Originally Posted by Hollywoodguy99 .
Great answer with great questions.
New cranks (Dimension 175mm Cycle Cross)
New Tangent 41 T Chain Ring
Starting with 7spd cassete and spacer
changing to Shimano 9spd Casettte (hub designed for 8-9 spd)
New Medium Swing Derailleur (Sram x7 or x9 series most likely) pairing with matching shifter.
The sheldon article is great, I guess I am trying to have to avoid reassembling my front drive train and measuring.
If your current crankset and your planned new crankset BOTH have
square taper spindles & crankarms, then you need to know that there is a great deal of
variety -- or, to put it another way,
little continuity -- in which spindle will work with which crank to yield a consistent chainring offset ...
One thing about spindle length (
regardless of type) is that it affects the chainring clearance, or lack of ...
AND/OR, crankarm clearance relative to the chainstays.
Without seeing your bike it is difficult to say what spindle length (
as you can see, I am presuming your bike currently has a square taper BB spindle) you should use, but if I had to guess I would say that you want a Bottom Bracket with a 113mm asymmetric JIS spindle.
If you will [COLOR= rgb(24, 24, 24)]eventually be using a different 4-arm 104BCD crank or other MTB crank, then your only option will probably be to mount the chainring on the inner shoulder -- THAT IS, if you were NOT going to replace your current crankset, then you would simply mount the chainring on the inner shoulder of the spider with some BMX chainring bolts ([/COLOR]
or, use spacers in lieu of the absent chainring[COLOR= rgb(24, 24, 24)]), or equivalent -- that is, as delivered from the factory, THE MIDDLE RING IS YOUR IDEAL CHAINRING OFFSET FOR YOUR FRAME ([/COLOR]
presuming a geared drivetrain[COLOR= rgb(24, 24, 24)]).[/COLOR]
In theory, to continue to use your current crankset, you would want a spindle that is ~10mm shorter ...
If you are trying to minimize your immediate effort, then you should simply buy a set of the fore mentioned BMX chainring bolts (
which you will eventually need for ANY double-to-single crank conversion) & mount the current outer chainring (
which I presume is a 42t chainring) on the spider's inner shoulder as I have described OR buy the appropriate tooth count chainring (
is there a reason that you want a 41t chainring?) & mount it on the inner shoulder of your existing crankset rather than buying a new crankset.
OR, to put it another way, the ONLY reason to change to the referred to CX crankset (
whatever THAT is supposed to designate vs. BCD measurement unless it means that the crank comes with 48/38 chainrings) would be for cosmetic reasons (IMO) whereby you will be able to mount the chainring on the outside shoulder OR if you want a 5-arm spider OR ...
et cetera