So what does it mean for riders?
The ‘Fox’s Ears’
It means that you can accelerate the hardest at 45 degrees of lean, which seems odd, but have to roll back the throttle as your lean angle decreases and the front of the machine starts to lift.
Riders need to be acutely aware of the dangers of ‘High Siding’.
The ‘Fox’s Nose’.
This also shows a rider can brake (briefly) at up to 1.5g when upright(ish). This is twice as hard as the Highway Code standard.
This is probably from top speed due to the drag on the rider and bike preventing it flipping over. 1g tips most bikes at lower speeds. You can also briefly brake harder as energy is dissipated rotating the bike during weight transfer.
The ‘Fox’s Jaw’
The ‘jaw’ show a linear relationship between lean angle and braking, up to the extremities of banking – red lines. So track riders can brake deep into corners using the front brake, gradually releasing it proportionally as the lean angle increases.
Riders need to be aware that grip levels on the road can vary considerably, and the dangers of a front wheel ‘wash out’ and ‘Low Siding’.
The DVSA advice, which should be taken, is for road riders to complete their braking before corners, and only use the rear brake in an emergency. Applying the front brake mid corner, as opposed to carrying it into the corner, flips the machine up. This will make it run wide, potentially through the scenery or into oncoming traffic.
However, with training and practice, road riders can be trained to carry the front brake into corners in an emergency, which can be a life saver. But braking into corners routinely just significantly diminishes your safety margin, and likely increases impact speeds.
It’s not sensible to ride on the road anywhere near the limits of grip. However, on a track, it’s necessary, with care, for fast lap times. You need to know where the limits are.
We tried applying the standard traction circle maths to motorcycles in 2015, looking to see what traction should be available for braking as the lean angle increased.
If you use Mohr’s Circle, you get what we called the ‘Cats Claw’ which is the shape of the calculated additional area of grip.
It didn’t look right, and showed far more grip when banked than was available in practice. The question was why?
We looked at Cossalters ‘Motorcycle Dynamics’ which shows an oval, which looked better, but not perfect. 1g on one axis for braking and accelerating, 1.6 g for the other when banked.
There was a recent post on LinkedIn from Mikko Bartolossi, a MotoGP Engineer, introducing a paper from Biral, Francesco & Lot, Roberto from 2009, showing an alternative traction circle for motorcycles.
https://www.researchgate.net/publication/267715875_An_interpretative_model_of_g-
It looks like a fox’s face!
The diagram shows the lateral and tangential g force acting on a motorcycle when cornering, and either braking or accelerating at the same time.
The left and right hand areas show the g force acting on the machine when it is banked. The braking force is shown on the lower half, and accelerating on the top half of the diagram.
The tip of the ‘fox’s nose’ shows that a rider can momentarily brake at around 1.5 g as long as the machine is nearly upright. This will be very briefly as the bike will flip forward otherwise, and is probably from top speed relying on wind drag to stop the bike from tipping fotwards. But shows how a high level of skill can reduce stopping distances. Most motorcycles will flip forward at 1g. (For E-Scooters it’s only 0.4 g). The Highway Code assumes 0.67g.
Riders need to be aware of the dangers of snatching the front brake and skidding and falling, or on machines without ABS. Also somersaulting, when can also occur with earlier ABS systems without pitch control
The red lines at the bottom show a linear relationship between lean angle and the maximum braking force that can be applied, when you’d probably expect the grip to diminish exponentially as the lean angle increases (Cat’s Claw).
This will be using mainly the front brake, as the rear brake will have little effect due to the weight transfer forwards, making a rear wheel skid very likely.
But what is even more interesting, are the ‘fox’s ears’. Accelerating on a motorcycle is limited to 0.9g not by tyre grip, but because the machine will flip over. This time backwards, not forwards as in hard braking.
It shows that motorcycles can be accelerated harder when banked, the peak shown at 45 degrees of lean. Why is this? It’s probably because the centre of mass is lower and to the inside of the corner, and the front of the machine is held down partly by the centrifugal force. The weight is transferred to the rear tyre from the front tyre at the same time, giving more grip at the rear.
This is where racers can gain an advantage, but for trackday and road riders this is where ‘Highsides’ happen. The rear tyre loses grip, slides sideways, then grips again when the rider instinctively snaps the throttle shut in response. The rider is usually thrown up into the air, often over the top of the machine.
We know traction control will not necessarily prevent this. It’s too quick and too brutal. However, modern bikes with Inertial Measurement Unit (IMU) are better and can sense tbe limit aporoaching.
Modern MotoGP and WSBK bikes have traction control, (BSB bikes don’t) so it very rarely happens now in world racing, but many older road going sports bikes also don’t.
This makes older sportsbikes quite difficult to ride safely, particularly as grip levels on the road, as opposed to a track, can vary considerably. There are also two generations of traction control for road bikes, the latest being IMU’s are ‘lean sensitive’ which makes them more effective and safer.
We know from experience at ‘The School’, that riders can still lose traction by accelerating too hard at extreme lean angles., even with traction control. However, the newer systems seems to prevent ‘high sides’ (so far), with the bike ‘low siding’ and the rider just slipping off the side of the machine.
The new Yamaha R9 and other top end bikes now have 6-axis IMUs (Inertial Management Unit) which makes them ‘lean sensitive’, so should be safer in this respect, although the Laws of Physics will eventually intervene at the extremes.
So a 10-year mystery solved, it’s not a ‘Cat’s Claw’, it’s a ‘Fox’s Face’.
Were now working with Prof Owen Williams on a 660 Aprilia fitted wirh a 9-Axis IMU. Next step?
Mike Abbott, British Superbike School
17th June 2025
Updated 16.8.25
British Superbike School 