I’m looking for advice on converting a DT240s 135mm QR rear hub to single speed. What do I need to do this?

Current spec is:
Absolute black 32t oval chainring. Shimano 10sp cassette.
Shimano hg95 10sp chain.
Shimano zee derailleur.
DT 240s 6 bolt hub.

I’m not after throwing money at the most expensive solution. Initially I was thinking of using a single sprocket from my cassette and a spacer or two. Research into that idea leads me to believe that using a single sprocket from my cassette will not be favourable as the freehub will get chewed up. Not sure how true that is or to what extent.
But If the only solution is to spend a lot of money then I’d still like to hear it.

Thanks!

Just use a cog such as Gusset Double Six which has a 7mm wide base.

This one?
https://www.gussetcomponents.com/shop/hubs-and-cassettes/double-six-converter-16t/

What else is on the market?

Do I need a tensioner or can I shorten my chain to suit?

Do I need a tensioner or can I shorten my chain to suit?

Depends on the frame but given your asking the answer is probably tensioner.

Magic ratios do not last.

Half links are shit and become the weak point in the chain.

Fixed tensioners just work

I bought a 2nd hand Specialized hardrock years ago that had a single speed conversion. It was used as a jump bike before I got it. It didn’t have a tensioner and the chain never came off whilst I had it.

What’s a magic ratio?

Half links are shit and become the weak point in the chain.

I’ve never had any problems with a half link and they’re useful if you want to get sliding dropouts or an EBB into a specific location to alter chainstay length, seat tube angle or BB height.
Unless you’re extremely lucky it’s too coarse an adjustment, on its own, for chain tensioning.

Magic ratio is just what you described, when you find a lucky combination of gears that works. Can work for a little while but if it’s slightly tight it can actually crack the frame especially if there’s a high spot on the chainring, and as soon as there’s any wear to the chain in a few hundred miles it’s baggy.

Sprung tensioner is generally the faff free option.

The only time I’ve ever had issues was when it was a fraction of a fag paper off being a magic ratio but just too tight. Adding one whole link then gave insufficient chain wrap and it would skip on steep hills. That’s when a half link comes in handy. Or 1t on the front, 32t to 33t won’t be noticed in your legs but is about the same as half a half link.

Using a ring from your cassette will gauge the freehub – it’s narrow and you’re putting a lot of pressure through it. Get a wide based cog to spread the load. Buy some spacers of varying widths so you can get the rear cog lined up with the front chainring. Unless you have horizontal drop-outs you will need a tensioner. Sometimes you can get lucky with a “magic ratio” which simply means you find a ratio where the chain doesn’t require tensioning – it wont stay “magic” for long though – the chain will stretch though at which point it will eventually come off. I converted my old 26er to singlespeed back in January. Bought most of the kit from velosolo including a rather colourful set of “rasta” spacers. I run it with a surly singleator tensioner and it has been utterly brilliant if not a little pricey, chain hasn’t come off once and no faffing about. You can use an old rear mech as a tensioner – doesn’t look as clean though.
Singlespeed stuff from here: VeloSolo
Singleator from here: Cyclestore

if you want to get sliding dropouts or an EBB into a specific location to alter chainstay length, seat tube angle or BB height.

all things that would make such little difference to the outcome that chain tension would come first before i let a half link anywhere near my bike again.

OnOne Groove Armada is another inexpensive, wide base, rear sprocket option.

This one?
https://www.gussetcomponents.com/shop/hubs-and-cassettes/double-six-converter-16t/

Yes, those are the cogs I use. The cogs are available separately (eBay, for example) in wide range os sizes from 13 – 21. Buy a cog and separate spacers so you can get chainline correct rather than the set spacing from the whole kit.

Velosolo do a nice set of spacers with good range of adjustments.

The one fat and one slightly skinnier ones that come in the kits from dmr/gusset /on one….are a bit shit in that they generally offer you two positions and neither work well with fat cogs.

Tensioner on the derailer hanger work well. Also makes it easy to remove the rear wheel.

It’s a slippery slope this single speed addiction.

Just buy a custom titanium single-speed specific frame now and get it over with.

Last time I looked the halo spacer kit was good and cheap.

Surly cogs are expensive but are dished for chainline adjustment if required, have a wide base, and wear well.

Half links are fine if required for your frame/gear choice. I’ve broken far more quick links than half links.

Existing chain will be fine or whatever cheap 8 or 9 speed you like.

Chain devices that mount to the BB or iscg mounts if you have them are a good way of tensioning the chain. Something like the blackspire Stinger with just a lower roller that can be pushed upwards. Rear fixed tensioner would be my next choice, rear sprung tensioner my least favourite – they have the same disadvantages as a mech.

Chain devices that mount to the BB or iscg mounts if you have them are a good way of tensioning the chain. Something like the blackspire Stinger with just a lower roller that can be pushed upwards. Rear fixed tensioner would be my next choice, rear sprung tensioner my least favourite – they have the same disadvantages as a mech.

Just for balance, push up tensioners (at either end) only really work for less than a half link worth of adjustment before you hit the chainstay.

I’ve always had a surly singulator, it’s been sprung pushing down for almost 15 years now and still works. I don’t think you can really say it has any meaningful disadvantages.

Surly shipped them as push down, and you could buy a push up spring (precisely because push up only works in some cases).

If a BB mounted tensioner fits, they make getting the wheel out slightly easier as you don’t need to derail the chain. But they’re still a faff to re tension. Compared to the fit it and leave it 20,000miles Surly, I wear sprockets out more often than I have to adjust that thing!

Just for balance, push up tensioners (at either end) only really work for less than a half link worth of adjustment before you hit the chainstay.

Ring /cog and chainstay dependant of course.

Ring /cog and chainstay dependant of course.

Yep, within the bounds of normal hardtail chainstays is there much variation though?

And I meant with < half a links worth of slack, not that you have to use a half link. I’ve got a stinger-style device sat in a box doing nothing but it never quite seems to work.

It probably works better with something big like a 38-21 where you’ve got more room to push up than the more usual 32-18.

There’s also the option of a ghost chainring. But lots of people say it results in firey death to baby robins and children’s faces.

Sure – you’ve got to be in the right ball park for chain length for a fixed type tensioner to work. Adjustment is quick and easy though – just tap it with a handy log 😉