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Discussion Starter · #3 ·
I've had many of bikes over the years, most modern ones are very accurate. I guess I will ask a dealer if there is any way to adjust it.
 

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With the bikes I have, most are around 10% off...if I can trust those roadside "Your Speed Is" monitors.
This is also true of my truck, but not true of my Corvette.
 

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The truck is an '11 Ram 3500 Diesel Dually...the Vette is 2019 ZR1.

I suspect it has to do with the year of manufacture.
 

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7-speed manual...non ZTK

Tire Wheel Car Vehicle Water


To bring it back on point: NO speedo error.
 

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Has anyone contacted a dealer to see if they have any way to calibrate speedo?
Its off by 8 mph at 70 mph.
In my experience all bike speedos are overly optimistic by around 10%. It's pretty much an industry standard
As a technical service representative for 2 major Japanese manufacturers for most of my 50 year career in motorsports I can tell you without a doubt that most every bike out there has about a 10% optimistic speedometer.
That guy who thinks he actually did 200 mph on his early Hayabusa was really only going about 180....

I used to get to deal with unhappy customers who were obsessive disordered and were upset when their GPS showed their 400cc scooter was only going 45 and the speedo showed 50. How could they calculate accurate fuel economy?? And at trade-in time their bike would show more miles travelled than actual..... believe me, I had some very intense conversations.

There are devices made by the aftermarket that can allow recalibration, designed for those who change gearing in their bikes where the speedo is an electronic pulse from the transmission output shaft (most bikes). Not sure how or if they work for bikes using the rear wheel sensor, which is usually also the ABS sensor.
There are a few (very few) bike manufacturers that have very close to accurate speedometers. Something to do with liability and lawyers I think.
I do not believe MV will have a way to adjust the speedometer reading inside the ECU software...but I could be wrong.
 

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Discussion Starter · #12 ·
It's odd because I changed the rear tire size and don't see any change in the speed display. Normally a larger tire will have a small effect. Could be the stock tire was on the larger side of a 180, and the replacement was on the smaller size of 190.
 

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Discussion Starter · #13 ·
The bike has a GPS module, maybe speed could be calibration with that somehow. It's not a big deal, just surprised that a modern bike is this way.
 

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If you change the size of the rear wheel, the bikes indicated speed wont change, as it uses the rear wheel ABS sensor for speed. This means if you change the gearing, it will compensate, but if you change the rear tyre, it wont know, it will just see the number of rotations and calculate the speed based on rotations per time period.

GPS is not always available, which is why its not a prime input for speed indicators.

As for accuracy, they are normally over as they allow for manufacturing precision, but also for different manufacturers of tyres with different profiles, and how worn they are, i,e. brand new, correctly inflated and warmed up all increase the actual speed per revolution. It all goes to pot when you lean anyway.
 

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A larger tyre has a larger circumference, but the bike does not know that. It just knows the wheel has gone around R times in a set period. It knows the tyre has a circumference of X therefore X*R in the period provides theoretical speed.

OK you will actually be going faster, but the speedo will display the speed assuming the original tyre size. The bike Will compensate for anything upstream of the tyre circumference, i.e final gear ratio, internal gearbox ratios, primary reduction ratio as they are before the abs sensor, the tyre is after the sensor.
 

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If you are comparing to a radar speed gun yes, as the indicated speed will remain constant. GPS on phones is not as good, GPS on a good data logger Aim evo 5 etc is pretty good too.
 
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