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  • SS Oval Chainrings – Potentially Daft Mechanical Question Content
  • wombat
    Full Member

    Please can someone reassure me that my thinking is correct on this entirely hypothetical issue?

    If someone built a singlespeed hardtail without a chain tensioner and used an oval chainring it wouldn’t work would it?

    The daft bit of my brain suggests that the chain would not either fall off or not turn at all because the length of the chain with the chainring vertical would be the same as the chain length with the chainring horizontal (thinking of it as a oval like a rugby ball even though they’re not actually all that oval).

    The sensible bit of my brain says it wouldn’t work because those chain lengths are different.

    I think that the sensible bit of my brain is correct.

    dawson
    Full Member

    Just leave the tension a fraction slacker – the ovality (probs not a real word) then takes up the slack as it turns

    wbo
    Free Member

    You’re forgetting the teeth. The only part actually pulling is that from the crank to the sprocket – teeth on the crank pull on the sprocket via the chain, when the ‘long’ side is horizontal there will be some slack chain underneath, but that doesn’t matter.

    In reality it will fall off a bit more often on bumpy ground, but ignoring that, it will work

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    moff
    Full Member

    It does work, there’s very little difference in effective chain length between the two extremes, don’t over tension it and you’re good.

    *Nearly 10yrs of Singlespeeding with oval rings.

    kayla1
    Free Member

    I think the effective chain length doesn’t actually change that much when you use an elliptical ring on a singlespeed so I think it works ok. There’s some variation and the chain does sag/tighten a smidge* though. I’ve looked at the my OH’s bike (36t elliptical ring on it) when he’s pedalling along and the rear mech doesn’t move much at all.

    * metric smidge, obvs.

    tazzymtb
    Full Member

    been using ss with elliptical rings since rotor brought out the q ring, so well over 10 years.dead easy to set up. sort chain tension with crank at 4 oclock postion and away yiu go. no drops, no skips, no worrying noises. always best to go up 2 teeth with an oval on an ss, so 34t q ring if you were using rotor…. or no teeth if you use absolute black as they shed then quicker than shane mcgowan (although to be fiar they may have got better in past few years)

    wombat
    Full Member

    Thanks folks, I’ve been thinking this through for a while now and couldn’t make up my mind what the answer was.

    As I don’t have the spares/time/space to actually build one I though I’d ask here 🙂

    Northwind
    Full Member

    I figure that at any time, the chain is wrapped around almost exactly half of the ring so the total distance of chain engaged is the same/very nearly the same?

    wombat
    Full Member

    @Northwind That was my thinking too but I couldn’t convince myself that I was correct

    snotrag
    Full Member

    It works fine. Think about it, when the chainring is moving round and distance from bb to TOP is decreasing, the distance from BB to FRONT of ring is increasing.

    luket
    Full Member

    Another one here. I’ve had various bikes on the go with this setup for nearly 10 years. I do have one bike that drops chains when it’s a bit on the slack side, but this is fixed by keeping an eye and adjusting for chain wear every now and then (which you’d do with a round ring anyway). The other two never have.

    DanW
    Free Member

    Here is a less biased video:

    There has to be a difference in the gear length (right words?) otherwise all the “harder gear in the downstroke, easier gear in the transition part of the pedal stroke” wouldn’t exist.

    Many people use oval rings SS and have no issues but the slackest section really bugs me and if there is something on the bike which is distracting (even if only mentally) then it is a no for me.

    I also find oval rings too choppy and find it harder to control smooth power delivery which is exacerbated on a SS. Some people love them, some hate them, some notice no difference.

    Early on I had issues with AB rings clogging with mud and when I got in touch about it the reply was “who rides when it is muddy anyway?”. Not impressed. Plus I don’t think I have ever worn a chainring as quickly as an AB.

    Northwind
    Full Member

    “Early on I had issues with AB rings clogging with mud and when I got in touch about it the reply was “who rides when it is muddy anyway?””

    AB guy is an absolute **** tbh. Habitual liar, insisted narrow/wide was stupid and that every other company was doing it wrong and he had a better way of doing it, sold a bunch of those rings then quickly started selling narrow/wides when it turned out they didn’t work at all but never offered a refund or replacement to the poor saps who’d fallen for it… Then because he was in a rush to get the narrow/wides out, didn’t bother to test them properly and it turned out they didn’t work well with KMC chains or high end Shimano chains, so he blamed KMC…

    I’m still a little salty about the fact he told me “it’s in the post” twice then weeks later “there have been some production problems, we haven’t made yours yet”, but told a different lie to his UK distributor then got offended when we compared notes and the distributor called him out for it… But, when it arrived,the ring was alright at least.

    theotherjonv
    Full Member

    give or take the chain has to do half a chainring and half a cog, and then the top and bottom runs. As there’s the same number of teeth in half a chainring whether it’s the pointy half or the flatter half, and the cog’s round, that means the amount of chain for top and bottom runs is the same.

    So on an oval it comes down to trigonometry. The chain run is broadly a hypotenuse to a RA triangle, with the long side being the chainstay (A) and the short side (B or B’) being the difference between the radius of the chainring and radius of the cog, two numbers because an oval chainring has a major and minor axis.

    You can do the maths to see what the difference is for both cases; TL:DR is that A >>> B or B’ hence the actual difference in hypotenuse is very small, and within the tolerance of chain tension.

    13thfloormonk
    Full Member

    always best to go up 2 teeth with an oval on an ss

    Not sure I agree with this?

    If you run a 32 standard, then going 32 oval means the ‘highest’ gear is (for sake of argument) equivalent to 34 tooth, and the ‘lowest’ gear is equivalent to 30 tooth.

    If you deliberately buy 2 tooth bigger, then all your knees see is a lowest gear that’s no lower than before, and a highest gear that’s 4 teeth higher! All well and good if you’ve suddenly got stronger or WANT to be pushing a bigger gear, but I’m pretty sure the benefits of oval only exist if you give your knees an easier gear to push over the top of the stroke.

    38 tooth oval rotor ring on my singlespeed, yeah the chain is a bit slack at parts of the stroke but for road use I’ve had no issues.

    theotherjonv
    Full Member

    alternatively – your capability is built on being able to push 32 over that dead spot, and you could be achieving more at other points in the cycle, so why not do it?

    On a round you’re compromising your best ability because of your worst capability

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