Tandem Cycling - Cannondale Hollowgram SL BB30 tandem crankset

I noted on the tandem weight thread (http://www.bikeforums.net/showthread.php/390272-What-s-your-tandem-weigh?p=14821138&viewfull=1#post14821138) that Calfee had posted on FB an album of pics of a new Dragonfly 24.12 lb (http://www.facebook.com/media/set/?set=a.448474638529872.99085.127955283915144&type=1), featuring a BB30 Cannondale Hollowgram SL crankset (http://www.cannondale.com/gear/component/2012-sl-road-crankset-39-53-21717).


http://sphotos-b.xx.fbcdn.net/hphotos-ash4/391752_448474725196530_436512363_n.jpg
BB30 cranks. What BB30 eccentric is available?

http://sphotos-a.xx.fbcdn.net/hphotos-ash3/564639_448477555196247_155018127_n.jpg
Is that an eccentric being used for a stoker's crank BB shell? Note the dremel work on the chainstay to provide clearance for the Gates sync pulley. I'll bet this clearance issue was discovered after the crank install was attempted!

http://sphotos-a.xx.fbcdn.net/hphotos-snc6/250174_448474735196529_1185554559_n.jpg
Stoker's crank left side.

http://sphotos-b.xx.fbcdn.net/hphotos-ash3/545748_448474681863201_243106302_n.jpg
Cannondale Hollowgram SL BB30 crank in double (no triple spider available for SL cranks).


How is it that a C'dale Hollowgram SL crankset can be used on a tandem? This is apparently a crossover. The design of the SL is more akin to an ISIS or square taper crank, with both the left and right side pedals and spider removable from the bottom bracket.

A few points:


Calfee has demonstrated that a Cannondale SL crank can be adopted for a tandem.
Calfee has apparently sourced a BB30 eccentric (Co-Motion has one (http://www.co-motion.com/index.php/blog/detail/new_model_year), apparently).
It almost looks like the BB30 eccentric is used as the stoker's crank BB shell.
There is no triple Cannondale road (130/74 BCD) spider. Cannondale or someone would need produce a triple spider to make the C'dale SL a viable tandem crankset option.
Sources state that the 2013 Cannondale RT3 tandem will be BB30. Might Cannondale be the source of the BB30 eccentric?
The Cannondale SL crank is a quite light, and well regarded high-end crank. Having a new tandem crank option is a boon.
The BB30 standard has mixed reviews. But it is potentially well suited for tandems as the spindle diameter is larger.




http://carytownbicyclecompany.com/wp-content/uploads/2011/12/cannondale_2009_crank.jpg http://media.cannondale.com/media/catalog/product/cache/3/image/370x/9df78eab33525d08d6e5fb8d27136e95/c/_/c_2011_ka014_blk_3.jpg
http://farm3.static.flickr.com/2718/4364969785_b105fc1bbb.jpg
http://2.bp.blogspot.com/-ccD7-VsgfL0/Tji7Qds61EI/AAAAAAAAAW0/-vUCTXoANpc/s1600/3.jpg

How is it that a C'dale Hollowgram SL crankset can be used on a tandem? This is apparently a crossover. The design of the SL is more akin to an ISIS or square taper crank, with both the left and right side pedals and spider removable from the bottom bracket.

A few points:


Calfee has demonstrated that a Cannondale SL crank can be adopted for a tandem.
Calfee has apparently sourced a BB30 eccentric (Co-Motion has one (http://www.co-motion.com/index.php/blog/detail/new_model_year), apparently).
It almost looks like the BB30 eccentric is used as the stoker's crank BB shell.
There is no triple Cannondale road (130/74 BCD) spider. Cannondale or someone would need produce a triple spider to make the C'dale SL a viable tandem crankset option.
Sources state that the 2013 Cannondale RT3 tandem will be BB30. Might Cannondale be the source of the BB30 eccentric?
The Cannondale SL crank is a quite light, and well regarded high-end crank. Having a new tandem crank option is a boon.
The BB30 standard has mixed reviews. But it is potentially well suited for tandems as the spindle diameter is larger.



I have seen several of these apart on single bikes. Pretty much this is ISIS on steroids. The rumored downfall of ISIS was the small bearings. This overcomes that plus offers a large spindle.

Personally, I like a proper spline design over square tapers. Done correctly, working on the bike is easy, just torque and go. Systems with the integrate shaft on the right side arm have been known to have issues also. This in my opinion favors a three piece crank, or a proper design left side stoker crank arm attachment that stays tight with no Loctite.

The downside of BB30 from my experience with it relates to how well the frame manufacturer machines the BB shell AND how the bike is fabricated. I have not seen how Co-Motion builds their BB30 frame. I just question the ability to machine the BB shell, the snap ring grooves, then weld it, heatreat, and retain a precision bore without post heatreat. A composite frame could easily accept any machined part and relies solely on the adhesive bonding.

BB30 is neat, but I'm not sure it is the final answer. The best may have already been here, Shimano Octalink series with the roller bearing bottom brackets. Small, compact, light, low drag, brutally tough and last a long time.

PK

The Calfee is very nice, but you should mention that Cannondale cranks are not exactly cheap. Then using a secondary eccentric and dremeling the chainstay seems odd as the main thing about these cranks is that they are light and stiff.

THinking about exotic standard, BB30 IMHO is not the right standard for a tandem. To start with 50% of installations creak horribly and require regular dosages of loctite, which is why BB30PF was invented. This uses a larger diameter bearing seat to allow the bearing to be held by a plastic seat to stop creaks.

Secondly the problem with BB30 is that it's solving the wrong problem for a tandem. It allows a stiffer bb axle, which nobody really needed. Instead the issue on the tandem is frame torsional stiffness, in part limited by the dimensions of the keel tube, which is in turn limited by the dimensions of the bb shell and chainring clearance requirements. Here using a wider shell would allow a more efficient structure (untill the keel tube or eccentric and frame is wide enought o interfere with the chainrings). At 60mm the BB30 shell is narrower than a standard 68mm road shell so it's worse not better.

Instead I would also take a close look at BB86, BB90 and BB Right (Left) standards - if clearance for an eccentric at the front is not possible using BB90, then a BBLeft installation should still be possible (it's basically the same as BB30 on the drive side, then on the non drive side bearing sits further out).

The Calfee is very nice, but you should mention that Cannondale cranks are not exactly cheap. Then using a secondary eccentric and dremeling the chainstay seems odd as the main thing about these cranks is that they are light and stiff.

THinking about exotic standard, BB30 IMHO is not the right standard for a tandem. To start with 50% of installations creak horribly and require regular dosages of loctite, which is why BB30PF was invented. This uses a larger diameter bearing seat to allow the bearing to be held by a plastic seat to stop creaks.

Could the creaking be caused by lack of manufacturing accuracy? I remember a dealer bragging that with this new design he could slide new bearings in and out with his fingers. As I understand it a good press fit shouldn't creak. Traditional press fit rear hub bearings, crank bearings and headsets rarely creak. If builders were not trying to trim costs of manufacturing by allowing variances in BB internal diameter size shouldn't the design work well? It appears that rather than spec accurate IDs they have come up with the idea of a plastic insert that will need to be replaced in the future.



Secondly the problem with BB30 is that it's solving the wrong problem for a tandem. It allows a stiffer bb axle, which nobody really needed. Instead the issue on the tandem is frame torsional stiffness, in part limited by the dimensions of the keel tube, which is in turn limited by the dimensions of the bb shell and chainring clearance requirements. Here using a wider shell would allow a more efficient structure (untill the keel tube or eccentric and frame is wide enought o interfere with the chainrings). At 60mm the BB30 shell is narrower than a standard 68mm road shell so it's worse not better.


Hmmmm are we saying a 73mm BB is slightly better than a 68mm in this respect?

As for mounting a triple chainring to the Hollowgram cranks, then it should be no problem to just use Cannondale's 130mm BCD spider plus a Tripleizer ring in place of the inner ring (I believe TA Specialites still makes them). You'd then have a 74mm BCD for the inner ring.

This would basically the same as the setup on the Shimano R603 tandem / Ultegra 6703 cranks (except that the middle ring on those gives a 92mm BCD for the inner). You'd have to check that there is frame clearance for the inner ring (probably no problem with such a small ring, and you could go with something smaller than a 30 tooth if that helps) and you may be limited to using only the innermost half of the cassette with the small ring due to chainline / cross-chaining, but that is all you need the small ring for anyway.

Using eccentric BBs should remove part of the problem with BB30. Most problems with BB30 are due to the BB shell in some frames not being quite perfect, so the bearings don't fit as well as they need to. The tolerance should be easier to achieve inside an eccentric BB, and if it isn't right then you can just swap the eccentric out for another one. This is why some manufacturers are now using the PressFit 30 instead of the pure BB30 (and Specialized uses the similar OSBB system on their S-Works road frames), so that the bearings don't press directly into the frame (it's the same reason why Chris King criticized the design of integrated headsets for so long). This may therefore be why they use a second eccentric for the stoker's BB, although a PressFit 30 would surely have been a lighter solution.

My personal opinion is that if Shimano's 24mm axles are stiff enough for Mark Cavendish's and Bradley Wiggin's bikes (they, and the rest of Team Sky, were normally using Dura Ace 7800 cranks), then there is no need for me, or almost any other tandem teams, to need crank axles any stiffer than that. I do believe that the hollow 24mm axles are stiffer than the old square taper setups, which is why I wouldn't consider square taper axle cranks for our tandem. Our current solution is to use a pair of Shimano 105, 5603, single-bike cranks on the tandem - using only the middle and inner rings (42-26) for the drive chain, and the timing ring in the outer position. This gives us a broader range of crank lengths to choose from, so we can have our preferred 165mm cranks front and rear. Someone recently posted a thread here showing how you can have this kind of setup while still keeping an outer chainring as well as a timing ring outside of that. With all these options, then there really is no need for special tandem cranksets.

Could the creaking be caused by lack of manufacturing accuracy? ?

Yes, supposedly. On aluminium frames I can understand it as the shell can be distorted from welding. But I find it hard to understand on carbon frames where a precisely machined tube can be bonded in. But in my experience more likely because the bored mechanic attempts to wreck the shell by pressing bearings in skewed, perhaps because the shell needs a chamfer to press the bearing in.


Hmmmm are we saying a 73mm BB is slightly better than a 68mm in this respect?

If you like wider q-factor cranksets and the wider shell is used to allow a 5mm wider keel tube, then yes. Stiffness is related to the cube of diameter, so an extra 5mm on a 60mm tube is significant.


As for mounting a triple chainring to the Hollowgram cranks...

Or you could use an Cannondale MTB triple spider. The system is modular so you can just swap it. But admittedly the rings might be a bit small for some tastes.

Completely agree re. 24mm spindles being stiff enough. But let's see a picture of your cranks Chris_W - sounds likd a good solution.

They should have used the new one:

277927

They should have used the new one:

277927

Yes, the Hollowgram SI SL2 (http://www.bikeradar.com/road/news/article/cannondale-expand-hollowgram-crank-offerings-34365/) is interesting, with its integrated spider and chainrings. It is a forged piece, I believe by Praxis. To be widely applicable to tandems, what the C'dale SL needs is a road triple version. I don't know whether a triple is more likely to originate from a new conventional spider, or a triple version of the integrated chainrings. Or whether a triple is a forlorn hope.

http://cdn.mos.bikeradar.com/images/news/2012/06/23/1340408382273-sb7bdnzdb4wz-670-75.jpg
The OPI chainring set will fit any generation Hollowgram crankset

http://cdn.mos.bikeradar.com/images/news/2012/06/23/1340408382267-eb6geoe1my4q-800-75.jpg
The OPI rings incorporate shift ramps on some of the 10 spider arms



Edit:
Available at Canndondale: $325
Cannondale SpideRing Road Chainring Standard 53/39T - KP244 (http://www.cannondaleexperts.com/Cannondale-SpideRing-Road-Chainring-Standard-5339T--KP244_p_1749.html)