BO15 All Downhill

horsefarmer · Jul 11, 2020

A search of my 3pc crank inventory revealed many duplicates of the mtn bike crank that was no go. Have a few big ole road cranks 54t ! Cool but massive size hit chain stay... :cry:

Then found this guy. - Shimano RSX FC-A4105 170 mm crank - only 170mm but looks to fit the frame.

The 46t chainring combo with Shimano 5 Speed 14-16-20-24-28T Freewheel / 26 x 1.95 tires
should = 42 to 85 gear inches.
1st gear 28t 42 gear inches.
2nd gear 24t 50 gear inches.
3rd gear 20t 60 gear inches.
4th gear 16t 75 gear inches.
5th gear 14t 85 gear inches.
Compares pretty well with my Cannondale!
Cannondale Hybrid Bike H300
8 speed Shimano Alivo rear - 700c wheels.
Calculated the gear inches using stock 42 t high front cog.
1st gear 30 t = 36 gear inches
2nd gear 26 t = 42 gear inches
3rd gear 23 t = 47 gear inches
4th gear 20 t = 55 gear inches
5th gear 17 t = 64 gear inches
6th gear 15 t = 73 gear inches
7th gear 13 t = 84 gear inches
8th gear 11 t = 99 gear inches

Considering the crankset is just setting there, I'm thinking the chainline is much improved.

This build has a ball bearing bottom bracket. The axle I used was offset some to the crank side, I could swap that out but it would move the teeth closer to the chain stay.

OddJob · Jul 11, 2020

Because of the cross chain effect, 'big - big' 1st gear in rear to big chainring never works well. Stay below that combo, and your chainline is prob good to go.

kingfish254 · Jul 12, 2020

How much of the round seatpost is sticking inside of the square one?

horsefarmer · Jul 13, 2020

kingfish254 said:
How much of the round seatpost is sticking inside of the square one?

Maybe 1 1/4" or so is exposed at the top.. The clamp I'm using has a tab that stops it from going too far down the post.
The handlebar is pushed about 3" inside the old 1 1/8" steerer. I wasn't sure how strong the bar material would be so I thought I would back it up with the square tubing.