Ken Cox

First, thanks to whomever turned me on to the 42 tooth biopace ring.
I found one at Yellowjersey.

Because Shimano intended the 42 tooth biopace ring as an inner ring on a road bike, it has its chain ring bolt bevels on the "wrong" side.
I think because of the "wrong" sided bevels, this ring has more adjustment for position than the rings I would normally put on my crank star.

Using Sheldon Brown's chainring-centering method (I can't find a link to it right now), this new chainring centered up better than any of my other chainrings, round or biopace.
This, and the small size of the 42t biopace, let me adjust my chain much tighter than I could in the past, making for a significantly no-slack chain, round or biopace.

Using a KMC 810 chain and a 17t EAI cog, I have 64.9 gear inches and the quietest chain I have ever experienced.
Absolute total dead silence.

So I went out for a test ride on my regular 12.5 mile training loop.
This loop goes through rural, suburban and urban traffic with an up and down of about 1000 feet.
Actually, about two ups and downs of 1000 feet.

I have ridden this training loop regularly with both round and biopace rings, at 82 gear inches, 77 gear inches and 72 gear inches.
I have the same personal record of 53 minutes for this 12.5 mile and 1000 foot dynamic range training ride, at all three gear inches.

However, because of the dramatic drop in gear inches to 64.9, I expected the reduction in my top speed to significantly increase my time for my training loop.
During my ride, I seemed so much slower, especially on the downhills and flats, that I assumed a confirmation of my expectation of increased time.

Imagine my surprise when I completed my training route at my personal record of 53 minutes.

The same training ride, whether ridden at 64.9 gear inches, 72 gear inches, 77 gear inches or 82 gear inches takes the same amount of time: 53 minutes.
I think the hills have something to do with it, and I suspect the lower gear inches make for more consistent speeds, if not as fast on the flats and downhills.

Anyway, I noticed a dramatic improvement in control and agility at 64.9 gear inches, for the same average time.
I also noted a significant improvement in my ability to analyze my spin and consciously input changes, especially going over the top, from about 10 o'clock to 12 o'clock.
Placid Quiet's visualization of directing the knees towards the bars really helped in this regard, as did someone else's visualization of "scraping the bottom."

So, by gearing down, I have a better spin training tool, more control and agility, and, in the area in which I ride (with its hills), no penalty in overall time from one destination to the other.
Kinda interesting.

Shiznaz

Gearing down is always good.

I have tried 3 different biopace rings on fixed gear or SS bikes before and its never worked properly (crazy looseness and binding). Maybe I just suck at the mechanics of it.

I ride 43x17 (66.5 gear inches) most of the time and its great. I can still burn out my legs if I really want to.

For the track I like to undergear a bit as well and tend to ride around 70-75 gear inches. Keep those legs full of oxygen!

mander

Hmm when I get my cash situation in order (I need to finish my MA thesis and get a ****in job) I think I will try riding the 65 inch horse. Small gears ftw!

roadfix

Yes, gearing down makes a lot of sense. I am more refreshed after a long ride pushing 65 inches vs 75 inches, for instance, with not much difference in overall ride time.

Ken Cox

I think biopace magnifies several mechanical issues.

I had a little difficulty with a new crank, and I attributed it to an out of round crank.

I discussed it on this forum, but eventually got around to talking to one of my more respected lbs's about it.
They described all bikes as demonstrating symptoms of "something" out of round.

This particular lbs attributed out of round symptoms to out of round cranks, out of plane cranks, out of round chainrings, bent crank spindles, and out of line frames.

In the case of road bikes, the system of derailleurs and chain tensioner masks these out of round conditions, and they don't really show up except on some single-speeds and all fixies.

A biopace ring, by design, has two tight spots and two slack spots on every revolution.
If one adds a normal out of round condition to this equation, then one adds the extra tight and slack of an out of round to the tight and slack of the biopace.
With a square taper spindle, this gives the chain at least eight different tight and slack combinations, one of which involves a reasonably tight slack point for the first 180 degrees of rotation, but a puzzling extreme slackness for the other 180 degrees of rotation.
This extreme slackness defies a logical fix and can drive a person crazy.
I think it involves either a slightly bent spindle, or an out of line bottom bracket, or both.

In the case of this 42t biopace ring, because of having the bevels against the star, I had more movement in the chainring than normal, and Sheldon Brown's centering method REALLY worked well.

Now that I have two years experience with biopace, I don't recommend it for anyone other than an avid hobbyist.
I really like biopace, but then I like fiddling around and experimenting with my bike, and I have a wall full of chainrings, cogs and chains.

So, short story made long, I don't think Shiznaz has any deficiencies as a mechanic, but simply encountered one of the difficulties of playing with biopace.
If he wants to take another run at it, this 42t ring might work for him, since it has more centering potential.

In any event, I feel very pleased with my 64.9 gear inch experiment, and I may spend the summer at this gear inch.
Thanks to my fellow riders who encouraged me to try it.

Shiznaz

Thanks for the explanation. In biopace's defense I was using rings pulled off of some pretty beat up bikes, and I didn't give it much of a chance after installation. I got a 42t ring working for a while on some crazy bmx bike I built, but that was just a spare bar bike for friends so i didn't really care. The bigger rings I installed barely allowed me to rotate the crank around in a full revolution; I just decided it was more trouble that it was worth and bought a cheap chainring (I was just trying to avoid a trip to the lbs really).


and more on topic of gearing down, I find if I can keep the aerobic work going without breaking the anaerobic threshhold I can keep going forever. Its when I have to mash against a headwind or up a hill that I start getting it taken out of me. Low gears keep the oxygen and lactic acid flowing in the right direction.

kyle!

i'm finding my legs getting a little sore. my bike came with 48x18. i liked it but felt i was spinning way too much on downhills and even flats. so went up to 48x17. i think i wanna go back. i think my knees will thank me.

andre nickatina

I went from 61 gear inches on the old bike to 67.4 on the new one.

I would not recommend 61 gear inches no matter how hilly your city is. Even though it's fun to have that fast acceleration from standstill and be able to climb hills easily, going down any reasonable hill results in way too high of RPM's, as does sprinting on the flats.

With that said, 67.4 seems to make a pretty reasonable gear ratio. I can skid it fine, I can climb one of the biggest hills in my city without getting off the bike and walking it (33rd and Fremont for the PDX kids), and downhills / flat sprints are still fine for how fast I go with cars around me.

With that said I think I want to go put a 16 or 17t cog on the other side of the hub so I can have 75-80 gear inches and learn to ride like that in the city and develop more leg muscle as I force myself up hills, and if I end up disliking that way too much I can atleast keep it for the rare occassion that I make it to the velodrome. I don't think a higher gear ratio will hurt the knees as I have denounced backpedaling for the most part and just throw skips now for slowing down. Backpedaling sucks as far as I'm concerned...

rykoala

I have two fixed gear bikes, both with 48 tooth biopace rings. The trick is to tension the chain just a *little* tight with the cranks vertical. Then, when you turn the cranks horizontal, the chain will be just a *little* loose. I used to drop chains all the time before I figured this out.

mihlbach

Ken,
Your post interests me. I've been thinking about experimenting with different gearing combinations. I currently ride with 75" and am pretty happy with that. My area is pretty hilly, but the hills are low and not very steep and I can generally maintain a good cadence when climbing with my current gear. They are actually great training hills..the perfect length for sprinting up. I occasionally wonder what would happen if I geared down slightly..on the other hand I sometimes wish I had something higher. What I really need to do is experiment with different ratios to find my optimal gear. What I do know, is that I tend to climb way faster on my 75" fixie compared to my geared road bike, where I usually spin a much lower gear uphill. At any rate, how do you explain the similar times with different gears? Would you say that you ride with a similar speed throughout the ride, but at a faster cadence, or is it more of a case of climbing faster and descending slower, thus producing a similar average speed.

roadfix

Same here........but what about on a much longer one hour sustained climb, for instance? I personally can hold a decent cadence pushing 75" on very short climbs only.

marqueemoon

Wow. You are a spinning mother****er.

goldener

low gears ftw +100

if you can't spin a 69 or 70" gear up to 22+ mph you are a weak rider. period.


I ride 44*18 (66" on 27's) and 42*16 (69" on 700x23s).. yum... I can hang with the peeps who spin 47*16 (77")and the like..

Kilgore_Trout

i geared down for the winter and felt like i could really spin a lot better; even though i felt like a monkey on crack sometimes. i'm just kinda worried that in gearing back up my legs are going to die.
but glad to hear you're trying out different gearings to get a feel for what's up.

Sakae Custom

I find that i spin out with 75s in the flats here in chicago, i used to ride 79, but i dropped to 75 for skid patches, and brakeless knee happyness. Any smaller gearing and i would going crazy. I should move up to 175mm cranks.

Fugazi Dave

Lower gearing is awesome. I'm running 47x18 now and I've found a sweet spot for my legs. I was running 45x18 before but wanted something with just a little less ultraspin on descents and more skid patches. I think the new gearing is still only like 67 gear inches.

mihlbach

Honestly...I use my geared bike for rides like that.

roadfix

Good answer.

Ken Cox

I climb faster on my fixed gear bike than on my geared bike, up to a point, and it has something to do with aerobic and anerobic stuff...I think.

My older son, the world's most physically fit human being, says my ride takes the same watts regardless of the gear; and the high gears give me speed on the flats and downhills, but the lower gears give me more consistent speeds and better long climbs (more aerobic)...or so he says.

I would like to know more about this aerobic and anaerobic thing.
I think it has something to do with why I can outclimb geared bikes on some hills and not on others.
I know I do a lot better now on my longest hill with this lower gearing than I did before, and I suspect Shiznaz has some insight into this.

Plow Boy

From my experience, I tend to push it up the hills. 46x16, 50x17 seems to due the trick middle to late summer. As of right now, 44x17 is just right.

dirtyphotons

check out joe friel's cyclist's training bible, if you haven't already. and there's lots else written on it.

with a huge grain of salt though, the fun is what's really important.

Momentum

Sounds like an interesting experiment Ken.

It's also interesting to see what people define as a low gear. I started riding 42/16 (around 70") when I first rode a fixed gear as most of the sources I found suggested it was a good gear. I have stuck around this level (I now ride 47/17) and find that is the most suitable for me to ride on flat to undulating terrain.

There is a long history of fixed gear riding in the UK, especially as training in the winter. 42/16 was known as "evens" as it gives approx 20 mph at 100rpm.
Fixed gears are also popular here for time trialling and there used to be, and still are, fixed gear TTs where you are limited to a maximum gear. The "medium gear" class has a max gear of 72" and they measure this out at the start line. The current record for a 25 mile TT is 55:03 - that's an average speed of 27.27 mph and an average cadence of 127!

It goes to show that good rider will be able to move pretty fast with a "low" gear and will still be able to get up hills a bit more easily.

There's more info here https://www.fixedwheel.co.uk/

666pack

i ride 38x18 most of the time and it's a blast. so much more fun than a high gearing, if not a bit more exhausting. i ride pretty much all hills out here, so it's nice to be able to keep up with traffic on uphills where i gotta make a quick left turn at the crest.

Ken Cox

It helps to know what a person can do if he practices.

I don't think I'll get anywhere near this type of performance in this life, but it gives me an idea of the possible and a target at which to aim.

If I could average 19 mph (my 72" average) at 64" it would greatly please me.

Revolution Smmr

Speaking of Biopace, I'm converting my wife's old Schwinn to SS (not fixed) and it has 42 and 52 tooth biopace chainrings. I wasn't planing on using a chain tensioner since she has pretty long horizontal dropouts, but because of the biopace rings, will a chain tensioner have enough play in it to keep a good tension throughout the revolution, or should is just use the method stated above (tension the chain so it's just barely tight/loose depending on the point of the rotation)?