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One of the presenters on Mountainbike Radio (on either "Just Riding Along" or "The Path"[bikeshop show]) reckoned that proper SS cogs only really work with pre-set chain tension (i.e track ends, sliding dropouts, EBB). He said that if you're using a sprung tensioner, you need teeth shaped more like cassette sprockets to avoid chain jump.
The easiest option will probably be to get as close to a magic gear as you can, with the tensioner acting as insurance and accounting for a bit of chain wear.
Emyr-
Interesting, I would have thought the opposite. I'll see how reducing slack helps.
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The more I read the more I think the amount of engagement is the issue. I think I'll try the half link first as it is the cheapest and easiest.
It only happened a couple of times on the way home and again only when setting off (and even then not every time). I couldn't replicate it when I wanted to so I'm guessing it is borderline. Even Gipsy Hill couldn't make it slip.
However, yesterday's and today's times up GH were both 5 seconds off my Strava PR for GH considering it's been about six months since I tried it on one gear so I'm still really happy with the bike.
stevo_com
I built up a single speed commuter around a road frame I got for free. All is good apart from very occasional chain jump. It only seems to happen when I set off from a standing start on an incline, and not every time. On my 8 mile commute, it happened only twice. It is a very small jump too, the chain does not come off and it's not enough to cause me to flail dangerously.
This was the bike I was going to try to get a magic gear on but gave up on that idea and when for a chain tensioner.
I thought it was happening under load but I went up a few hills yesterday, out of the saddle, and it was fine.
Brand new 8-speed KMC chain and 3/32" single speed specific sprocket and chainring.
I have a couple of theories if the hive mind could also chime in, that would be great.
1 - the chain is too long so the tensioner is having to take up more slack so that there is not enough chain wrapped around the sprocket. So, if I stop and the chain is not under load and maybe gets moved back and forth a bit, it's not sitting fully engaged with the teeth so when I set off, it slips. It doesn't slip when climbing for example because it has had a chance to "settle" and the few teeth that are engaged have a good hold.
2 - The factory chain lube is sticky so as per #1, when stopped and moved around, the tacky lube is preventing proper engagement.
My potential solutions are;
A - I can't remove a whole link so get a half link to shorten it slightly to take up more of the slack. Not overly keen as I'm already using a chain tensioner so seems a bit much.
B - go 1 tooth larger on the sprocket for chainring (already 49x18). I like the current ratio so which would change it the least?