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Oval chainrings

I’m considering putting some oval absolute black chain rings on my bike. Anyone have experience and / or thoughts on these? Any issues using them with Shimano Dura Ace / Di2?

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  • I had them on my P5 for a few years. Used them on Rotor cranks with 10spd Di2 Shifting. No real issues. I am not sure if there is a real benefit or not to them. Someone more scientific like @John Withrow who I think has used them might have a different opinion. I went back to round...

  • I ran ovals for a few years. Did not notice any difference at all in feel or data numbers. I do believe round rings shift better.

  • I have used "non-round" rings for ~5 yrs and switched back to round this yr.

    I went a step further than Oval and used the Osymmetric Chainrings for most of that time.

    I have a dorky engineering brain so read up on all of the reasons/advantages many years ago when I went down this particular rabbit hole. I do believe that they create a smoother steady force on your muscles as they give you a bigger gear exactly when you are positions to more easily create more torque (i.e between 2-O'clock and 4-O'clock on the down stroke) and give you a smaller gear ratio where you are in that awkward dead space (10-2 O'clock at the top, and 4-8 O'clock at the bottom). Some of the really good/smart Professional TT guys use them as well (i.e. ever heard of Chris Froome?).

    They do come with downsides though. I had the Old 10-speed Di2 on my P5 and they would shift, but I had to be very careful about exactly when in my pedal stroke I would make my front shift. And I dropped my chain at least once every ride (including during Ironman Mt Tremblant). I got so frustrated with the dropped chains that I took the Osymmetric rings off and switched to the Oval Rotor ones that are much less aggressive. So with the Oval rings, I didn't notice as much of a difference throughout the pedal stroke, but my shifting was much improved over the Osymmetric ones and I hardly ever dropped a chain. And had exactly 0 chain drops in IMWis last September.

    Fast forward to this summer when I was going through the fit process for my new bike which ended up being a ground up build of a Ventum One. My fitter is every bit the bike nerd that I am and we got into a discussion about the Oval Chainrings. He told me to remove them and go back to round. When I gave him all of the reasons why I put them on in the first place, he agreed with pretty much everything I said. And said for Chris Froom, they absolutely make sense... But then he said that for Ironman Triathletes, he actually likes that small "dead space" at the top of your pedal stroke. His "theory", and he readily admitted that it was just a theory was that that tiny deadspace at the top and the bottom gives your legs a tiny micro rest on every revolution. So he "thinks" the Osymetric forces might be "too smooth" and that he wants variation throughout the pedal stroke so I can actually run after my TT...

    I have know idea if his theory hold water? Or if my analysis of why they "should" work is even real. Ultimately, I was also building a 1x and I don't have to shift the front anymore, but with the giant cassette, I was worried about chain slap with the size of the length chain I would need to run... So I changed to a 52T round 1x chainring and haven't looked back.

    The jury is still out though. I haven't been able to put out the same power levels this yr as last yr (FTP and 5hr power are both materially lower). But I have gone with much shorter cranks on my new bike, AND a round chain ring AND a completely different fit all around AND my training has been less than ideal... So too hard to know which of those variables has had the biggest negative effect on my power numbers (not to mention it's a different power meter all together).

  • or it could just be that you are getting old @John Withrow 🤣😂🤣

  • @John Withrow Rather than worry about FTP drop, the more important number, of course, will be, how fast can you go in the race(s) that matter. A clue to that might lie in a data calculation not often referenced, which I call Speed divided by HR (V/HR). That ratio should be as high as possible, meaning either going faster at the same HR or going the same speed with a lower HR (which presumably allows a faster run). MIcro-rests every pedal stroke, a better fit, a bike which is faster on the flats and downhills all might play into that sign of improved fitness, some of which comes from factors outside your body.

    There may be some courses/routes you regularly ride which can give you the data you need to help re-assure yourself that you are not, in fact, losing fitness for the thing that matters ... getting thru the bike/run in Kona as fast pr faster than before.

  • @John Withrow , @Al Truscott , @scott dinhofer , @tim cronk thanks to all for lots of good info. @John Withrow I’m an engineer so I think like you! I did run Rotor oval rings for a while on my P3.... power felt smooth but shifting was noisy and not great...never dropped a chain though. I’m on a BMC TM01 now with round rings. Was considering ovals... but after this post I might stick with round. I’m running standard rings right now... will probably change out for compact... seems to be the better choice. @Al Truscott I really like your input on V/hr... sounds like a really good way to eliminate some variables when looking at fitness across changing bike setup... very clever.

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