Hi. I am planning to convert my current 10 speed bike into a single speed bike. My first step is replacing the crank and crank arms. However, I do not know what size to choose and whether or not I would need a new BB. Can anyone help me through the process?

Man, I hate to say it, but you aren't going to get step-by-step help.

Start here: https://www.sheldonbrown.com/fixed-conversion.html
and here: https://www.bikeforums.net/showthread...ed-Start-Here!

Forums are good for getting answers to specific questions or help with specific problems. But, you are starting a project...from scratch. This is like saying, "I'm building a house. Just bought a plot of land. What's next?"

If you don't have much experience with bikes, converting one can be a very frustrating and expensive experience. The key to most successful conversions is knowledge and experience.

My advice:
- Look for a local co-op for help
- Look to a local friend for help
- Look for a local bike shop for help
- Consider buying a new bike ($300) and be riding by the weekend and save the 10-speed for longer rides

consider keeping the bike geared, I heard the coolest new thing is old road bikes, NOT converted to FG.

That would be a rare sight!

Would people on those be the real hipsters??

it's more ironic to not convert working road bikes now than to convert them.

I wouldn't say replacing the cranks and crank arms is the first step. Before you do that, you need to figure out what you're going to do about chainline. If you're going to buy a new set up fixed gear wheels, that will determine the chainline and which crankset and bottom bracket you should get. If you're going to respace and redish the existing rear wheel or use a set of spacers and a cog that slips over a freehub, then you can set the chainline to whatever you want and you have more freedom with your crankset bottom bracket choice.

Post pictures of what you have -- close ups of cranks and the rear hub -- and you'll likely get more helpful advice.

get a sealed BB no matter what, even if you just install one the same size as your current unit

TBH, since you are doing a 'conversion' you should get your rear wheel 1st (get proper width!) and check your chainline... That way you can see if your chainline is OK before you dump loads of cash into cranks that you might not need.... The last conversion that I did used the same chainwheels and cranks, but just needed a little narrower BB. For some reason it used to be a road-double, but it had a road-triple (aka MTB) BB... weird. Anyway, it's fixed now! (53/17x700c... big chainring!)

I like the flip-flop hubs too, you can usually run them with no dish in the rear, so it makes for a very strong wheel that is super easy to work on.