Hello. I have been riding my c.1985 Centurion Ironman for a month or so now after dusting it off and installing some replacement parts. I have been wondering how to get a bit lower gearing (I am not as young as I used to be). It came with a 52/42 chain ring and Shimano 600 13 - 24 6-speed freewheel. So, I thought I would look into upgrading to a 7-speed freewheel. I did some reading on the subject and it sounded like it might just work. Some articles said that you might have to widen the rear frame and re-dish the rear wheel due to the chain hitting the frame. Well, I thought I would go for it.

I ordered a Shimano 7-speed Hyperglide freewheel (13 - 28, same exact sprockets except for the 28-tooth) and a SRAM chain from Harris Cyclery. When I set the two freewheels next to each other, the 7-speed was about a half-cog wider than the 6-speed. I popped the freewheel on and, lo-and-behold, the rear wheel still fit on the bike. I shifted the chain into the highest gear and the chain still had (a little) clearance. Another worry was whether the rear Shimano 600 derailer would be able to shift to the 28-tooth sprocket; that too worked. I took it for a spin and it all works great.

Now I have a 14-speed bike with a decent low gear for all those hills (in Western Washington we have lots of hills).