Cycle computer for 29'er

[juice0276]

Does anyone know of a computer that will accurately register 29" mtb wheels with a 2.0 tire that translates to about 700x52.

[Josh Whitmore]

You should be able to use any computer. I think most should accommodate the tire size. All computers come with a chart to translate wheel sizes into wheel circumference. I doubt that there will be an entry for a 29er wheel.You will need to do a "roll out test" to get the correct measurement.

1. Make a mark on the ground. Start with the valve stem over the mark.
2. push the bike forward, putting some pressure on the bars to simulate body weight.
3. When the valve stem comes around again, mark where is meets the ground.
4. Measure the distance between marks- the linear distance of the circumference of the wheel.
5. Put this number in the computer set up.

You will need to figure out what units the computer needs as input. Some go on MM, (aprox 2200mm?) and some use CM (220cm?). All that I have seen are metric.

good luck!

[juice0276]

That doesn't work with any computer that I can find. Even "maxxed out" the readings still come up about 10% short.

[juice0276]

Most computers stop at a 700 X 42 tire (largest tire reading) 29 mtb tires measure 52 or 54!

[Josh Whitmore]

Oops, good to know. I wasn't aware that they would max out.

Another idea, although annoying, is to divide your wheel circumference in half, plug that into the computer and just know that your actual speed/distance is twice as much. Hmm, maybe.

Let us know if you find one.

[Wrenchmeister]

Adding to Josh's idea, if you're maxed out, divide the number in half then put TWO magnets on your wheel. Put them opposite each other, not next to each other. Each revolution will count twice, thereby doubling the calibration number and giving you the correct speed.

As an alternative, do a rollout measurement for the wheel/tire combo you want to use. All computer manufacturers now have their installation manuals available online. Spend some time hunting through various brands and models until you find one that shows it will accept the number you measured. Focus on newer models, as they often have updated firmware that accepts more sizes than similar models from just a year or two ago.

[juice0276]

Those are great ideas, I will see if I can get it to work. In the mean time I will still be on the lookout to do it the lazy way.

Thank you

[ridgerunner]

OJ,
I just got a Cateye Mity 8, it goes up to 300cm circumference.