I have finally accomplished a long sought after goal of outfitting my bike with the "perfect drivetrain"...at least in my opinion it's perfect. Here's some background in my quest. I had previously worked in a shop for almost three years. After many company outings to demo models we were selling and countless hours building and servicing many bikes both new and old, I came to a logical conclusion: I really dislike 9-speed drivetrains on mountain bikes...or at least on my mountainbike. But I tend to be a perfectionist, so I'm sure that many of you get by just fine with 9-speed.
Here's why: in my OPINION, 9-speed has too many inherent problems for practical use in mountain bikes, especially the current breed of 5-6" FS bikes like the one I currently ride. The problems are the following.
(1) The cassette cog spacing is narrow enough that the attention to proper adjustment is much higher than in 8-speed. It's like that Porsche in your neighbor's garage that runs really great from time to time but he's always under the hood trying to keep it in tune. With long travel FS bikes the cable system is put through a lot of movement and stress. The smaller the tolerances for proper function the harder it is to keep the shifting operating properly.
(2) The narrower cog spacing is such that a narrower chain is required vs. 8-speed. A narrower chain is an inherently weaker link in the system.
(3) This third problem is one hundred percent my opinion but I do feel it holds some merit. The industry has forced the consumers to upgrade to a system that has brought few tangible positive traits and several glaring negative ones. List any possible positive trait of a 9-speed drivetrain and I feel that you could achieve the same or better with 8-speed. 9-speed is a fix for a problem that doesn't exist. Then they go and stop making high-end 8-speed stuff knowing that the consumers that buy the XT, XTR and XO level product--the consumers that are most likely to continually upgrade their bikes--will have no where to turn but 9-speed.
On the other hand I should be fair and say that there are a few things I like about 9-speed. You can get a 34t cog on the cassette and...um...well...that's all I've got. Many honest people who have had long-term experience with both 8-speed and 9-speed drivetrains will agree with my observations and can probably add some details that I have omitted.
OK, enough with the ranting. So there I was recently, laboring up a questionably steep climb on my first day back on the bike after several months (don't ask) and I'm wishing I had that 34t cog on my cassette (I just keep getting older and for some reason it's harder to maintain fitness than it was ten years ago). I get back from the ride, sit down at the computer and run across the answer to the final glaring omission in my perfect drivetrain: a way to achieve a granny-gear combo even better than the 22-34 9-speed standard, with my 12-32 8-speed cassette. On Mountain Bike Action's website was a small write-up on this company called Action Tec who is making a 20t chainring for the 64X104mm four bolt cranks that are now the industry standard. Google "gear inch calculator" and you will find that a 20-32 combo is just a bit lower than the 22-34 standard of 9-speed.
Here's my drivetrain set-up. I am currently running a 12-32 8sp XTR cassette (the one with three ti-cogs) available at Cambria, XT 8sp shifters available from various sources, XT 751 9sp crankset (the first model with the Shimano splined BB), and a 20 tooth granny chainring available from Action Tec!
The trick to running the 20 tooth chainring on the now standard 64mm 4-bolt crankset is that in my particular case I had to use a dremel and a file to remove a bit of metal from the crankarm spider to make it work.
Let's see if I can explain this simply: The spider has four lugs where the small chainring actually attaches. The chain will barely touch the chainring bolts while wrapped around the 20t chainring in an ideal situation. The trouble was with the lugs that the small chainring attaches to being slightly larger in diameter than the chainring bolt heads. So, the chain was hitting the lugs and not making full contact with the chainring in that particular chainring valley. I simply used a dremel and a file to remove just enough material from the lugs so that the chain rested more securely in the valleys of the 20t chainring. A tip is to screw the chainring bolt fully into the lug before performing this surgery. With a steel or ti chainring bolt there is little chance of damaging the bolt and it will serve as a guide for approximately how much material to remove (do not use aluminum bolts). You only need to remove enough material around the top radius of the lug to allow the chain to fully seat on the chainring.
Using the 20-32 combo is a huge upgrade in climbing performance vs. the 22-32. So, now I live in a perfect world. I have bullet-proof 8sp shifting, the light weight XTR ti cassette, and a 20-32 granny to more than match the standard 22-34 9sp climbing ability!
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Thread: Drivetrain Perfection...
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