Q Factor on new SRAM XX Chainsets
TheJackal
Posts: 169
I know how the Q Factor is computed but how do I know which one (156 or 166) is suitable for an old Scott Scale 20 that I'm refreshing?
Is it how wide the rear stays are apart? The width of the BB, or just what I'd prefer?
Currently there is a Shimano Hollowtech II BB on it and some measuring indicates that the XT cranks that are on there are more than 149mm apart.
Like most I couldn't give a flying fig about the Q factor other than I don't want to purchase 156 only to find they are too narrow for the BB and frame. Problem is I can source the 156s cheaper than the 166s.
Is it how wide the rear stays are apart? The width of the BB, or just what I'd prefer?
Currently there is a Shimano Hollowtech II BB on it and some measuring indicates that the XT cranks that are on there are more than 149mm apart.
Like most I couldn't give a flying fig about the Q factor other than I don't want to purchase 156 only to find they are too narrow for the BB and frame. Problem is I can source the 156s cheaper than the 166s.
2012 Santa Cruz Highball Carbon 19 lbs
2009 Ibis Tranny __ lbs
2009 Ibis Tranny __ lbs
0
Comments
-
It's the width between the outside faces of the cranks. Plenty of frames don't have the chainstay clearance for 156s, hence their being cheap. Find out which was specced on the old Scale RC and buy those, it may have had 156s.0
-
I measured the distance between the outside faces of the existing XT ones and it's 179.
Subtracting the width of the cranks themselves (30) I got 149 which provides adequate clearance.
That would indicate to me that 156 or 166 would fit??? What do you reckon?
It's a 2006 Scale 20 and I cant' seem to find any info on Q Factor.
Was it actually an issue in those days?2012 Santa Cruz Highball Carbon 19 lbs
2009 Ibis Tranny __ lbs0 -
No, the 156mm is the outside face, so if you subtract the width of the cranks on the XX the internal width is more like 125mm.
It's more of an 'issue' on the road, doesn't matter as much on the MTB.0 -
Hmmm!
Just measured from the outside of the chainstays and it measures about 128mm!!!
Not sure, now!2012 Santa Cruz Highball Carbon 19 lbs
2009 Ibis Tranny __ lbs0 -
SRAM give a clearance of 2 X 65.7 for the 156. That makes a total of 131.4.
Presumably the 156 cranks are 24.6mm thick at the end which means that I've got about 3-5mm clearance in total!
Too close for comfort?
The 166 gives a 141mm clearance.2012 Santa Cruz Highball Carbon 19 lbs
2009 Ibis Tranny __ lbs0 -
It is close - get some flex from frame or cranks and could rub!0
-
Exactly what I thought.
Plenty of 156s getting sold on for the same reason, me thinks.
Looks like I'm back to the drawing board or shell out for the 166s.2012 Santa Cruz Highball Carbon 19 lbs
2009 Ibis Tranny __ lbs0
