Warning to all looking to increase compact gearing!

guilliano
guilliano Posts: 5,495
edited July 2010 in Road buying advice
If you have an Ultegra (and probably 105) compact chainset DO NOT purchase an aftermarket chainring to increase your smaller chainring gear ratio. I have recently gone to a 36t TA chainring and my shifting is now awful (esp to the smaller ring) as the ramping pins are covered by the chainring. I now have to get a 34t Ultegra ring before next weekend or I will not be able to do Ride To The Horns as I can't shift to the smaller chainring without a huge amount of luck!
http://www.flickr.com/photos/guilliano/

Comments

  • gsk82
    gsk82 Posts: 3,471
    i changed by 34/50 105 chainrings for 36/52 and have had no problems, if anything it works better than the original did
    "Unfortunately these days a lot of people don’t understand the real quality of a bike" Ernesto Colnago
  • maddog 2
    maddog 2 Posts: 8,114
    Not had a problem myself running a 36t TA ring

    what exactly is it doing to be so bad?
    Facts are meaningless, you can use facts to prove anything that's remotely true! - Homer
  • anto164
    anto164 Posts: 3,500
    Don't want to sound like i'm insulting, but are you sure you put the chainring on the correct way round? Some chainrings are directional..
  • mostly harmless
    mostly harmless Posts: 162
    Sounds like you've made an elementary error of some sort.

    I run 33, 36 or 38 TA rings on a compact Ultegra crank and my shifting is spot on.

    The cheap Stronglight ones are also doing fine on the winter bike.
  • guilliano
    guilliano Posts: 5,495
    The chainring is on the right way round, it's just a little bit too big for the ramping pins to work properly I think. It shifts to the big ring OK half the time, but just sits on top of the small ring instead of shifting down properly so the cranks turn but just rub on the chain instead of shifting onto it.
    http://www.flickr.com/photos/guilliano/
  • amaferanga
    amaferanga Posts: 6,789
    Is the spacing between the two rings the same as it was before? With non-Shimano rings you might need a spacer.
    More problems but still living....
  • mostly harmless
    mostly harmless Posts: 162
    The symptoms you describe sound similar to what happened when I was running a shagged out 36T ring where the teeth were very poorly defined. I'm guessing this isn't the case here.

    I'd measure your TA ring and the original Shimano one (using a micrometer if you've got one, if not put them on a flat surface and compare where the teeth are). You might find a little light filing on the inside of the TA ring's tabs will move it closer to the big ring and allow better shifting.
  • alan_sherman
    alan_sherman Posts: 1,157
    I had the same problem occasioanlly with a stronglight chainring (36) on the R700 compact. I've since changed both rings to TA rings and the shifting is fine.

    The issue is that the shimano outer ring is only really designed for a 34 inner ring. The profile of the inside of the shimano 50 ring is designed to direct the chain onto the 34 ring. With a bigger ring the ramp for the downshift is too far outboard to ensure the shift completes. So the chain occasioanlly rides on the inner ring before it engages.
  • guilliano
    guilliano Posts: 5,495
    Well with a 93 mile hilly sportive coming up I've bought a new 34t Ultegra inner ring to make sure my shifting is OK. Now I just have to fit that, new brake cables (my outer split by the calliper on the front brake) and new bar tape on Saturday night before the ride on Sunday morning! Hard night as I am working Saturday.
    http://www.flickr.com/photos/guilliano/

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