Chainring BCD - Will it work??
 

Hi.. Ok so I just bought a rossin bike and found this engraved chainring... I want to buy it but I'm not sure how to tell the seller to measure the BCD...

Does anybody know the BCD for campy Nuvo / Super Record cranksets? I will probably buy a crankset on eBay and pop this ring onto it..

I believe it belongs on a super record crankset??? Not sure

Side note: that crankset is obviously the wrong model... Maybe someone knows the BCD of the G.S. crank arms so you can sell me righ away if it will work??

The seller wants $40 for just the Rossin chainring or $75 for the whole crankset... what should I do? Is the cleanser worth more than $35 if I sell it?

Thanks!

http://i1087.photobucket.com/albums/...e/3b69b8ac.jpg

A NR/SR is 144BCD and GS seems to have come in both 144 and 116 so this must be a 144 crank.

check sheldon's website for measuring the BCD without the tool that Park foolishly stopped making.

I generally dig into all the dusty catalogs I have around here but this is a great site lovingly maintained by one of our members (or maybe a former member?) and has lots of great stuff on it.

http://velobase.com/Default.aspx

144bcd. Always ask Sheldon first!

http://sheldonbrown.com/cribsheet-bcd.html

quick check - measure the distance (mm) between 2 adjacent crank bolts and multiply by 1.7013 = bcd.

As I mentioned it too bad Park no longer makes this tool. should anyone know the where abouts for one no one needs....

Thanks! Yea.. That tool would be handy...

Thanks! I asked the seller to do this to reconfirm

I'd buy the whole crank... but yeah, its 144 without a doubt.

1.7013 ?? :p
Really? You think we can measure the c-c of the bolt holes to the accuracy required where the .0013 comes into play? ;)

sorry, couldn't pass that one up.

And the GS stuff is getting more expensive; I guess because the survivors are rarer as compared to Record stuff. I'd pay the extra for the crank.

Haha ^ I was using a 1962 edition of "CRC standard mathematical tables", it has a neat chart for figuring "area, radius of inscribed and circumscribed circles for regular polygons". It carries every thing to 5 decimal points.

Thanks! I just got confirmation that it is 144 from the seller (just like everybody had said)

I will buy the whole crank then =)

Also I'm assuming nuvo and super record are both 144 as well?

Yup.

I don't know why the manufacturers won't just measure cranks using bolt center radius instead so one can just pit a ruler against the mounting bolt center and the chainring bolt center.

Chombi

Bcd = bcr x 2

Math Equals nothing without proper measuring
 

1.701x is also only on a 5 arm crank if you have 3 4 6 or 8 there is other math involved Also center to center measuring is ridiculous just measure edge to edge much easier

I don't know if they still do this, but FSA chain rings used to come in a cardboard sleeve that had a BCD template for just about all known sizes printed on the back. I had a couple, but I think they were lost when I closed my shop.

Since pretty much every manufacture marked/marks crank length on the back of there cranks and other details on the rings. Would it kill them to mark the BCD also?

+1

Yes, unless you're talking about very early Record cranks, which were 151mm BCD.

We need an "APP" for this

The 116 bcd would be the three-pin GS, I'm guessing.

No, there was a 5-arm 116mm BCD Gran Sport crank as well; it later morphed into the Victory and Triomphe cranks:

http://www.velobase.com/CompImages/C...F8912810B.jpeg

Right!! Forgot about that one!!

Quick? Youse engineers guys..

I've got one of those, thought it was some kind of artwork.