I realized after getting my 2014 Taro in the spring that long and steep uphill climbs were getting to my 57-year-old knees. I went with the Taro because it was great value and fit my 6'6" frame. So, to save the knees, I went searching for cheap ways to get the gearing a little lower from the 32t it had up front. With only a 104 bcd on the crank arm to work with and limited budget, I had few options with the 1X9 set-up with FSA ISIS BB and cranks. Two things to note: 1) the chain ring on the Taro seemed to be lined up as if it were the outer chain ring on a triple crank (as noted on other forums), which meant room to the inside for a chain ring; 2) the Taro frame doesn't allow a double chain ring (really it doesn't allow a front derailleur).
First option, get the RaceFace 30t ring that works with 104 bcd. I didn't think it would give enough of a lower gear. I wanted something lower. If I could get to a 28t front and combine with the current 36t rear, I would have the equivalent of a 32t front and a 42t rear (what many are going to on their higher end 1X10/11).
Second idea. This led to trying a triple and just using the inner chain ring. Problem: the crank arm was too wide; it just got pushed against the BB and then did not spin. I didn't want to get into a new BB just yet.
Third idea was drill and tap the crank arm at 64 bcd. And that's what my son and I did. The FSA crank is actually set up for two chain rings, but only drilled for the one. When you pull the crank arm you will see flat spots for drilling at 64 bcd. We created a template to center the 28t chain ring (from Blackspire) on the crank arm; we used a punch tool to mark the precise spots to drill, drilled out the holes using the right size drill (1/4 inch I believe) and drill press, then used two taps to create the threads. We used both a regular tap and followed it with a bottom tap to get the threads as close to the bottom of the hole as possible. We also cut off the tabs on the crank arm that held the original chain ring to make the unit nice and simple looking.
Two things to note: We used American standard sizes for the taps and bolt because they were easier to find, and we ground down the tops of the rounded stainless steel bolts to save weight (haha just kidding).
After a couple of test rides, everything is working well. The front ring is lined up better than the original set up and I'm not getting aching knees after rides. Bonus is that I'm actually using my higher gears getting to my local riding spot near Seattle.
All in all, the cost was $14 for both taps and $2 for the four SS bolts. The taps are hardly worn since they were only used for aluminum. Hope this helps someone in a similar situation.
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