Using a Triple Crankset as a Double - Any Issues?

[Irving]

I have in my possession some Sugino XD triple crankarms and am looking to use them as a wide range double crankset (outer 110bcd chainring guard, middle 110 bcd 42t chainring, inner 74 bcd 26t chainring).

Has anyone done this and is there anything I need to watch out for or are there any downsides to running something like this?

I'm planning on using some Shimano bar end shifters, either 9 or 10 speed.

[Iron Rider]

I've been told that 14 tooth difference between adjacent rings is the largest that you can run without derailleur problems. 42-26 would exceed that. However I have never tested this advice.

[Jamie]

That's a 16 tooth gap, and I now that compact cranksets use up to a 16 tooth gap (my SRAM cranks are 50-34). But I wonder whether compact cranksets have some special design features that allow the 16 tooth gap to work fine. Someone here will know for sure.

JAS

[russell...@yahoo.com]

On a touring forum I frequent someone mentioned using a setup like you mention.  Middle ring from a triple and the inner ring.  There is no reason for you to use a guard in the outer position.  Just get single ring bolts and leave the outer position empty.  You can run any difference between the middle and inner rings.  I had a triple with 45-42-20 rings.  Used bar end shifters and it shifted fine.  I'd suggest getting as short a square taper bottom bracket as possible to get the cranks as close together as possible.  Get the inner ring so its almost rubbing the chainstays.

[Lin Osborne]

Yep, it's technically possible with no real downside, as long as you consider the drive train and shift controls as a complete system.

As Russell notes, you may want to fiddle with BB spindle width. A narrow spindle will reduce tread (Q-factor) and may reduce knee stress. If you plan to only occasionally be on the 26t ring, narrow. If you plan to use the 26t regularly, given that the crank was designed to run as a triple, a slightly wider than manufacturer-specified spindle will improve chain line, reduce drive train stress, and reduce the potential for missed/sluggish shifts (at the risk of putting more stress on your knees, though). Good articles that gets into the tech aspects: http://sheldonbrown.com/chainline.html and http://sheldonbrown.com/bridgestone/1991/pages/bridgestone-1991-13.htm

The 16t spread you mention should work w/any older (e.g., 70's, 80's era) MTB/touring FD, or modern FD designed for compact double, provided the frame accepts a a clamp-on FD such that you can establish an appropriate gap between FD and your "big" ring (about 3-5mm). 

IMHO, the best FD for this task would be an 80's, 90's era MTB/touring FD. These were made to mate with 46t-48t outer rings, and thus will more closely match the arc of your 42t ring. The less closely the der and ring arcs match, the more likely you are to experience hard/slow shifts from small to large. Needless to say, this assumes "friction-only" front shifting. Old ders won't work well with indexed front shifters. I know the Shim-9 shifters are compat. Don't know about their 10.

This "small front double" will be easier to set up with a 9spd drive train since 9spd is compatible with 7/8spd (and obviously 9spd) derailleurs. I personally wouldn't attempt it with a 10spd system. 10spd tends to be more sensitive to "edge of mechanical tolerance" conditions, and too many potential mechanical incompatibilities to expect it to work comfortably well.

HTH,

Lin

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From: "russell...@yahoo.com" <russell...@yahoo.com>
To: ran...@googlegroups.com
Sent: Thursday, February 7, 2013 10:18 AM
Subject: [Randon] Re: Using a Triple Crankset as a Double - Any Issues?

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[Bill Gobie]

I use 56/36 on one bike and it shifts fine. The tooth difference you can achieve depends on the particular derailleur and bike. Don't expect a wide range setup to upshift under load and as rapidly as a stock Shimano or Campy ring set. If the shifting is terrible, try these: Check that the outer ring is oriented correctly. There should be an alignment mark, like an arrow, that lines up with the crankarm. That puts the pickup pins, ramps, and gates in the nominally correct orientation. Second, try turning the inner ring to alter the synchronization. Ideally one of the chain's rollers drops exactly into a valley between the teeth on the big ring. Third, try turning the outer ring, since the shift aids are probably not optimized for a 26T inner ring.

A rapid downshift, such as you get with an indexed front shifter, can throw the chain past the inner ring, so you might need a Jump Stop or other inner chain guard. With a bar end you should be able to make slow enough downshifts that this won't be much of a problem. Even so, synchronization matters a little bit on downshifts so you might still need a Jump Stop if the chain skates on the ring without engaging.

That said, why not use a triple? On a poorly planned wide range double you can find yourself in a speed range where you have to shift the front frequently. Your cassette needs a wide enough range to give you three or four gears of overlap between the chainrings, which calls for a cassette with big steps. You can get the same overall range with finer steps and less front shifting with a triple.

Q-factor sensitivity is personal. Unless one of your goals is narrower Q-factor I wouldn't worry too much about getting a narrower bottom bracket.

Bill

[Roy Yates]

I'm doing this, running 42-26 using the middle and inner rings on a shimano 6503 ultegra triple crank. The shifter is a shimano 5700 double brifter. The FD is a 6603 shimano triple with the wide side cage. The shifting between front rings is fine, but not as good as an ordinary double or triple with a smaller jump. The advantage is that I spend 90% of my time i the 42 ring, with a lot less front shifting and no trimming. Because I use an 11-34 rear cassette, I only use the granny ring when the hill is really steep, say 15% grade or more.

The one disadvantage i found is that the 26 is really useful only in the first 5 cogs of rear cassette. In higher gears, the chain rubs the big ring in a diasageeable way. Still, since I only use the granny ring for steep hills. I'm ok with that. By contrast, the old 6603 triple crank with 52-39-30 rinfs was happy crosschained in the 30 ring and small cogs in the back.

[Iron Rider]

 I wish someone had posted this question before my recent bike assembly. Your 42-26 with an 11-34 sounds like a very suitable rando combo.

[Peter Mathews]

On my first recumbent I ran 69-42-26 for quite some. It exceeded the
capacity of the der, but changed quite happily at the front. The only
problem was that on the granny gear the der was folded up on itself.

PeterM

On 08/02/13 01:49, Iron Rider wrote:
> I've been told that 14 tooth difference between adjacent rings is the largest that you can run without derailleur problems. 42-26 would exceed that. However I have never tested this advice.
>

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Peter Mathews
pmat...@alphalink.com.au
m: 0439992130 p: +61398906089 w: +61399052192

[NormC]

I have exactly this setup, but without the outer guard, and it works fine with a basic Shimano mountain triple front mech I picked up in a sale at the LBS. I use it with an SRAM 11-30 9-speed cassette. I'm surprised it's not done more often. 42-11 spins out for me at ~30 mph. I'm happy to freewheel above that. Means fewer front shifts. I only drop to the inner ring as a last resort on steeper hills.

Inevitably, the mainstream bike component makers have completely ignored such a nice setup and made it difficult or impossible to implement with most component groups, of course.

[Irving]

Thanks for all the tips! I'm trying to avoid a triple crankset, since I already have that on my touring bike (which I use almost like a reverse half step... use the mid and low, and rarely use the big chainring)

On my rando rides, I find that I'm usually comfortable coasting downhill and something in the mid 90's in terms of gear inches will be fine for me.

I'm still playing around with chainring options but wouldn't mind going 42/28 or 40/26 if that eases the front shifting.

[Tom Durkin]

I use the 42/28 combination on the Stronglight  crank. The front derailleur is Suntour road, shifts fine and is lighter than mountain bike parts. Other option include the new Herse cranks. 

Sent from my iPhone

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