Speedometer Calibration - K-Bikes.com - Excellence in Motion
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post #1 of 11 (permalink) Old Oct 7th, 2006, 10:20 am Thread Starter
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Speedometer Calibration

Is there a way to calibrate the speedometer without adding something like the Yellow Box?

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post #2 of 11 (permalink) Old Oct 7th, 2006, 7:12 pm
 
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Does yours need it? I was out on mine today for the first time with the GPS unit and according to that, the speedo was only out by 2-3 mph at speeds between 30 and 90mph. Have you checked yours against a GPS or used other means?
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post #3 of 11 (permalink) Old Oct 7th, 2006, 10:00 pm
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Before you start the standardisation / calibration process all the other variables like tyre pressure, load and rider position should be known and constant during the runs. A number of 2 way runs at constant speeds over a section of smooth flat road should keep it simple.(wind, minimisation of difference between actual vertically curved road surface distance and GPS vertical curve / chord lengths) The reason for a number of runs is to establish corrections at different gauge readings. Test points at common legal limits are useful. A decent quality GPS should also be useful as the standard. Probably the most useful approach is to simply determine the correction needed to be applied to the observed speedo readings at whatever speeds that are of interest to you. Speedos commonly read fast from standard at +2% to +6 or +8% in cars and bikes.
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post #4 of 11 (permalink) Old Oct 8th, 2006, 5:37 pm Thread Starter
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Speedometer Calibration

That is not good enough for me. I want it to be right on at 70 mph. I will ride an actual 77 without fear of a ticket so I want to know right where that is. I prefer accuracy over the entire range if achievable.

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post #5 of 11 (permalink) Old Oct 8th, 2006, 6:35 pm
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There's a similar discussion on the new K1200GT forum but now nearly as in depth as this one, at least at the moment. Has anyone opened the speedometer yet? I haven't but if the speedo has as similar calibration adjuster then here's how I set my K11LT speedo bang on.
And if you think this is nuts you won't hurt my feelings.

1. New rear tire.

2. Measure the circumference of the rear tire exactly.

3. Calculate the number of revolutions that the rear tire must turn per minute for three different speeds. 20 mph, 40 mph and 60 should work.

4. Borrow or buy a strobe tachometer.

5. Stick a small piece of reflective tape exactly in the center of the rear tire tread making sure that it won't fly off.

6. Make sure the bike is secure on the center stand. It's best to have the front tire against a wall.

7. With the speedo open for adjustment fire up the engine and up shift through the gears to top gear.

8. Hold the rear wheel speed at the pre-determined rpm point and adjust the speedo to match the exact indicated speed for the tire rpm. Check each point and readjust as necessary.

I know of other methods that require a computer and other equipment to set the speedometer but this method is simple and bang on too.

Regardless of the method, good luck.

John
06 CGM KGT

Last edited by John06KGT; Oct 8th, 2006 at 6:58 pm.
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post #6 of 11 (permalink) Old Oct 8th, 2006, 6:51 pm
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What you want and the practicalities of delivering it are two different things.

A laboratory determination of gauge error and subsequent adjustment can't correct for the input variations in the field. The rolling radius of wheels / tyres varies with tyre pressure, load and at higher speeds the effects of centrifugal forces. A 17 inch (431mm) diameter wheel plus tyre sidewall height at say 85mm makes the radius around 300mm before it is in contact with the road. If the tyre flexes under a constant load to say 280mm radius, basic maths tells us that every 2.8mm (1%) change in that rolling radius will cause a 1% change in the actual distance travelled for each wheel revolution. Bearing this in mind, if you have access to a wind tunnel to develop the aerodynamic lift performances of the bike and can spin the wheels at the correct speed at the same time then you will be somewhere near a fully controlled environment standardisation.

I very much doubt that this will be a linear function with index and scale error neatly derived - the real equation is a lumpy polynomial with multiple variable functions and it's much easier to pull values out at nominated points than try to program it into the available gear.

In simple terms my recommendation would be to do the best you can with ensuring instrument accuracy (lab standardisation and adjustment, speedo healer etc) and then do the field test for a final determination of the corrections required at various indicated speeds as I suggested earlier. If you want to push the envelope to within a bee's dick of the limits of the 10% tolerance margin that is generally used by authorities, be advised, you are looking at parting with time and money on all fronts.
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post #7 of 11 (permalink) Old Oct 9th, 2006, 11:52 am
 
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The problem with devices like speedo healers is that they affect the odometer reading too. After my ride on Saturday, I checked the mileage as recorded by the GPS and it came in at 177.3. The tripmeter which had been reset at the same time showed 178.1, an over read of 0.8 miles. That's an over read of a mere 0.45%. My speedo is only out by a maximum of 3%. I can happily live with both. But don't ask me about the accuracy (or lack of it) on my Triumph Sprint ST!!
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post #8 of 11 (permalink) Old Oct 9th, 2006, 1:23 pm
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Thought I would post my obeservations after trying out my new nav3 . The speedo seemed to show an error depending on speed from anywhere between 2-4 mph. At 70 the gps stated the bike was doing 67mpg. At 80 the gps stated 77mph. I then came up on a speed trap with a sign posting the speed . I slowed to 63. The gps stated 60. The sign stated I was doing 63. Which would you beleive. It boils down to calibration but which device?

Last edited by tonysrep; Oct 9th, 2006 at 2:07 pm.
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post #9 of 11 (permalink) Old Oct 9th, 2006, 2:16 pm
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there is no way to have a perfect speedo....to many variables you can get close but thats it.......if your getteing 2 mile flux at 70 ...your good. if its right on at 70 then your lucky...but it will be off somewhere else in your speed range...if your going to ride at 72 and you can keep it right on 72....then you should get a LEO friend to clock you and see where 72 really is 0n your speedo....i think thats the best you can do...unless you get a GPS....and that can even be off a hair
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post #10 of 11 (permalink) Old Oct 9th, 2006, 4:59 pm
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If you really want to get to nit at posted highway speeds, I've found that a speedometer check section and a stop watch is the best method. It's best doing the test two up with a steady throttle hand but you'll know pretty quick just how far off your indicated vs. your actual is.
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