The Avon Tyres British GT championship heads to Snetterton this weekend, a difficult circuit made up of fast straights and long sweeping corners. Finding the optimum balance between grip and straight-line speed will cause a major headache for the teams.
Pistonheads has looked to Cadena Motorsport star Gavan Kershaw for advice on what it takes to get an optimum set up for Snetterton. As an official test driver for Lotus and driver of the Cadena Aston Martin, Gavan is ideally placed to guide us through the challenges that his local track provides. After a recent test in the GT3 spec Aston Martin DBRS9, Gavan and the team collected significant data that will no doubt help the team to prepare for this weekend’s British GT race. Here he talks us through the keys areas to focus on when setting up a car and how to achieve the best balance between cornering and straight-line speed at the demanding Snetterton race circuit.
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Snetterton is reasonably smooth and has no great compressions or rises. This means that you can typically run a stiffer set up than places like Croft and Thuxton. There are four main areas to consider when trying to get a good compromise setup here: (1) Aero, (2) Braking, (3) Damping, (4) Wheel Alignment.
1. Aero
Readout for low and high downforce
Snetterton has one of the longest straights and a long uphill pit straight, so minimum downforce is often at the top of a team’s setup ideas. But this can be at the cost of stability and confidence through two long fast corners. ‘Coram Curve’ is a long steady corner where the car has reached maximum roll and lateral acceleration and needs downforce to keep the tyre working and retain stability. A similar but slightly slower corner is ‘Riches’. During testing it is usual to run a minimum aero set up and benchmark the top speed and general stability of the car. Then a team will try a setting with good levels of downforce. It is strange that often the lap times will be very similar but achieved in very different ways.
The low aero maximises top speed on the two straights up to 20kph faster than the higher drag, but the increased downforce gives faster speeds through the high speed corners. The team will then try to find the best compromise between the two.
2. Braking
During a single lap of Snetterton, there are three heavy brake areas. The first is going into 'Sears', pulling up to 2.0g with slicks and 1.3g in a good road car. The heaviest braking area of the lap is at the end of Revett straight – you’ll be braking from 150mph to 30mph in 150 meters here. You are also turning left into the Esses and often the biggest time gains at any circuit are in the braking areas, so as a driver you must understand if the aero and damping set up are affecting this. Then the third stop is into Russells. The brake disc temperatures will be getting up to around 600C at this point.
3. Damping
As mentioned, Snetterton is quite smooth so higher spring rates and much higher damper force is often used. Damping is talked about as compression (bump), and rebound (extension), but more useful to a race engineer is the velocity of the damper.
Low speed this is where the damper is moving up to 0.15 m/s. This is the point when the driver will be most aware of the rate of roll and pitch, and also how fast the car reacts to steering inputs. Too soft and the braking becomes worse, traction is poor and often there is too much understeer or oversteer. Too hard and the car lacks agility, feels bouncy, weaves under braking and rolls too fast.
Then there is high speed damping, where the damper moves up to 3m/s but with very small displacements. These are typically seen over curbs and small ripples in the circuit. The main aim is to get the car to ride curbs well so that speed can be carried across Russell chicane without damaging the suspension.
4. Tyres
In some regards we are lucky in British GT as there is no choice of compounds, so set up is done to just maximise tyre grip against wear. Snetterton has some very similar tyre wear characteristics to Thruxton due to the long high G corners. These corners cause the loaded outside part of the tyres to really push onto the shoulder of the tyre and the inside unloaded area is having the tread pulled off it through these corners due to the camber on the tyre.
No choice of compounds for British GT
As with any circuit you will see the Avon Tyre engineers measuring the tyre temps across the tyre. This is done with a probe to measure the compound temp not the surface temp. The cambers are adjusted to give up to 10°C hotter on the inside of the tyre than the outside. At Snetterton the front-engined cars will be most worried about the left front (LF) tyre and the mid-engined the left rear (LR). If the first driver pushes too hard some cars will struggle to keep competitive lap times for the whole hour.
The British GT cars run to tight homologations, but within these regs most of the cars have some adjustment in the following areas:
Ride Height– Using the adjustable spring platform, minimum allowed is often best but we will try more rake (higher rear or higher front).
Spring Rate– Often selected before you even get to the circuit, based on the roughness/ smoothness of the circuit. In GT3 pre-homologated rates are given and with the DBRS9 we have three fronts and three rears to choose from. The spring rate selection is often down to the tyre. Slick tyres can deal with much higher spring rates than a treaded tyre, for example a Lotus Exige on slicks will be 2.5 times stiffer.
Corner Weights – This is done on a flat area using scales. Weight can be put into a corner or diagonal by raising or lowering the spring platform. Typically raising the corner ride height will put more weight on that tyre and then you get more initial grip from that tyre, but it will overload and loose grip quicker.
Anti Roll Bar – Some cars are fitted with an adjustable roll bar. The drop link position is adjusted making it stiffer or softer thus giving a fine tune to the spring/wheel rate. Roll bars are often disconnected in the wet to make the car softer without the need for changing the spring.
Damper– Adjustable on some cars with up to four ways of adjustment:
Low speed compression High speed compression
Low speed rebound High speed rebound
Wheel Alignment – Adjustable camber, caster and toe in or out. These can be adjusted for both the front wheels and rear wheels
Tyre Pressure – Avon Tyre’s recommend a hot pressure of around 26 to 29 psi. As the tyres heat up the pressure inside the tyre rises, driver will find a point where pressure in the tyre makes it feels like it has lost grip. This is called the ‘hot’ pressure and often reached after 5 laps. Tyres will be set to as low as 18 psi cold.
Add in aero, brake bias (how much front vs. rear brake pressure), brake pad compound and you can have a very busy few hours testing, and ultimately getting that set up right!!
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You can see Gavan and the Cadena Aston Martin at Snetterton this weekend. Race one is on Saturday the 7th June and race two on Sunday the 8th June.