Using Rotor Q-Rings Fixed

Got some of these bundled with cranks I've just bought, so I might as well try them out.

What I'm unclear on is how best to position them.

Sheldon Brown wrote that the advantage of Biopace over previous non-circular rings, was that they reduced stress on the knees by having "...the small radius engaged when the cranks are horizontal, the large when they are vertical... ...Since the rider doesn't push as hard during the power phase of the stroke, and motion is slower when the leg is changing direction, the Biopace design is gentler on the knees than even round chainwheels."

However, Rotor also claim to reduce stress on the knees doing the opposite "Q-Rings change the equivalent tooth size by decreasing it before the dead-spots and increasing it when the rider is in the power mode...", resulting in "...Mitigation of knee pains: Since Q-Rings imitate a circular (but smaller) chainring around the dead spots, minimize muscle requirements at the dead- spots, just when your knees need it."

I'd appreciate that there will be a certain amount of trial & error, but I'd rather start in the ballpark as my left knee is still recovering.

How will you account for the changing chain tension on a fixed length drivetrain?

Inverse shim obv.

Magnets obv

By fitting a derailleur, obv.

Jokerz gonna joke.

But srzly:
"People are often astonished to learn that I ride Biopace chainrings on fixed-gear bikes. They imagine that there will be tremendous changes in chain slack as the chainring rotates. In practice, this is not the case. A 42 tooth chainring will generally engage 21 teeth against 21 chain rollers, regardless of its shape.

There is a slight variation in tension resulting from the varying angle between the two straight runs of chain as the axis of the chainring rotates, but this has not generally been of a sufficient magnitude to cause any problem in practice for me.

[I've tried this too, but I'm not as happy with the change in tension. The sprocket is smaller than the chainring, so the chain doesn't meet the chainring at two points precisely opposite one another -- John Allen.]"

And this.

My 52t Osymetric ring was equivalent to nearly a 56t when the largest diameter was engaged andthen 48t when the shortest was. I liked the feel of them. But even with a derailleur the chain was all over the place.

Q-rings are very subtle in comparrision. Partly because they are less deformed from the circular, and partly because they change gradually from each extreme, and dont have suddenchanges like the Osymetrics.

My next road bike is getting QXL rings. Which I hope to be inbetween the the two.

I cant believe any of these rings would work well fixed. Half of the teeth are engaged what ever the position. I get that. But the tension is still going to undulate madly between high above the chainstay, low below, and vice versa.

Well there's only one way I'll know and that's to give it a whirl myself.

I think I'll go with the Biopace position first and spin it up on the workstand and see what happens...

I havent tried Biospace. But having the highest pedal resistance at the point where I have barely a fraction of my average stroke power. Seems ridiculous.

But like I say. I've never tried them. Maybe I'm totally off.

Would be nice if they worked in the designed position. Out of the saddle pedalling feels a bit easier with oval rings.

According to Sheldon the Biopace position evens things out (rather than maximising the power stroke), slowing the change of direction of the leg which is easier on the knees.

Adopting a "safety first" approach, I'll start with this before trying them as Rotor intended.

However Biopace and Q-Rings aren't the same shape, so even if they do function in this position, they might not produce the same results...

Whatever you do; do not over think this.

A "balls first" approach you say?

using my very basic thinking, the two halves of an ellipse are the same length, I just checked. so why would the tension therefore change at all, the circumference is a different shape but the exact same length? food for thought...

Edit: ignore the lengths haha, it was drawn on the corner of a section of a house, but they did measure the same...

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But I doubt he'll be running a 50t sprocket. So there will be more than 50% wrap.

If you have the parts to hand. Try it. Preferably on a turbo trainer or something.

I'm kinda intrigued by this.

Meh.

For sale: Rotor Q-Rings...

Even with the chain too tight with the greatest radius engaged, it was way beyond track slack with the small radius.

So how come Biopace work and Q-Rings don't? I suppose the shape is too extreme, Sheldon writes that "The shape of genuine Biopace chainwheels is not a simple ellipse, but a more complicated shape which Shimano described as a point-symmetric egg curve." Where as the Rotors are (closer to) a pure ellipse.

The 40t inner looks less extreme, but TBH I CBA. :(

I might give it another go if I happen upon some Biopace though...

What size are they @Scilly.Suffolk ?

53/40 135mm pcd.

Also interested.
Although the plan was to get 110bcd QXL in 52/36.

You need to consider the whole Picture. Not just the chainring. The lengths of the eclipses on the chainring may be the same length. But there is considerable difference in the length to the sprocket and back With the difference in angle through the pedal stroke. Hence the non constant Chain tension.

Sure, I just find things easier to grasp in practice than theory and I had the opportunity to experiment.

Dibs noted, we'll see what Pifko says.

I'll pass the dibs on to #probuyer SF. I'm not worthy.

Ha.

I've been a pro seller of late. I hardly have any bikes left, and paypal seem to think I'm Money laundering :(

I'm moving from a 38 to a 36 though, in an effort to spin-it-and-win-it. So I also pass.

Amey doesn't do Campag does he...

Ha.

Didnt mean to sound condesending with my above comment BTW. I would have chucked them on to see myself. So I'm with you on this. Just thinking out loud, after you'd shared the result.

i guess all we have a big range of confortable cadence (thinking in geared bikes), and allways think that with a little more cadence you can achieve what biopace claims (less stress in knees) and what q-ringns or rotor claims (more power or shorter dead spot).
i think a lot about this oval rings, but still can´t see the real advantage. if someone can illuminate me..

I always thought folk like Wiggins used Osymetric, as it allowed them to deliver the Power they already have. But while in a relatively Extreme aero position.

I feel I'm able to maintain climbing Power a bit better while on them. Not giving a higher Power output as such. But a smoother one. Definitely could just be imaginary though.

So. Not more Power as such. Just a subtle change in how you can deliver the Power availible to you.

If that makes any sense.

Also #selfconfessedbuyer