Jockey wheel diameter replacement and design questions

[meb]

Two weeks ago I clipped a curb with my RSX rder on a recumbent knocking off the jockey wheel and its bushing, bolt and end washers. I recovered all but the bolt, leaving them in a pair of pants till I could rob a bolt off another rder. I gave explicit directions not to bother those pants. Well-they got washed so say so long to the jockey wheel and its hardware.

Tonight I pulled a jockey wheel off an as yet uninstalled mountain bike rder I was intending to install on an electric bike, and used those parts on the recumbent rder.

Unfortunately, the mountain bike jockey wheel diameter is larger so the distance from the sprocket to the jockey wheel is too small and the chain doesn’t turn smoothly nor shift smoothly, so I’ll need replace it with one of appropriate diameter.

Are all Shimano road bike jockey wheels of the same diameter?
I believe I have a spare Exage rder, would the jockey wheel on the lower component group perform as well? I know I have a couple of spare 30 year old Schwinn Super Sport rders-is that jockey wheel interchangeable?

Is the larger jockey wheel of the mountain bike there to assist in handling the higher wrap of the mountain bike cassette? Is the smaller jockey wheel better for shifting due less torsional loading? Or, are there other design reasons for these differing diameters?

Thanx

 

[JeffWills]

meb wrote:
>
> Are all Shimano road bike jockey wheels of the same diameter?
> I believe I have a spare Exage rder, would the jockey wheel on the
> lower component group perform as well? I know I have a couple of
spare
> 30 year old Schwinn Super Sport rders-is that jockey wheel
> interchangeable?
>

Older derailleur pulleys have 10 teeth, many newer pulleys have 11
teeth, and a couple oddballs have 13 teeth.

The pulley from the Exage is probably identical to the one from the
RSX- Shimano doesn't make that many different pulleys. The ones off of
the Super Sport might work, but they may be wider than the current
pulleys.

Watch out- the upper pulley has a little side-to-side play to aid
shifting. This is called "Centeron" in Shimano-ese. The Centeron pulley
always goes in the upper position.

Larger pulleys reduce friction by a tiny amount, and wrap more chain,
which makes for a less-ungainly-looking wide-range derailleur.

Jeff