Campagnolo compact chainring offset?

TommyS
TommyS Posts: 27
edited September 2010 in Workshop
Hello all,
apologies if this has been covered before (I couldn't find it searching although I raised a similar question 6 months back or so, but with no resolve)

I run a Campagnolo centaur alloy ultratorque compact chainset.

I've recently been seduced by the wonders of cyclocross and want to transfer this chainset to my cx new frame (note it will be my only bicycle).

I want to run a 46 tooth chaniring as my largest.
The smallest compatible ring is 48tooth.

What exactly is the "offset" used on campag rings?
Is this something I could replicate on a non campag specific ring with a pillar drill + lathe and several other workshop tools?

I'm really not up for the idea of buying another new chainset and still having to fit new rings on that too.

Any ideas?

Cheers
Thomas

Comments

  • Wappygixer
    Wappygixer Posts: 1,396
    The Campag offset really is an offset as the bolt that bolts the rings to the crank is offset from everything else.
    The only rings that seem to be available are genuine Campag or TA Nerius.The offset is actually 110mm but as I said before the bolt that fixes the ring to the crank is a bout 2mm longer.
    With the tools you have available I don't think it would take much to modify a standard 110mm pcd to fit it though.
  • TommyS
    TommyS Posts: 27
    Cheers Wappygixer

    I was hoping that one of the bolt holes was going to be a bit further towards the centre of the crank axle and it would simply be a matter of elongating one of the holes to fit this lower position.

    I'll be building up my new frame next week so I'll take the rings off the chainset and have a good look.

    Cheers
    Thomas
  • TommyS
    TommyS Posts: 27
    As a follow up (just in case anyone else was interested) and to answer my own question, it is very easy to fit 3rd party "non compatible" chainrings to campag' ultra torque compact chainsets.

    I fitted a 44 tooth outer to lower my gearing (34-44) to a level more suited to my style of cyclocross riding.

    The bolt hole directly behind the crank arm is approximately 2mm further out (in a vertical plane, away from the BB axle) than the others.
    Ie it sits on a BCD slightly larger than 110mm. All one needs to do is drill or file the 5th hole so it is slightly elongated to accomodate this difference.

    Easy.

    My fried with all the nice work shop tools was away so i did this on the kitchen table with a rat tail file.

    Assuming the outer ring you are using is the same thickness as the campag ones you will have no problems.

    However If it is thicker (as in my case) you'll have to thin the chainring arms.
    This isn't so fun and without decent tools will take a very long time.
    I gave up when the wobble in the ring got to an acceptable level.
    Once I can get to a lathe and sharp chisels I'll finish it off, but it does the job for now.

    Fitting a different inner ring will present more problems as you'll have to countersink the new hole position to accomodate the crank bolt. However I'd guess it is the outer ring that most people would be changing due to the limitation on compatible sizes.
  • BrenD
    BrenD Posts: 260
    I have done this using 36 & 48 chainrings from an old square taper Campag compact chainset. There is one other problem though, & that is the little pin that stops the chain dropping between the larget ring & crankarm. I had to drill & tap a new hole to move this pin.
  • satanas
    satanas Posts: 1,303
    You can probably get suitable rings from Chris Bell (google eggrings), or from one of the smaller Italian makers like PMP or FRM. However, they may not be cheap(!).

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