Why Mercedes is treading a fine line with its anti-dive approach

When the latest cars were properly revealed in Bahrain we were able to see what had really been going on in design offices up and down the grid. The replicas and renderings now commonly used for car launches have never fully represented the finished article, partly because Formula 1 is the ultimate ‘Just In Time’ industry with components arriving sometimes just hours before they are needed – and partly because designers don’t
want to show their hand until the last minute.

One might think this secrecy is misplaced but showing the spark of an idea two weeks before you really need to enables your rivals to gain two weeks in the whole research-design-produce cycle. That could mean a replica of that idea appearing on a rival’s car a full two races earlier than might otherwise be the case.

In the initial renderings this year the standout was the Mercedes front suspension. It appeared to show an additional suspension element. Had it been another team I might have put this down to artistic licence on the part of the person producing the render but, since the Brackley team has a reputation for suspension innovation, I spent some time pondering what it was up to since what was shown didn’t appear to comply with the rules.

In Bahrain, it wasn’t until the last day of the test that all became clear when the car was run with the rear leg of the top front wishbone in a new, lower position where it attached to the monocoque. This gave the suspension the highest degree of anti-dive I’ve seen on any car. There was precedent for this. Last year Mercedes had lifted the forward attachment of the wishbone to the chassis with a similar but far less extreme effect. It wasn’t alone. One major change on the Red Bull between 2022 and 2023 seemed to be an increase of anti-squat on the rear suspension, anti-squat being similar to anti-dive but applied to the rear of the car.

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So, what is anti-dive and why has it become a talking point in the past couple of years? To understand this we need to appreciate the common suspension layout used on competition cars, which is known as double-wishbone suspension. In this layout, two suspension arms, which resemble the wishbone of a chicken, attach the wheel to the chassis. Forget about springs and dampers for a moment and we can see that if the inboard wishbone mounts are attached to the chassis such that the wishbones are parallel to the ground, then the wheel can move up and down vertically.

If we now dropped the rear mount of the top wishbone, as Mercedes has done, and moved the wheel up, the lower wishbone would still move vertically – but because the axis of the top wishbone is now inclined it will move backwards as it moves upwards. This means the wheel is rotating about an instantaneous centre somewhere behind the wheel centreline when viewed from the side. The mathematics of this are very simple and those inclined to do so can find the governing equations on the internet.

The Mercedes W15 front suspension grabbed attention in its launch renders back in February

Photo by: Giorgio Piola

We’ve discussed the wheel moving up and down as if a vertical load is applied to it but that vertical load could arise as a result of the car braking. Imagine a small box on a table. If you push sideways at the top of the box it will tilt and its effective weight will be applied to the edge you’re pushing toward. The other edge will be clear of the table and carrying no vertical load. This is analogous to a car braking. The braking force pushes load onto the front wheels and off the rear wheels.

So far we haven’t mentioned the springs but, irrespective of whether the springs are operated by a pushrod, a pullrod or even mounted between the lower wishbone and the chassis as in older cars, it makes no difference. If the wishbones are parallel to the ground then any vertical force moving the wheel will be entirely reacted by the spring and, under braking, the car will dive at the front. If there is a degree of anti-dive then not all the reaction force will be reacted by the spring; an amount of it will be reacted through the suspension attachments to the chassis and therefore, because the spring is seeing less of the load, the car will not dive so much. The mathematics are slightly more complex when we consider forces rather than pure motion but still not too challenging.

Anti-squat is essentially the same thing applied to the rear of the car but instead of resisting braking force, it resists the car squatting under acceleration.

Adding a percentage of anti-dive or anti-squat will help to stabilise the aerodynamic platform but it comes at the expense of ride quality and, therefore, low-speed tyre grip

But why are we seeing a renewed focus on these aspects of suspension geometry? The answer lies, as it does so often, in aerodynamics. The current generation of cars produce most downforce when at low ride heights – in other words, close to the ground. If you can limit any change in ride height you can maintain high aerodynamic load so reducing changes in height brought about by braking or acceleration allows the car to run lower, thus increasing the downforce in corners.

It might appear, then, that running high anti-dive and anti-squat is the obvious thing to do – but unfortunately, it has a downside. Imagine the extreme, and rather silly, case where the wishbone axis was turned through 90 degrees. Then no load would go through the springs and dampers and the suspension would be effectively rigid. The car would have no suspension and would just bounce on its tyres. Adding a percentage of anti-dive or anti-squat will help to stabilise the aerodynamic platform but it comes at the expense of ride quality and, therefore, low-speed tyre grip.

As always, the best engineer is the one who chooses the best compromises.

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Photo by: Andy Hone / Motorsport Images