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www.engineeringnews.co.nz 7 Motorsport at Fort Dunlop in Birmingham. “We have some development partners that have commercial deals, but because there is such a demand for our product, it walks out of the factory on its own, we don’t have to embark on huge marketing campaigns -- it sells itself.” In developing a race tyre Dunlop starts with slick tyres. It might look easy because there is no tread involved, but it’s not. A lot depends on the construction of the tyre and a range of compounds used. “Sometimes we take seven or eight different compounds to an event,” says Meenan. “Some cars are highly tuned to certain conditions that require certain types of tyres and then there are the more general products for the less highly tuned cars which just have a soft, medium or hard compound combination. In between all that, for our development partners we would have smaller gaps in the performance of each compound.” The word ‘compound’ is confusing here – when talking about finished tyres it is used to differentiate between actual tyres. As a constituent in the manufacturing process it refers to the particular mix or recipe of the rubber. “We have quite a range of compounds and we can choose from this range for particular circuits and it can be very dry at the start of the lap and damp or even wet at the back of the circuit. The grooves are only 3 to 4mm deep and they are cut with a variety of blades in a hand cutting tool which heats up to the temperature of a cool soldering iron. The finished result looks a bit like a track day tyre (like those fitted to the Lotus Exige). Dunlop looked at the possibility of automating the tread cutting process but it’s not as quick as cutting by hand. The tread cutters are a little bit like sheep shearers; they are very deft in what they do and they can cut tread very quickly. They set their blades so that they don’t go anywhere near the bandage (the fabric part of the carcass). If the process was automated in situations where the bandage is closer to the surface an automated machine could cut into the bandage whereas a tyre cutter can feel where the bandage is relative to the tread cutting blade. “Because this is part of the development process having the tread cut by hand means that we can change the pattern instantly without having to reprogram any machine tools or produce more tyres,” says Meenan. “It can’t be moulded in because we’re changing the product so regularly – this wouldn’t be cost effective.” “The tread pattern generally comes from us and it’s based on feedback from tests. We would try a range of different patterns and converge on what we think is a good compromise for all conditions,” continues Meenan. “A lot of theory goes into tread design and we have a number of our own programs to help us choose the optimum tread pattern for particular conditions. Things like a water clearance analysis for sections of tread produce the required volume of rubber and you work out the appropriate clearances at any position across the section to give you the pattern at a particular point. The hand cut grooves give you enough water clearance to make a slick tyre work in variable light rainy conditions and on longer laps like Nurburgring where it could be dry for three-quarters of the lap. “It’s very difficult to tweak a compound (swap tyres for better grip) in these kinds of conditions as it’s either going from dry to wet or wet to dry, so the best you can do is provide the possibility for water clearance when it’s encountered,” says Meenan. “Recently the BMWs started on cut slicks at the beginning of the race and after five laps they were ahead by over a minute to the rest of the pack. The Dunlop intermediate gives you about 30 percent water clearance; the wet is about 40 percent and what they call the monsoon tyre gives about 50 percent water clearance. The cut slick gives you about 15 to weather conditions,” continues Meenan. “If it’s wet we have what we call a cut slick option, which is a soft slick tyre with cuts in the surface ‘tractor style’ (angled cuts from around the middle of the tyre outwards). For race tyres these are all hand cut at the factory.” The cut slicks are used in situations where there is light rain, but not enough to go to intermediates. This is particularly useful for circuits like the Nurburgring where ...having the tread cut by hand means that we can change the pattern instantly without having to re-program any machine tools or produce more tyres.


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