Originally Posted by
SoSmellyAir
Bicycle cassette (rear chainrings) standards | BikeGremlin
You plan to go from a 10 speed cassette (37.2 mm wide) to an 11 speed Shimano MTB cassette (40.6 mm wide), a difference of 3.4 mm in width.
In theory, if the outer edges of both cassettes (as installed) are in the same place, the center of the new cassette is 1.7 mm closer to the center of the bike.
In practice, this is a very small difference, and you may not need to move the chain ring(s) inward at all, especially if the 42T cog is just a bail out gear which sees only occasional use. What rear derailleur, bottom bracket, crank, and chain ring(s) are on this bike?
I have new rebranded Sugino 42/26t cranks to replace my old BB30 FSA 50/34t cranks.
I am planning to install FSA BB30 to English threaded adapter. Then I will add a 68mm square JIS BB for these cranks. Since BBs come in different axle lengths I can just get the correct size.
Here is my math.
My bike has chainline of 44mm, with a new cassette I will need 44-1.7=~42mm.
According to the shop, my new cranks have 43.5mm chainline with 68x116mm bottom bracket. A standard Shimano UN300 can be bought in 113mm. This should bring the chainline down to my target of 42mm. Plus/minus.
Did I get this right?