Bicycle Mechanics - Why the difference in derailleur pulleys?

This morning I broke my bike down to give a well needed clean before a big climb tomorrow. I pulled off the derailleur pulleys and while cleaning found the they are different.

Can someone explain why the g-pulley has a metal glide shaft and the tension pulley slips on plastic.

Is there a version that uses sealed bearings to reduce the friction that I am feeling - or am I missing the point?

Thanks
R

Sorry - its a 105 component .. RD 5501

R

Some shimaNO der's will stepup to ceramic bushings in the pulleys to lessen the friction. However there are after market sealed bearing pulleys. FYI Suntour XC Pro used sealed bearing pulleys.

Originally posted by Raedeke
Can someone explain why the g-pulley has a metal glide shaft and the tension pulley slips on plastic.
R

Because the g-pulley has to center the chain over a cog, it gets more use laterally, hence the use of a steel shaft. Weight can be shaved in the tension pulley.

Fwiw I tried the Performance sealed bearing pulleys a few yrs ago and found them trash. The chinese sealed bearings appeared to have been assembled by 10yr olds on the beach and were much worse than the OEM sleeve bearings. The OEM bearings have a very long life span if occasional clean and lube is done. Steve

Lateral slop in the jockey pulley is the technological paradigm shift which made indexed shifting possible. Indexed systems depend on the chain's ability to pull the jockey pulley slightly to one side or the other, as necessary to form a straight line to the selected cog. Back in the days when men were men and bikes had friction shifting :), the cyclist had to adjust the derailleur cage position more precisely than an indexed system can.