Forum home Mountain biking forum MTB workshop & tech

chainring spacing

rickbst170rickbst170 Posts: 228
edited May 2014 in MTB workshop & tech
Might have made a minor booboo.

I have an m770 triple chainset. Read up on chainrings and although not ideal, I read a renthal sr4 would be ok to use instead of the middle ring and drop the big ring, giving 2x10. Whether it shift without pickups etc, not sure, will find out at the weekend.

Problem - it's really thick so double chainring bolts fit flush. Great, except it puts the granny really close to the middle ring position (I guess the middle ring shifts over by 1mm due to thick chainring wall). If I space the granny using 1mm deep washers, will it be ok? Do I stick an extra 1mm bb washer on to shove it all back over? If so, won't the bb then not be equally spaced so apply strain etc?

Ugh. Should've bought a standard ring.


Flush chainring nut face

IMAG0236_1.jpg


Chsinring nut fouls on chain

IMAG0239.jpg


No photo yet, but imagine the granny is 1mm further left (closer to bb) due to washer behind granny chainring bolt


Thanks!

Rick

Posts

  • nicklousenicklouse Posts: 81,520 Lives Here
    Have you fitted it the right way round?

    The hole is recessed one side.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • rickbst170rickbst170 Posts: 228
    Yeah, flat face against crank arm, recess houses the nut on inside. Looks funny as the text is on the inside, not showing outside.

    I reckon it'll work, but don't want to stress the bb. Ill fit the bb with equal spacing unless someone knows better.

    Cheers as always.
  • rickbst170rickbst170 Posts: 228
    Washer behind granny ring...

    IMAG0244.jpg

    IMAG0245.jpg

    The more I look at it, the more I think it's not significant at all. What's 1mm is the grand scheme.
  • nicklousenicklouse Posts: 81,520 Lives Here
    rickbst170 wrote:
    Washer behind granny ring...

    The more I look at it, the more I think it's not significant at all. What's 1mm is the grand scheme.
    Washer looks big. Make sure it is not coming in contact with the chain.

    1mm is about 20% of a shift distance. If you are using indexed gears have fun.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • rickbst170rickbst170 Posts: 228
    Yeah, it's clear of the big ring if the granny is spaced by 1 washer. Without the washer, the chain catches the mid ring chainring bolt. Chain doesn't catch granny washer.

    I showed the guy I bought the brakes off my spec list, and he shoved a 36t chainring with pickups in the box in case this setup won't work. What a hero!
  • jimothy78jimothy78 Posts: 1,407
    Use it, then. Not sure why you were using that Renthal ring as part of a pair, anyway. Yes, you can probably get away with it, but it was never going to bring any advantage over a ring designed for shifting.
  • rickbst170rickbst170 Posts: 228
    It was a bit of an impulse buy. Figured I hope to be in that ring 90% of the time and as a single ring it's designed to hold the chain well. Only need the granny for climbing (which I don't think I'll do too much of tbh).

    It's more of an indexing thing than anything. If it's all shifted over, should I space the bb differently (one. Not 2.5mm each side, but have 3.2 driver side and 1.8 nds) or will that stop the bb being square and stress it?
  • Are you sure its not single ring specific?
    I seen no shift ramps and thr first few pics on google are on bikes running single ring.

    If so, that would be your problem.
  • As I thought.
    http://www.bikeradar.com/gear/category/ ... -09-35133/

    This ring will not work on a 2x10 setup.
  • rickbst170rickbst170 Posts: 228
    But then look at this...
    http://www.renthaltest.com/sr4_120/

    They changed bcd to suit sram cranks and now it's a double. Read a bit on it and reckon it's a light, tough ring which holds chain best in class, and can work for 2x10 (if a little slow shifting).

    Imagine it did have pickups. Then, would you space the bb 2.5 and 2.5 or 1.8 and 3.2?

    Thanks as always. Appreciate all input (even if it means I'm wrong and it'll never line up properly and I have to give up on it. I can always sell it).
  • jimothy78jimothy78 Posts: 1,407
    rickbst170 wrote:
    Imagine it did have pickups. Then, would you space the bb 2.5 and 2.5 or 1.8 and 3.2?

    What size is your BB shell? - you should normally be using three spacers (on a 68mm shell) or one spacer (73mm shell).

    Anyway, how are you going to do that? have you got half-size BB spacers? If so, I can't see anything going desperately wrong if you try it, but it still seems like a lot of effort to fit a less-than-ideal item in a les-than-ideal way.
    rickbst170 wrote:
    But then look at this...
    http://www.renthaltest.com/sr4_120/

    They changed bcd to suit sram cranks and now it's a double
    No, it says they've been changed to fit a SRAM double crankset, not designed to work as part of a double-ring setup.
    Renthal wrote:
    If you want to change your current SRAM 2x10 set up to the more trail/race aggressive 1x10 format, we now have just the chainring for you.
  • rickbst170rickbst170 Posts: 228
    Ah, I see. censored .

    63mm shell and new bb comes with 3 spacers; one at 2.5, one 1.8 and one 0.7. It's so you can put 1.8 and 0.7 one side (which makes 2.5) and a 2.5 the other side to even out. If you've got stuff fitted (bb mount tensioner etc) you can drop off a spacer as required.

    Looks like I might have a chainring for sale next week :/
  • jimothy78jimothy78 Posts: 1,407
    rickbst170 wrote:
    63mm shell and new bb comes with 3 spacers; one at 2.5, one 1.8 and one 0.7.
    Ah, didn't realise they'd changed the spec recently - probably because so many people are moving to 1x and 2x setups these days.
    Looks like I might have a chainring for sale next week :/
    What tooth count?
  • rickbst170rickbst170 Posts: 228
    38t. Not brand new, got it off a guy who ran 1x10 for a very short time. Looks almost new. Happy to swap ;)
  • jimothy78jimothy78 Posts: 1,407
    rickbst170 wrote:
    38t. Not brand new, got it off a guy who ran 1x10 for a very short time. Looks almost new. Happy to swap ;)

    Ah, no - too high for me - I'd be looking for 34 max, for a single-ring setup :wink:
  • rickbst170rickbst170 Posts: 228
    Works pretty well. Fiddly fecker to set up but does what I need for now. The new bb actually comes with 2 off 2.5, 1 off 1.8 and 1 off 0.7mm spacer, so used 2.5 each side with 1.8 extra on driver side. Changes up ok from 5th cassette chainring upwards. First 4 cassette positions don't have the chain far enough over for a quick clean shift up but that's fine. Chainline ok and no rub on front mech.

    Pics show big to big, big to small, granny to big amd granny to small

    IMAG0304.jpg

    IMAG0303.jpg

    IMAG0305.jpg

    IMAG0306.jpg

    IMAG0307.jpg


    24t granny seems small actually, might have been better with 26 or 28 granny and bigger big ring. Need more time out on it really to decide.
Sign In or Register to comment.