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Front shifting with oval rings

amaferangaamaferanga Posts: 6,789
edited October 2011 in Workshop
My SRAM Red rings needed replacing and I impulsively bought some Stronglight CT2 Bioconcept rings which I believe are very similar to Rotor rings in the middle position. Happy with them in general, but I just can't get the front shifting right. The front mech has to be raised a bit to clear the high point of the ring meaning it's a bit further from other bits of the ring and consequently front mech set-up seems to be critical.

But I either get really sluggish shifting or throw the chain off the outside of the big ring.

So what's the secret? I've tried rotating the mech in a bit and out a bit, it's as low as I can go and still clear the big ring, but no matter how finely I tinker with the limit screw I still either get censored slow shifting or throw the chain. I've heard of a shim that re-angles the front mech so it matches the oval ring better - is this what I need and if so where can I get one?

I'm liking the rings, but I'll be back to round rings by next spring if I can't get the shifting sorted.

Anyone?
More problems but still living....

Posts

  • PokerfacePokerface Posts: 7,960
    I try and bend my mech up a little at the rear so I can lower it closer the the ring without it catching. Otherwise, it's just a matter of getting the limit just right. Like you say - it's finicky.
  • BigLee1BigLee1 Posts: 449
    Bloody hell!! I had a Biopace chainset on my `88 Muddy Fox Courier, they were censored then as well!!!
  • Finicky is the word. But once set up, shifting is the same as normal.

    I swap my crank with oval rings between two bikes, one a steel audax, was perfect first time, the other, spesh tarmac, took forever to get right. I didnt find a secret - just trial and error with height, angle and limit screws!

    jon
  • napoleondnapoleond Posts: 5,990
    I'm still yet to find the secret...

    Oh, and I've got a 1986 muddy fox courier with a set of knee-wreckers on. The rotor rings are quite different...
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    ABCC Cycling Coach
  • amaferangaamaferanga Posts: 6,789
    BigLee1 wrote:
    Bloody hell!! I had a Biopace chainset on my `88 Muddy Fox Courier, they were censored then as well!!!

    Only the new generation of oval rings are fundamentally different to the Biopace and they're not censored .
    More problems but still living....
  • My chain rings need replacing and i was looking at Rotors. Having done a lot of research apparently there is always a compromise with shifting performance. Before I purchase I would be interested to know what you mean by 'sluggish'. Is it really bad? As I may stick with round rings if it is not good.
  • RedJohnRedJohn Posts: 272
    amaferanga wrote:
    BigLee1 wrote:
    Bloody hell!! I had a Biopace chainset on my `88 Muddy Fox Courier, they were censored then as well!!!

    Only the new generation of oval rings are fundamentally different to the Biopace and they're not censored .

    Hmm - that's what people said about Biopace, with reference to '70s versions of the concept ...
  • amaferangaamaferanga Posts: 6,789
    RedJohn wrote:
    amaferanga wrote:
    BigLee1 wrote:
    Bloody hell!! I had a Biopace chainset on my `88 Muddy Fox Courier, they were censored then as well!!!

    Only the new generation of oval rings are fundamentally different to the Biopace and they're not censored .

    Hmm - that's what people said about Biopace, with reference to '70s versions of the concept ...

    Plenty of websites explaining the difference if you're actually interested.
    More problems but still living....
  • I've got Rotors on my XC and time trial bikes and, although the shifting, especially shifting to the big ring, is a bit sluggish, the advantage I feel the rings give me is worth it. Getting the set-up right is a bit of a ball ache but is do-able... at least you're not trying to fit the Osymetrics that Wiggins and Millar use... I read a quote from the mechanic that he almost lost the will to live.
  • Even if shifting from small ring to big ring is 'sluggish' - how often do you actually make that change and how much difference is the 1/2 second longer it takes to make that shift going to make in you ride?

    The benefits of the rings far outweigh any slow shifting issues you might have (and I've personally not noticed ANY shifting issues myself).

    Anyone who thinks Rotor rings are a silly idea should actually either try them or read up on them first. There are very good reasons why they are becoming more popular (even amongst Pro's) and why they are NOT anything like Biopace.

    They are not for everyone - but should never be discounted out of hand.
  • mrdsgsmrdsgs Posts: 336
    part of the solution is to change little to big ring or vice versa smoothly at the same point of your crank rotation. For me the change is more or less instant and I have three bikes with Q rings. I tend to change big to little and vice versa naturally with the right crank at between 1 o'clock and 2 o'clock, i.e. just BEFORE the Q rings are at their biggest. If you change at 3 o'clock my 53/39 setup is then effective 56/41 (both Q rings on default position 3) then the effective 15 tooth difference is a bigger climb or drop for the front changer, hence the sluggish change some people find.

    With perhaps a 52/34 compact setup this difference would be even more pronounced.

    In terms of setup I just aim for a 1-2mm vertical gap between big ring at its biggest and the nearest point on the front mech outer plate. On one bike this meant slight filing to extend the top of the channel of my braze-on front mech bracket!

    There is also a bit of a knack with most front changing (I use old style shimano ultegra 10 and Campag Record 10 on different bikes) to change without having pedal cranks under full load when front changing. It does come with a bit of practice and whilst it might "waste" half a turn of full pedal force the impact on speed must be negligible and is more than compensated for by the slick front change it enables.
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