CHASING THE FINE LINES OF BTCC SUCCESS
How boffins tackle the tin-top aero secrets
With so many mandated parts and a base bodyshell that is determined by what’s available in the marketplace, it’s easy to think the British Touring Car Championship is not an environment that immediately lends itself to the intricate world of aerodynamics.
While the rulemakers do their best to make sure that the UK’s leading tin-top series is a level playing field – certainly in terms of power output – that means any tiny gain can quickly put a team in the boxed seats.
The airflow over the car is something that most outfits will take into account when they are opting for a new machine. The coefficient of drag on any car’s silhouette is uppermost in most minds.
Ace engineer and designer Kevin Berry has been responsible for some of the most successful BTCC cars in recent years, including the BMW 125i M Sport, revamping the VW CCs and working on the 2017 title-winning Subaru Levorg as well as myriad other programmes.
He explains: “The way that the power is balanced, the incentive is to go for a car which has the lowest-drag shape to start with so that you can make the most of that.
“There are other things that you look at as well. For example, the rear wing is positioned to achieve a fixed level of downforce and so you want to achieve that with as little drag as possible.
You have to take that into account when you are assessing which type of car you might want to put on the grid.”
But some teams do not have the ability to pick which model they want. Commercial aspects can have an influence, and if a squad is a worksbacked operation, then the paymaster’s desires have to be taken into account, and this is where the compromises can begin.
Berry adds: “A saloon-type shape rather than a hatch shape can be a better base [because it smooths out the airflow around the rear of the car]. But when you are having that discussion, you have to take into account marketing or what a manufacturer wants to sell. There is always a conflict there somewhere.”
Berry also explains that the overhang of the bodywork beyond the wheel arches can also be crucial as this enables a larger area in which to work in tweaks to assist the car.
An example of a team that was required to use a particular model is Speedworks Motorsport, run by Christian and Amy Dick. When it gained Team Toyota GB backing for 2019, it built up a new Corolla. The chassis offered plenty of plus points, but its boxy shape was something the team had to put some serious thought into.
At the end of 2019, Speedworks contacted D2H Advanced Technologies to help scrutinse the airflow over the machine.
D2H’s Chris Hebert – previously head of aerodynamics for Toyota’s TS030 Le Mans prototype team – was on hand to offer some real insight for the Cheshire crew. He didn’t take long to get to grips with the car.
Hebert explains: “[Speedworks] had manufactured bodywork using the best tools they had and what they’d learned from the [previous model, the] Avensis. What they were looking for was a more engineered solution, so they could increase performance, and improve the way everything went together. We received a scan of the Corolla in January and had to complete a full computational fluid dynamics programme [CFD], design and manufacture bodywork for the season launch in mid-March.”
The intense programme impressed Christian Dick, and it allowed the team to take some significant strides with aerodynamics that might have taken much longer – and cost much more – to
“We had taken a step forward in 2020” Christian Dick
unlock otherwise. Dick says the initial work was reinforced by the help of
D2H. “[Previously] we would take the car to a windtunnel with some pre-made panels – sometimes a block of foam cut to a shape – to find out where we could improve, and how we could influence air getting over the car. This can be very time consuming, and very costly.
“With D2H, the process is completely different. They run hundreds of different combinations through their software to find sensitive areas of the car. That gives us a direction of the parts that we can leave alone, and the areas we need to focus on. It’s almost like going from analogue to digital, from where we were.”
In the BTCC, once the design has been locked in at the start of the year, that’s it: so it is all about making sure that the initial work done on the car is correct. This is where the midnight oil is burnt ahead of any new campaign.
Berry explains: “It is all about getting the most downforce for the least drag but, as ever in engineering, there is a compromise. There is a point where you can have features that generate more downforce but they have a heavy drag penalty. Things like little winglets, undercuts, pockets in front of the wheel – it is ideas like that. Generally sharp changes of direction [on the bodywork] which look like they would generate downforce also generate drag.”
This pre-season work also has a compromise when the calendar is taken into account. The BTCC will generally race at nine or 10 vastly differing layouts over the course of a 30-race season, and a vehicle is never going to be perfect everywhere. This is where the black art of engineering can set the tone for an entire campaign.
Berry says: “Think about the difference between Silverstone National and Knockhill, for example. Because you can’t change the package over the year, you have to find the right compromise to start with. If you go to the windtunnel or do some CFD, you might see a particular feature that is going to add 6% of downforce but add 2% of drag.
You then have to decide whether you will accept that as an overall gain on the whole season with all the circuits you go to or not.
“I have got some metrics I have worked out that simulate all the BTCC tracks we’d go to in a season. I put the numbers from the windtunnel into that and you should be able to see where the gains and losses are across all the tracks in the calendar. Then you will make a decision based on that.”
The work of D2H on the Corolla ahead of 2020 was extremely detailed and went into a realm most squads could only dream of. Hebert says that the initial designs from Speedworks were a great starting point, but then the computer power got involved.
“The vast majority [of what D2H did] was refinement,” says Hebert. “It was the areas where things connect; the wheel arches to the floor, the splitter to the bumper, and the lower you get, the more sensitive [it is]. When we summed up the improvements we had made, we reckon if they implemented everything, we would have saved them a chunk of lap time.
“Aerodynamics happens on an extraordinary number of lengths and scales. If I split the domain into a few squares, I am not going to capture those details. But if split it up into millions and millions of squares, I’ve got a chance of resolving these details. Until I can resolve those details correctly, I won’t be able to accurately predict the drag and downforce on the car. We’ve got half a billion cells in the domain that the car sits in. You need that refinement to capture what’s going on.”
While Speedworks had access to some top-level support, other teams on the grid choose to go their own way. That is mostly defined by the budget and engineering skills available to them, but Berry says that most top teams will visit a windtunnel at some point.
“Ideally during a programme, I would want to do some CFD work and then do a couple of days in the windtunnel,” says Berry. “But everybody has different views on it and lots of people don’t like the full-sized windtunnel because there are some compromises. A lot of the aero is dependent on the wheels rotating. If you got to a full-sized tunnel, generally it doesn’t have a moving floor, so the wheels aren’t rotating. You lose that effect, and also there is a layer under the car where the air is moving but the ground isn’t – that is not quite a real situation when you deal with a race car.
“A windtunnel – particularly a scaleddown one – is a quicker way of doing things if a team doesn’t have any computer-aided design. You can mock-up some bits, bolt them on and check them in the windtunnel and see the effects.”
So the first part of the compromise is the level of downforce as opposed to the drag it creates. It isn’t about making the car fast through the air though, as Dick knows. “What you’re learning throughout that process is it’s not as straightforward as just making a car slippier in a straight line,” says the team boss. “It can be a very small gain on lap time, but keeping or improving the aero balance to give you a better tyre wear over a longer distance.
“Most circuits we’ve taken a step forward with [in 2020], so I’m really pleased. What that means is delving into the detail to work out where the best areas of improvement are – there’s certainly more aero work to be done on the BTCC Corolla. We’re not blessed with the biggest budget in the world, so we’ve got to spend the money wisely and chip away at it.”
It is where to turn the spotlight that can be the biggest dilemma for teams, who are all trying to make the financial numbers stack up. Going from having a quick car to a competitive one is all about those decisions, and choosing which of the finer details to concentrate on.
“Within the BTCC you can build a car and get racing without a lot of development work and be reasonably competitive but if you want to make the next small gains, then suddenly all the little details are important,” adds Berry “That might be chassis set-up, that might be engine, cooling or that might be the aerodynamics. And it is when you get into this area that the gains are quite small for the money you have to spend.
“Some people will do nothing and crack on and they might be pretty good. If they are running well, they might wonder why they should spend any money just to try and move a few more places up the grid. But the BTCC is so tight and you are generally looking for such small gains, but this is where the big investment needs to come in.”
As if that situation isn’t complicated enough already, the external aero is only part of the story when trying to turn a BTCC-level tin-top into a title winner.
Berry says there is lots more to think about: “There is also the internal aero to consider too. The way the aero affects the cooling systems and the intercooler is probably more important, actually, in terms of performance.
“You could make the inlet smaller and you have less drag and more downforce maybe, but then you are strangling the airflow to the engine. You need to think about the intercooler layout too, and all the pipes and making sure you get a good flow in those too. It is a massive jigsaw – but one that I love.”
While a BTCC car might retain its resemblance to a machine that can be driven away from any dealership, the level of detail and the staff hours spent on making it absolutely the best it can be mean that the story only starts when a team has finished the build of a car.
It is a fine example of motorsport’s never-ending quest for perfection.
“The aero side is all about a downforce vs drag” Kevin Berry