wim said:Perhaps the person who warned you thought your Tricross was a multi-geared derailleur bike. Multi-geared derailleur bikes have a rear dropout spacing of more than 120 mm.
Commonly 8 speed and greater bikes are 130 or 135 mm spaced. With the exception of the SS Tricross and the Redline Monocog (there may be others, consult the tape measure to be sure) most other single speeds are 135 mm spaced due to the MTB nature of their use. A quick way to tell, but not always accurate, is to look if the hub has a freehub body or threads for a freewheel. Older pre-8 speed (road) freehubs were 126mm spaced. Threaded Freewheel hubs are generally 120mm, but will have options for longer axles and spacers for wider rear ends.