Originally Posted by
jhefner
In regards to the horizontal dropouts; what is the "correct" position for the rear wheel? As long as I have been around bikes, I have always moved the wheel as far back in the dropout as I could. But, others have made mention of "your wheel is too far back"; and the adjustment screw found in some implies that it should not go all the way back.
So where should it go? As an experiment, I moved my rear wheel to where it was at the intersection of the seat and chain stays, and it is easier to shift onto the largest rear cog when the chain is on the big chainring (it is an early 70s ten speed.)
-James
Most derailleur manufacturers also offered dropouts with geometry engineered to optimize the performance of their derailleur. In general, this is achieved when the axle is lined up with the axis of the seat stay.
Vertical dropouts become popular with the advent of indexed shifting. Indexing performance is greatly affected by chain gap which is distance, along the chain, between the points where it contacts the cog and jockey pulley. By eliminating the fore/aft axle positioning which affects chain gap, engineers were able to eliminate one variable that the home mechanic could inadvertently disturb and upset the performance.