Oval rings.

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KM2
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Joined: 23 Oct 2008, 5:38pm

Oval rings.

Post by KM2 »

Are biopace rings oriented correctly for a recumbent, whereas the more modern oval ring is going to produce a biopace type effect on your legs?
I’m assuming that the desire is to produce a larger effective gear on the power area of the stroke, which wasn’t the desired effect originally with ShImano.
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fausto99
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Joined: 19 Sep 2011, 10:06am
Location: NW Kent

Re: Oval rings.

Post by fausto99 »

I think the “recumbent” in your question is irrelevant. It’s the orientation of the chain ring to the crank that makes a difference regardless of whether your leg is pushing horizontally or vertically during the power part of the stroke. Isn’t it…?
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fossala
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Joined: 21 May 2013, 8:29am

Re: Oval rings.

Post by fossala »

I used rotor rings on recumbents, I now use absolute black on my uprights with gears (including rohloff).
KM2
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Joined: 23 Oct 2008, 5:38pm

Re: Oval rings.

Post by KM2 »

You’ve moved the force through 90 degrees but the chainline remains the same.
The maximum diameter of chainring should be approximately at 90 degrees to the chainline.
Doesn’t this mean it presents a smaller gear on the maximum power position on a recumbent?
Jdsk
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Joined: 5 Mar 2019, 5:42pm

Re: Oval rings.

Post by Jdsk »

Isn't there a difference between recumbents and uprights in the ability to shift weight onto the pedals? And the ability to brace your back on a recumbent isn't related to the position of the cranks.

Those might change the optimal relationship between mechanical advantage and crank angle.

Jonathan
KM2
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Joined: 23 Oct 2008, 5:38pm

Re: Oval rings.

Post by KM2 »

The ability to brace yourself against the seat would imply that the ring oval must be in the optimal position for maximum effect.
Therefore the crank should be vertical as the maximum diameter is vertical which goes against the ovals used on uprights.
Jamesh
Posts: 2963
Joined: 2 Jan 2017, 5:56pm

Re: Oval rings.

Post by Jamesh »

Do they work!!

I'll get the popcorn :lol: :lol: :lol:
KM2
Posts: 1323
Joined: 23 Oct 2008, 5:38pm

Re: Oval rings.

Post by KM2 »

Who knows?
Probably a little better than L shaped cranks…

But the question really is, are the modern oval rings compatible, in efficiency terms, with a recumbent where the force applied is at 90 degrees to the direction they were designed for?
bgnukem
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Joined: 20 Dec 2010, 5:21pm

Re: Oval rings.

Post by bgnukem »

For an upright I think you'd want the major diameter at 90° to the cranks, so as to give an effectively higher gear during the power stroke, i.e. when the pedals are approaching horizontal.

I think the Shimano Biopace 'rings were ovalised around 90° out of phase to this, giving a higher gear ratio during the dead spots between power strokes, which seemed wrong to me.

For a recumbent, the power stroke might be when the cranks are near-vertical, given that the rider is pushing the pedals almost horizontally (away from the seat back). Since the chain leaves the chainrings and angles downwards towards the cassette (vs. horizontally, on an upright), I'd think the chainring major axes would need to also be rotated slightly away from the 90° orientation w.r.t. the crank arms to reflect the different orientation of the chain run.
KM2
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Joined: 23 Oct 2008, 5:38pm

Re: Oval rings.

Post by KM2 »

Exactly bg, which make the biopace rings good for recumbents, but the modern ones not.

The biopace rings were supposed to mimic walking , slower movement in the vertical.
NickJP
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Joined: 24 Sep 2018, 7:11pm
Location: Canberra, OZ

Re: Oval rings.

Post by NickJP »

The only time I ever had cramps in a bike race was in 1989 after I had bought a new race bike that had Shimano's latest Biopace chainrings. I cramped on about the second race on the bike, and again a couple of races later. As I'd been racing for years, and had never had cramps before, I decided to remove the chainrings and fit round ones. No more cramps...
rmurphy195
Posts: 2199
Joined: 20 May 2011, 11:23am
Location: South Birmingham

Re: Oval rings.

Post by rmurphy195 »

Jamesh wrote: 17 Jan 2022, 4:50pm Do they work!!

I'll get the popcorn :lol: :lol: :lol:
Had them on a mountain bike years ago, when they were fashiponable! Couldn't keep up a steady pedalling rythm like I could on the tourer with round rings!
Brompton, Condor Heritage, creaky joints and thinning white (formerly grey) hair
""You know you're getting old when it's easier to ride a bike than to get on and off it" - quote from observant jogger !
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RickH
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Joined: 5 Mar 2012, 6:39pm
Location: Horwich, Lancs.

Re: Oval rings.

Post by RickH »

I had a bike with a biopace chainset (Shimano 600?) bought around 1988. I only noticed they were biopace when I replaced one of the chainrings due to wear. I then ran it for several years with one round & one biopace until I eventually changed the other ring. I don't remember noticing any difference even when running the mixed chainrings! :lol:

Don't some oval rings (Rotor?) have a disc, rather than arms, with multiple mounting holes so you can find the optimum orientation for you. Probably a bit like finding the optimum relative positioning of the cranks on a tandem.

Somewhat OT: In my mad student days (as opposed to my later just mad days :twisted:) I tried putting both cranks on a square taper chainset pointing the same way. I found it worked surprisingly well! Cue confused onlookers who could obviously tell there was something odd but weren't quite figuring out what. :lol:
Former member of the Cult of the Polystyrene Head Carbuncle.
KM2
Posts: 1323
Joined: 23 Oct 2008, 5:38pm

Re: Oval rings.

Post by KM2 »

Rotor rings do have multiple holes but the arc of adjustability is about 30 degrees.
Bob999
Posts: 39
Joined: 22 Jan 2015, 7:59pm

Re: Oval rings.

Post by Bob999 »

You may interested in this 'EGGring' information, it includes a reference to recumbents:

https://www.cornant.uk/info/ovals02.html

RIP Chris Bell.
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