Newbie triple to double swap

jayess

Hi everyone,

I've bought my first proper bike a few years ago - a 2010 specialized allez sport triple (http://www.specialized.com/us/en/bikes/ ... iple#specs) and have been really happy with it. I'm guessing it's somewhere between 5000 and 7000 miles and only had the chain replaced once. Looking at it now, a lot of the teeth on the chainrings are quite hooked. As they'll need replacing, I'm thinking about changing to a double and (while the sprockets look OK to my untrained eye) changing the cassette for a wider range as well. On the steepest climbs I do still use the lowest gears but don't need such narrow gearing. I tend to run out of gears even on relatively modest descents.

Currently, I have 50/39/30 on the front and 12 - 25 on the back. I'm looking at going to 50/34 with 11 - 30, keeping the same crank length. Looking at Sheldon Brown's calculator this should give me a slightly lower bottom gear but quite a bit higher top gear and obviously wider spacing between gears. Have I got this right? How much of a difference am I likely to feel from it?

Assuming this is a good idea, I'm not sure how easy a switch it will be. I believe I can set it up so that the front mech is activated using the top two positions on my three position shifter. I'm looking at a Sora Double (http://www.ribblecycles.co.uk/sp/road-t ... himchar491) to replace the Sora Tripple. Will this be a straight swap?

Thanks,

J

The Rookie

You'll probably need a new front mech so the ramps on the mech clear the chain when it's on either chainring.

Check the rear mech will work with a 30T, otherwise consider something like the Ultegra 12-27 perhaps.

With a 50:12 you should be doing about 50mph, are you running out of gears or pedalling ability (speed)?

jayess

Thanks for the advice. I've just checked on the RD and it's rated for a max 27T sprocket. New front and rear mech on top of the chainset will make the change more than I'd be willing to spend at the moment. I'll stick with the triple for now.

Interesting that you say that about 50:12 and 50mph. By 35mph I feel like my legs are spinning fast and hardly getting any power down. If there is much of an incline then I go faster by stopping pedalling and tucking in more. The fastest part of my commute is about 40mph (normally 39.5ish) and I really don't think I could spin the cranks anywhere near fast enough to engage the freewheel there. Guess I should be working on faster legs rather than worrying about the gearing...

The Rookie

I suspect you need to work on your legs, I have logged on GPS 46mph on a 46:11 although that was just starting to get to be too fast.

90rpm cadence will see you at 32mph in top, so 120rpm which is relatively normal will see you at over 40mph, single speeders I ride with can manage 160rpm for shortish (upto 5 mins) bursts.....

jayess

I've tried checking my cadence, just by counting revolutions over 15 seconds and multiplying by 4. It seems I've been doing about 80 relaxed, 90 going a bit harder but maintainable and 100 for shorter periods (maybe 10 mins).

I wouldn't normally have gone higher than this. In trying to do so I found I tied quickly and if I went very fast (didn't count but probably only 120 or 130) I was bouncing on the seat and definitely not being efficient. I have a large saddle bag (Topeak Dynapack DX) attached to the seatpost which I think amplified the effect but I'm guess it was poor technique which was the root cause. Keeping up that sort of rpm seems crazy to me at the moment and 160 just seems inhuman!

I'll put some work into improving this - is a computer with a cadence sensor worth getting? Or is it just a case of always spinning slightly faster than is comfortable?

gozzy

You'll barely notice the difference between 50/12 and 50/11, it'll definitely be better to work on technique than throw money at it.