Damn, this was hard!
It took me month to get a Campagnolo chain ring with a BCD (bolt circle diameter) of 151 mm. I didn't care if it was for a 3/32" or 1/8" chain. It just had to be affordable / available at a reasonable price.
And finally I got exactly what I wanted! 3/32" is ideal, because most of my other rings have that size. That means good compatibility. And this ring should go on a very small bike, maybe for a junior rider, so the no. of teeth should be not too high. 48 teeth is ideal, because I can also use it myself, for example with a 14 or 15 teeth sprocket.
What's the deal with the 151 mm BCD?
To be honest, that's a bit of a problem. When I bought a Campagnolo Pista chain set, I was convinced that the BCD was 144 mm, same as the sets on my other track bikes.
What I wanted to finish the build (I thought I had all the parts), it turned out that things didn't fit, because of the crank's BCD. What a mistake!
Even then, I thought that it wouldn't be a huge problem to get a fitting chain ring. Well, I was wrong!
First of all, these rings are very rare. And because of that, other buyers push the price up sky high. Or the sellers know pretty well what these rings can be worth and ask insane prices.
Then the last hurdle: this is the 3rd 151mm chain ring that I've bought, but the 1st two are still "on the way". And so is another, 144mm, ring. It looks like postmen in U.K. or The Netherlands collect chain rings. I doubt if these 3 missing rings will ever show up. Waiting already several months now and the busy month of Christmas is already far behind us.
But at this moment I'm so happy that I received this part. And it's all perfect: affordable price, 3/32", 48 teeth, Record style and New Old Stock!
For the bike in question (Rossin), I prefer the Record "double rim" chain ring style over the more prestigious Super Record. I remember that "Record" looked more average or even cheap, while a Super Record had the image of quality, value, pro, etc. We all know how much of a snob or poseur we are if that makes the difference, but that's how things go.
Super Record may have more prestige, but this Record is just nicer!
What's the story of the different BCDs?'
That's the Campagnolo history / time line.
During the ages, they changed the diameter a couple of times.
Maybe a larger circle (crank spider) offered more stiffness and less wobbling chain rings, it limited the choice of (small) chain rings.
The original size of a 5 arm spider was 151 mm, introduced in 1958 (?).
Later (1967?), it was reduced to 144 mm, the current standard for track cranks (that don't need a second or third small ring). This can take 41 teeth chain rings, vs. 44 teeth as a minimum for 151 mm cranks.
The actual BCD (since 1984?) for road cranks is 135 mm for Campagnolo (smallest chain ring 39 teeth) and 130mm for Shimano and most other manufacturers. "Compact" cranks for double rings go down to 110 mm, an old MTB standard.
23 hours ago