The Most Important Part of a Racing Car

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 80’s and 90’s series we run in and using Evo track would have meant only being eligible for the 90’s series.  

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 with out degrading. It can take a lap or two to get enough heat in to the tyre, but once warmed up, the tyre will allow greater cornering, braking and acceleration. The tread pattern and compounds for list b & c tyres can vary enormously depending on what type of tyre a competitor is looking for. For the Lancia we run Nankang NS2-R tyres when in the wet. These more groved tyres have a tread pattern designed to shift water and prevent aquaplaning through standing water. When we ran these tyres for the first time at Croft in the pouring rain, we were able to lap the field between 1 and 2 seconds faster and resulted in our maiden victory in the car. Later the same year the same tyres saw us dominate a wet race again and we took our second victory overall at a very wet Donington Park, coming through from 6th to take the lead by the end of the first corner. When dry, we run the Nankang AR-1 tyre which is focused on ultimate lap time in the dry and performs remarkably well in damp conditions but struggle shifting standing water when really wet. The Nankang NS2-R and AR-1 cost about £140 each delivered. The NS2-R tyres being wet weather are good for 4 or 5 races (heat cycles) before they become hard and less effective. These are sold on Ebay and replaced with fresh rubber. The AR-1 tyre will last at most an hour and a half on the track but would have given up is best after around 40 minutes.  

Free Choice – in reality, this means slick tyres, a harder compound for dry and a softer compound for wet with groves cut in to the tyre manually by a mechanic. I had the opportunity to race using slick tyres during Festival Italia at Brands Hatch this August. Being a one-off event, the rules are very relaxed and open for any type of car and configuration with the tyres being “free” (choice). The difference between slick tyres and semi-slick is quite remarkable. The load a driver is able to transmit through to the road is significantly increased in all areas and it re-defines what is possible in a race car. I was able to drop seconds from my previous best by carrying more speed in to corners and turning in harder and later than is possible with our usual tyres. Braking performance was also improved, however Brands Hatch doesn’t have any big braking areas so this somewhat masked the difference than a circuit such as Snetterton would show. The other key difference is the amount of “warning” you get when the driver puts too much load through the tyre and you have tyre slip (or skidding). With slicks, the “slip to grip” ratio reduces much more aggressively than track day tyres. With track day tyres, when the driver asks the tyres to do too much, they slide progressively in a controlled and liner fashion which in turn means a driver can recover (relax the steering & apply some power) without suffering a complete loss of traction. Racing with slicks is much more dancing on a knife edge with the consequences being metered out swiftly with the added advantage of you going much faster when it happens! There is a video on our channel which shows two laps side by side for comparison, search for “Lancia Delta Racing comparison of slick v semi-slick tyres” on YouTube. Nankang don’t offer slick tyres for the UK so we put on some Yokahama Advan which were £220 each delivered. Every time you use a slick tyre it gets harder and slower, as a result you would want to change every 30 minutes of use (if you had the budget to do so).  

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 tyre and completely destroyed a brand new set of slicks. Luckily a mad dash to Milton Keynes Yokohama distribution centre saw us with some harder rubber which lasted the weekend despite a spin in qualifying flat spotting one of the tyres. If you search for “Lancia Delta Racing Destroying Tyres for Festival Italia” you can see the end result for yourself. 

rthurbin

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.