Most (not all) German made Isetta's rolled out of the factory wearing Metzeler tires. The British made Isetta's typically were fitted with Dunlops. Both of the German built Isetta's I'm restoring have (had) Metzelers. The rear Metzelers have a pretty aggressive knobby tread pattern, while the fronts have a less aggressive tread pattern. The tread on my original tires really isn't that bad, but the tires are severely cracking and need to be replaced. I have to say that there is not a very big selection of 10" tires available in the United States.
Ever since Kumho quit making their 145R10 radial tires, 10" tires have been getting harder to find and more expensive. A couple of years ago I paid $27.00 each for Kumho's from TireRack.com. The least expensive radial tire I've been able to find recently are Falkens (made in Japan) from Coker Tire which sell for $53.00 each. If you're planning on running radial tires on your Isetta, due to their wider profile, you might also want to consider using the wheel spacers that I mentioned in a previous post on your front hubs. Isetta's originally came with bias tires, so if you're wanting to use bias tires, Coker also sells BF Goodrich bias tires available in whitewall or blackwall. The BF Goodrich 480-10 bias whitewalls run $117.00 each. The blackwalls run $102.00 each. Coker also sells the correct bent stem 10" inner tubes for $13.95 each.
Hey Bibendum, where's Isetta on that list of small cars?