Again apologies for what I’m sure is a very basic question. But how easy is it to convert a fixie into a single speed freewheel please?
I know it’s possible to get bikes that have flip flop hubs, but I’m talking now about a bike that’s a fixed gear only.
What would be involved in such a conversation and how expensive, assuming standard easily available parts are used please? Is it a case of just changing the rear hub and installing brakes or am I being completely naive?
Thanks

It is extremely easy. You simply unscrew the lockring and fixed cog, and screw on a single freewheel. If it does not already have a front and rear brake, then you add them as well. You do not need to replace the rear hub or wheel.

Great, thanks. Sounds as though even I could manage that!
Just looking at different options

Just be aware that you will need special tools to remove the fixed cog. You will need a lockring tool to remove the lockring and a chainwhip to remove the cog itself. If you don't already have these, then it might be cheaper to have a bike shop do this for you. When installing brakes, you will need a cable and housing cutter.

I don’t have any of those tools. There’s a decent bike store about 30kms from us with a service/repair centre, so as you say that may be the safest option IF I need to go down this route. Thanks

Those tools are inexpensive and useful, cable cutters can get expensive, but you can effectively replace them with a Dremel tool and cutoff wheel if you already have that.
doing your own bike wrenching can be satisfying and rewarding.
learning how to switch or modify components can add a lot of flexibility to your search for the “best” bike for your current needs.

The simplest way is to replace the fixed sprocket with a single freewheel of the same tooth count. Then, you don't have to worry about whether you need to change the chain length, or if you can set the proper axle position in the dropout slot. If you do change the tooth count, if you keep it within one tooth of what you currently use, you'll probably be ok. Beyond that, be prepared to get a new chain as well.

Another silly question. Two actually!
Firstly how easy is it to swap rear cogs on a single speed?
Secondly, how expensive are replacement cogs?

You need the right tools and then it’s easy
to take off the lock ring and change the cogs.
cog prices vary, just google around for the size you need or ask around.
I have one of these and another similar tool on another bike. They come in handy even at home. You will also need to buy or make a chain whip.

https://www.retro-gression.com/colle...os-trixie-tool

If it's a single freewheel (as opposed to a fixed sprocket) you'll need the tool to remove the freewheel:


If it's a fixed sprocket, the procedure described by @TejanoTrackie above in Converting a fixed gear to a single speed is what you need.
Single freewheels can run anywhere from ~$10US to over $100US for a fancy one. I recommend avoiding the cheapest ones. Shimano single freewheels are reliable and affordable; I've had good luck with them.
Individual fixed sprockets come in a similar range of price points. Again, avoid the cheapest ones; they tend to be stamped from plate and have poorly formed threads which can damage your hub. You can expect to pay $20-$50US for a decent quality machined (not stamped) sprocket from Shimano, EAI, Miche, etc.

Thanks both very much indeed. I’m just thinking now about experimenting with different cogs on an existing single speed freewheel bike. So I’m assuming that would be easier? Also presumably changing the cog means adjusting the chain tension?

You'll need the right tools either way for swapping fixed cogs or freewheel assemblies; they both just spin on and off of your hub with the tool. You want a chain whip for both, and then a lockring tool for fixed, or, freewheels have different tools so you need the right tool for your brand of freewheel. The chain tension can be adjusted by moving the rear wheel forward or back, but if you're making a big change you may need to adjust the chain length to get it right, so another tool possibly needed for that.

You can also consider changing the front chainring. What kind of bike do you have? What are you looking to accomplish with changing the gearing?

Unless the sprocket change is within one or perhaps two tooth counts of the original sprocket, you will also likely need to add or remove chain links.

Thank you. I’ll have to build up a tool kit for my bikes for sure. I have the basics, Allen keys, tyre levers, pedal spanner etc but none of the specialist tools.
As you can tell I’m new to this and know very little.
I’m still looking for a single speed bike or possibly a fixed gear with flip flop hub that can then be used as a single speed. But I’ll probably be buying online, used and untried. I’m looking for a Fuji Feather or something similar.
My riding is done around a lake route 2kms in length and on smooth tarmac. There are a couple of slight climbs (nothing much and definitely nothing steep). I do 30kms every morning just for fitness/weight loss.
I currently have a Giant Escape RX hybrid and a Specialized MTB that I use in wet conditions.
I find I only use 2 gears on either bike, so thought a Singlespeed might be a viable option for me, assuming I can find the right gear for my needs so that I can get up the rises and not spin out on the flat.
I thought about a fixed gear but I’m not sure I can adjust to riding one!

Chain whip isn't necessary for a single freewheel; just the proper extractor tool and a wrench or bench vise to hold it.

Ah right on; so you have a handle on how gear ratios work then; my easy answer for riding on flat and especially if you're already conditioned/in shape is that the stock ratios you see will be comfortable enough to get you started no problem; usually some mix of 44-48 up front and 16-18 rear; a 30km ride will tell you if you want a taller gear but you'll be able to ride with whatever the bike you like comes with most likely and go from there. I personally think a fuji feather would be great for long lake path rides, give it a shot!

Most singlespeeds aren't actually sold as fixies, things like the feather can be a slight exception in that it comes fixed gear, but is still sold with a front brake at least and possibly both brakes, has brake compatible rims and most come with a flip flop hub. Only dedicated track bikes come with fixie only hubs and no brake tracks or brake mounting holes. The felt tk2 for example, which was a particularly common track bike in the 1700-2000 dollar range, came with flip flop hub, rim brake style rims, and brake mounting holes front and rear. So it shouldn't be hard to find something.
As for the tools, especially with SS/Fixies, getting the tools can save you some hassles in the long term. Park is great, and probably most common for chain whip, lock ring tools, and freewheel removers. But you don't need to pay their price for everything. Their cable cutter is nice but over priced for what is a wire cable rope cutter, places like farm and tractor will sell you the same tool but half the cost. Mine is made in Japan and was half the price, just watch for the ones that are exactly like the pedros brand, the handle squeezes close enough to pinch the skin on your palm.

The problem out here is actually sourcing things. There’s one decent bike shop in the nearest city which stocks some very expensive bikes and parts. But not things like Fuji. In fact no singlespeed or fixed gear bikes at all. Hence I’ll need to buy used online IF available.
As and when I find one I’ll be able to see if I need to change anything
The Fuji Feather is one model I’ve seen in groups being used here. Affordable and seems decent value. The roads I ride are all smooth tarmac twin lane. So easy to ride

Yes I’m coming to realise that unless I can find a fixed with a flip flop hun plus a front brake, I’m looking at a singlespeed. Fixed in principle sounds good but I think I’m too old to get used to riding one and I’d be a danger to myself.
I’m going to go back to the large bike shop I found in our nearest city to see what tools/spares (cogs)they stock. But I’m doubting it will be any of the brands you mentioned, so just have to find similar quality