Circular ring equivalent of Rotor QXL

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Tinea Pedis
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by Tinea Pedis

Has there been anyone actually measure this? Or are we taking the word of articles such as this?

http://www.bikeradar.com/au/road/gear/c ... -13-47699/

I use QXL on my TT rig but was under geared in my last TT that had a fast, downhill, run to the finish.

https://www.strava.com/activities/50307 ... 2082403402

you can see power and cadence were high - I was in the 11 and needing another gear. Two of the boys who had a faster time in elite had a 55 big ring and they didn't max out. Can't help but feel I wouldn't have been in the 11 if the power phase was truly the equivalent of a 57.

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Krackor
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by Krackor

The mechanical advantage in the power phase is easy to calculate. Just measure the diameter of the chainring and find the circular chainring with the same diameter. This means your foot speed and torque in the power phase will be similar to what they would be on a 57t ring. However your foot speed and torque in the deadspot would be similar to that of a 49. On average you're still going to have to turn the same cadence you'd have to turn on a 53t round ring. If you can sustain a higher cadence on the oval then you can get a net benefit, but that may not be the case.

Not sure what you want to have measured.

eric01
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by eric01

Maybe want to change the title. I saw "Circular ring equivalent of Rotor QXL" and thought to myself... isn't the answer every other chain ring manufacturer out there?
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Tinea Pedis
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by Tinea Pedis

Diameter at widest point would about cut it, hadn't thought of that. I suppose it's comparing gearing sizes, only not sure how that was achieved with a non-circular ring.

And thanks, I'm happy with the title :roll:

Marin
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by Marin

You're running a 53 then, right?

I use oval rings too, and while I've found that they let me push a longer gear e.g. one cog smaller in the rear on climbs, I also feel that I don't like spinning them as much, and find doing high RPM on round rings easier.

So in your described case a larger oval ring or same-size round ring would probably have suited me better. For yourself, you'd probably have to go out and experiment?

wingguy
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by wingguy

Tinea Pedis wrote:you can see power and cadence were high - I was in the 11 and needing another gear. Two of the boys who had a faster time in elite had a 55 big ring and they didn't max out. Can't help but feel I wouldn't have been in the 11 if the power phase was truly the equivalent of a 57.


But that's the idea behind the oval ring - pushing more where pushing's easier and pushing less where pushing's harder. If you have or can borrow a rotor power meter you could use their OCP optimisation program to compare pedalling profiles between your QXLs and some different sized round rings.

At the end of the day though speed for a given cadence is purely down to number of teeth. If you're spinning out on the downhill you need more teeth. If that means you sometimes need a less elliptical or round ring on courses with long declines then you just need to pick the right equipment for the right race.

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Tinea Pedis
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by Tinea Pedis

wingguy wrote:At the end of the day though speed for a given cadence is purely down to number of teeth. If you're spinning out on the downhill you need more teeth. If that means you sometimes need a less elliptical or round ring on courses with long declines then you just need to pick the right equipment for the right race.

That's what is occurring to me. The choice now though (and what I am trying to work out) do I simply go a 55 round or a 54 QXL. Which is still 1 tooth less than I am looking for.

I like oval rings, but have moved back to round on my road bike and thinking now of doing the same for the TT rig.

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wheelsONfire
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by wheelsONfire

I was told i should do a one leg test spinning all rings. It is ok with round rings, but with oval (Q-rings) it was almost not possible.
So i wonder how spinning could be easier?
To me it seemed it was the opposite?

Sadly i could not try my kit for very long as i realized i had a hard time using the crank length i bought.
I bought 175mm.

After this, i borrowed 2 cranksets. 170 and round ring 175mm.
I usually use 172.5mm.

Testing all 3 back and forth, i found that 170 was easier than 175 by far, but it felt like the crank was too short.
Maybe i tested to short of a time, but to me it was obvious that 172.5mm was best for me.

All in all, i am back to round rings which seems best. Ofcourse this is personal.
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Krackor
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by Krackor

A 54t oval ring at 120 rpm is 74.6 kph. A 55t round ring at 120 rpm is 76.0. It's a small difference that won't amount to much time difference. You have to weigh that against whatever performance benefit you expect to get from the oval chainring. On that Strava segment you might see a 1s improvement in your time if you can put out one tooth's additional power. Will the chainring switch hurt your time on the rest of the course by a total of 1s or more?

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