Subject: Re: Big ring / medium or Middle ring/small? Posted by: Robert on December 10, 2001 at 04:26:41: In Reply to: Big ring / medium or Middle ring/small? posted by Scot on December 09, 2001 at 09:58:30:

Message: >I have been doing a lot of riding lately on a relativly flat packed dirt path, so I am cruising along between 12-14 mph, which for me is a good pace. >I have noticed that its about the same gear ratio if I run the middle ring and the two smallest cogs in back OR if I use the big ring and the middle cog and maybe one slightly bigger. >I know not to run extreme gear combinations (big / big or small/small) but the chainline appears about equivalent for both and I'm not getting any differnt front detrailer noise with either setting (by the way, how to you trim out that last bit of front derailer noise with Shimano shifters?) >Any thoughts? >SGM It sounds like both those combinations are good, that is not too much side-to-side variation, but there is one advantage to bigger 'rings/gears. If you did the math on two 'equivalent' gear sets, you would find that the bigger the gears the less tension on the chain. For a quick example comparing a 52-16 to a 42-13 (which are nearly equal gear ratios), gives you this for stress factors. Say that there is 100 pounds of force entering the chain in the 52 setup. The equivalent pressure at the rear wheel (thus the same forward drive) in the 42 gives 124 pounds of force on the chain. That's a 25% increase in chain stress, which could be said to give a chain life 25% shorter than the 52 selection. Also the chainrings and cassette cogs would wear 25% faster in the 42 vs. 52. Another reason for selecting which 'ring to be in depends on what and how you ride. Where this comes in is say you are going over hilly terrain where you can climb the hills in the middle 'ring and the big 'ring (with the same gear at the wheel) is great for the downhills. When going down you would want to shift to the big 'ring when you start spinning out in the middle, rather than up-shift in the rear to keep up (for a while). When you hit the bottom you'd drop into the middle and you'd be all set for the next climb. Depending on the situation, shifting just once for changes like this can be better for the quickness of getting where you need to be (in the gears), and ease of shifting once instead of 6 times (or more). The ease of shifting once vs. 6 times can make a big difference when you'r off road and hitting rough terrain. The more you ride the more you will find out what you need. As for the other question, Jim has it right about there not being much adjustment with many Shimano 'Rapid Fire' shifters (from your trouble I'm assuming that's what you have). If you want to be able to fine adjust the front derailleur there are two thing you can do. Either find a thumb shifer for the front (they are friction and can be adjusted as much as you want) or get Grip Shift shifters. Grip Shifts have fine steps for the front, not just three selections like some Shimano units, so with them you can find a setting that works well. Other than that get a Walkman and crank the tunes!