Chainring Size

I am converting a older road bike to single speed, is it possible to use one of the original chainrings for the single speed set-up. If so which would be best 39t or 53t all my riding will be on mostly flat roads....

You can use your current crank + one of the current chainrings if you want ...

You have to decide on the gearing that is best for YOU -- it really depends on the cog size you decide to use on the rear.

I recently set up a Single for riding on mountain roads! So, the gearing that I chose was close to my normal low (not counting the bail-out cog!) ... in my case, I ended up with a 32t chainring + 22t freewheel which yielded the equivalent of a 39t chainring + a 27t cog (actually, ~26.8125).

A bazillion years ago, I would probably have opted for the 52t + a 16t freewheel for Flatland riding ... now, I would probably choose the 39t-or-42t + a 16t!

I also set up another Single with a 43t chainring + an 18t freewheel ... I haven't decided if that is the right gearing for the non-mountain riding, yet.

If you initially choose the 39t, then you probably want a 16t cog/freewheel in the rear.

But, because each person is different, you may want to log a few miles with whichever gearing you initially choose to decide if you want easier-or-harder gearing.

ONE thing that you can try is to choose either the large-or-inner chainring on your next ride, and only choose-and-use ONE cog in the rear for the entire ride. OR, if in mid-ride you decide that the gearing is too high-or-low, choose another gear for the rest of the ride. After you pick a gear that seems to work with either chainring, then you can select the freewheel size that you want to use.

BTW. Typically, whichever chainring you choose is mounted on the inside shoulder to accommodate the chainline ...

If you're using a wheel which has a freewheel, then if you are planning to use a BMX freewheel, you will probably want to re-dish the rear wheel.

I would go for the smaller one. I can do 20mph on a 42/17 without spinning out. Plus, high cadence training is good for the legs.

I think you should consider whether you'll be wearing lycra tights and lowering the bar all the way before wanting to go any higher.

I am using 50X18 with 26" tires