What do these numbers mean for a rear derailleur

[rastoma]

Hello again,

Another newbie question that I couldn't find in a search.

Looking at a rear derailleur this time.

What do these numbers mean?

Max Cog: 30
Wrap: 40
Speed 5,6,7

I assume on speed, it's saying on the rear sprockets, it supports 5, 6 or 7 sprockets? That's not the 'speeds' of the bike itself is it?

[RobAR]

Hi Rastoma. Yes, the 5, 6 or 7 refers to the number of rear cogs. It's not as big a deal as most manufacturers make it out to be BUT - as we gained numbers of rear cogs, chains (and derailleurs) got narrower. Any 5, 6 or 7 should be fine for even up to 8.

The 'max cog' refers to the largest number of teeth on the large cog that the drlr was designed to handle. For example, an 11-30 stack.

Chain Wrap is the capacity that the drlr has for keeping the chain from going slack between extremes. (Large chainring - small chainring) + (large rear cog - small rear cog) = chain wrap capacity.

For what it's worth, (not being condescending, just informing) hardly anyone who is into bikes will use terms like "21 speed" or "28 speed" anymore. They will, of course, know what you mean. A 21 is a 7 spd with a triple up front. A 18 would be a 9 spd with a double.

Welcome to BT!
Rob

[nfmisso]

(11-23-2011, 07:01 PM)RobAR Wrote:  ........
A 18 would be a 9 spd with a double.
........

Or a 3 x 6

My World Tourist and Sierra Sport are both 2 x 7, and our T50 is currently 3 x 7, and in a month or so will be 3 x 9.