Wednesday, September 12, 2012

38/26, 38/24 whatever it takes...

As much as I prefer Shimano's mountain bike components, they sure make it hard to supply a customer with exactly the desired component.  Take the crankset, for example.  Years ago, crank and chainrings were easily modifiable.  Don't like the stock 26/36/46 ring set up?  Easy, replace the ring you want to change with any by Specialized or Sugino (my all time favorite cranks and rings, by the way).  And without ramps and pins, they shifted great.  However, as six became seven which became eight ... and that became ten, chains got skinnier and shifting suffered so chainrings had to be profiled and ramps and pins were added to move the chain between rings.  

And even that was no problem because you use an appropriate width chain to match how many gears you have and it all works.  This brings me to my frustration with Shimano.  Recently, I built a really nice bike for a customer - custom frame, hand built wheels, Shimano XT...a real dream bike for someone who had been through other bikes and now wanted to treat himself to something really special.  We decided to go with an XT crankset with 38/24 rings instead of the 38/26 because of the 29" wheels.  He's tall, so 180mm cranks were also in order.  He also wanted to go with as many silver components as possible.  No problem.  Shimano's XT crank is available in both black or silver, up to 180mm length, and with 38/24 ring combo.  Okay, that's a problem.  Yes, all those options are available in an XT crank, just not all together.  

Solution:  Bring in the XT 180mm silver 38/26 cranks and swap out the 26t for a 24t.  How difficult could that be.  Maybe not so difficult if Shimano hadn't created different 38t rings based on if they were going to be used in conjunction with a 26t or a 24t.  Okay, small set back.  Time for more research.  Go to the Shimano tech doc page and look up part numbers and check compatibility.  Nope not listed.  At face value, any old Shimano 10 speed 24t ring isn't necessarily compatible as a double with a 38t outer.  They have these pesky two letter codes that need both rings need to have in order to be compatible.  No distributor, and not even Shimano, have a 24t ring that is compatible with the 38t ring from the 38/26 crankset.  

Now, if this was my bike, I would have put on a "non-compliant" 24t Shimano 10s ring and it would have probably shifted fine.  However, this was someone's dream bike and they were spending big bucks on it and I wanted it to be right.  In the end, the only thing I could do to make it exactly right was to bring in another XT crank (175, black) with a 38/24 ring combo and swap rings.  You want your dream bike, I'll make it happen.  

Shimano Mtn Double
Check out the pocketing and ramp profile of the 38t rings:  38/26 on the left, 38/24 on the right.  I'm sure Shimano with all their engineering expertise could have figured out a way to make one 38t ring that worked just as good with either a 26t or a 24t ring.  They are smart that way.  This is the kind of stuff that drives folks to their competitor, SRAM. 

(What's playing:  The Beatles Money)

10 comments:

seraph said...

Solution: don't run Shimano cranks. I run E.13 personally with a 22/36 (the same ratio I used to run with 9-speed as well) double with 10-speed SRAM X.0 drivetrain. E.13 ShiftRings work great, especially with a Shimano 2x10 front derailleur and a TRS+ Dual guide.

Bokchoi Cowboy said...

I hear you about the incompatibility factor. First it was designed-in incompatibility between brands (Shimano not working with most SRAM and vice versa) then it started within different component level internal to the brand.

Things like this make me understand the retrogrouch tendencies of some...ala Peterson or Yehuda Moon.

I myself am running a 90's Suntour XC-LTD crankset because I like it's "works with anything" nature. I just dread the day it needs replacement.

Anonymous said...

IIRC, SRAM did the same thing on their MTB doubles.

jimmythefly said...

If Shimano could have made a 38t ring that would work equally well in either case, why didn't they?

My understanding is that having only to manufacture/produce/ship/assemble/stock a single part would be better business-wise than making two.

So the only reason for making two different 38t rings I can think of is either A.) designing and making two is actually cheaper than paying the design cost and making of one "spork" ring. or B.) no matter how good they made the spork, it still wasn't as good as either of the specific rings individually.

Maybe my business-understanding is off, I'd love your take on this.

blackmountaincycles said...

jimmythefly - my thoughts exactly. Why not optimize a single 38t ring to work with either a 26 or a 24. Makes too much sense based on having fewer skus and it helps the consumer immensely.

However, Shimano is a company heavy in the engineering department. I can't help but think that since the 38/26 came out first that the engineers learned something along the way when they did the design of the 38/24 and changed the 38t ring shape.

Engineering drives Shimano and I'm pretty sure that they strive to produce something like this crank to perform at an optimum level and aren't willing to sacrifice even a few percentage points of performance. Now, how that translates in the real world to actual riders feeling the difference...

Andrew said...

For the record, I ran into this problem on my 2013 Giant XTC; I put a non-spec chainring (Raceface 24t 10s) on the 38-26 XT crank. The bike shifts exactly the same as it did with the 26 tooth.

blackmountaincycles said...

Thanks, Andrew. I'm sure there are a lot of options to get the 24t gear that works great.

filip said...

THANKS, all helpful stuff!!
so what if I change my
24/32/44 deore to
24/38XT/Rocking, would that work as long as I get 38 - for 24 inner ring?

If I swap for 26 in future do you think that could harm shifting too? I doubt, but you might have the experience..

blackmountaincycles said...

filip, even though Shimano makes specific rings for specific combinations, I don't think it matters if you mix them up. There are also plenty of aftermarket chainrings that can be mixed and matched. Check out e-thirteen's double shift rings.

Richardjca said...

Jimmythefly suggested making one 38t ring would be better business sense if they could. I disagree. Shimano knows that bikers spend endlessly so why not sell them a second 38t if we make them think it's necessary? I suspect it is easy to make cosmetic changes on the 38t rings to make them appear different so people would think they are functionally different, but are they? Until someone does a side by side, blinded comparison between the matched and mismatched sets, I'm skeptical.