Originally Posted by
Andy Stanton
I went to my LBS yesterday because I noticed a funny sound coming out of the chain when my gears were in the 1 position at the front (left hand shifter) and 7 in the rear (right hand shifter). The mechanic told me that extreme positions (such as 1-7 or 3-1) should be avoided as they can put undue stress on the chain. I wondered if this were true or the mechanic was making an excuse to avoid fixing my chain.
Looking for an answer online I found this on Yahoo answers - does it make sense to you all?
Running your chain across the big chain ring and biggest cog or smallest chain ring and smallest cog will cause extreme chain deflection and this will cause a great deal of drive train noise and this same gear can be found by using your middle ring and one of the middle cogs which gives a much better chain line and reduces stress on the drive train.
Derailleur drives tend to have a good deal of gearing duplication so a 21 speed bike running with a triple and 7 tooth cassette or freewheel probably has 13 usable gears if a standard triple crank and standard cassette and freewheel are used.
Some custom set ups can eliminate a good deal of duplication and more importantly, give you a better chain line for a given gear.
I have a 48/52 half step with a 28 tooth granny mated to a 6 speed block in the rear... the SRAM X5 derailleur has enough take up to handle the very large capacity and will allow shifts to the 52/26 and 28/14 combination but both of these gearings are exact duplicates (the only ones in this set up) and the same gear can be found on my middle chain ring and the 24 tooth cog in the middle which gives a straighter chainline.
A good strategy for clean and quiet shifting is to use the triple so that when you are in the small ring you use your 3 largest cogs, use the 3 smallest cogs with the big chainring, and use the middle chain ring to cover them all... these are your 13 effective gearings and this keeps the chain line as straight as possible will improve efficiency.