I have been considering converting a late 1980's, early 90's Peugeot 12 speed, to a fixed gear bike. I am new to the fixed gear phenomenon so my question may seem naiive. The question is, why wouldn't I just leave the current configuration, keep it in a high gear, and resolve not to change gears or coast? Does it have something to do with the chainline?, efficiency?

I should point out that I am 59 years old, in reasonably good shape, but at this point should I even be considering a fixed gear. I am intrigued by the potential fitness aspects.

I mostly ride my Sirrus Comp at present, sometimes the Peugeot, and some times a Trek Navigator 500.

Riding in the highest gear all the time will mess up your knees.
The gear you select for a single speed should be right in the middle, so you can climb and also sprint.
You can experiment with your bike before converting to figure out the right one. I suggest use the
small chainring and pick a middle gear in the back.

Deciding not to change gears or coast is not the same as riding fixed. You don't have the same intimate
connection to the road. You wont be able to back-pedal either, which is the easiest way to make small
decelerations on the fixie.

thanks for the input, makes sense.

Besides, if you have enemies, as I do, and they try to eliminate you by cutting the brake cables on your bicycle, their plans will be thwarted because you can stop using your chain, thereby living on to fight another day.

The fitness aspects of riding your current set up with no coasting is greater. On your fixed, your pedals will carry your legs through the "dead spot". Also you'll be more inclined to tackle hills on your geared bike. Just sayin.

So you recommend not converting ?

If you want single-speed, the reasons for doing it properly, rather than simply leaving it in one gear, are mostly about it looking nice. Fixed, however, is a quite different riding experience. If you don't want to experience what it's like not to be able to coast, and to be able to slow down with your legs, then there's no reason to do it. If that sounds interesting and potentially fun, then the only way you can do it is by converting to fixed.

I have a single-speed road bike. It has no particular advantages (small weight savings, and chainline aside) over a multi-speed simply left in one gear, but it looks MUCH prettier, in my opinion, plus, when I'm riding, if I'm tempted to shift, I can't. There's a certain freedom to not ever having to think about changing gear, and if you still have all your gears, the thought is still there, I guess. It's not a big deal though. My two fixed gears are a completely different experience. I've posted my SS below - doesn't that make you want to get rid of the gears?

I can't say that outright in here can I? I'd suggest you set your bike up however you think you'd ride it the most, as that's really where you'll gain the most benefit regarding fitness and enjoyment.

Even though this forum is full of fg advocats, lots of people don't like it. If you want to just try it, just buy a cog and do the suicide hub route (keep your brakes on!)

Sweet ride, and makes me think I should pursue the fixed gear conversion.

Thankyou! That one isn't fixed, it's single speed freewheel. My fixes are below - an EG Bates track bike (lots of fun, but a rattly ride, and the track fork doesn't like the front brake much. Soon to be used just for track), and a Nigel Dean conversion. This bike is ridiculous. I built it to look cool and it does, but more than about 6-7 miles and it's really getting uncomfortable. The fact is, I put a lot more miles on the SS bike than on either fix, which makes me think I ought to build another fixed gear, but on an appropriately sized road frame (the Nigel is too small, really), with a sensible, normal stem!