Tech Corner: Finding the right balance
WorldSBK is all about variety. With a production based series the compromises of the road are felt on the track. The balance of power can shift quickly with a “game changing” bike. Last year this happened with the Ducati V4R, which was a radical departure from what had been seen in Superbike racing.
How a Ducati makes its laptime can be very different to how a Yamaha, Honda, BMW or Kawasaki achieves their times. Last year this was manifested by the top speed advantage enjoyed by Alvaro Bautista. His size and riding style, where he sacrificed corner entry to hit the exit as fast as possible, were a perfect balance for a high top speed. By using this style Bautista was able to exploit the Ducati’s strong engine performance and also present a challenge to the other riders. How could they find a way to beat him?
To make up the difference you needed to be very aggressive on entry to the corner. If you couldn’t beat him on the straight, you needed to be better on the brakes and through the corner. With Bautista and Ducati dominating the early races of the 2019 WorldSBK season Pere Riba, crew chief for Jonathan Rea, said: “We need to push to the maximum in braking and cornering to give us a chance of winning. The Ducati with Alvaro is like a rocket but we can still win.”
At the time it seemed like the bravado of a championship winning team refusing to accept the reality of their situation; their time at the top was coming to an end. Obviously since then it’s been made clear that you doubt Jonathan Rea and his Kawasaki squad at your peril, but the manner in which Kawasaki had to approach last year was clear. They had to maximise everything around them to get the most from their package. This has continued in 2020 with the margins closed between the bikes and now from track to track one bike has been in the ascendency.
In WorldSBK, chassis regulations are such that you can’t find a solution out of thin air like in MotoGP. You can’t suddenly change your chassis to flex more or design and build a new swingarm. By regulations you have to stick closely to the homogated model for that season. In effect, you have to dance with the girl you brought to the party, and there’s no point looking around for someone better looking.
“The unfortunate thing for a Superbike rider is that you can be the best rider in the world, the cleverest engineer and crew chief, but you’re restricted to a production based bike,” explained Rea. “There are only certain parameters you can change, so it’s hard to suddenly change things by magic. You can’t have a new chassis or swingarm. You have to build a bike that works for Pirelli and you can’t just go to the factory and find something different. It’s all about compromise. You have what you have in WorldSBK. The good thing for Kawasaki is that our bike is mature, so we understand a lot and now try and make changes to our geometry and electronics; and these changes can make a big difference, but only once you understand the package.”
What are those changes that you can make? In terms of geometry, the simple solutions are finding ways to change the centre of gravity. The engine and the fuel tank are the key elements of a bikes weight to consider. Can you move this mass forward or backwards to change the handling? To do this you can or change the front ride height by adjusting the forks or lengthen the swingarm at the rear.
The force of gravity is a constant in the world, but it’s not constant on a race track where the centre of gravity is King. The weight of the bike standing in pitlane is very different to how it reacts out on track under acceleration and braking. As a body moves, so does its centre of gravity with the forces exerted on a bike moving to the rear under acceleration and then to the front under braking. Dealing with these changes is the key to setting up a bike.
If you move the weight towards the front it means you suffer in the braking zone, there isn’t enough weight on the rear so the bike jumps onto its nose in the braking zone. A rider therefore has to be less aggressive with braking and also brakes earlier…a sure recipe for being overtaken in the cut and thrust nature of WorldSBK.
Why not put the weight on the rear in that case? This will allow a rider to be very aggressive in the braking zone because the front won’t be overloaded, but it will also mean that as you open the gas mid-corner the bike can run wide on the exit. You’ll need to manage the throttle and your exit speed is compromised. If you’re already struggling for top speed, the easiest way to compound this is by not being to accelerate fully out of the corner.
Too much weight on the front and you overload the tyre. Too much weight on the rear and the bike won’t turn. A compromise is needed if you’re going to be able to get the most from the bike. With a fresh tyre you can overcome any shortcomings, but as the race progresses the flaws of your bike setting can appear. This is exaggerated by tyre wear and fuel loads throughout a race too.
As a tyre wears, the grip level changes for a rider. The engineers job is to find a way to keep loading the tyres. In the early stages of a race, with a fresh tyre, it’s easy to load the rubber because it has maximum grip and this masks problems. As the grip starts to fall, the mass that is applying the weight becomes much more important. If you can’t generate enough load on the front of the bike it will start to slide and push the rider wide. This will cause the tyre to wear in the wrong places and exaggerate the issue continuously lap after lap. It’s a snowball rolling downhill that keeps getting bigger and bigger.
Finding a compromise comes from weight distribution and wheelbase. The longer the bike the more stable it will be, but the shorter the bike the easier it is to turn. Engineers try and find the right weight bias from the outset of their season and then tweak the bike by stiffening or softening the suspension throughout a session based on rider feedback.
Making the bike stiffer or softer has a big effect in all areas of the track. A stiffer front end is very strong and stable in braking, but can be a handful when the bike is leaned over and running through a corner because the feedback is negative for a rider; they feel every bump. Go too soft and the front end crashes aggressively in braking and you can’t attack on corner entry. You will however have a supple bike over the bumps when it’s leaned over. Compromise is key and so is understanding the balance between weight bias and stiffness.
Last year Riba and Rea wanted to find a solution that allowed Rea to be aggressive on the brakes when compared to Bautista, and make up time in the braking zone which then allowed him to attack the corner. With Bautista opening the gas earlier than his rivals, his corner speed in the initial phase was very low but with the bike loaded up he could exit a corner carrying a lot of corner speed. By riding alone at the front, in the early stages of the year, he could do this. Once he was battling with riders, this strength was taken away and Ducati had to go back to the drawing board to find a solution. Compromise is always the key between what you need a bike to do and what you want a bike to do.
Kawasaki found a way to fight in 2019 and this year the goalposts have moved again. In racing, even if the bikes stay similar from year to year, the evolution continues to force teams to find new solutions.