05-04-2009, 11:30 AM
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#17 |
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Join Date: Feb 2009
Posts: 331
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What I see as being a problem, is accuracy- seeing as these are designed for bicycles- you can't just set the circumfrence to the diameter of your ATV wheel- as bicycle tires are very thin, while ATV tires are just the opposite. Nor can you set it to the tires diameter for the same reason.
There probably is a mathematical formula one could devise to determine the proper input for ATV use- or one could just experiment if one has another menas of acuarately measuring the speed, etc..... I'll let yous guys figure it all out!  Looking at my crude diagram, if you were to set the speedo for a 10" wheel diameter, it will be grossly inaccurate, because the bicycle wheel of 10" diameter will turn many more times in the course of a mile than the ATV wheel. You can't "beat it" by instead setting it to tire diameter, because the magnetic sensor would be in the wrong place, being mounted on the rim (the only way that would work is if you could mount the sensor on the tire, about an inch from it's edge, to duplicate where it would be mounted if it were installed on a bicycle.) Somebody who knows geometry could figure out a conversion equation though, I'm sure. This is a matter for minds greater than mine! (I wonder if the guy in the link I posted previously is a aware of this? -or if he just mounted up his sensor, and set it to his wheel diameter, and went on his merry way, being oblivious to the fact that his readings were probably off by 50%?!) |
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05-04-2009, 12:37 PM
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#19 |
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Join Date: Feb 2008
Location: Terrell and Grapevine Tx.
Posts: 1,585
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With a low preasure ATV tire it might be best to mark the tire and roll it on the ground to measure the distanse the tire travels in one revolutions. Or do 10 revolutions and devide by 10 to get a little more accurate. Thats the number needed to set up the speedo.
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05-04-2009, 12:43 PM
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#20 | |
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Join Date: Feb 2009
Posts: 331
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Quote:
It would seem to me, that it would matter- because the speed is determined by how frequently those revolutions occur. i.e. a given wheel will rotate x number of times over the course a fixed distance, regardless of whether it is going 2MPH or 70MPH. The interval between the magnet passing the sensor is what determines the speed- and exactly where you place the magnet on the radii of the wheel, will effect how fast it passes the sensor. The closer the magnet is to the axle, the shorter the interval will be and vice-a-versa. Thus, if you took two identical wheels, and mounted the magnet near the outside perimeter of one and near the axle of the other, you would get vastly different readings when both wheels are traveling at the same speed. I'd imagine that, for bicycles, these things are probably made to be mounted on the rim flange, c. an inch from the outside edge of the tire. (I could be wrong). If that is so, it would be impossible to mount it in the same location on an ATV tire. |
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05-04-2009, 02:01 PM
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#21 |
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Join Date: Aug 2008
Location: Tracy, California
Posts: 83
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No.
The speed at which the magnet passes the sensor is not important. It is the time interval between passes of the magnet, and the circumference of the wheel that determines speed. Speed = Distance / Time |
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05-04-2009, 02:11 PM
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#22 | |
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Join Date: Feb 2009
Posts: 331
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Quote:
The time interval at which the magnet passes the sensor is the same thing as the speed at which it passes the magnet. |
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05-04-2009, 02:25 PM
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#23 |
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Join Date: Aug 2008
Location: Tracy, California
Posts: 83
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If the wheel is revolving at 3 revolutions per second then the magnet is also revolving at 3 revolutions per second regardless of where the magnet is on the rim. The quad will be travelling 3 circumferences of the wheel per second which can be converted to speed in any units you need using the earlier formula.
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05-04-2009, 05:31 PM
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#26 |
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Join Date: Oct 2008
Location: New Port Richey, FL.
Posts: 24
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I did this with a digital schwinn speedo from walmart. I created a bracket to mount the sensor at the rear disk rotor. Then I took a bolt and drilled a hole in the head just big enough for one of those small but powerful neo magnets from the craft store. I didn't even have to glue the magnet in. Once it grabbed into its hole it isnt coming back out! Next I put my now magnetic bolt through one of the existing holes in the disk where it doesn't interfere with the brakes and voila, instant digital speedo. According to my K-band radar gun it's spot on. The formula is to measure the circumference of the tire and convert it to mm. In my case it's 1422mm. I'll try to post a pic later for illustration purposes.
__________________
'08 Haili Icebear 110cc '05 Roketa RTB-90x '71 Honda Z50A Mini-Trail |
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05-04-2009, 06:36 PM
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#27 |
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Join Date: Jun 2006
Location: directly under the earths sun............NOW
Posts: 2,302
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I put a trail tech vapor on my wifes raptor (ATV) before we even got it out on the trails and you just have to mark and measure as has been stated and plug that data into the speedo computer and its good to go.
Of course I had to slip and run the front axle cotter key into my hand but if you dont give blood on a project your just not trying hard enough. |
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05-04-2009, 07:05 PM
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#28 |
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Join Date: Feb 2009
Posts: 331
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Wow! It's great that this actually works- and that you can put a cheap speedo on any ATV!! (Leave it to me to overcomplicate something).
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05-05-2009, 07:41 AM
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#30 | |||
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Join Date: Sep 2008
Location: Nashville, TN
Posts: 588
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Quote:
I use the same computer for both bikes. It has an "A/B" choice that can have different settings. Someone already posted: make a chalk mark on the floor and tire. Roll the bike to make one revolution and make another chalk mark on the floor. Measure the distance and convert to mm's. Make sure to sit on the bike. The weight on the tires can make a big difference in the reading. Especially those mushy ATV tires. Bill |
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