Racing tyres: they’re black and round and stick to the ground. And that, by rights, should be all we need to say on the matter.
At Thruxton circuit, however, tyres were one of the hottest topics during this weekend’s Dunlop MSA British Touring Car Championship event.
A combination of an abrasive track surface, high average lap speed, unforgiving kerbs and high ambient temperatures (for Saturday’s qualifying sessions at least) place a toll on the rubber that’s peculiar to the Hampshire speedbowl.
Dunlop supplies the control tyre for the BTCC, and has three dry-weather, slick compounds of Sport Maxx cover to choose from: soft, medium and hard. All three compounds are derived from the same construction.
For Thruxton only the hard compound – developed specifically with the track’s demands in mind – is used.
Adding a further challenge is the BTCC grid’s mix of front-wheel-drive and rear-wheel-drive cars, as well as different car setups favoured by teams, which don’t get many chances to test at Thruxton and have to aggressively chase the optimum set-up in practice.
The unenviable task of trying to juggle the demands of all of the teams in the pitlane falls to Dunlop Motorsport UK Events Manager Michael Butler.
“Thruxton is the most abrasive, high-load circuit on the calendar,” he says. “Around here a BTCC car is on full throttle for 75% of the lap and never really in a straight line; it is always turning. Less than 5% of the circuit is straight. The kerbs through the complex, Church and the chicane are very aggressive – if you hit one of those you’re a passenger in the car.”
It’s not just the wear rate that is a factor – indeed, Butler is confident the compound is well suited to the track – but Thruxton punishes the actual construction of the tyre.
Butler and his band of tyre engineers issue the race teams with operating guidelines aimed at maximising tyre life and preventing punctures. Teams aren’t obliged to heed the advice and occasionally one or two will take a risk on a setup that strays outside of recommended parameters.
In addition to advised cold and hot tyre pressures and suggested settings for camber and caster, the tips include a suggestion to avoid hitting kerbs in the first five laps of a practice session or race.
“The tyre pressures are still building up in the first five laps and tyres have not reached their optimum operating temperature,” says Butler. “The tyre sidewalls will over-deflect upon impact with the kerb, and this runs a risk of a failure.”
On front-wheel-drive cars the left-front takes the most punishment around Thruxton, and on rear-drive cars such as the BMW 125i M Sport and Subaru Levorg, it is the rear-left that soaks up the most abuse.
“The track surface is very coarse and you have to remember that the track doesn’t really get used very much for racing during the season so there isn’t a lot of rubber laid down," explains Butler. "It is very green when we get here for practice. It is all about tyre management. Being quick for two or three laps doesn’t mean anything around here. You need to be consistent over each of the 16 laps.
This time at Thruxton half a dozen teams completed full race simulations during free practice to get an accurate barometer of tyre wear. The message they unearthed was clear – look after the rubber or the final few laps of each race could be a time to dig out the lucky rabbit's foot and cross everything.
The track is a challenge for teams, drivers and the tyre supplier. Sunday’s three races around the superfast sweeps will offer a fascinating indication of not only who is the fastest and bravest driver in the BTCC, but who is the best at intelligently conserving their equipment.