Notes on installing 33 TA Chainring and Custom 11x27 10 speed cassette
I'm sorry if I'm losing some of you by discussing bicycle technical issues rather than software. I'm still working in software, but my time has been sucked down by a project which I'm not in a good position to discuss. I think it will be all positive, but if you aren't interested in bikes then you might want to wait until my next entry where I both praise and bash Microsoft, which is one of my favorite pastimes. Until then you'll have to read about bike gearing.
Coming from mountain biking I like to turn a high cadence when climbing. Mashing pedals doesn't work on technical climbs. My new road bike came with compact gearing with a low of 36x23. While many riders claim that should be plenty of gearing, I personally don't think it is sufficient for recreational riders interested in climbs in Marin or the Sierra. I confirmed this over the weekend. Many advanced riders were running wide gear ratios.
When my parents bought my first Bianchi 20 years ago (thanks Dad) it had a 5 speed freewheel and friction shifting. The steps between gears were pretty wide out of necessity. The only riders who had single step freewheels were road racers and my guess is even some of them could have used a wider range. Today's road bikes have 10 speed rear cassettes. Thats a lot of gears, which makes it possible for mere mortals to run tight gear ratios, but for my current level of fitness I wanted to take advantage of the large number gears to run a wide range with only two front chainrings. Again I like to spin a high cadence when climbing.
My first upgrade was to move from an 11-23 Shimano Ultegra cassette to a 12-27 with the stock 50x36 compact crankset. While I gained a couple lower gears, I lost the 11 at the high end. That didn't seem like a big deal, but I can spin the 50x12 out on a moderate downhill. So my plan was to combine my two cassettes to build a custom 11-27 10 speed cassette. That would provide the full range of gearing possible with a 10 speed, giving up only a few close gears in the middle of the range.
Last night I installed a range of 11-12-13-14-15-17-19-21-24-27. I removed the 16 from the 12-27 and installed the 11 from the 11-23. Gearing Nirvana! Or so I thought. It turns out, while on the outer chainring, the derailleur has a hard time ramping from 15 to 17. The shift requires a lot of coaxing, and doesn't provide the crisp action that is expected from a high end road group. Oddly it works fine on the inner chainring. The stock 10 speed cassettes available from Shimano all have a one cog spacing up until the 17.
Harris Cyclery has the best selection of gearing options I've found anywhere, but all the custom cassettes are 9 speeds. My limited experience here suggests that the trade off of running a 10 speed cassette is that it requires a tighter ratio to shift well. Tight ratios are not common on mountain bikes, which would explain the absence of a 10 speed mountain group. With that info, I would have probably preferred a proven 9 speed setup, but it isn't available on any new groups available from Shimano above the 105 group. Hmm. Looks like I'm stuck with 12-27.
But that was my first upgrade. My second was to reduce the inner chainring from the stock 36. After climbing 2500' on Mt. Tam, I realized I could use another bail out gear. The common compact setup is 50x34 up front with 110 bolt spacing. After reviewing the tons of options at Harris I opted for a 33 which is an uncommon size and the smallest available for a compact crank. The TA chainrings are expensive, but are a work of alloy machining art. But here's the dig. It doesn't fit my fancy carbon TruVativ crank. The ring is so small that the chain rides on the spider above the mounting holes. I have a few options here. Leave it how it is. File down my new $200 crank. Switch back to the 36. Or eat the cost and buy a 34. I'm going to have to drop Harris an e-mail to see what they say about this. TruVativ makes some of the most popular compact cranks (second to FSA) and are a Trek OEM. I can't be the only one with this problem. I am also skirting between too short of chain and too long. If Google sends you here, I wouldn't push your luck with the 33. It isn't worth the hassle for one tooth. Get the 34.