Take the 2-minute tour ×
Bicycles Stack Exchange is a question and answer site for people who build and repair bicycles, people who train cycling, or commute on bicycles. It's 100% free, no registration required.

I am attempting to build a single speed bike for commuting from various spare parts. I'm unsure of what kind of crankset would be compatible with my frame. I have read from a couple sources that I can use a typical road double crankset with one chain ring removed, but I'm still a bit unclear on how to precisely determine compatibility with my frame.

My question is, in the most basic terms, what factors need to be considered when choosing a crankset?

The frame in question is a single speed cyclocross, a Bianchi San Jose.

share|improve this question
add comment

2 Answers 2

up vote 1 down vote accepted

The most important thing to consider is your frame, not your crankset. You can make almost any crankset work for a singlespeed.

Your frame needs to have horizontal dropouts so that you can tension the chain. Or you can use a chain tensioner, which is essentially the spring part of a rear derailleur. Looks like the San Jose has horizontal drops, so you're fine.

As for the crank, all you really need to worry about is maintaining chainline, which means that your rear and front cogs are lined up. You can affect this on the front by moving your one chainring into the large/small position on the crank, or using washers to move your chainring slightly over. EDIT: Now the overall position of the crank will be affected by the length of the bottom bracket spindle, as this will also affect the chainline. In practice, I wouldn't worry about this too much, again, because you can slightly adjust the position of the chainring after the fact.

In the rear, you can shift your hub axle slightly if you really need to, but you should focus on getting the front right before you resort to this. Note that this only applies to freewheel style hubs. If you are going to run cassette hubs for a single speed, then you can sometimes run spacers to get the rear cog exactly where you want it. There are some less other common configurations that I won't deal with here as well.

The other thing to keep in mind is that chains are meant to bend somewhat, as seen in normal use on a geared bike, and so a small offset angle is not going to hurt you.

share|improve this answer
    
Thanks, great info. One thing I'm also curious about that you didn't address is bottom bracket compatibility. Any thoughts on that? –  Ben Siver Apr 3 at 19:55
    
Edited the general post. Now, you said you had spare parts. Do you already have a crank? If not, what kind were you thinking of using? –  Booker Apr 3 at 21:27
    
Also, will you be running a freewheel or cassette? –  Booker Apr 3 at 21:39
    
Thanks again for the help. I do not currently have a crank, as I want to ensure I find one that will work with my setup. I don't really have thoughts on what kind of crank I'd like to use, other than a general idea of the gearing (likely 42t). I do plan to use a freewheel. –  Ben Siver Apr 4 at 16:26
1  
As for cranks, the short story is that almost any crank will fit on your frame. A crankset is usually coupled with a bottom bracket, and that bottom bracket needs to fit your frame. The bottom bracket you'll be needing must be English/ISO –  Booker Apr 4 at 16:54
show 1 more comment

Bottom bracket compatibility is usually determined by the crank— the manufacturer will specify a length. You can run into clearing issues using an MTB crank with a road bike or vice-versa, but that's not an issue for you.

However, if you're using a road double crank converted to a single, you won't really be in the normal usage spec of the crank, and exact BB length will likely be best determined by trial-and-error. You probably will want to use a shorter BB than what's specified for double use, since the specified BB length is generally designed to put the midpoint between the chainrings at the middle of a cassette. Best to buy your BBs from REI or another company allowing easy returns.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.