I thought a good idea would be to get a set of 21"/530mm diameter racing tyres for my occasional playing around out on the track. Sure, it would lower the gearing, but who actually gets up around 240 km/h on the track. The 20 km/h that smaller diameter tyres would knock off the theoretical top speed isn't used. And that smaller diameter would lower the car another inch and improve its handling.
The problem I found was that I could only find 21"/530mm diameter tyres to fit 13" wheels. You'd think the racing tyre companies would realise you can always put a bigger diameter wheel on a car, but you can't fit a smaller diameter wheel on over your brakes, and make all their tyres in low profiles to suit large diameter wheels. But, that I can see, they don't seem to.
Unless someone who has seen a tyre company selling, say, a 7.2/21.0x15 tyre or its metric equivalent.