Advice on Cranks
By MrFixie
It is nice to find a bike that can be made fixed without having to replace too many parts. If you’re lucky, you may only have to reconfigure the rear wheel.
New cranks are a step you may have to take. Some of the better old road bikes have cranks and bottom brackets that can be reused in a fixed gear setup. When choosing your bike, look for cranks that have chain ring bolts as opposed to rivets.
If the bike has rivets that can’t be removed, you have two options: 
Run the chain on the inner ring and leave the extra chain ring on OR replace the cranks.
If the existing bottom bracket isn’t a common English threaded square taper or if the bottom bracket is in poor shape, you may need to replace it along with the cranks.
Some of my favorite cranks to use in fixed gear conversions are bulletproof cranks. These inexpensive BMX cranks come in several finishes and lengths and are comfortable, strong and lightweight.
