Re: Chain idler efficiency - roller vs. toothed

The angle at which the chain enters and leaves front sprockets and
derailleur idlers is the sine of the angle which is the lateral offset
between the two ends of the chain span divided by the free span
length.  Therefore, the longer the chainstays and the fewer the gears
on the sprocket cluster, the smaller the angle between chain and
sprocket plane.  The angle causes lateral sprocket tooth wear and
idler wheel wear.

Jobst Brandt