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Do oval chainrings affect the performance of VPP suspension?

Aug. 12, 2020, 9:26 a.m.
Posts: 3
Joined: Aug. 12, 2020

I saw a thread covering a similar topic, but I want a more specific answer if possible. I have a 2020 Santa Cruz Blur using their VPP suspension that comes stock with a 34t chainring. I'm getting an Absolute Black 34t oval chainring but I don't know whether or not that will affect suspension performance.

Aug. 12, 2020, 10:49 a.m.
Posts: 397
Joined: Jan. 2, 2018

They certainly can. Chain Ring diameter affects anti squat.

With most oval rings the "effective" chain ring diameter is greatest at the most powerful part of your pedal stroke.

So that means you have less antisquat at the part of the pedal stroke versus a round chainring with the same tooth count. Secondarily it means the anti squat level varies some throughout the pedal strike.

In my case I've found the effects to be desirable for seated pedalling and less so for standing and hammering. I ran and oval on my previous Bronson and now on my ripmo AF but I'm going to switch back to round because I like to stand and hammer on a regular basis.


 Last edited by: Kenny on Aug. 12, 2020, 10:49 a.m., edited 1 time in total.
Aug. 12, 2020, 11:43 a.m.
Posts: 779
Joined: Jan. 31, 2005

Oval on VPP sounds like a bad idea.

Aug. 12, 2020, 12:39 p.m.
Posts: 998
Joined: May 11, 2018

I can't say specifically for vpp. My evil is way better with oval. My process 134 was awful. Pedaling activated the suspension like crazy. I switched to round and it was significantly better. The only thing I can surmise is the higher position on the chainring negated the antisquat?

Aug. 12, 2020, 1:33 p.m.
Posts: 3
Joined: Aug. 12, 2020

The main reason I'm asking is because I know VPP relies on chain tension to pull suspension to the sagged position. Absolute Black says a 34t oval chainring will feel the same as a 33 or 34t round chainring. So if I keep the same tooth count, do you think that'll have a huge impact on anti-squat and overall performance, or only a marginal one?

Aug. 13, 2020, 5:52 a.m.
Posts: 138
Joined: May 1, 2018

I had this discussion on PB with a frame / sus designer. He was adamant and blunt I was wrong, ring doesn't noticeably influence kinematics. He had all kinds of numbers to prove me wrong, although I noticed a few weeks later he was more equivocal. 

In my personal experience, oval rings do influence suspension - it was really noiticeable on my Yeti 5.5, and my 27.5 Spartan, so I run a round ring now.

Absolute Black mean the ring will feel the same under pedalling loads, but they'll feel vastly different on suspension depending on orientation of the ring/crank.

Aug. 13, 2020, 8:55 a.m.
Posts: 393
Joined: Feb. 24, 2017

I don’t think oval has much effect on kinematics based on my experience with a Oneup on a Bronson one. But that Bronson was designed around three chainrings. It may be the uneven pedalling stroke that causes issues though. I didn’t find any real difference in performance with oval so I just use round now. Others feel an improvement though.

Aug. 14, 2020, 1:20 a.m.
Posts: 5
Joined: Jan. 12, 2018

I used oval chainring on my Bronson V2 and now on my Megatower. No problem with oval - just love it :) Never go back to a normal round...

Aug. 14, 2020, 11:34 a.m.
Posts: 1198
Joined: Nov. 21, 2002

I appreciated oval rings on a hardtail, but much less favourable on a full suspension bike. I think this is due more to my hardtail climbing style tendencies, and to me I feel that the oval ring seems to highlight that to the point it makes the FS bike feel less efficient than it actually is.

I think they say a 30t oval feels like a 28t on the easier part of your pedal stroke, and a 32t on the power delivery portion of the stroke. Most FS designs nowadays should work well enough kinematicaly for that range, and if anything the 28t typically provides more anti squat and more efficient pedaling.

So basically what andy-eunson said

Aug. 14, 2020, 12:48 p.m.
Posts: 3
Joined: Aug. 12, 2020

Posted by: UFO

I appreciated oval rings on a hardtail, but much less favourable on a full suspension bike. I think this is due more to my hardtail climbing style tendencies, and to me I feel that the oval ring seems to highlight that to the point it makes the FS bike feel less efficient than it actually is.

I think they say a 30t oval feels like a 28t on the easier part of your pedal stroke, and a 32t on the power delivery portion of the stroke. Most FS designs nowadays should work well enough kinematicaly for that range, and if anything the 28t typically provides more anti squat and more efficient pedaling.

So basically what andy-eunson said

So when your pedals are level, the ring would be closer to the 32t, right? Seems like that would be closer to the power range, thus the bigger size, etc. If that's the case, it would reduce anti-squat and make the suspension bob more, correct? Or do I have it in reverse, and level pedals would increase anti-squat?

Aug. 14, 2020, 2:54 p.m.
Posts: 393
Joined: Feb. 24, 2017

Posted by: Ranger_720

The main reason I'm asking is because I know VPP relies on chain tension to pull suspension to the sagged position. Absolute Black says a 34t oval chainring will feel the same as a 33 or 34t round chainring. So if I keep the same tooth count, do you think that'll have a huge impact on anti-squat and overall performance, or only a marginal one?

Thing is, if a VPP is that sensitive to ring diameter, they’d probably tell owners to only use a 32 tooth because smaller or larger will have a different chain line in the vertical sense.

Aug. 14, 2020, 10:43 p.m.
Posts: 1198
Joined: Nov. 21, 2002

Posted by: andy-eunson

Thing is, if a VPP is that sensitive to ring diameter, they’d probably tell owners to only use a 32 tooth because smaller or larger will have a different chain line in the vertical sense.

For my case, I think it's more a full suspension phenomenon combined with my hardtail climbing style, not specific to VPP. 

I could see an issue arise from the changing anti squat point of view -- it's not so much whether kinematics are optimized around 28t or 32t, it's the constant changing from one to the other twice per revolution. At the 28t areas of the ring you've got more AS and less pedaling force. At the 32t areas of the ring you've got less AS and more pedaling force. Unless I have this reversed and just described original Shimano biopace

Sept. 12, 2020, 7:33 p.m.
Posts: 397
Joined: Jan. 2, 2018

I got my 30t oval ring changed out for a 28t round ring and it definitely confirms that the oval ring produced what I can only describe as a sort of "inch worm" effect, especially when standing and sprinting. 

Ripmo AF so not vpp, but also a multilink setup with a fair amount of Anti squat. I imagine the bike now has more Anti squat on average since the chainring is smaller. 

I think the oval might be more appropriate on a hardtail. To me the round feels better.

Sept. 12, 2020, 9:36 p.m.
Posts: 456
Joined: Nov. 25, 2013

Oval on a Horst-link is fine - I do notice it when "locked out" a bit, but when in squish-mode, its fine. Climbing tech - amazing.

Sept. 13, 2020, 8 a.m.
Posts: 4
Joined: June 25, 2020

I use a 30t blackspire elliptical ring on my Forbidden Druid and it works great.

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