mtb chain rings - interchangability?

[kosmonooit]

Got a very naaice Raceface Atlas crank in today but alas no chainrings ..... silly me. It's a 4 hole.

 

Happy with the Truvativ rings that came with the Noir cranks fitted onto one of my other bikes, will these 4-hole Truvativ Chain ring (like those listed on CWC) fit the above? I was under the impression that they are either 4 hole or 5 hole - but they say "Replacement middle chainring for Truvativ MTB cranksets" so wtf?

 

Is BCD also a variable? What exactly is that measurement?

 

Thanks.

Edited March 22, 2011 by kosmonooit

[RodTi]

My limited knowledge on this, gleaned from scouring the net this evening in my attempts to sort out a SS crankset - suggests the following:

 

The BCD of different cranks can be variable - but 104mm appears to be quite a common standard amongst most of the Shimano cranks... Not sure about RF though...

 

I would reason you hit CRC or the actual RaceFace website, and get technical info for your Atlas cranks - you should be able to confirm what the BCD is for them.

 

With this - you can then check out the various chainring options that you're considering - they should also list their BCD in the spec section... I presume if the bolt-number and BCD for your crank and chainrings match - then they should work...

[kosmonooit]

Thanks - managed to find out what BCD is - 104mm seem the standard for the larger two rings

 

http://www.bikeman.com/images/stories/Pit-Tech/BCD.gif

 

Compatibility is not really mentioned, but I did fit new Raceface ring set to Shimano XT cranks a while back. Think I will give CWC a call tomorrow to confirm, but still not sure all 4-hole 104 BCD rings are the the same fitting

 

Shimano 44 T Hollowtech

 

http://www.cwcycles.co.za/sites/default/files/imagecache/product/xt44.jpg

 

 

Truvativ 44T

 

http://www.cwcycles.co.za/sites/default/files/imagecache/product/truvativ_44t_black_chainring.jpg

 

Same?

 

 

btw Raceface web site is dead - the company closed down

Edited March 22, 2011 by kosmonooit

[pierremerv]

I recently bought a set of slx rings for my mates raceface evolve cranks. Both are 104 mm. The granny and big ring fit perfectly but the middle ring has a plastic moulded piece on it that seems to help the chain up from granny gear to the middle ring. If you look at the chainring the plastic piece is also on the most inner piece of the ring where the bolts fit. I had to file some of that plastic away and then it fitted fine. You don't interfere with the working of the plastic piece at all. Not sure if the xt rings are the same though.

[Tankman]

Thanks - managed to find out what BCD is - 104mm seem the standard for the larger two rings

 

http://www.bikeman.com/images/stories/Pit-Tech/BCD.gif

 

Compatibility is not really mentioned, but I did fit new Raceface ring set to Shimano XT cranks a while back. Think I will give CWC a call tomorrow to confirm, but still not sure all 4-hole 104 BCD rings are the the same fitting

 

Shimano 44 T Hollowtech

 

http://www.cwcycles.co.za/sites/default/files/imagecache/product/xt44.jpg

 

 

Truvativ 44T

 

http://www.cwcycles.co.za/sites/default/files/imagecache/product/truvativ_44t_black_chainring.jpg

 

Same?

 

 

btw Raceface web site is dead - the company closed down

 

Those two are the same.

They might look different but as long as they are both 4 hole 104mm BCD, they will fit.

[kosmonooit]

Spoke to CWC - they said generally all interfit except some Shimano models to not fit onto other Shimano.

 

Something to bear in mind when buying cranks. And check cranks come with rings! The last crankset I got (Noir) did come with rings, these Atlas ones not. Was not specified on the CRC specs for that crank.

 

I have now ordered a Truvativ set. All I need now is a Lefty Max 140