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ravingbikefiend
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Discussion Starter · #1 ·
I thought a few people mind find this interesting...

I know that many folks here are too young to remember Shimano's Biopace chainrings and there's a pretty clear division between those of us who love them, (that would be me and Sheldon Brown), and people who hate them.

My old '87 Kuwahara was originally equipped and was still running a Deore crank and Biopace rings and when I converted it to a singlespeed some weeks ago I kept the 38 tooth Biopace middle ring and the 175 mm Deore cranks to build my single and mated them to an 18 tooth Shimano BMX freewheel.

It will be getting a flip flop rear hub so I can run two gears as the bike serves as both a commuter and off roader and a 38:18 is too steep a gear for a lot of the singletrack we have here.

After logging a few hundred km on the old girl I have to say that I love the set up as the Biopace is well suited for higher cadences and it's design makes it feel like you're running a much lower gearing when you're climbing as the gearing reduces itself a little on the power stroke and helps one spin through the dead spot.

It's too bad Shimano screwed up in their marketting and didn't properly promote the advantages of the Biopace for high speed riding and climbing as this is where the design really excels.
 

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Doesntplaywellwithmorons!
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10,939 Posts
After building a SS up with a steel 38T biopace ring last summer and trying it on a few rides, and generating some comments after posting it on here of (doesn't that ruin the tension 50% of the time.... ermmm NO.... its always a 38T ring....) I tracked a set of the deore xt biopace rings (which are aluminium) down on ebay. If I'm gonna setup a 38T to something, its gonna be as light as possible.
 

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Birthday Collector
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2,610 Posts
rockyuphill said:
The chain length never changes with an elliptical (or wobbly) ring, it elongates the same amount as it squeezes in so that there is no net chain growth or shortening.
Totally right - the amount of teeth that the chain wraps around is always at (just over) 1/2 of the teeth on the ring - therefore, if the ring changes shape in an oval (or something close to it...) there will be no difference in chain tension. Of course, that is assuming that the bolt holes are drilled concentric to the spindle, and the crank is good as well... My Truvative crank on my SS has a slight offset on the holes on the arm - only about 1/2mm or so, and it makes for a small (but noticeable) change in the chain tension. Nothing I can't fix with a Dremel if it bothers me TOO much - but hasn't yet. I have a couple of Biopace rings around, but would need to add a few teeth to the back on my 29'er to compensate. Might be fun to test around town...
 

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RockStarRacing said:
...ive heard, that you have to gear up a little, is that true?...
It's more that the minimum size you can fit is a few teeth larger. The minimum diameter of the oval chainring has to fit the cranks, so you can see the larger diameter will push up the tooth count.
 

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Birthday Collector
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2,610 Posts
Yeah - one thing to consider before you run out and buy an old Biopace Ring - make sure that you have a crank it will fit - like the old Shimano with an (I believe) 110mm 5-bolt pattern to fit the holes in the ring... Most of the later cranks are 104mm 4-bolt and the Sugino/Suntour "Microdrive" were 94mm 5-bolt. Should be easy to pick up a used crank cheap - but make sure the rings aren't worn out!
 

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Doesntplaywellwithmorons!
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10,939 Posts
Biopace was never made for anything but 74/110mm mtb cranks, and 130mm road cranks. I have several sets of dura ace and ultegra 42/52 biopace gen 2 rings in NOS shape still. I once had maybe 40 of the rings (paid $1 each for 'em) and had been cutting them up to make windchimes with.
 

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Use this space for what?
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219 Posts
I still have the old Sugino oval ring on my SS. It seems to work well around here, but I will be swapping it out this year.
 

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Sweep the leg!
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3,804 Posts
DeeEight said:
been cutting them up to make windchimes with.
Same here. I've made several over the years with the chainring serving as the support from which I hang various parts... SoftRide stem dogbones, seatpost/steer tube trimmings, worn cogs.... they've made great end of season gifts to teammates. I've got one haning in the back yard too.
 

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Doesntplaywellwithmorons!
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10,939 Posts
My fave one uses two rings, a 42T and then a 52T below it, and suspended in the center is a syncros titanium seatpost shaft to lend a large mass damper to the structure (keeps it from flapping madly in a 40mph wind), and slices of biopace ring and UG cogs as the chimes.

 

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ravingbikefiend
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2,322 Posts
Discussion Starter · #16 ·
From Sheldon Brown:

https://www.sheldonbrown.com/biopace.html

" Biopace is a patented non-round chainwheel design made and licensed by Shimano. To a casual glance they resemble elliptical chainwheels, but on closer examination they turn out to be the exact opposite of the classical elliptical design. The product of extensive research and computer-aided design, Biopace chainwheels have the small radius engaged when the cranks are horizontal, the large when they are vertical. This is because the Biopace design is based on a dynamic analysis of the motion and momentum of moving cranks and legs, unlike the static, geometric analysis that produced classical ellipticals.

The theory is that during the power stroke, when the cranks are more or less horizontal, you are using the power of your legs to accelerate your feet, which get going quite fast in the lower gear provided for that part of the stroke. The momentum of your feet then carries the pedals through the "dead spot" when the cranks are near 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.
"

My commute is 26 km round trip (30 -35 minutes on the SS) and I stick to the bus routes on the way to work to make time and then come back via one of our excellent trail systems that runs through the heart of the city. It's a mix of rolling XC and has some excellent singletrack sections that I hit on the way home which were made all the more challenging due to the snow cover.

We have a little bit of snow here... this is our outdoor riding park which is at the trailhead.



This is the old girl taking a rest...



Here's what the XC trails look like...it was too dark to take pics when I hit the singletrack.



I have to say I love the setup as I don't think I'd get the same performance out of a conventional round ring or feel as good as I do after tearing up the trails on the way home.

I'd like to hear feedback from anyone who decides to give this SS option an try.
 

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biopace and chain tension:
YES it does engage the same number of teeth at any given point in the rotation as a round ring..
BUT it does have a mild effect on chain tension (which is negligible)
BECAUSE the angle of the chain coming off the top and bottom of the ring will be different than a round ring given the same toothcount, therefore creating a different distance to the cog.
 

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ravingbikefiend
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2,322 Posts
Discussion Starter · #19 ·
The effect on chain tension is really nominal and I have been thinking that I might also try mating a Biopace ring to the drivetrain of my 3 speed hybrid / commuter that is running an SA 3 speed ionternal gear hub... it is currently fitted with an beautiful Shimano 600 road crank and a 40 tooth ring that I can swap out for another 38 tooth Biopace.

Off to the shop we go...
 

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IFSDlxSS IFTiFLWMtb GFAdv
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242 Posts
1990 Gary Fisher AdvanSS

Here's a pic of my first SS conversion/restoration using a 38t Shimano LX Biopace chainring. I got this GF back in 1990 and didn't use it for more than 10 years. So I decided to make it my project bike and first SS.

It was exposed to the elements so the nice red finish it used to have was barely visible. I took the frame to this guy that specializes in refinishing frames and had him copy all the original graphics and logos. Instead of the orginal candy apple red, I had him use a special orange that was specific to a 1971(?) BMW M1. And instead of using stickers for the name and logos, I had him paint them on and clear coat them so they can't peel off.

I was able to salvage some of the original parts. (Handle bar with "Gary Fisher" logo etched, seatpost, and cranks which turn out to be old school Shimano LX with bb)

Another cool find is the seat post clamp. About 2 years ago, I made a purchase on ebay without checking out the details. I thought I was purchasing an XTR quick release clamp like the Salsas and the Hopes. Little did I know, it was an old school Shimano XTR seat clamp that was unused. It just happened to fit perfectly on this frame. All it cost was $9 shipped from Norway!!!

I'm using a 38t Shimano LX biopace chainring and an 18t generic rear cog. The drive train is working ok with the generic tensioner I'm using in this picture. I recently replaced the tensioner with a Rennen Rollenlager and this setup doesn't like the biopace ring. Since the Rennen is push up tensioner and not spring loaded, the change in chain tension from the biopace ring doesn't do the drivetrain much good. I'm now waiting for my regular chainring to arrive in the mail and I'll do away with the bio pace setup.

It was good while it lasted, but I didn't like the spring loaded tensioner much. The adjustment screw kept coming loose and I kept dropping my chain on really rough fireroads. Not a good thing.....
 

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