Tuesday, July 13, 2010

Behold, the watt.

"In terms of Classical mechanics, one watt is the rate at which work is done when an object's velocity is held constant at one meter per second against constant opposing force of one newton."

Blah, blah, blah. What the hell is a newton anyway?

Just kidding. I'm a nerd. I know what all of this means. Basically, a watt is a way to express the rate at which work is being done. When you're dealing with electricity, volts x amperes = watts. I actually think that transposes to mechanics easier than the crazy jibberish above.

The weight you apply to the pedals is like Volts. The speed you're cranking on them is like amperes. The combined work being done can, in fact, be expressed in watts.

I mentioned this a few days ago: fixed gear doesn't seem to have slowed me down at all. When I first hopped on the Wabi Special, I gave myself twice the time to get to work, just in case. I figured that I'd have a hard time climbing hills. I also figured I'd have to take it slow going downhill. To me, this whole thing sounded like a recipe for a slower commute. I got to work as fast as usual. Maybe faster. I didn't have a cyclometer, but total elapsed time with stops was 25 minutes, which is par for the course. This has been puzzling me for a few days. I keep leaving a little early. I keep thinking maybe I'm just hammering it harder than usual to make up for the time. I keep getting to work in 25 minutes. The return trip home is also about the same. What's going on?

When I'm riding on my own, I tend to fall into this pace. It's not particularly fast, but it's not very slow, either. I always thought this had something to do with my pedaling cadence. I'd adjust my gearing to keep my cadence somewhat stable.

Riding fixed gear, though, I've found out that I have settled into roughly the same pace, even though my cadence is all over the place. I'm now starting to understand how this all works. It's not about cadence, it's about watts. Without being able to trade-off effort for crank revolutions with dozens of gearing combinations, I still exert roughly the same amount of energy per minute regardless which bike I'm on. I just push harder on the uphills than I normally would, and spin faster than usual on flat land. The same amount of energy exerted moves the bike roughly the same speed on average.

Bonus: the fixed-gear drivetrain is actually more efficient and feels more connected to the road. You'd have to try it to know what I mean. The end-result is a remarkably simple, efficient and fun way to get around, so long as you don't have many steep hills around.

Mystery solved.

6 comments:

Apertome said...

I'm glad you're enjoying the fixed gear. I have to admit, I'm jealous. I've never ridden one.

Another factor is wind resistance. As you go faster, drag increases exponentially -- of course, this is true regardless of drivetrain. So, drag contributes a lot to the fact that your cruising speed is the same on both bikes.

rorowe said...

I second Apertome's jealousy (and maybe fixie curiosity). I've never ridden one, and I think I would likewise give myself a lot of extra time riding fixed for my commute.
Your conclusion makes sense, though. I'd be interested to see what a cycle computer says.

Jordan Day said...

I've never ridden a fixed gear... I just can't imagine trying to go down a hill with any sort of incline at all, at least without taking my feet off the pedals. So, I'll third on the curiosity point. Still, a fixed gear seems like it fits that vacation cliche -- nice to visit, don't know that I'd want to live there, though.

I do ride a single speed quite frequently, and yeah, the simplicity that comes with not shifting is very nice.

Noah said...

Basically, you ride the brakes on your way down steeper hills, and you push back on the pedals a bit to tame the smaller descents.

It's really strange how much momentum this bike picks up even on the smallest declines, though. It feels like a cannonball rolling down the road. Sections that seem flat but are actually slightly downhill become instantly apparent as the bike slowly picks up speed without any extra effort, just a faster cadence.

I rode The Twelve this morning. There are a few complaints I have about this bike, and fixed gear in general. The complete lack of eyelets for a rack is a big no-go for me. As Jordan said, nice to visit, but wouldn't live there. If I could easily mount a rack for my panniers, it might be better.

The other thing is the ass-hatchet that this thing shipped with. Combined with the extra taint-crushing weight of being forced to wear a backpack on my daily commute, it's not comfortable. Easily fixed, but this is a demo bike. I already had to provide my own (cheap resin MTB platform) pedals to test this bike. I don't have a spare saddle laying around, though.

carfreepvd said...

My LBS built-up a Surly Steamroller recently that has a Sturmey Archer 3-Speed fixed hub. Possibly the best of both worlds. It keeps you "fixed" but allows you to get a little bit of mechanical advantage for those big hills (like the 1-block long 12% grade on my commute home). You can check it out here. (you'll have to scroll down, their "blog" doesn't link to individual posts.) I like the concept, but it's not the bike I'm looking for right now.

Meredith and Ben said...

Hey Noah!

I haven't checked your blog in a while and I'm glad your trying a fixed gear. I'll be riding mine to the Dark Side ride tomorrow night. I've been commuting on it daily from JCCC downtown and I'm really loving it. See you there!

Ben

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