These pictures are of my '91 Bontrager Off-Road and a '97 Race Lite. I've tired to show the differences between various models. The first few are changes that carried through into the "Race" model, and in these cases I've attempted to note when the change occurred.

Description	Off-Road Picture	Race Lite Picture
Head tube Race Lite frames have material removed on the leading edge of the tube. Neither the Race or Off-Road frame has this feature.
Decals All frames had square-edged decals until early '94 or so.
Seat stays All frames came with two piece seat stays until some time during '94. Later models had a single piece tapered stay. Generally bikes with the single piece stays are considered to be post-Trek, and two-piece are pre-Trek. However, this is not necessary true. The change to the two-piece did occur about the time of the Trek buy-out, but there was some overlap.
Rear drop outs Off-Road frames (at least some) have horizontal dropouts. Race and Race Lites do not. I'm not sure if this change occurred with the model change, or this was by request.
Cable guides Early frames have bonded cable guides, and later frames are TIG welded. I believe that this change occurred with the introduction of the Race in approximately 1992.
Front derailer stop Until about '94(?) frames used bottom pull front derailers. The cable was rerouted via a pulley (not shown) to allow top tube cable routing. When this change occurred the cable stop was moved from the rear of the seat tube to the front right.
Rear canti stop The rear canti stop on the Off-Road frames is significantly different than the Race and Race Lite frames.
Down tube gusset Although rather hard to see in this picture, the down tube gusset is more bulky on the Off-Road than the later frames.
Chain stay gussets The drive-side gusset is significantly longer than the non-drive on the Off-Road frames. The non-drive is shown on the Race Lite as the drive-side is complete obscured by the chain rings.
Chain stays Off-Road frames had an extra bend in them (on both sides) near the dropouts. Race and Race Lite frames are straight.
Mono-stay tube The end of the mono-stay tube is not capped on the Off-Road. It is capped on the Race and Race Lite. (Note that the bike is upside down in the pics.)