I'm almost kind of half-thinking about maybe being convinced by carbonfibre wheels. Almost.
In next week’s issue, you will find our annual Britain’s Best Driver’s Car contest, two of whose competitors (not a spoiler alert, I don’t think), the Alpine A110 R and Ariel Atom 4R, arrived on composite wheels. Both were expensive cars, but previously I’ve generally tried rims like this on high-end supercars.
Just a few weeks ago, I drove a Porsche 911 S/T, which doesn’t have composite wheels but does have magnesium ones. Porsche’s engineers were keen to point out the similar reason why they had used this material: a reduction in wheel weight.
In particular, it’s a reduction of unsprung mass: the bit on the road side of the springs, so the tyres, wheels, hubs, brakes, wishbones and so on. Reducing this is helpful dynamically. The lighter it all is, the easier it is to control the wheel’s movement.
I wondered if lighter wheels improved a car’s ride: the 911 S/T rolls more easily than the 911 GT3 Touring, with which it shares suspension hardware. But no, not particularly, said the engineer from Porsche.
What they do help is traction (because a lighter wheel is deflected less by bumps and then finds the road again more quickly) and acceleration and braking (because a lighter wheel has less rotational inertia than a heavier one). So it’s easier to get it going and easier to stop it. The car therefore feels – and is – more agile.
Again, this isn’t a spoiler, because you will have had the chance to read about them already, but the A110 R and Atom 4R do feel particularly feathery. Mostly this is because they are: the Ariel weighs 700kg, the Alpine 1082kg. But I do wonder how much the way they respond to even small throttle inputs – and they are particularly responsive – is down to their light rims.