bikex10

I am in the process of building up an old Giant road bike. I am wanting to make it a 9x1. I am wanting to use a road crank with only the large ring, but respace the crank so the large ring will be at the proper alignment. How does one determine the proper bb width to achieve the alignment?
I have thought of buying a track crank, but I can purchase new 105 for less money and in the color (black) that I want.
Thank for any input.

TallRider

(I'm assuming you have a square-taper BB/crank since it's an older road bike.) Your current bottom bracket probably sets the crank up for a "road" chainline where the centerline between the chainrings is at 43.5mm. You now want the outer ring at 43.5mm. And whenever I've measured road cranks, the chainrings are 7mm apart (this includes a 9-speed FSA compact double - chainrings are same width apart as an old Schwinn-approved "Le Tour" crank). So you want to move the outer chainring 3.5mm closer to the bike.
Assuming you have a symmetrical bottom bracket axle (which ain't guaranteed) you want to get a new BB whose axle is 3.5mm shorter on each side, so a BB axle that is overall 7mm shorter.

Now, since you're going with a new crank, you may be out of luck because the 105 you're probably talking about uses an Octalink BB, and I think the Octalink BB for road bikes has its smallest BB axle in design for road doubles. Meaning that you probably can't find one that gets you a narrower chainline. I don't remember 105 ever being produced in black except with an Octalink BB.

It may be worth getting a square-taper crankset, say one that used a 115mm bottom bracket for proper road-double chainline, and then mating it with a 107mm bottom bracket.

You'll also need new chainring bolts - narrower bolt-stack is necessary if you're only holding one chainring to the crank. This costs about $5 usually.

bikex10

Timcupery:
Thanks for the reply and info. It will help me with this build.

dobber

Just out of idle curiosity, why bother shifting the crank. In it's current position the outer ring worked fine when it was a fully geared setup, right?

If you're worried about chain jump, leave the front derailleur on or get one of those roller mechs specific for the task.

Just my two cents

Steev

Because this will mean you are effectively cross-chaining when using the lower gears, something that people are always told not to do to avoid excessive drivetrain wear.

LóFarkas

All 9 cogs will never work decently with a single crank. That's a huge distance for the chain to travel sideways (Cf triple cranks: people don't use the middle ring with the largest, nor the smallest cogs). You're best off guessing which cogs you'll use most and shifting the alignment towards that region.

TallRider

Lots of people run 1x9 commuter bikes, especialy on touring or cross frames that have longer chainstays. It works well enough and most of your riding is done in the middle range of gears anyway. Also, 1x9 isn't really any different than 1x8 since the cassettes are the same width.

I run a 1x5 on my commuting bike.

I agree that this ain't ideal on a bike with shorter chainstays though.

Rowan

Not in my experience. I think you will find many riders use their centre ring on triples the most, and range between the biggest and smallest rear cogs without a care in the world. Cross-chaining occurs primarily going from the little-to-little and big-to-big, plus one or two cogs either side. Chainline is the critical measure to using a 1x9 satisfactorily.

erader

i run a 1x9 and i agree. my big cog is a little noisy because i spaced the BB out 2mm on the driveside so my 36-tooth ring had a little more clearance (my mtb frame was designed for 34-tooth max, i figure).

still, i shift across all nine cogs with no problem.

ed rader

erader

hmmm. can't you run the ring on the inside and space the BB out half the difference between your chainrings?

or are those BBS not adjustable?



ed rader

sivat

There are some decent, black single speed cranksets out there. I know IRO has one (I think its 110bcd though) and I'm pretty sure the sugino RD comes in black.