how bout this spedometer

[xxsokol32xx]

so i found a speedometer on ebay...kinda nervous about it. The guy said he has a production factory that he makes these in. doesn't really speak English so its hard to get much information from him. he has videos for both of them on those pages...What do guys think?

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=110647691737&viewitem=&sspagename=STRK%3AMEWAX%3AIT

and

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=110647691122&viewitem=&sspagename=STRK%3AMEWAX%3AIT

[GSXFJim]

I notice where the stationary magnet is mounted on the rotor.. but they list the 'tire' sizes.. which diameter is accurate? the diameter that the magnet is spinning on or the diameter of the 'rim' which is the correct measurement or the over all diameter of the tire? and can you calibrate it??
Looks good tho... if it works out for 50$ its a deal..

[xxsokol32xx]

well he has a Q&A on the page...its kinda confusing tho because he doesn't do English too well....


************************************************** *************
Q: Hello, In the video I see that you install the sensor on the brake disc. But you ask for specifications of the tire size. How does the sensor fit to the wheel? can I program it myself if the preset configuration does not work properly? Feb-15-11
A: Hello, dear friend. The information in the purchase of the project, it is necessary motorcycle tire size you are prompted. We will shipping your motorcycle tire size projects. Kind regards.

************************************************** ***************

so yeah, thats why i am so nervous.....but it seems llike an awesome deal...mabye i should ask him about calibrating it myself, but i doubt he will understand

[GytRDunKat]

I don't know, the murdered language would have me spooked.

[xxsokol32xx]

yeah me too, wish i knew someone who could talk chinese to this guy

[xxsokol32xx]

Ok so here is a string of email between me and the seller with a better translation. still dont feel like i got anywhere so probably not going to go with this one.


Me:***************************

Hi, this is Drew, I have been emailing you about the Digital Speedometer e2. I was trying to find some reviews of the item to see if others have liked it. I also would like to know what I will be able to change or adjust. Such as Clock, Odometer, Calibrate Speedometer, Calibrate Tachometer. I would also like to know what the significance of the tire size is since the magnet is mounted to the rotor as opposed to the tire itself, wouldn't you need the circumference of the area that the magnet is going to go rather than the tire itself. I appreciate all the help.

Thank You
Drew
******************************
Him:****************************

Hello, dear friend.
Instrument is based on a fixed size of tire production.
Time can be adjusted. There are two buttons to adjust the meter time.
Magnet sensor head is installed in the tire on the brake disc.
The length of the brake disc is corresponding to the tire in motion the process of mileage display.
You can see my tips?
Thank you for your message.
Kind regards.

*******************
****************
me:

Okay, So there is no way for me to adjust the speedometer itself...such as if i were to upgrade my tire size....or to adjust odometer to show my current miles.

Also, I am confused as to how the magnet location compared to the tire is going to be the same for all bikes, because some bikes may have bigger or smaller rotors on their rims...

Thank you again for all the help

***************************
Him:

Hello, dear.
We have no way to upgrade the instrument can produce.
You may not be very clear about my tips.
Our instruments are made in accordance with the size of the tire.
The magnets installed in the brake disk. Is fixed.
The brake disc is the speed of the tire along with the work. Their mileage is the same.
Tire size is everything.
Running around the tire, brake disc is followed by running around. Their position is common.
****************************
I just dont get how he could have this programed. If the sensor could be different lengths from the center, then how can he assume that its going to stay the same circumference for the magnet in each spot. the only possibillity is to be able to adjust the speedometer to match the position of the magnet, or have the exact disc he has....any ideas or mabye just stay away from this one. I guess i could always get it and get a speedo healer, then adjust that way, but id rather be able to adjust on my own

[Bart]

I guess this would all depend on a few things. The only thing I can relate to is a digital speedometer used on a bicycle. There, you put a magnet on one of the spokes, and the sensor on the fork. Every time the magnet passes over the sensor the tire has made one rotation. If you know the exact outermost diameter of the tire, the computer knows that one rotation equals so much distance, and just does the math to determine speed.

If that's the case here then the diameter of the circle upon which the magnet is moving (i.e. the diameter of the rotor, if the magnet is on the end of the rotor) is pointless information.

I only took a brief glance at this thing, but I saw something about a rotating cable or something, in which case you've got a good question. Kinda neat looking, but seems like cheap junk from China to me. Wouldn't you have to replace your whole dash to put this thing on?

[xxsokol32xx]

yeah it would be a complete dash replacement project...and it might be worth looking into if this works...i guess your right on how to do the math that way if it counts 1 rotation=distance traveled rather than rotations/time...or whatever, guess i didnt really think that out.

[GSXFJim]

The magnets installed in the brake disk. Is fixed.
The brake disc is the speed of the tire along with the work. Their mileage is the same.
Tire size is everything.
Running around the tire, brake disc is followed by running around. Their position is common.

I have to call BS...
calculating the speed based on the circumference of the rim when it has tire variables.. like a 120/70 vs. a 120/60 not to mention a 19" of a cruiser

circumference is the diameter times pi
Pi=3.1416 to four places

so our Kat 17" front wheel X 3.1416 = 53.4072" / 12" = 4.4506'

now we calculate wheel revolutions per mile by dividing 5,280 by the rim (not tire circumference) circumference in feet

5,280/4.4506= 1186.3567 revolutions per mile

If someone measures their front wheel from ground to edge of tire we could get closer

now.. you could have a fixed magnet and a pick up that could count the wheel rotations and do the math internally.. and spit out the results.. which it might.. I just don't see how it could be pre-calculated based on the rim size and be accurate with the magnet located in different places based on different bikes rotors and hole patterns.. and what if you have make a hole for it to fit, the ones in the kat rotors are pretty big

I looked a Dakotadigital and electrosport and they both have calibration modes where you 'zero' the gauge and drive one mile and then 'set' the gauge and it calibrates it's self to how many revolutions the wheel made... compensating for the revolutions of our 17" hoops (+tire) and a cruisers 19" hoop (+tire)

[jeremy_nash]

I had a vapor gauge that measured the speed based on revolutions of the tire. outside tire circumfrence is the only part that matter, as it doesnt matter where the magnet is mounted on the rim, the magnet is only going to pass the hall effect sensor once per revolution.

ok so I just checked out the second one, and if you have a pre, I would go with it as there arent any calculations to be made. it uses the stock cable assembly. in mechanical speedometers, the speedo's are set to work with a set number of revolutions per mile to decide speed. the accuracy is set in the gear drive at the wheel.

[Kattie]

so i found a speedometer on ebay...kinda nervous about it. The guy said he has a production factory that he makes these in. doesn't really speak English so its hard to get much information from him. he has videos for both of them on those pages...What do guys think?

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=110647691737&viewitem=&sspagename=STRK%3AMEWAX%3AIT

and

http://cgi.ebay.com/ebaymotors/ws/eB...K%3AMEWAX%3AIT

So how many of you think this second one will work with a pre..? because if it will and all the functions will work right and i would like to be able to set my current mileage i will buy one and be the guinea pig...lol

[jeremy_nash]

as far as setting your current mileage, I'm gonna go out on a limb, and guess not. but other than that, with a little wiring, it could work fine

[Kattie]

as far as setting your current mileage, I'm gonna go out on a limb, and guess not. but other than that, with a little wiring, it could work fine

Might get it then...I guess i could just add the mileage from my old speedo to the mileage on the new one if i decide to sell the bike...Do you think all the features will work when wired to the katanas harness...I mean i dont see why they wouldnt...Another thing...I wonder if the mileage resets itself if you were to unhook the battery or if it saves it and has some sort of reset switch on it?

[Wild-Bill]

From http://www.rbracing-rsr.com/tirediamcalc.html:
Tire Diameter in Inches = Rim Diam Inches + [ (2 x Aspect Ratio x Section Width) / 25.4]

By that formula, the stock 110/80/17 tire (on a pre) will have a diameter of 23.93" and a 120/60/17 will have a diameter of 22.67. That's a 5% difference.

Assuming that the speedo is calculating your speed using (wheel rotations) x (assumed tire diameter) x pi for the distance traveled per wheel rotation -- I think that's a pretty safe assumption -- then you're looking at it having about a +-5% error. In other words, at 100mph it could be telling you that you're traveling anywhere between 95 and 105 mph. That sounds like it's a lot of allowed error but most mechanically driven speedos run up to 10% error internally.

A premium electronic speedo is going to have additional circuitry to let you calibrate it for your tires but this is definitely not premium stuff. It's probably only about as accurate as your stock gauges.