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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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.
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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.
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Bike computers are becoming a common sight on the handlebars of nice bicycles, but unless you’re racing or bicycling as part of a specific physical fitness or health program, you may not really need one. A bike computer tells the rider basically anything he or she could ever want to know about their riding. Depending on the sophistication (and expense!) of the model, it will detail speed, distance, temperature and wind speed, heart rate and pulse, calories consumed, pedaling cadence, and even provide geographic information like altitude, slope, or directions.
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It sounds like you’re creating problems yourself by trying to solve this issue instead of looking at why their is a problem in the first place
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I bought one of these cheap computers on Ebay and it claims to show RPM without the need to make any adjustments to the wheel input or fancy wiring changes. BUT…… when you input the wheel circumference of say a 700c or in my case a spinning bike with a cir of 144cm, the RPM readout is way way to high. All other functions like speed, distance etc are all accurate.
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This is the motorcycle world that Harley-Davidson has reinvented, one that seems–and is–a century removed from the Milwaukee shed where William Harley and Andrew Davidson first collaborated in 1903. Harley today has more to do with fraternity than with machinery. You buy a Harley, you join a ready-made motorcycle gang: the 600 U.S. HOG chapters, operated under the dealers’ aegis. Style is as important as speed. On dealers’ floors, leather-draped mannequins can outnumber the bikes. Harley has artfully parlayed the romance of the road and the independence of the biker to capture baby-boomers. Its core customers have reprised their 1960s rebelliousness with a product that bespeaks their 1990s success.