non-oval rings on a pedal assist e-bike (was: Human watts, Erider and Cycle Analyst)

[bikeboy999]

Hey all

Before I get back to rocking on my newly minted e-trike. I am going to ask if anyone has any experience with non-oval rings on a pedal assist e-bike?

Brian


(moderator edit: changed title to "non-oval rings on a pedal assist e-bike" from "Human watts, Erider and Cycle Analyst", since that original title didn't actually have anything to do with what's discussed or mentioned in any post of the thread itself).

 

[markz]

Hey all

Before I get back to rocking on my newly minted e-trike. I am going to ask if anyone has any experience with non-oval rings on a pedal assist e-bike?

Brian

https://endless-sphere.com/forums/viewtopic.php?f=3&t=83783&p=1228340&hilit=oval+rings#p1226921

 

[Balmorhea]

Before I get back to rocking on my newly minted e-trike. I am going to ask if anyone has any experience with non-oval rings on a pedal assist e-bike?

Did you mean non-round? Or oval? (Because all normal circular chainrings are non-oval.)

I've not used them on e-bikes, but I've used them in different orientations on regular pedal bikes. One of the tradeoffs I can see is that I often pedal my e-bikes at pretty high RPM. The faster you pedal, the weirder elliptical rings get, because the pedals accelerate and decelerate twice per revolution when you're riding at a steady speed.

 

[bikeboy999]

Man do I ever screw up on this site. Yes, I meant to say oval. I have 53/39 Qrings, and I am getting a bottom bracket that measures human watts. I am curious if the non-round rings will change the human watt readings. BTW, when I did a search to see if there was a post on this I used the Qring brand. When I should have checked oval. You guys are great at helping, thanks.

Brian

 

[MikeSSS]

This won't help much, but I rode 5 1/2 years using pedal with throttle assist on a bike that had Biopace rings. Next bike had a couple different sized round rings. I never felt a difference, they both worked well. The Biopace rings shifted very well.

 

[Balmorhea]

Man do I ever screw up on this site. Yes, I meant to say oval. I have 53/39 Qrings, and I am getting a bottom bracket that measures human watts. I am curious if the non-round rings will change the human watt readings.

When oval chainrings first became popular in the 1950s, the thinking was you put the tall part of the ring corresponding with the strongest portion of the pedal stroke, to maximize power output. It might have worked, a little, but not enough to generate real world results and become normal.

When Shimano came up with Biopace in the 1980s, they based it on a deep analysis of pedaling mechanics that suggested putting the short part of the ring in alignment with the strong part of the pedal stroke, to build up kinetic energy in the legs that carries them through the dead spots. It works well for moderate levels of effort and moderate pedal RPMs. But even though that makes it a good match for how a huge majority of cyclists actually ride, it made athletic riders hate it. And of course whatever racers prefer must be best for everyone, right? So it failed in the marketplace.

My inclination is to use round rings with my e-bikes, so I can spin faster and more smoothly. But I'm not concerned with getting my highest possible output at the pedals. If I were trying to maximize pedal power in combination with motor power, I'd try traditionally oriented oval rings to see if I could make a few more watts, or make the same wattage with less perceived effort. But I'd surely do controlled tests against round rings of the same tooth counts, and not assume that one is better than the other.

 

[donn]

But even though that makes it a good match for how a huge majority of cyclists actually ride, it made athletic riders hate it. And of course whatever racers prefer must be best for everyone, right? So it failed in the marketplace.

Ha, well said. I agree that they are optimal for a lower cadence. In the usual case, it would make sense to advocate for that lower cadence, on the theory that perhaps a high cadence is just because we're compensating for round chainrings. But with motors, we're sometimes stuck with high cadences just because the gearing leaves us no alternative, and in that case it seems like a waste.

 

[amberwolf]

The one thing that the Biopace rings did for me was to reduce the loading on my knees for the same effort, by just enough to reduce pain to a more tolerable level.

Exactly what / how that happened, I don't know...but it did work, on the upright bikes. Unfortuantely on the semirecumbent ones, the pedal position vs chain angle is different, and it didn't work anymore. I'd need to get or make spiders or adapters that would allow me to rotate the rings to a relative position equalling that of the upright bikes. Never got around to that....

 

[Balmorhea]

Unfortuantely on the semirecumbent ones, the pedal position vs chain angle is different, and it didn't work anymore. I'd need to get or make spiders or adapters that would allow me to rotate the rings to a relative position equalling that of the upright bikes. Never got around to that....

Did you try rotating them back by one bolt (72° angle)? I know that's more than the difference between a normal bike and a recumbent, but it seems plausible that it might help.

 

[amberwolf]

It's been so long that I don't remember the exact details, but AFAICR, it's not possible with the ones I have, as the spider's/rings' "BCD" is itself ovoid. If they weren't actually ovoid, the holes were not spaced evenly around the circle.

I don't remember if it was all three rings, or just the smallest one, but I just remember it wouldn't work.

I'd also wanted to put them on shorter cranks arms (or longer? can't remember) but they also wouldn't fit any other arms than what they came on, whcih I think were 170.

What I recall concluding was that the only way to do it with them would be to make an adapter that bolts to teh spider of a crank (of whatever kind) that has the ovoid of bolt holes matching the rings, and either a ring of holes matching the BCD of the bolt holes on the crank to allow experimentation, or simply determining the "correct" angle and having one set of holes at the right BCD.


I'd also wanted to mix/match some of the ring sizes, and couldn't do that either--wanted to get the smallest ring and the largest both on teh same crank, but the BCDs were different, or something.


I'll have to see if I can dig them out and do some measurements to find out what the full problems were.