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go 1 tooth larger on the sprocket for chainring (already 49x18). I like the current ratio so which would change it the least?
If you do both (50/19), it will take up as much of the slack as removing half a link while dropping your gear by less than 2.5"
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Can you mount the tensioner in a way so it pushes up on the chain from below?
Would give al lot more chain wrap and seems like the only sensible way to use these tensioners.
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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.
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Chain not wrapped around properly on the sprocket is why it kept jumping.
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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?