Comparing Mileage

Today I rode past a billboard advertising a Jeep SUV of some sort, proclaiming the beast gets 39 miles per gallon. That’s not too shabby — build a carpool around that vehicle and you have decent efficiency. It made me wonder, as I pedaled along: what sort of mileage am I getting?

Strava estimates that at my rather-slow cruising speed along a straight, flat road (fair for comparing “highway mileage”) I’m putting out about 150 watts of effort (or less, but I’m rounding in favor of cars). Pessimistically I’m burning about five times that in stored food energy (my gasoline equivalent); the rest of the energy winds up as heat in my muscles. So I’m consuming about 750 watts to roll along at 15 miles per hour. That’s fifteen miles for 750 watt-hours, or 20 miles for one kilowatt-hour.

A gallon of gas has the energy equivalent of about 37 kWh, so were I running on gasoline, I’d get about 20 x 37 miles, or roughly 740 miles per gallon — let’s call it 700 to avoid any pretense of precision.

700 mpg! Not bad! If I lost a little more weight my mileage would get even better (or more likely I’d just ride faster).

Calculating Calories is Hard!

I’ve been using both MapMyRide and Strava to track my bicycle rides recently. In addition, I’ve been using the activity app on my slick new Apple Watch. Each estimates how many calories I burned on my ride, but the numbers are very different. For example, on my ride to work yesterday morning:

MapMyRide: 814 Calories
Strava: 643 Calories
Watch: 757 Calories

Dang – those are quite different numbers, especially when you consider that MapMyRide and Strava are using pretty much the same data and coming to very different conclusions. What gives? CAN I EAT THAT DONUT OR NOT?

Strava and MapMyRide use speed and (maybe) elevation change in a formula with the rider’s weight to come out with an estimate of how many calories the rider burned. Strava lets me set the weight of my bike; I don’t know what MapMyRide assumes. I’m pretty confident that neither really uses elevation changes well. And headwinds? Forget it.

Both services can come up with a better wild-ass guess if you use a special crank or pedals that directly measure how hard you are working. They directly measure the output of your muscles, so the only remaining guesswork is how many calories you burned to do that work (some people are more efficient than others). There’s a Garmin setup that will tell you if one leg is doing more work than the other. I have no such device.

The most accurate way available to measure calories burned is to measure how much carbon dioxide one exhales. Rather than measure the work you did, you’re measuring how much exhaust you produced. This is impractical on a bike ride, however.

Which brings me to the gizmo strapped to my wrist. It estimates calories based on my heart rate. I have no idea what formula it uses, but hopefully it incorporates my resting heart rate (which it measures throughout the day) and my weight (which I have to remember to tell it), and maybe even my age. The cool thing is that heart rate is directly related to carbon dioxide production. When I’m riding fifteen mph with a tail wind, I’m barely working at all. When I’m pushing against gale-force breezes at the same speed, I’m huffing and my heart is thumping. To Strava and MapMyRide, the rides look the same. The watch knows the truth.

When WatchOS 2 comes out (the “features we couldn’t get perfect in time for WatchOS 1” release), Strava will be able to access my heart data. I’m interested to see what that does to the numbers.

In the meantime, I’m listening to my watch.

Bike School — and Beyond!

6369080A couple of months ago I heard about a non-profit bike shop in my ‘hood called Good Karma Bikes, which is run by some pretty awesome folks who find a lot of different ways to help the community. The primary focus is on making sure homeless and working poor have transportation. They also provide training and stability for kids coming out of the foster care program, a segment of our population that generally gets tossed to the curb.

Unlike a typical bike shop, Good Karma has about a dozen workstations on its shop floor, to allow them to repair many, many bikes each week during ‘clinics’, when they fix bikes for those who can’t afford service. When clinics aren’t going on, people can drop by and use the workstations and all the tools in the shop for an hourly rate. What a great alternative to buying an expensive tool that you hardly ever use.

It turns out they also have instructor-led classes each summer, teaching people how to take their bikes apart and put them back together. It’s called ParkTool School (ParkTool is the Snap-on of bicycle tools) and it’s a great chance for people like me to learn the right way to do things, gain the confidence to strip things all the way down (“count to make sure you have an even number of ball bearings!”) and to fix up one’s own bike while there’s a safety net. You also get to use all the facilities and tools of Good Karma while you’re at it.

I am now the proud owner of a cheap-ass little certificate that says I’m moderately competent in bike repair. The course was eighteen hours of instructor-led class and lab activities. I also got to meet some fellow bikers who, like me, have reached a stage in their riding that it makes sense to be able to do repairs themselves. It was nice little bunch.

One woman in my class is the sister-in-law of a kid I knew in elementary school. Small world, man.

The instructor, Steve, was really good at explaining things, and combined with my general mechanical knowledge (the kind you get when you own a ’70’s-era Italian car whether you want to or not), I got things pretty quickly. Unfortunately for me, this didn’t prevent Steve from explaining the same point in many different ways. Sometimes that made it hard to concentrate.

The lab time was golden. I like to tinker, and as cars get less and less tinker-friendly, I now have new primary transportation that not just encourages a hands-on attitude, it requires it.

And get this: I can volunteer at Good Karma Bikes and tinker on other people’s bikes as well! I can hone my skills and help those in need at the same time. For free! I was already tempted when (at the sage suggestion of the Official Sweetie of Muddled Ramblings) I checked and discovered that my employer will match each hour of volunteer time I spend there with a cash donation.

There is seriously no downside to this, other than dirty fingernails. I’m pretty stoked.

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