The R40 series bikes could all be had with either above seat steering (ASS), or under seat steering (USS). Also either short wheelbase (SWB) or long wheelbase (LWB). Later on, ATP shortened the LWB boom and called the result a medium wheelbase (MWB). The R40 and R42 used 2" wide frame tubing, while the R44 and R45 used thinner 1.75" main tubes. The R 42 and R45 included upgraded components. All of these bikes could be had with either a 16 or 20 inch front wheel.
ACTION shot from ATP's 1999 collection
courtesy Dave Atwood

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  Note the front and rear suspension.