in a metal tube,
with each end of the rack protruding from that tube,
a rod, called a tie rod, connects to each end of the rack,
the pinion gear is attached to the steering shaft.
When you turn the steering wheel,
the gear spins, moving the rack.
The tie rod at the end of each rack
connects to the steering arm on the spindle.
The rack and pinion gear set does two things.
One, it converts rotational motion
of the steering wheel into the linear motion
needed to turn the wheels.
And, two, it provides a gear reduction,
making it easier to turn the wheels.
So, this system allows a better road feel,
and, requires less effort to turn.
Car's pretty heavy, and when you're turning a wheel,
you're fighting inertia.
If you're moving, the car wants to go straight,
and that wants to straighten the wheel.
Some folks need a hand when it comes to turning,
so that's where the power steering comes in.
- You know, I like to get certain amount of self-steering.
- And, self-steering is when you let go and it comes back.
- Yeah, I don't really let go let go,
but, you know.
- Spin it in your hand?
- Yeah, kinda yeah. - Okay.
- More, the better, to be honest.
'Cause, when we do like lock to lock,
it really quick, so if I try to feed
sometimes it's not fast enough.
- In this case, part of the rack's modified
to form a hydraulic piston and cylinder arrangement.
The cylinder's fed on two sides
by openings, to which fluid lines are attached.
The piston's connected to the rack,
and moves between these two openings.
When pressurized fluid is fed to any one of the openings,
the piston gets pushed, and moves in the opposite direction,
dragging the rack along with it.
At the same time, the other opening vents out the fluid,
on the other side of the piston.
This is how power's provided,
which, significantly minimizes the effort needed
to steer your vehicle.
The fluid's stored in a reservoir,
and gets pressurized with the help of a rotary vein pump
driven by the car's engine
through a belt and pulley arrangement.
It pulls the low pressure fluid from the reservoir,
and pressurizes it before supplying it to the cylinder
and the hydraulic steering system.
So, the fluid pressure does most of the steering work,
while the driver controls the direction of the turn,
with the help of a valve system.
We poked around on Dai's car and it ends up
being that hanging out with high horsepower monsters,
waiting for a run, heats up your steering fluid,
so it won't work right.
- These guys sit in a line with cars running
for like, up to three hours straight.
When you start boiling over the temperature
of the power steering fluid, it starts to break down.
So, then your power steering gets weak,
and then it eats other parts inside the pump
and you get cavitation.
You don't go this far sliding the car
in the wrong direction without power steering assisting.
- And, in your car, with a belt running off the engine,
even if you're not turning the wheel,
you're sucking a little power.
So, now we're seeing more and more
electric power steering popping up
to replace these old hydraulic bad boys.
Electric power steering uses input
from sensors on the steering wheel
to apply assistive torque via an electric motor.
Not only does this get rid of the drag
on the engine from the hydraulic system,
but, this is part of the same system
that gives us lane keep assist,
and camber control and crap like that
from the car commercials that repeat all the time on Hulu.
Okay, so what happens now when you turn the wheel?
Your car turns.
But, it's not one revolution to get the wheels
to turn all the way.
The steering ratio is the ratio
of how far you turn the steering wheel
to how far the wheel's turned.
For instance, if one complete revolution,
or 360 degrees, of the steering wheel
results in the wheels of the car turning 20 degrees,
then the steering ratio is 360 divided by 20, or 18 to one.
I like those odds.
A higher ratio means that you've gotta turn
the steering wheel more
to get the wheels to turn a given distance.
However, less effort's required
because of the higher gear ratio.
The gear ratio on most daily drivers' chosen
so that you gotta make up four complete rotations
of the steering wheel to get the wheels
to turn from lock to lock.
Generally, lighter, sportier cars have
lower steering ratios than larger cars and trucks.
The lower ratio gives the steering a quicker response.
You don't have to turn the steering wheel as much
to get the wheels to turn the same distance.
Dai's car takes only one and a half turns
to go from lock to lock.
And, lock to lock on this drift missile is 140 degrees.
So, he's got a steering ratio of four to one.
- Really?
- Yeah. (laughing)
- Wow, I didn't even know that.
- It's crazy!
And, some cars have variable ratio steering.
Which uses a rack and pinion gear set
that's got a different tooth pitch,
that's the number of teeth per inch,
in the center than it has on the outside.
This makes the car respond quickly when starting a turn.
The rack's near the center.
And, it also reduces effort near the wheel's turning limits.
So, now let's get into steering angle.
Steering angle can refer to two things.
First, it can be the degree to which a wheel can turn,
affecting the turn radius.
This is something that's different on all cars,
and it can be pretty easily modified,
but, we'll talk about that in a second.
The second meaning of steering angle
is the difference between the angle
of the two wheels when turning.
Why is this important?
Now, your car and Dai's car have
different problems to solve with that rack position.
So, let's start with normal people cars.
As far back as carriages,
people realized that the inside wheels
and the outside wheels follow different paths.
To correct this, we use what's called
an Ackermann steering angle.
It's named after Rudolph Ackermann.
But, he didn't invent it.
It was invented by the German carriage builder
Georg Lankensperger in Munich, in 1817.
Ackermann just patented it in England for ol' Georgie.
The solution of Ackermann steering is rather elegant.
If you take the rack, slide it back,
and angle your steering knuckle position
inside 90 degrees, you'll see that the tires,
when rotated, are at different angles.
Now, let's pull back.
Here's a motorcycle going around a circle.
It's just got two wheels.
So, there's none of the concerns we were just talking about.
We're showing the path of the center of the rear tire.
If we draw that line at 90 degrees from each tire,
you see that the turn radius is the intersection
of the angle of the front tire
and the angle of the back tire.
Easy peasy.
You also see that the path
of the front tire's slightly wider
than that of the back tire.
The longer the wheel base, the greater this difference.
Now, back to a car.
The angle of the tire that'll create the least slippage,
is the tangent line to the circle at that point.
It's different for the inside and outside tires.
If it's a straight rack and pinion
with the steering knuckle in line with the wheel,
the wheels are at the same angle to one another,
and they'd slip.
The elegant solution in Ackermann's patent
was to move the rack back, and place the steering knuckles
in line with the center of the rear axle.
Now, when turning the rack from left to right,
you can see that the two wheels angle differently
from one another, so while turning,
the two tires have different angles,
and follow sliplessly along the respective paths.
On cars, this connection's made with a tie rod
that connects the rack to the steering knuckle.
You wanna adjust how far your wheels can turn,
you can move the rack forward or back.
But, the steering angle is still determined
by the relationship of the knuckle
to the spindle of the wheel.
In racing, there's pro-Ackermann and anti-Ackermann setups.
This is an oversimplification,
but, because friction is grip,
sometimes you want your tires to grab more.
To determine sharp paths for the car,
rather than to follow them.
So, at rack position, further to the front?
- Gives it what they would call like a crab walk,
where both wheels are very parallel.
So, the thing can just go sideways,
versus it being back in this scenario
where it doesn't have as much
equal Ackermann steering angle,
which kinda causes the car to follow a track more.
Oval tracks are more likely to use a pro-Ackermann setup.
But, in sharp-cornering tracks,
it may be better to use anti-Ackermann.
But, that's probably another video.
Okay, now let's talk about drifters.
(solemn piano music)
No, people who race drift cars!
Okay, first you got so much crap up in those cars,
you probably won't be using a traditional setup.
Dai's car is right-hand drive,
so, he had to import a steering rack
from a heavy duty delivery truck
that you can only find in China.
That's research.
But, to fit everything around this,
and keep things from hitting anything else when he turns,
the tie rods connect in front of the spindle.
If you want to maintain an Ackermann setup,
you continue the angle you had before the wheel,
in front of the wheel.
But, in drifting, you might not want
an Ackermann steering angle.
Remember, Ackermann's designed
to help wheels follow a curved path.
Some tracks will require a car
to make a nice curved path around the turn.
In which case, the wheels should have different angles.
But, other courses couple these turns
with super straight transition,
where the car goes sideways, behind the front tires.
In these parts, you want the tires
to be at the same angle, all the way through the straight.
Like, to swing the back out 140 degrees to either side, man!
Look at that guy go!
(race car engine)
So, it's up to a driver and his crew chief
to figure out what setup's best
for their style, and the track.
Steering angles!
Make sure you subscribe, it's how we get to do cool things
and go to places like Dai's garage.
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We got a bunch of new shows on the horizon
and subscribing helps us make 'em.
Special thanks to Dai Yoshihara
for letting us visit his garage,
take a look at that sweet sweet drift missile.
Follow him @daiyoshihara.
Follow us @donutmedia.
Follow me @bidsbarto.
Check out this episode on turbo,
and check out this latest episode of Miracle Whips,
'cause it's pretty cool.
Don't tell my wife, I rented a garage next to Dai's.
That's not weird.