The last thing I expected was guilt.

Today is national Bike to Work Day, and I thought it’d be awfully hypocritical of me to write about bicycle commuting without actually having commuted by bicycle, so about a month ago, I decided to ride my bike to work.

Every day for the past month, I’ve tried to ride to work, and I have missed only three days.

Once, the day tornadoes tore through Kansas City, Kan., I saw lightning and parked the bike.

The second setback came the day I had to work in K.C.

And the third day was Mother’s Day, when I was running late and simply (pause for effect) chose to drive.

And that’s where the guilt comes in.

I’m not sure why I started cycling to work in the first place, but it coincided with a trip to the mechanic that was supposed to be short, but ended up lasting a week.

About that time, a headline in a magazine caught my eye: “How to Get Fit Faster (and save the world).”

The article extolled the virtues of bicycle commuting. Intrigued by the article, and since I had no car and didn’t want to bum rides to work for a week, I cycled.

I started more or less out of necessity, but by Mother’s Day night, when I was stunned to realize I felt guilty about driving to work, I realized I was hooked, and I’m not sure why.

I can quantify it in all sort of ways.

It’s right at five miles from my garage door to my workplace. Five 10-mile roundtrips — about 40 minutes each — a week equals 50 miles.

My car gets about 20 miles per gallon in the city, so I’m saving about half a gallon a day. At $1.40 per gallon, I’m saving about 70 cents a day, or $3.50 a week.

And then there’s the fitness factor. According to my handy bicycling.com calorie computer, 40 minutes at 14 mph at my weight equals 484.90 calories. Since one pound equals about 3,500 calories, I could, theoretically, burn a pound every 7.23 roundtrips — just under a pound a week.

And it was easier than I thought.

I ride recreationally, but I never rode to work for several reasons. I was worried about sweating my way through a workday and offending co-workers. I didn’t want to mess with traffic. I didn’t have time. I didn’t know what to do with my bike.

All issues quickly resolved themselves.

It’s hard to build up much of a sweat over just five leisurely miles.

Traffic wasn’t too bad once I found a back route into the office.

I found it took 10 minutes to drive and 20 to ride to work, so the additional time was manageable.

And, fortunately, my workplace has plenty of places to stash a bike — like the racks on a nice, high-traffic, lighted loading dock.

It helps that I have a somewhat flexible work schedule. I ride to work in the afternoon, then ride home for supper. Then I drive back to work in the evening and drive home again when I get off, at 1 or 1:30 or 2 in the morning.

I’d like to cycle all legs, but sometimes I’m afraid to drive through the drunken gauntlet at 2 a.m.; I’m not pedaling through it for 70 cents a trip.

There also are other intangible benefits.

Cycling advocates say bike commuting benefits the employer, too, because absenteeism declines among fit employees, and there’s anecdotal evidence a happy employee is a more productive employee.

I don’t know if I’m working better or smarter or faster, but I know I look forward to the ride in more than I ever looked forward to the drive, and, actually, I tend to get to work sooner. I try to build an extra five or 10 minutes into my schedule to accommodate a flat or some other mechanical problem, and, since I’ve had neither, those extra minutes have been spent at work.

And I know I feel better about myself.

Or I did until the other day, when I was spinning to work and overtook another cyclist.

He did a doubletake over his left shoulder, swerved onto the sidewalk and shouted, “Fat (rear end). What’s your problem?”

My problem, I thought as I pedaled away, was that I had just learned my (sniff) rear end was (boohoo) fat.

Lawrence might be a bicycle-friendly town, but it apparently isn’t a friendly bicycle town.

Regardless, I plan to continue to ride to work.

Heck, I can invest a few bucks in a handlebar-mounted light and make both roundtrips from work to home each day.

That’d be about 100 miles a week … or $1.40 a day … or seven bucks a week … or 979.8 calories a day.

And the sound that prompted me to take my car into the shop has started up again — close to a thousand bucks and a month later — and …

Yep, it looks like I’ll be cycling to work again.

Now if I can only do something about my massive fanny.