Diffusers: They’re why F1 cars suck

For an innovation that has changed car performance so much, the diffuser (circled) is remarkably anonymous.

These bits of aerodynamic genius are visible only from the back of the car, hidden in the shadows of the rear wing, and the word ‘diffuser’ doesn’t even crop up in FIA technical regulations.

But they’ve helped cars corner faster and faster, and they’ve also provided the world of F1 with some memorable controversies.

Lifting F1’s skirts

Diffusers began to show their potential with the arrival of the Lotus 78 (pictured) and 79 models in the second part of the 1970s.

Among the finest looking cars ever to grace the sport, these icons of F1 each took aerodynamic innovation to a new level.

They were the original ‘ground effect’ cars, introducing underbody aero elements and side skirts that lowered underbody air pressure and effectively sucked the cars on to the track, giving them much more grip, without increasing drag significantly.

So, what’s a diffuser?

At its simplest, it’s a device that makes the air under a car accelerate – this increases the pressure difference between the upper surfaces and the underside, pushing the car down on to the track.

To understand why this happens, you’ll need to read up on Bernoulli’s principle, which holds that, as a fluid (the air) speeds up, the pressure it exerts drops.

A basic diffuser is narrow at the front and grows in volume along its length (its top curves up and spreads out). That narrow section forces air to accelerate and creates a low pressure area under the car that effectively sucks it on to the track.

The back section of the diffuser slowly (relatively slowly) returns the air to its original speed.

Some of the current crop of F1 cars, most notably the Red Bulls, run with a very high ‘rake’ angle – the back of the car is noticeably higher than the front.

One of the most significant effects of this is to effectively increase the volume of the diffuser, generating more downforce as a result. There’s a lot more aero wizardry involved to keep unwanted air from being sucked into the diffuser, wrecking its effectiveness, but getting the diffuser working efficiently can give teams a huge advantage in terms of downforce and grip levels generated.

Double trouble

While teams have worked to improve the effectiveness of diffusers constantly since the days of the Lotus 78 and 79, a huge step forward took place in 2009.

That season, new regulations had slashed the amount of downforce F1 cars could generate but the Brawn (pictured), Toyota and Williams teams spotted a loophole in the rules that allowed them to build a double-deck diffuser – something other teams believed was illegal.

The engineering behind the double diffuser is complicated but not nearly as complicated as the politics and rows over the rules that surrounded the device.

It all boiled down to how various parts of a car’s underside were defined (Brawn, Toyota and Williams with one definition, other teams with another) and what engineering tolerances teams claimed to be able to manufacture to.

The three rebels’ definition allowed them to create holes which fed air to an upper diffuser deck. This created a much larger total diffuser volume and generated a lot more downforce as a result.

How much? No one was revealing that but, suffice to say, it is generally accepted that the double diffuser played a big part in Brawn winning the 2009 championship, giving Jenson Button his world title in the process.

Not surprisingly, other teams also exploited the loophole and, eventually, the FIA changed the rules so that every car had to have a 90cm wide single, continuous surface as its floor.

There was now no legal way of creating a hole to feed an upper diffuser – the double diffuser’s time was up.

But, of course, that didn’t mean there would be no further diffuser innovations…

Thar she blows

In 2010, an old innovation reappeared in a new guise to surprise the rarefied world of diffuser engineering.

‘Blown diffusers’ used exhaust gases above or below the diffuser to increase the airflow and, as we learned above, faster airflows exert less pressure – more downforce, in other words.

Additionally, the exhaust streams helped seal the diffuser off from turbulence caused by the tyres.

In fact, this wasn’t the first time exhausts had been used to energise diffusers – back in 1983, Renault did this with their RE40 turbo.

Eventually, blown diffusers fell out of fashion, largely because new engines didn’t function efficiently with the longer exhaust pipes needed to direct gases to the diffuser.

Additionally, there was one major problem with a blown diffuser: it relied on exhaust gases to generate downforce, and that downforce disappeared when a driver lifted off the throttle, suddenly.

However, Red Bull designer Adrian Newey revisited the blown diffuser in 2010, to great effect.

Red Bull’s RB6 (pictured) was designed with a blown diffuser in mind but, in initial tests, it was run with older RB5 exhausts, to stop competitors working out what was going on.

When the new exhausts were finally used in testing, Red Bull put exhaust-shaped stickers on the car to make it look like the old pipes were still being used.

Throughout 2010 and 2011, Red Bull continued to refine the blown diffuser.

That problem about downforce disappearing when a driver lifts off the throttle?

F1 innovated its way around that. Engines were programmed to keep feeding hot gases to diffusers, even when the driver had lifted from the throttle.

Red Bull were kings of this technique – listen to the racket an RB7 makes at Monza in 2011. That’s the engine blowing hot gases to the diffuser under deceleration, and it’s not a noise that other teams could fail to notice.

Blown diffusers were banned for that year’s British Grand Prix, but that ban lasted for only two races.

However, as is the way with F1, the process was completely banned the following season.

In aerodynamic terms, diffusers attract fewer headlines than their cousins the front and rear wings, but they play at least as big a role in a car’s success.

They may be hard to see and they may be the last part of the car to cross the finishing line – but they also illustrate perfectly how innovation in F1 affects every part of the car.