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Old 03-14-13, 03:48 AM
  #49  
PMK
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Join Date: May 2008
Location: Royal Palm Beach, Florida
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Bikes: 2006 Co-Motion Roadster (Flat Bars, Discs, Carbon Fork), Some 1/2 bikes and a couple of KTM's

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Originally Posted by Turbotandem View Post
I see that; when in the small 36t ring and high in the cogset going fast in small cogs the difference in cadence is highlighted. I was evaluating what I see as our normal riding gears, not the extremes. I wish I knew how to post a web image. Since I can, I can only implore readers to consider this cadence site, http://www.machars.net/bikecalc.htm and enter my gearing; what I see is that at speeds in the teens while riding in the 36t my shifts are a change in cadence btwn 10 and 12 rpm. However, I would suggest that we are more often in the 36t when climbing and therefore run at cadences of 75-85 so the steps again come down to 10rpm. And when riding at speeds in the 20's while in the 52t ring, the shifts are a change in cadence of consistently 10 rpm. All well within a ridable range, for us.

When confronted with the unlikely avaialbility of a triple di2, it seems worth evaluating if a cadence range of 10 is worth the gains of Di2 in a deep 2x10 configuration. It was a no brainer for me. And I am not saying it is for everyone, but the positions on the forum suggest the configuration should not even be on the table for consideration. Since the recent advent of the 11-36 light weight casette, it has opened up the potential for tandem di2 for a wide swath of riders. Ritterview's comparison of pro bikes might be more accurate to compare to pro mountain bikes where the range of speeds, including climbing, more closeley resemble tandeming range of speeds. On those pro mtn bikes wide range casettes are well suited as I suggest they are for tandeming.

I acknowledge that if you need more than 24" of gear for your climbs, triples are the only way to go. We sure don't grind to death at 24" of develpment until we get over 15% grades which is not often. Or if you need steps of 5 or 6 rpm.
Your comparison to MTB riders does support your choice. Where we live it is for the most part flat. Unfortunately we don't have the means to do a lot of climbing and then descents.

We ride both road and off-road tandems. The road tandem is a pretty tight spaced 12/25, while the mountain tandem is 11/34. Trail hopping and on some of the hard pack double track roads, the MTB tandem lets you feel the gearing jumps. These jumps are more noticeable, since we do ride a tighter spaced road tandem.

Not saying wide jumps don't work, just seems that on road, on the flats, tight spacing easily finds the sweetest rpm to turn.

With the flats often providing long runs in one gear, not sure electric shifting would be a plus.

Our luck, we would get caught in an intense thunderstorm, have lightning strike nearby and end any shifting at all.

PK
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