Mercedes made all the headlines on Day 2 of Winter Testing last week when they revealed
they had developed a Dual Axis Steering (or DAS) system which changed not just the steering
angle of the wheels but the toe angle between them
To help understand why this system is so beneficial we need to go over what toe is, so that’s
what we’re going to do in this video. Toe is technically part of the suspension
setup that will be adjusted for each particular track. It describes the angle of the wheels
relative to the perfect straightforward direction of the car.
So wheels with zero toe will point straight ahead.
Wheels with positive toe will point inwards, towards the centreline of the car.
Wheels with negative toe will splay outwards, like this.
Now I’m using extreme angles here to demonstrate the point clearly. In reality, differences
in toe setups will be a matter of maybe 2 degrees either way at most.
So what are the effects of toe? Common sense would have you think just get the wheels pointing
parallel - with zero toe - and then get them moving left and right together as you steer
the wheel. Why on earth would you point them off centre?
Well there are quite a few things that are affected by toe angle (or toe distance as
you can measure the toe as a difference between these two distances if you prefer).
The first thing affected by toe angle is tyre wear.
This should become quite apparent if you think about it. With zero toe, the front wheels
are pointed straight ahead so as you drive the car forward the front tyres are just rolling
freely on their axes. If the tyres are splayed out, the inside will
be dragging somewhat along the track, heating and wearing the inside of the tread.
Similarly, if the tyres are toe in, the outside of the tyre dread will be dragging somewhat
along the track causing temperature and wear issues that will need to be managed.
Now, again, I’ve exaggerated the angles and with only a degree of toe these problems
aren’t as catastrophic but they still need to be taken into account. To minimise wear,
you’d probably want to keep to zero toe, particularly on the straights.
Again, all things being equal, zero toe will give you the best straight line speed. If
you introduce toe angle to your front wheels, they are wanting to go in a slightly different
direction than straight ahead so you’re essentially wasting power dragging them along
the track instead of free-rolling as previously. It may only end up being a matter of a few
km/h but anyone familiar with Formula 1 knows that the little things soon add up.
Thirdly - cornering agility. Now we move into an area where zero toe might not be your best
friend. Let’s think about what happens when you
turn a corner. Let’s imagine you driving your F1 car into and around a right hand turn.
Your front wheels should trace out curves something like this.
What’s important to realise is the inside tyre is always tracing a tighter curve than
the outside tyre. You know - as the turning radius gets tighter
and tighter, so you have to steer more so ideally you’d want the inside tyre to be
more angled through the corner than the outside tyre.
This allows both tyres to more closely follow their turning curves, maximising their grip
and increasingly your speed and stability through the corner.
You can achieve this by adding angling your front wheel toe outwards.
Straight on, yes, the tyres look weird and splayed (again, exaggerated here). But once
you turn the steering to drive through a corner, the inside wheel is now more aggressively
angled to take the tighter line, while the outside tyre is more gently angled to take
the wider outside path. Toeing your wheels inward makes the car less
planted through turns as the car is more reluctant to turn as the closer you get one tyre to
the correct steering angle, the more you point the other away, causing drag and resistance
at the front end of the car. This leads us neatly to the last major effect
of toe which is straight line stability. Let’s put our cars back on a long straight,
but think about what we just said about cornering. Toe out makes the car absolutely ready to
turn. As soon as you start to turn the steering, the wheels are toed so that they encourage
the car to turn in, with the inside wheel angled aggressively to take the tighter line.
This means that while the car will keep pointing straight as long as you hold the steering
straight, the moment you make a slight adjustment away from centre, the car is more sensitive
to turning. And holding the steering perfectly centred
can be difficult when the car is bumping around or one tyre hits a crack in the road. Little
disturbances can make the car want to hoik itself left and right.
Conversely, when the front wheels are toed in, they are reluctant to turn. They respond
much more lazily to steering inputs which means the car will remain stable on the straights,
even if bumps and such some disturbances in the steering.
Now, normally teams lock in a toe setting that’s the best trade off between tyre wear,
straight line speed, cornering speed and straight line stability as determined by the track
and other parts of the suspension design and setup. Most setups are a matter of trade-off
after all where gains in one area result in losses in others.
But what Mercedes have now managed to do, without apparently breaking the rules, is
give the drivers the power to adjust the toe angle while driving by pulling back and pushing
forward on the steering wheel. The Dual Axis Steering system allows the driver
to pull back on the steering wheel to bring the toe-in, and push forward on the wheel
to pull the toe out. This has a number of ramifications. The obvious
one being that they can straighten up the tyres for the straights, to increase their
speed, reduce wear and rising temperatures on the inside tyre tread and give the car
more stability, while ALSO pulling the toe out for the corners for increased handling
and speed. A really simplified version of all the above
is zero toe good for straights, negative toe good for corners. Mercedes can handle that.
But of course, toe isn’t just a matter of in and out. There are fine adjustments in
between. All corners are different. If the Mercedes
drivers get a good feel for the DAS they can try and get the toe as close to perfect for
every different type of corner. A tighter corner would benefit from a more dramatic
toe out as the relative difference between the inner and outer lines is more pronounced.
On another note, I’ve sort of spoken about rising tyre temperatures as if they’re a
bad thing, but getting heat into the rubber is an important part of performance. And getting
the RIGHT amount of heat ACROSS the whole tyre is particularly important.
As mentioned, when tyres are toe out they tend to overly heat the inside rubber and
vice versa with when toe in. But the Mercedes drivers could potentially fiddle with this
on straights to balance the temperatures across the tyres. This is particularly useful on
outlaps to prepare the tyres for a hot lap, but even if they’re told mid race that the
outside rubber is getting a little cold, they can toe in to try and help that part of the
tyre get into the sweet spot. This is a great, clever, innovative system.
It’s not the be all and end all of a competitive car but it will help Mercedes particularly
across race distances when managing the performance of their tyres.
And this is a one year only thing as the rules for 2021 appear to not allow for such systems.
So enjoy it while it lasts and see if any of the other teams can squeeze their own version
in during the season somehow.