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The 420 rims are tough enough, but AC have a rep for using the smallest bearings they can get away with to appeal to weight weenies, which doesn't bode well for standing up to the streets of London's famous London. The track rear, for example, uses 6803 bearings 17x26x5 compared with the much more burly 6001 12x28x8 found in more common hubs which has almost double the load rating of the thinner bearing

I had a pair of 420 wheels and the hubs were, as mdcc_tester says, absolutely crap. They went through bearings at an alarming rate. American Classic claim to have redesigned the hubs but the bearings are still very small.