WTB: Wide range double crankset

[Joe M.]

I'm building a Sam and setting it up with a 12-32 8-speed cassette. I have a Sugino AT 24/34/46 that won't fit, even with a 122.5mm BB! It fits as a double but I want more granny gearing!

Does anyone have a wide range double that they'd be willing to part with. Ideally it would be 26/42. A Rene Herse or Specialties TA Pro 5 Vis would be the bees knees!

Thanks,

Joe from Los Angeles

[Ray Varella]

What crank length Joe?

The AT  may need a 127mm bb with a +5mm to the drive side. 

There is currently a cup and cone unit on eBay. 

Those ATs are pretty nice cranks, it may be worth sourcing the correct bb. 

Ray

[Bob Lovejoy]

I have had great luck using the IRD QB-95 BB (127.5) with the AT cranks, at times using a drive side spacer (sorry I do remember but I will guess at 3-5mm for the spacer).

http://boulderbicycle.bike/IRD-JIS-Bottom-Bracket-QB-95-lots-of-sizes-best-bb-option-REGARDLESS-of-cost.html

The AT's are great cranks if you stay with a triple... and the BB cost is going to be less than a different crankset.

Bob

Galesburg, IL

[Joe M.]

Crank length 170mm. The AT's are really nice. I'm afraid that going with that wide of a BB may not feel right. Can you folks with experience with the AT shed some light on this? I'm 5'10 with a PBH of 85. I imagine if I was taller I may not notice the wide Q. I don't have experience with anything that wide. Thanks!

[Bob Lovejoy]

I am not expert enough to explain where the differences come from, but different cranks use different bb spindle lengths to get the same configuration.  The Sugino AT's just happen to use a relatively long spindle but once installed they clear the chainstays exactly as they should.  That said, being a triple, the Q factor is going to be more than a double.

Sheldon's BB chart is here:  https://www.sheldonbrown.com/bbsize.html  (scroll down to the Sugino section for the Sugino AT)

I wish there were more Q factors filled in but hopefully there is enough info there to do some comparisons.

If you do go with a double, the IRD compact double (46/30) might be on your list... I have that on a Hilsen and it works great.  I am sure there are other great options as well.

http://boulderbicycle.bike/IRD-Compact-Crank-46-30-assorted-lengths.html

Hopefully other AT users (or ??) will chime in with more knowledge and experience...

Bob

[Patrick Moore]

Bob; It all comes down to arm flare. I got 160 mm Q with a Sugino XD2 and 113 mm spindle; I got a 160 mm Q with a TA Pro 5 Vis and a custom 145 mm spindle.

[Joe M.]

Ok thanks for everyone's input this is helpful. I'll look into making these work. 

But if anyone does have a wide range double they'd part with, I'd still be interested in possibly purchasing it.

[Ray Varella]

Joe,

I just measured the Sugino AT on a 127mm spindle. I get 153mm without cinching the bolts down. This is just a hand press fit with a gentle tap to make sure they are on straight. 

Since you want a wide range double, I’m assuming you plan on using the inner ring. 

By eliminating the inner ring and running a compact double that would allow running a narrower Q

I don’t think most modern cranks will improve on that for you. 

Hope that helps 

Ray

[Garth]

I also ran a AT triple with a UN72 127mm bb. I don't recall needing a spacer as it was on my '83 Stumpjumper that had excellent ring clearance, no bowed stays. It was perfectly centered. The tread width was still very low compared to anything "modern". I still have it around so maybe later I'll measure it uninstalled, a hand press as Ray did. In riding the extra length spindle made no difference to me. In a blind test I would not be able to tell a difference. Years later I'm riding a 170mm tread width triple and even that makes no difference to me. 

[Matthew P]

I've been going through this with a Toyo Atlantis with curved chainstays, which "get wider sooner" (closer to the BB) than straight chainstays.
That requires a wider BB/-spindle unless there is a straight section on the chainstays before the curve, as on my ~'84 StumpJumper.

I am also pretty convinced that, all else equal, a double requires a wider BB/-spindle than a triple because the smallest/innermost ring on the triple is smaller than that on the double, hence, it can fit it closer. You save Q factor (FWIW) with a double in that there are only 2 rings instead of the triple's 3. Stating the obvious JIC.
This "innermost ring" effect is the same thing as the 1x issue of the bigger the ring, the wider out it needs to go.

So, can that triple really not fit? If not, the solution to this problem is not a double; that will just require an even wider BB/-spindle.
Note: VO and RH doubles can only go down to about 28t I think, which won't fit into a smaller hole than your 24t.
And you can't just put a smaller inner ring on your triple. I guess 22t would be the smallest possible.

I'm a little stumped and wish I could get my eyes and hands on it. But you could try a spacer on the drive side but it does put that side out wider.
Another option: shave the bottom-inside of your crank arms to clear your chainstays. There is a Bicycle Quarterly article about this.

Or find a double crankset that accommodates a tiny (24t or less) inner ring - white industries? - get as wide a BB/-spindle as you need, but your feet won't be as wide as with a triple.

Is it possible you're threading in the drive side too far and the NDS not enough? There seems to be some "wiggle room" with BBs in this sense. There isn't an alignment for dead center. Group, is it ok to play with that? Is this not what a spacer does.
Oh, and does 68 mm vs. 73 mm BB come into play here?

Crank arm bow is new to me; makes sense; glad to pick that up in this thread.

-Matthew P
fiddling with the BB on the Toyo Atlantis for way too long, but intermittently. i'm really just lagging
oddly its those curves that i like so much. all love requires work :)
in San Diego, CA ( Kumeyaay ) 

[Nick Payne]

The AT with a 127mm BB is going to have pretty much the same with at the pedal eyes as, for example, an XD with a 107mm BB. The reason for that is that the XD arms bow out about 10mm each from BB end to pedal end, whereas the AT don't bow out at all. The only possible problem with the AT might be if you ride considerably toes-out, in which case you might have a problem with your heels brushing the cranks on each revolution.

Nick