Lets start with the basics, what is it? Basically a CX bike, nobbly tyres, drop bars with a singe gear ratio. If you want to look through a list of SSCX off the shelf bikes and frames head to https://sscxworld.wordpress.com/bikes-tech/.
There are quite a few ways you can kick off with SSCX and here are a few options:
Option1: Chain Tensioner: By far the easiest and cheapest “The Chain Tensioner”. You basically remove your rear mech and bolt the tensioner in its place. This gives the chain tension so that it doesn’t boune off you sprockets, as once you remove the rear mech, there is nothing to keep the chain tensioned. Regarding chains, some people opt for a thinker / stronger but heavier 1/8th gauge chain, basically a BMW chain. Super cheap, around £5 for a gold KMC. Or you can use a standard 3/32, but the chain will denote what width sprockets you decide to go with.
For your rear sprockets (I will get on to the choice of size shortly) you can buy various combinations. You basically remove your cassette and replace all those 9/10/11 gears with just the one. Obviusly sitting there on its lonesome it will rattle around, so you basically put a wide plastic / metal spacer either side. Then tighten with a cap like you would do a normal cassettte. You can buy a full starter type kit from Chainreaction here https://www.chainreactioncycles.com/dmr-simple-tension-seeker-single-speed-kit/rp-prod10009 for £25 that contains the tensioner and a sprcoket and spacers. All you need to get going.
If you want to swap out for a different ratio of rear sprockets to make your effort / ride easier or harder, than I choose Shimano DX sprockets; they are around £4 each and take a 3/32 chain. As the sprockets sit on your alluminium freehub, over time they do damage it due to the narrow width of the sprocket making contact with the freehub. To overcome this you can buy a number of sprockets that are considerably wider at the base, such as Halo Fat Foot or Surly sprockets, see below, which have a wide 6mm base, causing less damage.
The position of the single sprocket on your rear freehub should ideally be located on the freehub so that your chainline is as straight as possible, and deviaiton may cause additional chain wear or the chain to jump. You can get some spacer kits with smaller increments, such as 5/3/2mm so that you can accurately position your rear sprocket in the exact position. See below:
Option 2: Horizontal Drop Outs: This is basically a different way of tensioning the chain, instead of standard vertical drop-outs, you slide the wheel in and it moves around 15-30mm forward and backwards to tension the chain, these are originally from track bikes. Horizontal drops are frame specific, so you are basically going in full bore if you decide to purchase a horizontal drop frame (although there are some frames out there with a standard mech hanger). it is certainly easier to tension the chain, especially with some “Chain Tugs”. These are shown below in black, by adjusting the 2 small allen bolts at the back of the Tug it tensions the wheel. All you have to ensure is that you tension the chain equally both sides; if you dont you will find your wheel is not dead centre in the stays, and with disc brakes you may find the rotor is not totally parallel with the stay making it impossible to prevent it rubbing within the caliper.
The image below also shows a disc frame with horizontal drops, as you can see the bolts holding the brake caliper on are elongated, this is to adjust the caliper once the tenion in on, as over time the chain will stretch and the caliper will need to be moved further back.
Option 3: Eccentric Bottom Brackets: An Eccentric Bottom Bracket, or EBB is a bottom bracket that rotates WITHIN the standard BB shell of the frame. Some frames do come with EBBs, they essentially look the same, however the BB shell is generally bigger. The cranks then rotate within the BB shell making the chain length longer and shorter. These can be equally as easy to set chain tension, however there are a number of various manufaturers, and my experience is that they take a little more maintenance, cleaning and greasing to stop unwanted vocal creaks and groans.
If you are not lucky enough to have a frame with horizontal drops or an EBB, there are super clever components out there that enable you to install an EBB to you standard frame. The Wheels Manufacturing EBB below fits a pressfit and BB30 frame.
Or there is the Exzentriker that fits a standard BSA threaded frame. But these EBBs add in are a little on the ££ side starting around £120 – £200.
Option 4: Eccentric rear hub: This is a little specific and as far as I’m aware is not avialbe for disc frames, but White industries, the king-ding-aling of all things SS quality manufacture an eccentric rear hub called the ENO (One backwards!). These are pretty £££…..but the ENO is pretty trick. Here: https://www.stradawheels.co.uk/product/white-industries-eno-hub/