Wilfred Laurier

I am looking to replace the 1x ring on my fatbike, but I am confused by the BCD dimensions - the distances between the bolts are approximately 48mm, 53mm, and 63mm.

Is this a standard BCD for which I can easily find a replacement? I believe it is the original Comox crankset that came on my Norco.

I see most manufacturers have gone to direct mount chainrings, but I was hoping I wouldn't have to replace the whole crankset.

Thanks in Advance

MudPie

This link has a great discussion on BCD.. The BCD is not the distance between two adjacent bolts, but rather the measurement of a circle that goes thru the center of each hole. But knowing the distance between bolts can determine the BCD.

https://www.sheldonbrown.com/gloss_bo-z.html#bcd

HillRider

Also, "BCD" implies the bolts are equal distance apart and their location around the circle is symmetrical. Many modern cranks use a proprietary asymmetric bolt design so the old 5-bolt or 4-bolt chainring designs won't work. You may be stuck using a replacement chainring from the OEM crank supplier.

mpetry912 

that's a great link to Sheldon's article, thanks for that !

/markp

SurferRosa

It's better to avoid inclusion of any pics, so the threads last longer with more unnecessary posts with irrelevant questions. So few people have cameras these days as well.

SoSmellyAir

Come on, we all enjoy a full on differential diagnosis exercise harnessing our collective experience and wisdom.

grumpus

Stating only the BCD and bolt count (with implied equal spacing) is sufficient to specify many replacements, but unevenly spaced fasteners still have a BCD - I suppose they would additionally be described by the angles they make with the crank.

Hondo6

FWIW: some cranks don't have a single bolt circle. This link describes some that have bolts spaced at multiple radial distances from the center line of the crank spindle:

http(colon)(slash)(slash)pardo(dot)net/bike/pic/mobi/d.shimano-biopace-bolt-pattern/index(dot)html

I've had difficulties with the secure version of the link using Firefox (old TLS version on server), but the nonsecure version of the link works if your browser is set to allow nonsecure connections. Replace the terms in parenthesis in what I posted with what's in parenthesis and it should work.

This above link is from the Bicycle Museum of Bad Ideas page on the same site. The rest of the page is also a pretty good read.

http(colon)(slash)(slash)pardo(dot)net/bike/pic/mobi/index(dot)html

grumpus

I'm not sure why you didn't just post this for a link to that page. Presumably the weird spacing was so you couldn't fit the slightly Biopaced ring the wrong way round and spoil its magic.
It sucked me in - I'm not sure what's so fascinating about all the failures, I guess just the same as Just Rolled In for anyone who works on cars.

Hondo6

See the second item you quoted above. In some browsers, older versions of TLS (prior to TLS v1.2 or v1.3, as I recall) are permanently disabled for security reasons and cannot be re-enabled. Firefox after v97 or thereabouts is one such browser; it's now at v112+ (I have an update pending). Anyone using a later version of Firefox thus has the issue - and a fair number of people use Firefox instead of Edge/Chrome/other browsers.

In such a case, you have to load the web page using nonsecure http (no letter "s") - if the web server server hosting the page supports nonsecure connections. You may also have to change your default browser settings to allow nonsecure connections. Some recent browser versions have a default setting of "secure connections only".

The Bicycle MoBI page may be where I first ran into this issue. And yes, it's a fascinating look at "oopsies" from cycling's past.


Possibly - but Shimano didn't do that with their other Biopace chainrings, which use standard 110mm and 130mm BCDs. Can't see why they'd single this one out for a nonstandard BCD among all their Biopace chainrings, but maybe that was the reason.

grumpus

Weirdly the link I posted, which worked in "Preview Post" didn't work at first once posted: my browser (old and doubtless insecure) displayed the "Not Secure" message so I clicked "proceed - unsafe" and got a 404, but then I clicked it again and went straight there. I really should update this PC - there's nothing valuable on it but still ...