two chainring combinations- Mtbr.com
Results 1 to 20 of 20
  1. #1
    mtbr member
    Reputation:
    Join Date
    Jan 2004
    Posts
    1,158

    New question here. two chainring combinations

    So, maybe I'm not a purist, but I would like to run double front chainrings on my 1994 Litespeed Ocoee so that I have a better on-road option. Obviously, I'm using a chain tensioner ...the surly model ...so I think a can take up a little slack caused by switching to the smaller chainring.

    Because the smaller chainring will see lots of offroad, I cannot afford much slack in the chain. What size chainrings work for this configuration? My cranks are shimano 4 arm 110 bolt pattern. I currently have a 32 tooth on it. I'm thinking my best bet would be a 34 and a 39 chainring.

    Or...would it be better to just use two cogs on the back? I'm using an old XTR rear hub with spacers. I guess I can just put two cogs on back there.

  2. #2
    mtbr member
    Reputation:
    Join Date
    Jan 2004
    Posts
    1,158
    hummm

  3. #3
    Live, Freeze, and Ride
    Reputation: lobolator's Avatar
    Join Date
    Oct 2006
    Posts
    315
    You are probably better off finding 2 gears the same chain length or close, especially with a tensioner(unless you use a derailleur).
    I had a 34-20 and 42-15...trail and city gears. The drawback for me was I had no tensioner and the gears were different chain lengths by 1/2 link (and no horizontal drop outs).
    Not so elegant solution - 2 pieces of chain (10 links and 10 1/2 links) swapped out to change gears. It could be changed in a minute or less.
    I wasn't looking to change gears all that often so it works for me.
    Inbred 29er Dinglespeed
    Rush Hour SS
    4One5 SS
    Hard Rock SS/Fixie
    In the woodSS
    I work for a bike parts company

  4. #4
    mtbr member
    Reputation: logbiter's Avatar
    Join Date
    Dec 2003
    Posts
    2,821
    Quote Originally Posted by GlazedHam
    So, maybe I'm not a purist, but I would like to run double front chainrings on my 1994 Litespeed Ocoee so that I have a better on-road option. Obviously, I'm using a chain tensioner ...the surly model ...so I think a can take up a little slack caused by switching to the smaller chainring.

    Because the smaller chainring will see lots of offroad, I cannot afford much slack in the chain. What size chainrings work for this configuration? My cranks are shimano 4 arm 110 bolt pattern. I currently have a 32 tooth on it. I'm thinking my best bet would be a 34 and a 39 chainring.

    Or...would it be better to just use two cogs on the back? I'm using an old XTR rear hub with spacers. I guess I can just put two cogs on back there.
    another option to the surly tensioner is paul's melvin, it's designed for 2 rings up front. I was running a 46 & 34 with a single in back.


  5. #5
    mtbr member
    Reputation:
    Join Date
    Dec 2006
    Posts
    21
    Have you considered using a setup similar to WI's double freewheel/double chainring? Just make sure that the total teeth of the front and back add up to the same and you shouldn't need a chain tensioner or have any brake problems when you switch gears (i.e. 38 x 16 and 35 x 19). If your riding both street and trail its a great set-up.

  6. #6
    conjoinicorned
    Reputation: ferday's Avatar
    Join Date
    Jan 2004
    Posts
    3,525
    i vote changing cogs rather than chainrings.

    2 tooth difference in cogs is (very roughly) a 10% difference in gearing.
    2 tooth difference in chainring is (again roughly) a 5% difference in gearing.

    http://www.sheldonbrown.com/gears/

    so you'll get more difference in gearing for less difference in chain length if you go with a cog change.
    what would rainbow unicorn do?

  7. #7
    highly visible
    Reputation: GlowBoy's Avatar
    Join Date
    Jan 2004
    Posts
    3,179

    Not gonna work!

    Single-pulley tensioners like your Singleator can't take up more than a tooth or two's worth of slack. It won't even come close to taking up the slack when you change from 39t to 34t. Your options for multiple ratios (with a significant difference between them) are:
    • Do the 2 rings in front and single cog in back as you're suggesting, and get a double-pulley tensioner like the Paul Melvin or the Rohloff tensioner. These can take up to 20t worth of slack. Or, for no cost and a little more weight, use an old derailer that doesn't shift right anymore.
    • Find the "magic ratios" for your bike that don't require a tensioner. Then set up your bike with two rings and two cogs, same size difference front and back, that achieve those ratios. For instance, if 34:18 works as a "magic" gear for mountain biking, you can do 36:16, 37:15 or 38:14 as your high gear.
    • Stick with a single ring in front, put on 2 cogs in back and bolt on a derailer. But rather than hooking up a shfiter and cabling, do this: After adjusting the limit screws so the derailer can't move outboard of the smaller cog, slip a short piece of shift cable into the derailer all the way up to the barrel end, securing the other end with the derailer's clamp bolt. Now you can turn the adjuster knob on the back of the derailer to manually shift between the two gears! Note: this works with Shimano derailers, not SRAM.
    Last edited by GlowBoy; 03-06-2007 at 03:09 PM.
    "People like GloyBoy are deaf. They are partisan, intellectually lazy & usually very angry." -Jaybo

  8. #8
    IM Singleminded!
    Reputation:
    Join Date
    Mar 2007
    Posts
    9

    tensioner preferences...

    There is some great info going here. I have always wondered about the cog deference between front chainrings and rear cogs and what makes the bigger difference. Anyone have any experience between the Paul or the Rohloff?

  9. #9
    mtbr member
    Reputation:
    Join Date
    Jan 2004
    Posts
    1,158

    settled ...I think

    Thanks for all the advice! I think I'm going with this set up:

    Gear one: 34 x 21
    Gear two: 39 x 16

  10. #10
    velofix
    Reputation:
    Join Date
    Dec 2006
    Posts
    41
    The beauty of sliders:

    On my Monocog Flight, which has sliding rear dropouts, I run a 36 ring/16 cog on the outside for a 65" gear to get me down the road to the trail head, and a 32/20 on the inside which gives me a 46" gear for the trail. Notice the same 4T difference between the two chainrings and the two cogs.

    When I get to the trail, I just flip my bike over, pop the quick release, lift the wheel and move the chain to the inside cog and ring, then drop the wheel back into the dropouts, snap the quick release home and I'm ready to go in less time than it takes to describe it.

    Because I'm maintaining the same total number of teeth with either ratio, I don't have to move the wheel to retension the chain. You could go the other way with a trail ratio and a lower gear for climbing or snow. Just remember to select your ring and cog so if you go down so many teeth in front, you go up the same number in back and vice versa.

  11. #11
    Obi
    Obi is offline
    -_-
    Reputation:
    Join Date
    Oct 2005
    Posts
    4,746

    ... and if we just ...

    Cool you figured out the combos!!

    For anyone else trying to figure out a dingle combo, the rule is the gears add up to the same number.

    IE: 32:16...

    32+16=48

    Dingle Combo: 22:26

    (yeah, um, this is for explanation only, Boone is one of the few that makes a 26 available, huh?)

    So...

    22+26=48.

    Your chain length, and thus the tensioners wont need to be all adjusted.


  12. #12
    Trying a little
    Reputation: dusthuffer's Avatar
    Join Date
    Nov 2006
    Posts
    1,781
    OK dumb question the paul site http://www.paulcomp.com/frmsingle.html at the bottom of the melvin page says use your hand to move the chain between front rings, I can call them tomorrow but anyone know if you could use a front derailer? Because I gotta know tonight.

    I never apologize. I'm sorry, but that's just the way I am.

  13. #13
    highly visible
    Reputation: GlowBoy's Avatar
    Join Date
    Jan 2004
    Posts
    3,179
    Quote Originally Posted by dusthuffer
    OK dumb question the paul site http://www.paulcomp.com/frmsingle.html at the bottom of the melvin page says use your hand to move the chain between front rings, I can call them tomorrow but anyone know if you could use a front derailer? Because I gotta know tonight.
    Yes, you can. But it will actually make your drivetrain more complex than simply using a rear derailer. Unless mud and grit is a huge concern, might as well combine the shifting and chain-tensioning functions in a single device.

    Quote Originally Posted by velofix
    The beauty of sliders: ... Because I'm maintaining the same total number of teeth with either ratio, I don't have to move the wheel to retension the chain. ... Just remember to select your ring and cog so if you go down so many teeth in front, you go up the same number in back and vice versa.
    That's also the beauth of an EBB. I've been known to do the same thing on my Vulture:
    - 34x22 and 37x19.
    - 34x22 and 36x20.
    - 30x26 and 34x22.

    My Vulture's currently a pure singlespeed (34x22), but if I can obtain a 28t cog I will probably set it up 28x28 and 34x22 long term.
    "People like GloyBoy are deaf. They are partisan, intellectually lazy & usually very angry." -Jaybo

  14. #14
    No Justice = No Peace
    Reputation: Lutarious's Avatar
    Join Date
    Feb 2005
    Posts
    1,513

    Close enough, but...

    I run a double double on my DeSalvo (EBB) with 32 and 34 up front and anything from 16/18 up to 20/22 in the back. Although it works just fine, there is definitely a bit of error in the chain length. I think it has to do with the wrap around the sprokets, but any given combo will yield one gear with perfect chain tension and the other will be slightly off. Presumably, the error will increase as the diffference in sprocket sizes increases. Make sure you try each combo and adjust for the tighter of the two. In my case the taller gear is always the one with a little slack in the chain, which is no big deal because I usually ride it around town or on the fire roads in that gear. On longer/rougher rides, I opt for the easier gearing because I am old and weak....
    "Welcome to my underground lair...."

  15. #15
    highly visible
    Reputation: GlowBoy's Avatar
    Join Date
    Jan 2004
    Posts
    3,179

    Yep.

    Quote Originally Posted by Lutarious
    Although it works just fine, there is definitely a bit of error in the chain length. .... Make sure you try each combo and adjust for the tighter of the two. In my case the taller gear is always the one with a little slack in the chain, which is no big deal because I usually ride it around town or on the fire roads in that gear.
    The big ring/small cog combo will always give you a slightly tighter chain than the small ring/big cog combo. Agreed, I always set the chain tension in the taller gear (as tight as I can get away with it). There is more slack in the lower gear, but with SS-specific sprockets and good chainline there should not be any problems with the chain dropping.
    "People like GloyBoy are deaf. They are partisan, intellectually lazy & usually very angry." -Jaybo

  16. #16
    mtbr member
    Reputation:
    Join Date
    Oct 2006
    Posts
    155
    If you search my old posts you'll find my budget SS build, in which I am running 2 rings and 2 cogs:
    42x16 for getting around town
    36x18 for the trails
    Surly Singleator in push down mode.

    There is a 4-tooth difference between the two ratios, so like the others said, get the big ring combo as tight as possible. I've adjusted my chain length so that the Singleator barely tensions the chain on the 42x16, and pushes it down more noticeably on the mountain gear.

    It takes me about a minute to chainge gears: move chain to other ring/cog, then use allen key to adjust the tensioner alignment.

  17. #17
    mtbr member
    Reputation:
    Join Date
    Jul 2006
    Posts
    176
    Hey knucklesandwich, I found your post from a search looking for suggested gear ratios when on the road, commuting, paved trails, etc. I just went with 42:16 as you mention, bike isn't quite complete yet but was wondering if you were happy with this ratio for rolling hills, pavement, etc. When I asked my LBS about this ratio, the reply was "their your knees, not mine"

  18. #18
    conjoinicorned
    Reputation: ferday's Avatar
    Join Date
    Jan 2004
    Posts
    3,525
    Hey knucklesandwich, I found your post from a search looking for suggested gear ratios when on the road, commuting, paved trails, etc. I just went with 42:16 as you mention, bike isn't quite complete yet but was wondering if you were happy with this ratio for rolling hills, pavement, etc. When I asked my LBS about this ratio, the reply was "their your knees, not mine"
    hi scout

    i ride a 44x16 on my "road bike" which is a converted mtb. i ride in a very hilly city and so far i love the gearing, haven't found a hill yet that i can't climb and can still generate enough speed on the flats. i would not consider this gear very suitable to offroad.

    as far as your knees...don't climb the big hills while seated!
    what would rainbow unicorn do?

  19. #19
    mtbr member
    Reputation:
    Join Date
    Jul 2006
    Posts
    176
    cool, thats what I wanted to hear. I think he was kidding a bit but got me to wondering if I was a bit ambitious. this is actually a road bike converted, not going to be off road other than some reasonably flat dirt

  20. #20
    mtbr member
    Reputation:
    Join Date
    Oct 2006
    Posts
    155
    Quote Originally Posted by scout
    Hey knucklesandwich, I found your post from a search looking for suggested gear ratios when on the road, commuting, paved trails, etc. I just went with 42:16 as you mention, bike isn't quite complete yet but was wondering if you were happy with this ratio for rolling hills, pavement, etc. When I asked my LBS about this ratio, the reply was "their your knees, not mine"
    I've had no problems with 42x16 on the MTB- it's good for dirt paths, quick trips to the store, etc. But I think ultimately gear choice should come down to the rider. Play around with it, and just be mindful that you may want to go up or down a cog size depending on your terrain, fitness, etc.

    I commute 13 miles r/t most days with a good deal of elevation change, and rarely shift out of my 52t ring, and if I was to build an SS cyclocross/road bike (hopefully my next project)...I'd probably start with a 44 or 46t ring, but 42x16 is the sweet spot, for now, on my MTB.

Members who have read this thread: 1

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

THE SITE

ABOUT MTBR

VISIT US AT

© Copyright 2019 VerticalScope Inc. All rights reserved.