Vintage Peugeot conversion help and tips please

because you would need a new hubs that designed for fixed wheel (if you're keeping the original rims and spokes that come with the bike), the road one are designed both for freewheel and to hold numerous cogs, so it's not suitable for fixed wheel.

Just to add to Ed's comment.

It is possible to reuse the old road bike rear wheel as a fixed wheel but a lot of people say that you shouldn't. You have to 'suicide mount' the fixed cog which means that the lock ring is on the same thread as the cog and you use a hell of a lot of loctite to make sure it stays on. I used this method on my original conversion for a good few months without any problems but you have to make sure you know what you're doing and read up on it. Also read up on 'rotafix'ing your cog. This is a method of screwing you rear cog on really tight to make sure it doesn't move.

• The other thing to remember about doing this with the old road rear wheel is that it is dished to allow for somewhere between 5-10 cogs so you may have some trouble lining up your cogs/wheel with frame.
  
  

I can't stress enough how much reading up on with other people have done helps you to build your own. Just search for things that you hear mentioned and you'll get no end of really important info coming up.