Actually, tandems are all over the map when it comes to rear drop-out spacing.
Santana established a 160mm "standard" that a few other builders also use.
Co-Motion, Burley, Cannondale, Trek and most custom builders use 145mm as their "standard".
Cannondale used 140mm for several years
You'll find 135mm rear spacing on older (mid-90's) Cannondales and the current off-road tandems by Ventana and others.
You'll even find 130mm road-bike spacing on custom made or modified for racing tandems.
Last edited by TandemGeek; 01-30-05 at 09:50 PM.