JUL 20, 2009 – 12:00AM

I’m a natural-born quantifier and a to-the-bone geek, so when the first GPS devices designed for bike use hit the market, I was intrigued.

But as cool as I found them, I also thought them a bit too pricey.

I’ve had a variety of bike computers on my rides through the years. All measure the basic how fast and how far. Some had features like temperature or cadence.

But never before had I spent more than about 50 bucks on one, and the early bike GPS gizmos — that tell cyclists how fast, how far, where, when, how high and just about every other measurement available – ran well into the hundreds.

Then Garmin, the company that put the Gee! in GPS, updated its bike line a few years ago, and the basic black-and-white was replaced with a color display. The devices also featured map functions and turn-by-turn directions, and though I coveted, I didn’t think I’d ever be able to afford one.

Then by mere coincidence, two Garmin GPS gizmos fell in my lap in the span of about a week.

The first was a GPS watch to help track my runs. I found it on sale online, with a free extra heart-rate monitor, plus a $50 rebate. I had wanted something more accurate than the nifty but not very consistent Nike+ iPod dongle I’d used the past couple of years, and the price was right.

Then my brother called. He worked for a company and knew a guy who knew a guy who could get me a top-of-the-line Garmin bike GPS. Free. All I’d have to do was ride my bike, then upload the info to a Web site so this guy’s friend-of-a-friend would have some real data with which to work. I don’t know to what end, but it’s not like I’m giving out any state secrets or anything.

I have a grand total of one run and one ride on my new toys, and I have to admit to a bit of trepidation at first.

I keep track of all my runs and rides. Why, I don’t know, but I do.

Several years ago, I found my usual work commute was just a hair under 10 miles: 9.72, by the old-school computer that counts wheel rotations but can be thrown off by such parameters as rider weight or tire inflation. Not wanting a 9.72-mile commute, I added a short dogleg on my ride to work, bringing the round-trip total to 10.11 miles. I recorded it as a 10-mile ride.

Similarly, I measured several of my regular runs with my Nike+ doodad. The same run varied as much as a quarter to half a mile, so I always ran the longest measured run and tacked on a block or two just to be safe.

But once I had my uber-accurate GPS devices, I started to worry my world was about to shrink.

What if my regular five-mile run was really only 4.84238452 miles? What if my 50-mile bike loop really was a mere 49.999999999 miles? I would have been living a lie. Over the years, all those 10,000ths of a mile could add up.

I tackled the run first, and as I crossed the five-mile finish line, I cast a cautious glance at my watch. I was relieved to see it read 4.99 miles. I went just a few steps more and it ticked over to 5.00. Perfect.

Later, I rode to work and back and intentionally took the shortest of my routes home. I never officially measured that particular route — the battery died on my commute bike months ago, and I never replaced it — but assumed it was somewhere between 10 and 10.11 miles. With the Garmin in my pocket, I rolled into the garage and saw the display read 10.00 miles on the dot.

Now that that’s out of the way, I probably will mount the Garmin on my recreational road ride and leave it. I can’t get over the fact it costs a couple hundred more than the commute bike I ride almost daily.

I’m not sure what I’ll do with all the info I’ll have at my fingertips. I’m sure I’ll geek out at first before the stream of data loses its luster.

I do know I won’t be able to lose myself on another ride as long as I have my new toy along.

And I’m not sure that’s such a good thing.