Sunday, December 07, 2008

Retro-Direction Perfection?


I never quite know how my various bicycle projects will turn out. Once I'd gotten my retro-direct bicycle past it's initial proof-of-concept phase and into something I'd actually trust for my commute, I hit up against another problem. While the bike worked fine in a mechanical sense, my body didn't seem to like pedaling backwards to climb a hill. When I'd climb out of the saddle, I'd tend to slip into forwards pedaling and the leverage just seemed wrong. I gave myself a few days to adjust, telling myself that I'd spent years pedaling forwards and I tried different front chain rings in an attempt to get the low gear lower.

But the real problem was the bike didn't seem practical. It seemed always geared wrong and while the bike had a fun novelty about it, it really didn't feel like something I'd enjoy riding every day. I was pretty close to writing the bike off as "a good learning experience" when Jacob Slosberg stopped by the shop. Jacob is a former earn-a-bike student who also worked in the Bike Works shop a year or so ago. After hearing my problems with low-gear backwards pedaling, Jacob made this brilliant and simple suggestion:

"Swap the chain around. Make the backpedaling gear the higher one and the forward gear the lower ratio."

Brilliant, simple and the thought had really never occurred to me. Sure that Zoobomb guy had his bike geared as low forward, high backward but the Wikipedia article and most other articles I'd read describe having the lower gear be the one engaged by backpedaling so that's the way I'd set up my bike.

Oh well, it'd be easy to test. I rerouted the chain and went for a ride.

Not since Doc Brown installed a flux capacitor in his old DeLorean has a single hardware change had such a dramatic effect.

The bike went from being interesting to being wonderful. Instead of awkwardly thinking at a light "I'm starting from a dead stop, I'll have to pedal backward", I'd stomp the pedals in a normal, natural manner. As the bike picks up speed and I'd start to think "I wish I had a higher gear" and I'd recall that I do have a higher gear at my disposal. Engaging that gear by pedaling backwards is much easier and automatic when done in a moment of ease instead of a moment of stress. When the terrain resembles that Irish blessing and rises up to meet me, I pedal backwards until the effort seems wrong. And then, effortlessly, I switch to forward pedaling, engaging the lower gear. If the road steepens further, I rise out of the saddle. When I crest the hill, I settle into the saddle and backpedal down the backside. It doesn't feel odd, it feels natural. Those poor saps with their mono-direct bikes, they don't know what they're missing!

The first test ride was only 18 miles but within the first couple of miles I was sold on retro-direct, low-normal, high-reverse gearing. It suddenly made perfect sense, like back in high school when I learned to work an HP calculator. RPN and Forth programming expanded my young nerd mind three decades ago and now an old bike with an oddly routed chain has opened up a similarly expanded route through this wonderful world.

I did tweak one thing on the RetroTrek after that epiphany ride. I swapped the chainring out for something bigger. The RetroTrek now sports a 42 tooth front ring. With the 16 and 22 tooth freewheels, I have a low forward pedaling gear of 49.6 gear inches and a high reverse pedaling gear of 68.25 gear inches. My experience riding fixed gears had lead me to choose about a 70 inch gear for road, while my Monocog mountain biking had shown me a gear around 49 inches is right for me for that application. And now, those two gears (or at least very close approximations) are contained in a single bike. A bike that I pedal backwards sometimes.

A week ago I wrote: "I'm not going to try to convince you that a retro-direct drive bicycle is practical." I was wrong about that. I guess I am trying to convince you. Because I've convinced myself. No, scratch that, the bike's convinced me. Backwards is the new forwards. You heard it here first.

Keep 'em rolling,

Kent

12 comments:

Erik said...

This has been a really interesting series and I'm definitely going to post another link to this update from my NorCal Bikers blog. One question for you, how fragile a set up is this? It looks like the arm with the cog hanging low could get destroyed by a curb jump or something in the road.

Still, a very cool project!

Vincent Muoneke said...

Perhaps, after a few months of retraining your neuro-muscular system on the current gearing, try reversing it again.

Anonymous said...

Nice job man.

Lawrence Fieman said...

Kent, I happy to learn that this is working out. Sounds like big fun. By the way, what kind of handlebars are those?
Best,
Larry

Kent Peterson said...

Erik,

The arm is held to the bike with straps cut from an old inner tube. I haven't bashed it yet, but in theory the arm will flex rather than snap off. In fact it does flex a bit because the cheap Dicta freewheels aren't perfectly round.

The pulley does pick up a fair bit of grit and after yesterday's trip that involved a lot of muddy trails I've fashioned a coroplast mud shield to keep the worst of the crud off the front pulley.

Larry, the bars are flat mountain bike bars with Newk bar-ends. Newks aren't made any more, but I scored a set at Bike Works. I use the lower drops while back pedaling in the high gear and the upper bar-ends with the low gear for climbing.

Kent

Mike C said...

Sounds like that Wikipedia page could use a bit of updating, then, regarding the benefits of low-forward high-reverse gearing, from somebody who has (retro-)direct first-hand experience... :-)

Anonymous said...

Kent,

you're messing with the laws of nature. This ain't right, nice or moral. Pedals are meant to turn in one direction, and one direction only. Please leave things as they are and don't try to push the envelope too far. Just because things are possible don't mean that you gota try them.

My prayers be with you.

Cafn8 said...

Cool project.

I'm curious about the long idler arm. Is it there to reduce the lateral angle of the chain as it comes around the bottom of one cog and back over the other? I'm wondering since the retro direct XO2 looks more like your original setup (although apparently the iteration that looks most like your original setup wasn't quite perfect either.) Is it for length, angle or both?

I love odd bikes.

Kent Peterson said...

Cafn8,

Yep, the long idler arm does a couple of things. Having the idler pulley close to the crankset lets the chainline to the back freewheels be pretty straight. When the idler was further back the angles going into the freewheels wound up being more laterally extreme and things were noisy and tended to derail. The other trick with the idler arm is that it attached to the bike with bands cut from old inner tubes. It actually pivots slightly (with the bottom bracket shell as the fulcrum) so the chain tension stays constant, even though the inexpensive Dicta freewheels don't spin perfectly round. Since the outer freewheel is attached to the inner one, the out-of-roundness effect is kind of additive. The arm pulls up the slack in the system.

zzyzx_xyzzy said...

Hi Kent, I may soon become the third(?) retro-direct rider in Seattle. I'm hoping to make it a 2x(-2) with 2 chainrings (this bike I'm using came with a 40-50 crankset) and a sprung tensioner. I kept running the numbers and the most sensible gear spread for me looks like 16 small and 24 big freewheels, but of course no 24t freewheels are to be found. But! I found some freewheels made for electric scooters that use bolt on sprockets:

http://www.electricscooterparts.com/SPR-SB4H.htm

And if I'm measuring the picture right, that is (or is nearly) a 4x64mm BCD just like MTB granny rings! This might be the solution to the big freewheel problem. I have one on order and will let you know how it turns out.

Daks said...

Hi Kent,
I am becoming a Tech Ed teacher (shop teacher) in Vancouver, Canada and I am very interested in building a retro-direct bike as a project. I would love to ask you a couple of logistical questions, mostly about the two independent freewheels on the wheel.

Kent Peterson said...

Hi Daks,

If my previous posts (follow the links in this post or use the blog search function) don't answer your questions, drop me an email at kentsbike@gmail.com.

Kent