What makes an ideal road for tuning, where do Britain’s top chassis developers go to find the best ones and what influence do they have on how a car drives? To find out, we spoke to several veteran car testers and engineers.
Andrew Unsworth, head of vehicle dynamics, Bentley
Looking at the whole performance envelope of cars like ours means seeking out a very wide variety of roads. We need to assess ride comfort throughout the speed range, even beyond 150mph in our case. We need big primary ride inputs at times and sweeping bends for steering tuning. Loops are good – and we have a few – so we can keep driving the same corners and over the same surfaces to judge changes we’ve made.
One of our evaluation loops starts at the factory gates at Pyms Lane in Crewe, quickly takes in a road with a changing surface that’s deteriorating in places and then has A-roads and B-roads with truck grooves. We have an unofficial agreement with the local council not to resurface it, and one of the reasons it’s so handy is that senior managers can get a feel for a car during sign-off without travelling very far.
A bit further afield, there’s a loop we use in the Peak District that I like. It’s a sort of triangle of roads starting at Buxton and passing Bakewell, Leek and Longnor. It has surface changes, sunken ironwork and a mix of bigger and smaller topographical features. That’s probably where I would choose to go with, say, a final prototype. But we use North Wales plenty as well, particularly en route to and from Anglesey Circuit, which we also use for dynamic development.
In the early project stages, our cars spend almost all of the time on track, but by the end of a project, the total development time is probably 50/50 road and track. With the road miles, more of them are probably done away from the factory than close to it – but UK roads are definitely a factor in defining the capabilities of our cars.
Good clear white lines always help, because you can easily judge whether you’ve ended up quite where you intended on the road. But I like stone walls, too: they keep you honest.
Then, if I want to zero in to tune particular things – to do steering refinement, for instance – I find that narrow roads at night work well. You can see cars coming from a distance, which is useful, but more importantly, you can’t see the road as clearly, so you can’t anticipate as much. Your control of the car depends much more on the accuracy of the steering itself.
A good engineer should spend 80% of his time on roads that he knows well – but not as well, for instance, as those of his daily commute, so he doesn’t start to cheat on his inputs – and then 20% of it on roads that he doesn’t know at all, to gauge whether the car feels on your side when you’re dealing with things that you really haven’t anticipated at all.
It is, of course, very easy to stick with roads close to your base for the sake of convenience, but if doing that starves you of diversity, you really shouldn’t.