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Old 03-12-13, 06:09 AM
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Location: Ft Worth, TX
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Bikes: Custom 650B tandem by Bob Brown, 650B tandem converted from Santana Arriva, Santana Noventa, Boulder Bicycle 700C, Gunnar Sport

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Originally Posted by Turbotandem View Post
If Ritterview or Waynesulak could put the gearing in terms of cadence I think it would be more clear. What I get is this. At a given speed, let's say 18mph at a cadence of 105, right at the point you want to shift up. On the waynesulak gearing your cadence drops 10 counts to 95 rpm as you shift in to the next higher gear. On a Di2 gearing, like mine, you drop 12 counts to 93rpm. I have trouble believing 2 counts rpm difference is really making or breaking any team's power. Ritterviews charts are unlikely to distinguish 2 points of Rpm. Seems like a lot of analysis leading to the wrong conclusion, that you must have those couple points rpm. If 2rpm really broke the bank, one thing we do is this: 1) shift up, 2) stand into the pedals for a couple strokes, 3) sit and whala you are in your sweet spot cadence. If you can't hold on, it's more likely because the extra mph are just out of reach for your power. We've been there! We love to chase down singles, especially uphill, so we've been thru every scenario when the target single is just a little too good. I've been known to push time trial heart rates in those attempts.

I certainly concur with Akexpress, that our riding is much more fluid with the Di2 and I would never go back. Although I confess I do have the braze-on to the frame as a fall back should Di2 ever fall off the planet. I certainly don't make call-outs for gear changes lest my stoker buck. The shifts are so smooth she most often does not know we have shifted. You're over stating it Ritterview! I certainly advice teams that ask me, that the di2 is fabulous. Front auto-trim not to be overlooked in itself is a great advantage. I did recently learn that the SRAM Red 2013 double front der. apparently swivels as it shift and maybe finally solved the trimming needed on all other FD's. But still, that's a double.

Another factor we considered is that going to a 2x10 drivetrain was requisite in upgrading our tandem to a right side inboard belt. The gains in performance from that Paketa advancement was well worth the change to 2x10, while giving teams the option to go Di2 in the same upgrade. Going from a paketa left side to right side belt, I've measured far in excess of 5% improvement on things like our standard hill climbs every month, but I cut that figure by three and suggest the drivetrain adds 5% to our performance. That is certainly more than the potential reduction in our power when we drop our cadence by 2 more rpm than a tighter geared tandem. So my interst in di2 is compounded when compared to a team considering replacing their current drive train. Still, I'd make that recommendation by sharing my experience with Di2 here.
I think we have a different opinion of the change in cadence required by going from a 12-25 cassette to a 11-34 cassette. To put my example in terms of cadence lets look at an example:

We are in the 13 tooth cog under full effort, cadence 100 and the road rises slightly, our cadence drops to 95 so we would like to shift down one gear. On a 12-25 cassette we shift from the 13 to the 14 cog for a change of 1/13 or 7.69%. At the instant of the shift our cadence goes from 95 to 102 (95*1.0769). If we are running a 11-34 cassette then our shift is from the 13 cog to the 15 cog for a change of 2/13 or 15.38%. This is roughly twice the change in cadence at the same speed. The change of 15.38% results in a cadence of 110 (95*1.1538 rounded). For us that difference in instant cadence change 95-102 vs 95-110 makes it difficult. Form my point of view there is twice the increase in cadence 7 rpm vs 15rpm and that is over our tolerance for change. Our comfort level is about 13% change in cadence. More than that is a problem and we really like it lower than 12% when possible. This keeps the cadence range generally 100-90 with some instances of 105 and 85 when the terrain wind speed changes suddenly.

As a side note here it is the percentage change and not the tooth count that matters. A 3 tooth change from 25 to 28 is OK because it is only a 12% change( 3/25) vs a 2 tooth jump in the example above which is a 15.4% change.

Some of the jumps on the 11-34 are similiar to a 12-25 cassette so are OK and if I only used part of the cassette then it might be more workable. My style of gear shifting is to work my way up and down the entire cassette and so I cross chain more than some riders. The terrain we ride has lots of quick steep ups and down with sudden and constant changes in gradient. If we road more engineered roads with constant gradients then the requirements of our gearing would also be different.

Otherwise I am in TOTAL AGREEMENT with what Ritterview said.

Last edited by waynesulak; 03-12-13 at 06:25 AM.
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