When I put on a new cassette, chain, and chainrings recently on my bashguard 2×9, I did the usual big/big wrap plus two pins you recommend in your book, but I then added four more pins to my chain length, in case I want to change to a 36t chainring before this drivetrain wears out. But as it turns out, those extra four pins work awfully well with the 32t front ring, and it makes me wonder if a little extra chain length isn’t advisable with a 2×9 and 2×10.
The kicker is that I use that big/big (32/36 in my case) gear a lot, and I’m not sure having it stretched tight for extended periods is really efficient, or good for the drivetrain. With the four extra links, it looks about right, and that’s still six pins less than I had before, so the chain is still plenty tight. What do you think now that you’ve used yours for a while?
Cross-chaining always is harder on a chain, regardless of its length, and, even though you’re using rings in essentially the middle and inner positions, there is still plenty of cross chaining going on.
People often think that they can use all of the cogs from the middle chainring, and that chainline is not an issue. While on most modern mountain bikes you can use the full range from the middle ring, if you look at the chain line, you will see that there is a lot of chain angle at both extremes of the cogset.
Making the chain angle off as soon as it leaves the chainring or the cog wears the joints quickly, and it is the wear in the joints that causes a chain to “stretch.” It becomes longer simply because the joints become looser. So the cost of using your big-big a lot is increased chain wear and decreased intervals between chain replacement.
I personally do the same and feel the convenience of using the big-big combination is worth having to replace the chain more frequently.
You can get more chain life by running a straight chainline only, making sure that you only use the two gears that give you a chainline parallel to the frame, but what’s the point? The best way to have your chain last forever is to not ride the bike. If instead you choose to ride it because it’s good for your body and for your soul, why not extract all of the benefit it offers you?
The system is designed so that you can ride smoothly in that gear, so it’s a great gear to use.
As for extending the rear derailleur out by using a shorter rather than a longer chain, I’m sure that it does wear the spring in the lower knuckle faster, and it probably wears the jockey wheels faster as well.
On the other hand, the shorter chain reduces chain slap and potential for losing the chain on a bouncy descent when you’re in the inner chainring. If you have no problems with using a longer chain, it does reduce friction in the drivetrain (you can feel it when you spin the cranks backwards), so go ahead and experiment.
Putting links in, of course, is not recommended with today’s narrow 10-speed and 9-speed chains. You’re asking for a broken chain that way, so you might want to wait until your next chain before trying a longer one.
Just make sure you have a good chain checker (I recommend the ProLink, the Rohloff, or the digital Feedback) and use it frequently. You don’t want to fry your cogs and chainrings by letting your chain get too long from having fun in that big-big gear combo.