Wednesday, November 21, 2007

26 x 1-1/2 Does Not Equal 26 x 1.5

There are some things in the bicycle world that are just plain weird. The various ways bike tire sizes are designated is quite bewildering but, as is the case with many things bike related, Sheldon Brown has an article that explains things pretty clearly. That article can be found here:

Now I have read Sheldon's article and I have worked in bike shops and I've explained the weirdness of tire sizing to various folks over the years, so you'd think this would be ingrained in me. And mostly it is. I know what size tires fit the rims of my various bikes and I know to look for ISO/E.T.R.T.O. number to resolve any doubt.

Most of the time I remember that.

Sunday I am riding up in Redmond on my new-to-me "fast" bike. Note that "fast" is in quotes. In this context it only means that this bike is probably faster than the other bikes I currently have in rideable condition. In the larger universe, the universe that includes such things as carbon Parlees and Mario Cippolini, my bike is not fast. But still, the bike seems fast and in my head I sometimes hear Phil Liggett's voice telling me I'm a "spirited little climber" so I get to wondering how fast my fast bike really is.

This is how impulse purchases happen. I'm wondering something like how fast I'm actually going and then I realize that I'm right by the Redmond REI and maybe I'll just see what they have in terms of cycle computers. And they have a nifty Cateye Strada which is kind of small and pretty much has all the features I want and it even has mount that can go on the stem or the bars and by the way I have a bit of extra cash because a bunch of my blog readers bought NO WAR FOR CHAIN LUBE shirts and I just deposited the check from Cafe Press. And maybe I could blog about the cycle computer (this is the "blog fodder" excuse and it can be used to justify darn near any cycling related purchase or adventure). And didn't our president tell us that if we don't shop then the terrorists have won?

So I do my duty as a good American and then I'm at the bike rack at the REI, installing my new Cateye Strada. Another cyclist locking up his bike gives me the "computer, eh? I gave up on those years ago..." speech. I grunt in an ambiguous manner, not bothering to tell him that I've given the speech he's giving me a few times myself and besides I've quit bike computers more times than my uncle Buck gave up smoking.

So maybe I'm a little distracted. And the instructions are printed in a dozen different languages (no exaggeration, a dozen, I just checked) and so the instruction sheet, including the computer calibration table, is printed in some pretty tiny type. Anyway, I get the computer installed and mostly figured out and I punch in the number from the calibration chart and roll away.

This red bike is fast. This makes sense, Mario Cippolini will tell you that red bikes are faster than other bikes, everything else being equal and Mario being on the red bike. And even this red bike with me on it not only seems fast, it is fast. Maybe not Super Mario fast, but fast for me. Faster than I thought.

The warning sign comes when I get back to Issaquah and see that my new computer not only tells me that I'm faster than I should be, but also that it is a bit farther from Redmond to Issaquah than I remembered. That doesn't seem right.

Monday, I get the confirmation. I am faster than I should be on my 19 mile commute to work. Except my 19 mile commute is actually just a bit over 18 miles. I know that for certain. My computer is wrong.

I look again at the chart. The number I'd punched in, the wrong number, was 2100 mm. That's the number for a 26 x 1-1/2 tire. But I don't have a 26 x 1-1/2 tire, I have a 26 x 1.5 tire. I am an idiot. I'm also a little slower than I thought I was. My red bike is still my fastest bike, but it's not quite as fast as I thought.

With my computer properly calibrated with a setting of 2010, my commute numbers match up with Google Earth and the real earth. I won't be challenging Mario to any sprints any time soon.


Anonymous said...

Does it have the "some me something, anything but my current speed" function? That's a pretty necessary function in my book.

Kent Peterson said...

Michael, you need to get the optional "hunk of black tape" accessory to cover the top part of the display.

Anonymous said...

What? You mean to say it's not compatible with the "hunk of silver duct tape" accessory?

Anonymous said...


Good commentary ... You are certainly not an idiot. I did a similar thing but the switch was from a 1.25" tire to a 1.50" tire. My speed and mileage reading was off and I finally figured it out after a few rides that I had changed tires on my bike but neglected to switch the computer settings.

Whatever ... such is life :)

Chris ... Novi, MI

NobbyNick said...

Hola Kent! I love it that you are not afraid to constantly change your bicycling style and preferences.
Toe clips -> Power Grips -> Flats
Gears -> SS and back
Computers YES -> Computers No and back
What has never changed and I pray it never does is your love for wheeled human powered transport, and your respect for all it's variations. Thanks and keep on pedaling.

Anonymous said...

This is why I use a small handlebar-mounted GPS for my cycling computer. No calibration issues, and I can dump the data into a variety of programs and get elevation profiles, my route overlaid on a map, etc. Does it make me faster? Does it make me train harder? Nope! But it sure is fun.

TwoWheels said...

You must reach a state of Zen where the presence of a bike computer and the siren call of its data does not affect you.

Hobbes vs Boyle said...

Let's all take the vow of "Nothing but ETRTO". Speak after me: Never again shall I mention any tire size starting with 16-29, 650, or 700. (Okay, this doesn't quite work, because it would also ban all narrow tires from ever being mentioned. But that just might be a sacrifice we have to make).