Chainline help - moving cogs around

Discussion in 'Cycling Equipment' started by 10kman, Aug 11, 2014.

  1. 10kman

    10kman New Member

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    Looking to see if this can (reliably) be done -

    I have a bike I use for only climbing events. I run a Sram XX1 crankset (156 Q factor) up front with a 28 or 30t ring, and in the rear I run a 10 speed cassette in 11-28 flavor.

    On the worst climbing events I do, I'm in the 28t, trying to spin more than mash. I never need lower than a 1:1 gear, so I'm good with the actual gearing.

    What I've noticed is the drag caused from being in those largest 2 cogs in the rear. I can hear it, and I got a little crazy Saturday and threw the bike up in a workstand and did some tests to see how much it was actually dragging, and I'd say it's significant based on sounds and the feel of things while pedaling by hand. I can't actually back spin the crank and not have it stop almost instantly, but yet in my middle/smaller cogs, I can give the pedals a push backwards and they go around nice and easy.

    So I got to thinking that I'm losing a lot of wattage in that whole scenario, and I had this bright idea to simply shift the cassette towards the right (drive side), by removing the last 2 small cogs (sram cassette, mostly one piece), and putting the small cogs first onto the hub, then the cassette. Pretty much moving my largest cog outward, and making my chainline better in those gears. I don't use the 2 smallest cogs anyway, so figured I'd just rearrange. I had to use a small washer between my lockring and the cassette, but otherwise it was secure and good to go.

    Problem is that the derailleur (Sram Red) isn't at the correct angle to do this and i'm getting some binding. I messed with the B-tension screw, the stop limits on the derailleur, can't get it to happen.

    Is there any way I'm missing, that I can try, to make this possible?

    Thanks,

    10k
     
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  2. alfeng

    alfeng Well-Known Member

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    What type of FRAME are you using? I presume that the crankset you are describing is a MTB crankset ... FWIW. With a vintage Campagnolo Thron (110BCD) MTB crankset that I have mounted on a 113mm asymmetric Shimano BB the Q-Factor is the "normal"-for-a-Road-bike 150mm ... The inference is that if I were to mount the crank on a Campagnolo (ISO) BB and mate it with an appropropriate non-driveside crankarm that I would probably be moving the spider inward by at least 5mm. You can mount a Shimano XTR OCTALINK Crankset on a 109.5mm 105/Ultegra/Dura_ Ace BB instead of the 112.5mm BB spindle which Shimano specs for the crankset.
    • The non-cartridge Dura Ace Octalink spindle can be installed in a non-cartridge XTR Octalink BB cups if you need 73mm cups ... If your frame has press-in bearings, then you will need an appropriate adapter. Obviously, the shorter spindle will result in a narrower Q-Factor.
    BTW2. Apparently, you can substitute a Campagnolo for some SRAM derailleurs, and vice-versa ... A Campagnolo rear derailleur can easily handle a 28t rear Cog ... Campagnolo's B-screw directly adjusts the pulley cage ... I cannot guarantee that it will do-the-trick for you, but I think the odds are high that it may.
     
  3. 10kman

    10kman New Member

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    I'm using an older Scott road frame. The BB is a GXP outward bearings, the crank is as you guessed, a MTB crank. I used the narrow q factor model of it though, hoping to keep things in but this one last piece was bugging me and I started fiddling around more this weekend.

    I'm running a Sram Red rear der, cassette, and Sram R2C TT shifter for my rear shifting duties. I've read similar about the Campag rear derailleurs being compatible, but didn't know about the B-tension also moving the cage. That seems to be the issue, I need the derailleur cage to be 2 gears over, it's not the sizing at all of the gears, just the positioning.
     
  4. alfeng

    alfeng Well-Known Member

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    BTW. You can ALSO use a Shimano (Rapid Rise or "normal" rise) rear derailleur if you hubbub it to make it act like a 10-speed Campagnolo rear derailleur ...
    [​IMG]

    Of course, the "Rapid Rise" cage will move in a REVERSE direction (low to high) than a normal rear derailleur's cage will move.
     
  5. alfeng

    alfeng Well-Known Member

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    BTW. I presume that your Chainring is mounted on the INNER shoulder of the crank's spider ...
     
  6. 10kman

    10kman New Member

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    The XX1 crankset is a single ring setup, and it only mounts on one side. I was looking at that first to see if I could rig it inward somehow but no dice.
     
  7. alfeng

    alfeng Well-Known Member

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    Hmmmm ...

    Well, you can mount the Chainring WITHOUT A SHOULDER on the spider, BUT if THAT is something which would trouble you (not nesting the Chainring on a spider's shoulder), then I would suggest that you consider getting/using an XT Crankset (AFTER you confirm that there would actually be a beneficial, inward placement of the Chainring) ...

    FYI. After re-spacing a (steel) Road frame to 120mm, with the Chainring on the inner shoulder of an XT Crankset, the chainline is "off" on the particular (pictured) bike by less than 1mm ...
    [​IMG]
    While I could tweak the rear wheel to perfect the chainline, it isn't worth the effort and that would mean that the wheel would be "off' if it were installed in another frame which has 120mm rear spacing + a non-MTB crankset.
     
  8. 10kman

    10kman New Member

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    I was trying to keep this as close to "free" as possible as a mod, so I'm still looking, but if I used a triple crankset I could just use the granny gear and probably be better off, but like you said, I'd have to measure one up.

    All parts on this bike are proprietary to this bike, so no worries if it doesn't work anywhere else.
     
  9. alfeng

    alfeng Well-Known Member

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    I don't know what the backside of your Crank's spider looks like ... If there aren't re-enforcing RIBs which preclude re-mounting the Chainring on the inside of the spider, then THAT is undoubtedly your best-as-in-cheapest option ... If there are "ribs" then I would probably just remove the extra material with a hand file ... if you are not handy, then you may not want to follow suit..
     
  10. 10kman

    10kman New Member

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    Very handy with the tooling side, I always try to go the route of least destructive first especially with parts costing more than a few bucks.

    I'll have a look again tonight and see what pops into my head.
     
  11. oldbobcat

    oldbobcat Well-Known Member

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    This is interesting. We're talking about hubbubbing Campy shifters without even looking at the chain line or the chain, or the rear derailleur that you're actually using. With one cog up front and ten out back, this shouldn't be too difficult. But you're doing something that's very non-standard so a little faking it is necessary. I assume you're using a SRAM shifter with your Red derailleur.

    First, some questions. Your XX1 crankset is most likely made for a 73mm (or wider) BB shell, and the shell on your Scott is 68mm. How are you making up the 5mm difference in shell width?

    Now that you're thinking about this, let's look at the chain line. Since you're favoring the low end, shift onto the fourth cassette cog (from the inside) and eyeball the chain line. It should be a straight, or pretty darned straight, line from th cassette to the chain ring. If it veers out to the chain ring, you need to figure out how to get it closer to the frame. If it veers in, you need to figure out how to get it farther out. If the chain line is no good, refer to my first question for clues on how to fix this. If you don't get it, tell me what the chain line looks like and if there are any shims between the cranks and the bearings.

    If the chain line is good, let's look at the chain and rear derailleur. SRAM road rear derailleurs have a little pivoting plate that's positioned between the B-screw and the flat on the frame's derailleur hanger. Make sure you have that right. If the B-screw is hitting the plate, it is. If it's hitting the flat on the hanger, it's not. It will be easier to fix this if the B-screw is mostly retracted. It will also be easier if the shift cable is disconnected.

    Messing with the limit screws was a big mistake. Now that the cable is disconnected and the derailleur is ostensibly properly mounted, test your limit screws. Turning the cranks with your right hand, push the derailleur onto the big cog with your left hand. If it hits the spokes or the chain goes over the top, tighten the "L" limit screw until it lets you hand-shift onto the big cog without going into the spokes. Next, let the derailleur drop to the smallest cog. If it doesn't reach, loosen the "H" limit screw until it does. If it tries to drop the chain between the frame and the smallest cog, tighten it until it stops doing that. Now hook up the cable. Pay attention to the curved routing "anvil" with the groove on the bottom. pass the cable along the groove and attach it to the top of the pinch bolt. Make sure the shifter is all the way out before pulling the cable snug and fastening. Adjust tension and there you are.

    We're not done yet. Shift into your lower cogs and note the distance between the jockey pulley and the cog. If there isn't any, tighten the B-screw, until there's a little distance and the chain stops making noise. If the B-screw is all the way in and it's still making noise, your chain is probably too long. Also, standard (not WiFli) SRAM derailleurs nominally handle only 28t cassette cogs, so the 30 might be overreaching. If it works fine on cog 2 but not 1, this is probably the case.

    You know, this whole thing would be a lot easier if you'd posted a few photos of the situation. They'd be a lot more helpful than outtakes from alfeng's lovely family album.
     
    dhk2 likes this.
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