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Old 05-31-13, 10:15 AM   #1
dminor 
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Single-ring chainring for 2X setup - - Update

OK, I'm going to break with my norm of Friday silliness and ask a serious question for a change.

Any thoughts on advisability or inadvisability of using a single-ring-designed chainring on middle position of a 3X crankset for a shifting 2X setup? My reservation, besides the obvious lack of shifting pins and ramps is that the thickness of some may cause problems dropping to the smaller inner ring. And is the 26 up to 38 upshift too big of a jump to happen smoothly without the aid of ramps and pins?

Only reason I pose this question is because I'm finding a lot of single-ring 38T 104/4 chainrings reasonable but 38T shifting rings are harder to come by and fairly pricey (well, except Shimano steel ones, which I don't want). I have an X5 triple that I want to 2X with a bash/38/26 (104/64) and I'm wanting to keep the conversion under $50 (I have the bash already).
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Old 06-01-13, 11:22 AM   #2
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$50 is do-able, if you can go with a 36t ramped chainring -- not the 38, but much more common and cheaper.

I just measured my 34t Salsa SS ring and a 36t Shimano xt level ramped ring. The difference is not in the thickness of the teeth, but the depth. The teeth on both rings are 2mm all the way around. The depth of the Salsa ring is 6.50mm all the way around -- the depth of the Shimano ranges from 4.50mm to 5mm. The taller teeth of SS rings would be prohibitive to good shifting. I have never tried it before, so I can't fully say one way or the other. You might be saving more money in the long run by getting the ramped rings.
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Old 06-03-13, 05:17 PM   #3
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Hey, thanks for the reply - - sorry I didn't acknowledge it sooner. Ha - - didn't occur to me about the depth of the teeth. I'll have to measure my 38T DH rings. Hmmm . . . I have a somewhat worn 38 that I've since replaced with a Renthal. For laughs, I may throw it on and just see firsthand how things behave (or misbehave).
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Old 06-03-13, 06:30 PM   #4
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My reservation, besides the obvious lack of shifting pins and ramps is that the thickness of some may cause problems dropping to the smaller inner ring.
Small rings from doubles don't have ramps and pins, just shorter teeth in general and a few extra-short teeth to enable easier derailing.
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Old 06-03-13, 11:12 PM   #5
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Small rings from doubles don't have ramps and pins . . .
That much I know and is logical, since nothing has to climb up onto onto it.

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. . . just shorter teeth in general and a few extra-short teeth to enable easier derailing.
Another cool factoid I was not aware of, about the short teeth. Thanks.

BTW, I've found a fair number of 26T inner rings pretty cheap. Some are XT, although from what I read, even though they are standard 64 BCD, it sounds like the tab length is slightly different on Shimano rings? Will I need to do any grinding/filing for it to fit another make crank?

I'm looking at my old 38t FSA DH ring and thinking wacky thoughts. Like with a little creative Dremel work I could carved some crude shifting ramps into it. And the drill press, a very small tap and some itty-bitty set screws loctited in could be pins. Hmmmmm . . . . I have way too much time to think demented thoughts.
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Old 08-10-13, 09:30 PM   #6
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An update: I bit the bullet Monday night and swapped out the triple with what I had on hand: the 26t/64 that I got for about $16.98 shipped; my 38t FSA DH ring (no ramps or pins); and my razzoo Sunline poly bash. Reset my high limit screw on the FD and called it good shifts up like buttah. Tried it on the Wed. night ride and no issues at all. Shifts up to the 38 as if it were a shifting ring. Am pleased.
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Old 08-12-13, 11:48 AM   #7
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Cool! How's it shift down, though?
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Old 08-12-13, 12:11 PM   #8
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^^

That's actually a legitimate question though - - most of the time it dropped down fine; although I did drop it off the inside once. It could be with such a thick DH ring, it's dropping out of line with the ring below. 'Course it may just be a low-limit-screw issue too or a combination of both. Hafta look at it again. I will say it did it with the triple too if I didn't finesse that downshift a little.


BTW, I forgot to mention earlier that the 26t ring was an XT and it indeed has longer tabs than other 64BCD rings - - so it took some careful scribing and some gentle Dremeling to dress them down a bit to fit the SRAM crank tabs.
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Old 08-12-13, 08:38 PM   #9
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I figured that would be the case. I guess you can just make sure to setup any climbs well in advance. With my lack of skillz, though, being unable to dump into the small ring at a moment's notice would be an issue.
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