Over this year we have talked about engines, suspension, drive train, setup and racing but missed the most important factor of any competition car – tyres. Tyres are boring, black and round. Behind the other wheel, tyres are transformed in to your most cherished possession, giver of lap time and stand between you and heroism or abject failure.
As it is the tyres which directly connect the moving vehicle with the static ground, this contact patch is critical to maximising the amount of load which can be transferred. A typical road car has a total contact patch about the same size as a A4 piece of paper so the higher the force which can be applied, the higher apex speed can be achieved, the later one can brake and so on. As with everything, the laws of physics cannot be circumvented and there is always a trade-off. Super grippy tyres will generate more load, this generates more heat, this reduces the effectiveness of the rubber, reduces tyre life, makes the tyre more expensive and so on and so forth.
When designing and setting up the car we tried to get the largest width tyres underneath the Lancia’s arches and being a 16v, only managed to fit tyres the size of 235/35 R17. I am sure an Evo could get more rubber down but we wanted to keep the car compatible with the
Within the UK ammeter circuit racing scene, series and championships choose to operate in one of three “levels” of tyres; road, track and free. Helpfully the governing body of the UK motorsport scene (Motorsport UK) publishes a categorised list of tyres in which clubs adopt to define what tyre is allowed and what tyre is not. Road tyres are classed as 1A and have makes and models which most people chose to run on their daily driver road car. Track tyres are classed as 1b and 1c and offer significant performance advantages, more on this later. Finally if the tyre choice is “free” then that means you can put anything on the car you wish, without restriction.
Road Tyres – I have never raced on road tyres and would never wish to do so (except if a specific tyre was mandatory for the series). Why? Road tyres are much too hard for use in a racing application. They are designed to last thousends of miles with multiple heat cycles all through different seasons. The level of grip offered would mean seconds a lap would be lost against a competitor and would make any notion of competition pointless. For the Lancia, a Nankang Sportnex NS-20 cost about £60 each delivered, probably come with about 7mm of tread and have a life expectancy of many thousends of miles.
Track Tyres – Sometimes road legal, sometimes not, track day tyres (sometimes referred to as semi-slicks) offer a significant performance upgrade over road tyres. The grip levels are far superior to that of a road tyre, can be pushed harder for longer
Free Choice – in reality, this means slick tyres, a harder compound for dry and a softer compound for wet with
The key factors governing a driver’s tyre choice are; ultimate grip over one lap, longevity of grip over a race distance, tolerance to load and the weight of your car, availability, compliance to regulations and price. A tyre which is great over one lap, initially gains you loads of positions but over heats, drops lap time and sees the same cars passing you is no good. Likewise, a consistent and robust but slow tyre is no good either. Choosing a tyre is all about trial and error complicated by all the other factors which limit the amount of testing you can do back to back. Two days in June but with 15 degree temperature difference will produce different lap times on the same tyre so doing a real “A to B” comparison is really hard (without a endless supply of tyres, wheels and people to change them around for you). Even the race weekend before your test or rain the day before will change the surface of the track and give you less or more grip depending on the rubber on the circuit.
Finally, tyre pressures are a key factor in achieving as much grip from the tyre as possible. Pressures are only measured when “hot” and the car has just come in to the pits at racing speed. The ideal “hot” pressure is dependant on the advice from the supplier and the weight of your car. For the Lancia we aim for a “hot” pressure of 31psi all around. This usually means starting with pressures of 24psi in the front and 26psi in the rear. Tyre temperatures are also measured across the surface of the tyre (outer, middle and inner) to check there are no hot spots which suggest a setup change (either outer edge hot) or more throttle control required (middle hot).
The good news is with our slick tyres we were able to achieve a 3rd in class and 2nd in class during the Festival Italia event. There was some panic during the test session the day before when re realised we had bought the wrong compound of