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A clever way to use a bicycle computer as a poor-man’s tachometer. While I’m not sure about installing it in my car, I’m sure it’ll come in handy down the road for another project. "Sometimes you just have to know how fast a wheel or shaft or motor is turning. The measuring device for rotational speed is a tachometer. But they are expensive and not easy to find. Its cheap and easy to make one using a bicycle speedometer (cyclocomputer). In fact, the only thing you need is a functional cyclocomputer that reads speed in miles per hour. You won’t damage it, so you can even ‘borrow’ one from your bike, or add it to your bike once your done!"
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August 27th, 2008
In college, we drove this $300 car across the country. The starter didn’t work. The thing couldn’t get past 60 mph. And, oh yea… we used a bike computer instead of the speedometer because that speedometer cable broke. (we pulled it out mid-road trip). It works great… but it takes some time to get up to speed. i.e. it’s not good for measuring acceleration, but if you are running at a constant speed, it’s great.
October 10th, 2008
If you rummage around on eBay for bike computers, you’ll find one that has an RPM readout. Easy to spot, they’re the ones with two round push buttons under the display.
If you’re not interested in speed, set the wheel size to the smallest value (60cm circumference on mine) to get the maximum RPM value. If you don’t, it tops out at 99.9 miles or km per hour, thus limiting the RPM.
I use them on lathes & the like. Downside is they’re a bit hard to read.