Calibrating a stock speedo?

[snapdragonabs]

I have seen people talking about calibrating a spedo and was wondering, can this be done on a stock speedo? And if so how?

[Rebel]

The only ways I know to calibrate your speedo are to find a reduction gear that goes into the end of the cable housing on the wheel end of the speedo cable, or to find a correct size front tire that will turn the number of times per mile that you need. If you have a speedo that is about 10% off you need a tire that has an outside diameter that is about 10% greater or smaller than the stock tire.

The other way to get a correct speed reading is to install a bicycle speedometer or a Vapotech computer system and here is a link to get to it;

scooterrebels.proboards.com/index.cgi?board=otherreadonly&action=display&thread=590.

[jmkjr72]

it can be a massive pia to try and make a stock speedo more accurate
why is that unlike an old cable drive car speedo where you have 2 gears you can change
if your lucky the only gear you can change on a scooter is the cable gear as the drive gear is sealed in a case on the front wheel
now what some guys over on zumaforums have been doing is the figure out how much it is off then they take apart the speedo
when the speedo is apart they remove the needle and reindex it

but i love haveing a bike speedo on my zuma its accurate and it reads faster then i can go

[Rebel]

Ya, if it is an electronic one, and you want to make it more correct, changing the tire size is the only way to go, otherwise, bicycle speedos or the vapotech.

You need to remember that the speedo responds to the front wheel revolutions per mile, so change those and you change the reading on the spedometer. If it is reading 55mph and you are really going 50, you need a taller tire. Measure the distance the tire rolls in one revolution, in the 55mph vs 50 actual mph you have a 10% error, try and find a tire has a 10% longer travel in one revolution.

[snapdragonabs]

Wow I didn't even think about the tire thing. That is a good idea, Thanks!

[Rebel]

funny thing about speedometer error. the slower you go the less noticeable it is.

At a 10% error rate when you are riding at 10 miles per hour you are actually traveling 9 mph, not very obvious, at 20 mph your real speed is 18mph, still fairly close to the indicated speed. When you hit 30 mph now you are running 27 actual mph. If the speedo is reading 35 mph you are actually off by almost 4 mph and are really going 31.5. This makes it look like the accuracy is really not so bad at low speeds but much worse on top end speeds.

[bashan]

Feb 16, 2010 21:43:10 GMT -5 Rebel said:

funny thing about speedometer error. the slower you go the less noticeable it is.

At a 10% error rate when you are riding at 10 miles per hour you are actually traveling 9 mph, not very obvious, at 20 mph your real speed is 18mph, still fairly close to the indicated speed. When you hit 30 mph now you are running 27 actual mph. If the speedo is reading 35 mph you are actually off by almost 4 mph and are really going 31.5. This makes it look like the accuracy is really not so bad at low speeds but much worse on top end speeds.

I'm sure most of you guys have ridden or do ride MC's so you know they're like that too, you just expect it. My Vulcan 1500 Classic is pretty far off while everything else about it is high tech, go figure. My scoots speedo worked for about a week and then just started pegging above 35MPH. Guys that I ride MC's with use GPS's which I'm going to get. I thought I'd get a portable and use it when I ride the scoot too. Wouldn't this be easier than adapting gears and fake dials? I would like to know how fast I'm going, Southern cops you know. Bashan

[jmkjr72]

thats why i got the sigma bike speedo you can use it on 2 diffrent bikes scooters or motorcycles
the one i got is good up to 199.5 mph and is the fraction of the cost of a gps unit if you decide to pop it off to take it in because you dont want to leave it on your scoot while parked some where its very small and fits in your pocket very well

[Rebel]

Really the cheapest way to get an accurate speed is probably to use a bike speedo that is set up correctly, and there are a couple how to do's in our help section on that. A GPS is great, but you need to remember there may be a little delay on the updating of the speed you are traveling. I have a hand held one that does display a pretty accurate speed in my opinion.

But the question was , how do you calibrate a speedometer.

[xs650]

Rebel, I agree on the bicycle speedometer approach. It can be as accurate as your ability to measure your actual speed using a GPS or other accurate method. You can also calibrate one by distance traveled if you have an accurate measured distance. The instructions often recommend using the tire diameter to calibrate a bicycle speedometer, that is a good starting point but not as accurate as a GPS or precisely measured distance. It's still better than any stock speedometer though. One of the beauties of that type of digital speedometer is that if the odometer it right, the speedometer is right too.

Something to watch out for with bicycle speedometers is that not all of the work at high end scooter speeds. The "Sigma" brand, as has already been mentioned, is a good one. AFAIK all Sigma speedometers work to over 150mph but check the specs.

Actually calibrating a conventional eddy current speedometer (like most cable driven speedometers for the past 100 years) takes special equipment or a lot of dedication. Back in the day, most large and some medium sized cities had at least one shop capable of calibrating speedometers by changing the strength of the magnet, adjusting the return spring or changing the distance between the magnet and aluminum disk. If you find one of the few shops that still does that, assuming the will work on a Chinese speedometers, it would probably cost $100 or so and you would have to take the speedometer in to them with knowledge of how many input rpm you want at an indicate 60mph.

A less drastic method is to make a new speedometer face or overlay. Check your speedometer with a GPS and move the mph marks on your dial or make a new faceplate.

A bicycle speedometer sound better all the time ;D

Some info on eddy current speedometers
en.wikipedia.org/wiki/Speedometer

[Rebel]

An overlay would work, you would need to have a GPS or something to mark each speed position on the face of the speedometer or some other way to keep track. then transfer that data onto a template of sorts you would use. Print it off and install it, then recheck to see if it is correct. Be sure to print it off using an ink that does not fade from sunlight.

Too each their own, but I would since Chinese tires are not known to be the best, replace the tires with a larger size and see how that makes the speedometer work. I know a concern about clearance is out there, but you know, moving the fender up an inch or two is not that hard.

[oldchopperguy]

I didn't realize how lucky I was with the speedo on my Xingyue... It seemed close, so I checked it first with both my cars. At 50 mph, it reads exactly the same as my old Mercury, and my Honda. I also check regularly at night by peeking in the window of cars next to me and it's always within a mile or two of their speedometer readings.

Lately I got a police buddy to check me on vascar, and my speedo inicating 50 mph read 51 mph on his vascar. That's close enough for me, and I guess it's rather unusual.

I also checked the tach with a German mechanical tach that is very accurate. My scooter tach at 8,000 rpm reads 7,900 rpm on the German tach. Again, close enough for me...

Somehow the workers' paradise got my gauges pretty accurate. Now, if they could only do something about the square wheels... LOL!

Leo, cruisin' 50 in Texas...

[Rebel]

you are lucky Leo, but how is it you can read the speedo of a car you are riding next to? you must have telescopic vision. you are SUPER OCG!

[imagesinthewind]

I have one of these:
cgi.ebay.com/ebaymotors/Trail-tech-Vapor-computer-YZ-WR-RM-RMZ-KX-KXF-KLX-WRF_W0QQcmdZViewItemQQhashZitem5886fb5a0cQQitemZ380221741580QQptZMotorcyclesQ5fPartsQ5fAccessories#ht_500wt_975

and will try to get it on this weekend, after studying is done. (hmmmm. . .)
It' a speedo, odo, tach, temp (for my water cooled engine), or just about everything I need to keep a handle on what's going on on my scoot.

Ebay has a boatload of them for between $60 and $120.
If you are looking for one, type VAPOR TRAIL TECH into the search and see what comes up.

Good luck!

[Rocketdog]

That's a nice looking piece of hardware Images. The price is right as well. I've seen something like that for 2 hundred or so.

RD