Can anyone advise me which bottom bracket I need for a Campagnolo Mirage 175 groupset? It's going onto an old Dawes Reynolds 531 ST frame.

The frame currently has a Shimano BB-UN100 bottom bracket, but it seems way off from being a good fit.

Thanks in advance!


As requested, here are some photos of my Campagnolo Mirage cranks:

Campagnolo Mirage 175

Also, I was advised that this bottom bracket was the one I need:

enter image description here

which I have now bought, but there seems to be hardly any taper on it:

enter image description here

When I put the crank onto it, there is about an 10mm gap at the BB side:

enter image description here

and about an 8mm gap on the crank side.

enter image description here

Presumably, that's not a good fit?!

Maybe a spindle with a similar length but with a more sever taper is what I need?


I've now fitted the BB and cranks onto my bike. I've only done the crank bolts up hand tight, but I can't imagine they would slide on much further when fully tightened.

The problem I have now is that I cannot select the large chainwheel on the front. (I've fully adjusted the front derailleur, but it just doesn't have the necessary reach.)

So, pretty sure I have the wrong BB. Can anyone advise on my next move?

  • 2
    Could you post a photo of the crank? There have been several different Mirages over the years, and 175 is not a model number but probably crank length in millimeters.
    – ojs
    Commented Jan 10, 2022 at 19:01
  • 1
    @ojs I've just added some photos and more info. To confirm, yes, 175 is the crank length. Commented Jan 14, 2022 at 20:59
  • 2
    Re the new pictures, looks good. There will almost always be a witness mark from initial installation on the crank tapers. If you're feeling unsure about the taper engagement, you could torque them on and visually confirm the tip of the new spindle is kissing the old witness mark. Commented Jan 14, 2022 at 22:01
  • (it doesn't have to be perfect and might not be) Commented Jan 14, 2022 at 22:54
  • I've pushed the cranks onto the new BB by hand and the spindle is about 4mm short of the old witness marks. Do you think that will be OK? (I can't tighten them properly as I don't want to mark the spindle in case the BB has to go back. Plus I have had too many nightmares trying to get cranks off spindles...) Commented Jan 15, 2022 at 11:33

3 Answers 3


The bottom bracket you bought looks quite correct to me. When the crank bolts are fully tightened, the cranks will slide in a a couple of millimeters.

The cranks are not going to slide in all the way because of two reasons: First, the original bottom bracket that these were designed for didn't have an indent for Shimano style BB tool but a flat plate that extended over the BB shell and needed a tool that wrapped around it (source: I have Veloce from that era on my fixie and it's basically the same crank and BB). Second, you have English BB shell that is narrower than Italian one, and the spindle is long enough to clear the Italian BB shell.


Campy cranks want ISO tapers and all Shimano bottom brackets are JIS. From sheldonbrown.com: "If you install an ISO crank on a J.I.S. spindle, it will sit about 4.5 mm farther out than it would on an ISO spindle of the same length."

I think that number is trustable. I'm also fairly certain all Mirage cranks are from the symmetrical spindle era, and I'm presuming your Shimano BB is too. If so you've got all you need to get to a spindle length that's potentially better than spec, since you haven't told us about the rest of the bike, i.e. whether it's a bike that wants Campy's target chainline in the first place.

If it suits you, a formula can be constructed from the above, i.e. give a variable to current chainline, target chainline, and current spindle, all of which you can measure off the bike, and then you can solve for the target ISO spindle length. In practice when I have to do things like this, I draw out two simple number line type diagrams to show my current arrangement and my target one, because unless I see it expressed that way I always second guess myself.

  • Sounds like a good answer as it is but it probably would benefit greatly from an example photo of the diagram you mentioned. A picture speaks a thousand words and all that.
    – pateksan
    Commented Jan 11, 2022 at 2:29
  • 1
    Tbh I sat for an embarrassingly long time trying to get my brain to spit out the algebra, it is very simple but just not my strong suit. All you do is say okay, my chainline is x with spindle length j, switch to iso and it's 4.5mm less, and then to get my ideal chainline y I need a spindle c thats longer or shorter by twice the difference between x-4.5 and y. Commented Jan 11, 2022 at 21:02
  • 1
    Thanks for the reply. Could you have a look at my update. Need to be sure first that I've got the right type of spindle, then I'll have a go at the maths! :-) Commented Jan 14, 2022 at 21:01

Campagnolo Mirage is an older, lower-end groupset. I don't think that "Mirage 175" denotes a specific groupset version. 175 is probably the length of the crankset in mm.

Campagnolo square taper cranks have used the ISO spindle taper, whereas Shimano (and many others) have used the JIS taper. Per Sheldon Brown, ISO spindles have a longer tapered area and a smaller broach than JIS spindles. A glance at eBay shows that Mirage doubles probably had a 111mm symmetric spindle. Most square taper spindles are symmetric, but by my recollection (which is not 100% guaranteed), some Campagnolo triple cranks for their higher end groupsets had a 111mm asymmetric spindle. So, don't get those. I believe that Veloce and Centaur BBs, the two groups higher than Mirage), should also have used 111mm symmetric spindles. In principle, you could also get a Phil Wood if you can’t find any of the above BBs. Phils are durable but expensive. There could be other third party manufacturers of ISO tapered BBs, but I’m not familiar with them. Miche is an Italian company that might be a source for more affordable BBs, but they don’t have much of a presence in the US.

Addressing the update to the question (added photos with crank loosely mounted to a Tifosi 111mm BB): when you tighten the crank bolts, the crank arms will get drawn further onto the taper. Furthermore, I would expect a bit of exposed spindle to remain with a BB of this length.

You wouldn't see that much exposed taper once the crank was tightened down on a Chorus or Record crank, but those were designed around 102mm tapers.

  • 2
    For what it's worth, cheap ISO replacement bottom brackets are available from Token and Origin8. I have no idea about their durability but you can get five for the cost of a Phil Wood and one more for the special wrenches that Phil needs. I'm quite sure that asymmetric spindles were used only with triples.
    – ojs
    Commented Jan 10, 2022 at 21:08
  • 1
    Thanks for the reply. I've just added some more photos and info. BTW, I'm in UK. Commented Jan 14, 2022 at 21:00

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