Originally Posted by
rdtompki
Tandems will slow down slightly faster than singles due to the greater drag, but that doesn't sound like the case. Furthermore, it takes a good deal of friction to slow a tandem down. Surely, this should be evident on the stand?
Huh!
Under any normal circumstances, tandems have a higher mass to friction ratio (from all sources) and therefore will coast faster, and slow down slower. That's the advantage of tandems, and why tandems are usually faster than solos except in hard hill climbing which puts extra demand on riders unless they're well coordinated.
The problem with tandems isn't about getting them going, it's getting them stopped.
Meanwhile the OP should do some basic diagnostics, lift wheels and spin unloaded, check tire pressure, double check internal brakes (if any). If it has a coaster brake, make sure it runs free when coasting, etc.