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Currently running a Surly steel 32t chainring - had it 2 weeks, done about 80 miles so far.
New chain and rear sprocket both fitted at the same time.
Singlespeed bike with sliding dropouts
I've noticed that as I try to adjust chain for tension there is a definite difference in tension through-out a revolution of the cranks.
Admittedly the sprocket is a cheap-ish plain stamped steel cog, but not much different to the one that I took off.
Anybody else had experience of tight-spots/loose-spots when setting chain tension on SS bikes?
Could it be your bb?
Yep. Nothing's quiet bang on centre in any drivetrain IME.
i had the same on an old bmx
cause was : my cranks had a 22mm (?) hole cut out for the crank locator lug to go in, but the crank only had a 19mm (?). basically, the chainring was moving around a tiny bit with each rotation.
a cheapo adapter solved the problem
Coming from a trials world, we have this.
The issue is the thread on the hub is not centrally cut, so you get a wobble. Have a look at the next trials bike you see with a front freewheel. The chain will wobble up and down quite a lot.
Its an XT BB and crank - only about a month old - spins freely when chain removed
rear sprocket is a cassette type that just slides onto the splines on the cassette body, rather than a screw-on type.
Not really had chance to investigate it properly only noticed it tonight as I was adjusting chain tension.
When I get chance I might try removing chainring from crank and re-seating crank bolts - will also check sprocket on hub
Don't be concerned as it's quite normal, you just notice it more when the derailleur isn't there to take up the slight variations in tension. It occurs mainly due to very slight eccentricity in chainrings/sprocket. This isn't an indication of poor quality.
Find the tight spot and set the chain tension so you don't feel it binding when you rotate the crank (you want a small amount of slack in the chain at the tight spot, but not too much), then you'll be good to go.
@mokl - cheers, that's kind of what I've done, could have gone a fraction tighter at the tight point but was wary of overdoing it
Define significant. If I set up mine on the slacker part, there is a definite binding sensation when you rotate the cranks over the tight spot.
But set it up on the tight spot and the chain doesn't noticeably slacken when rotated, a few mm if you press the chain.
I noticed this when I went SS too.
It's never caused any issues. You don't want the chain too tight, puts too much pressure on the freehub.
Don't worry about it as long as long as the chain's not coming off. A lot of people, myself included, run oval chainrings on a singlespeed with no issues and I'll bet the change in tension is a lot more pronounced.
Perhaps 'significant' was over-egging it.
It wasn't binding at the tight point.
Will definitely try a bit more tension next time I adjust it.
Have you set up the chainline by eye or measured? Also I've never had to do it but have read about people centralising their chainring, slacken the chainring bolts enough to allow it to move give it a burly and nip up again.
Chain line replicates factory setup as it came.
There was some blurb on the Surly package that read along the lines of putting the chainring bolts in the wrong way round at first, to centralize the chain ring, but like typical man, disregarded that as I didn't think it necessary...
Will give it a go!
There was some blurb on the Surly package that read along the lines of putting the chainring bolts in the wrong way round at first, to centralize the chain ring, but like typical man, disregarded that as I didn't think it necessary...
Or ease the bolts off just a smidgen, tap the chainring backwards with a rubber mallet when the chains tightest, repeat until it's all good.
99% of the time it's the chainring installed off-center, but it makes little difference.
Set the chain up so that it's the right tension at it's tightest, unless something is really badly wrong the chain won't come off however slack it is elsewhere, but too tight will break stuff.