Shahmatt

I need higher gearing to get closer to traffic speeds on my small wheel folder. A 53T would do the job I think but I am worried about the increased resistance on the low end. So I'm considering getting a elliptical ring to compensate for this a bit.

Since elliptical rings have reduced resistance at the main "push" crank arm position, would it feel like the ring were of a smaller size than it actually is? I'm guessing the resistance should match circular chainrings of a diameter equal to the minor axis diameter of elliptical chainrings. Is my reasoning correct?

Edit: The Biopace 53T has a minor axis diameter of nearly 52T. Hence the subject line.

rhenning

The eliptical will not feel different and will make almost no if any difference in top speed. One tooth difference in the back is worth 4 in the front. That is not always exactly true but is very close. Yopu would need to go to a 56 to make the difference of changing from a 13 to 12 in the back. What kind of bike? How many gears? what size wheels? All come into the equation. What you are preposing isn't worth the effort. Roger

achoo

What kind of pedals are you using? It's really hard to go fast reliably on simple platform pedals.

What cadence are you pedaling at when you're trying to go fast? You should be able to get up to at least 90-100 RPM, and you'll be able to go faster with the same gearing. If not, you should work on your ability to do that.

Kopsis

I disagree with the statement that Biopace rings won't feel any different. I have an SR "Ovaltech" triple (same ellipse orientation as Biopace) on my commuter and it absolutely has a different feel -- especially at medium cadence (~80 RPM) on gradual climbs or acceleration.

However, it's true that it won't have any effect on speed. The Biopace concept wasn't about lowering pedaling resistance, it was about reducing the velocity of the knee joint when it changes direction (up/down) by slowing the foot at the top/bottom part of the pedal stroke. Power is power. To get the same effective power (and therefore speed) as a conventional 53T, you have to push faster (harder) through the downstroke so your foot/leg has the momentum to carry through the higher resistance bottom part. Overall you're putting the same amount of power into every complete pedal rotation, you're just doing it in a non-linear way that is potentially a bit easier on your knees.

Shahmatt

I get what you are saying here. So since the brunt of the resistance (possibly more than a conventional circular 53T) is happening late in the stroke cycle, and since this resistance is experienced after having gotten the necessary momentum, should not the overall stroke cycle also feel ever so slightly easier in theory?

fietsbob

you may feel the radius change , as your foot pushes the pedal around the stroke,
and part of the ring elipse is smaller, and gains your foot Momentum , that can be carried through BDC.

where there typically is less input to power .. but being at the larger radius of the ring shape , there is some input.

biopace didn't go long on the market.. Shimano creates and changes things they make Often. biopace is from long ago.

Q rings are made in Europe , now , and have some talented Pros favoring them such as Ms Vos ..
Rotor Bike Components

Shahmatt

It's not just about increasing speed. I need the lower end as well. Anyway the bike uses a Shimano Nexus 7 with 16" wheels. The rear sprocket is 16 teeth, the smallest it can go. I am proposing a chain ring increase from 48T circular to 53T elliptical. About 10% increase on both ends of the range. I'm hoping the 53T will feel more like a 52T so that my lowest gear will not feel overly difficult for me to push.

I prefer platforms. Reasons are too many traffic lights and too much traffic for clipless. Also spinning that much is uncomfortable for me. I am more comfortable at a rate of 60 to 80RPM.

Kopsis

For a few revolutions, it may "feel" easier (while all your power is coming from stored Creatine-Phosphate in you leg muscles). But after 10-30 seconds, riding at speed X with the Biopace ring will take exactly the same power and generally cause just as much muscle fatigue as doing it on a round ring of the same tooth count. Remember your pedal speed is not constant with the Biopace. You're essentially surging with every downstroke (in order to maintain constant forward speed). So what you save by having a "longer lever" you lose by having to move the lever faster.

Also keep in mind that on a big (53T) ring, the "Biopace effect" is far less pronounced than with smaller rings because the difference in effective tooth count is small with respect to total tooth count. Think about it -- a 1T effective difference is less than 1.9% on a 53T, it's 3.8% on a 26T. If you're comfortable with the gain ratio a 52T effective chainring will get you, why not just run a 52T round and increase your cadence by 2%?

Don't get me wrong, there are some good reasons to run Biopace rings (easier on the knees, less loss of traction on off-road surfaces, retro-cool conversation starter, etc.), but reduced effort vs. a conventional chainring of the same tooth count isn't one of them.

FastJake

Get comfortable with spinning more. Especially when trying to keep up with traffic, 60-80 RPM is too slow. Traffic changes speed a lot and keeping your RPMs up will make adjusting your speed on the bike easier. It's also better for your knees, better for your cardio, you get to keep the low gears on your bike, etc. A knee injury forced me to spin. I'm glad it did.

I agree that a Biopace vs. round ring will not make you go any faster. I can't spin a Biopace ring any faster/easier than a round ring.

bent-not-broken

53 vs 52 is less than 2% difference. I doubt most of us would feel any difference in a blind test, regardless of ring shape.

Al1943

As others have said, you need to turn a higher cadence. Once you get use to 90 - 100 rpm you'll never go back.

wheelreason

Higher resistance bottom part?

davidad

shimano will discontinue an idea that did not work. That's why they no longer make the bio-pace. The pros will ride anything that doesn't slow them down or endanger them because they are paid to.

fietsbob

I dont have access to the Account Books to know if the rider or the team chose things like Q rings ,
but I expect If the rider wants a particular component, the team manager's calls up the company
and gets a better deal than John/Jane Q Public's retail price,

because the folks like at cycling news take pictures of all the gear The team bikes use.

and get those Logos and mentions, on the websites.

particularly if the person won that Rainbow world champion's Jersey .

rpenmanparker 

Actually the Biopace chain rings are the first examples known of perpetual motion machines. You pedal them with the power needed for a 52T ring and, as OP suggests, they transfer the power of a 53T ring. It is small, but think of that on a multi-acre scale, a Biopace energy farm. As Earth becomes warmer and warmer, we need to find more ways like this to produce clean energy. I will be pleased if one or more of you will submit my name to the Nobel Institute for consideration for their next prize in Physics. I was hoping to win for inventing the microwave oven as a means for cooking bacon, but narrowly missed out. Maybe this time.

Sixty Fiver

Biopace worked and still works... Shimano just could not market it effectively.

Reynolds 

+1.

prathmann

The OP is confusing since it refers to Biopace and elliptical as if they are the same. They're not. There have been elliptical rings from various makers (such as Durham) while Biopace was a very different shape only made by Shimano.

But, as already mentioned by others, the difference between 52 and 53t rings is very small and usually not worth worrying about. If you want a higher gear then go up to something significantly bigger. E.g. my folder has a 60t large chainring and this gives me gearing equivalent to a 45t ring on a bike with 700c wheels - so the resistance I feel is also the same as if using a 45t ring on such a bike. In combination with a small cog of 11t this gives me a high enough gear for my rides.

Fine if the OP wants a non-round chainring for some reason, but the fact that he's using a bike with smaller wheels is irrelevant from the standpoint of round vs. non-round rings.

fietsbob

like wise .. I run a round 54t on my 16"Brompton , a 53t on my 20" wheel Bike friday .

if you build a wheel around a S-A 8 speed IGH, then the internal overdrive ratios gain a 300% 8th over a 1:1 1st..

as well for derailleur minibikes Shimano Caprio is a 9 to 26t cassette and hub for that cassette.\


what is the cog on the rear wheel now? 20" wheel? 16?,

Shahmatt

Apologies for the confusion. I meant to say asymmetric instead of elliptical.

I understand that there's only a very small difference between 52T and 53T. But consider this situation.

My current 48T setup yields a GI range of 30.5 to 74.5 (Sheldon brown's calculator).

The upper end is too low so I'm looking for about 10% more. The lower end is quite comfortable right now so I am wary of increasing it too much. As an experiment I tried starting off on gear 2 (35.7) but this was borderline difficult.

So it's a balancing act of how much I can increase the chainring size without compromising my hill climbing/starting off ability.

A 53T gives me 33.6 to 82.2 (10%). At 80RPM I should expect an increase from 17.7 to 19.2mph.

33.6 GIs may be just right but I'm still a ever so slightly worried. So that's when the asymmetric chainring idea popped into my head.

The Biopace reduces resistance on the push phase and increases resistance when the feet are at the end positions. The energy consumed does not change, but the overall spin becomes easier to do because of the more averaged out pedal resistance and power delivery.

Edit: A 52T will give me a range of 33.0 to 80.7.

So as an insurance, I'm hoping that the 53T will feel more like a 52T when trying to take off from a standing position. For hills and starting off it could make all the difference is what I think.

fietsbob

there are more exaggerated ovals .. and the Rotor Cam crank does that with Round chainrings ,
so you can seek out even bigger ones.

Reynolds 

Biopace + this FTW:

Shahmatt

Funny how in many of the threads I've come across users like to compare Biopace chainrings to the nonsensical idea you've posted above.

fietsbob

Someone didn't get 'the shortest distance between 2 points is a straight line', message .

Reynolds 

They quite comparable - both work as placebos IMO.