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Discussion Starter #1
I'm sure many of us would like a speedometer indicating true speed. In the absence of finding a Speedometer re-calibration unit for our recent Ducati you may be able to re-calibrate the speedo somewhat closer to true speed using the Tire Calibration function at the right time.

A larger diameter tire rotates at a lower "wheel rpm" than a smaller diameter tire for a given speed. Therefore, perform the tire calibration on your worn "smaller diameter" tire prior to installing your new "larger diameter" tire. As a result, your speedometer should indicate a slower speed with the new tire and thus reduce the speedometer's over-speed bias.
This is only theoretical as I just thought about it now and after installing a new rear tire.
For those of you about to replace your worn rear tire, give it a try and let us know if that helped and by how much.
 

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I'm sure many of us would like a speedometer indicating true speed. In the absence of finding a Speedometer re-calibration unit for our recent Ducati you may be able to re-calibrate the speedo somewhat closer to true speed using the Tire Calibration function at the right time.

A larger diameter tire rotates at a lower "wheel rpm" than a smaller diameter tire for a given speed. Therefore, perform the tire calibration on your worn "smaller diameter" tire prior to installing your new "larger diameter" tire. As a result, your speedometer should indicate a slower speed with the new tire and thus reduce the speedometer's over-speed bias.
This is only theoretical as I just thought about it now and after installing a new rear tire.
For those of you about to replace your worn rear tire, give it a try and let us know if that helped and by how much.
Not sure that this calibrates the speedometer to the rear wheel speed. How would it know the speed?

My understanding is that this is calibrating the front and rear wheel sensors so that traction control knows the baseline condition between the two wheels.
 

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Discussion Starter #3 (Edited)
The spedometer's speed sensor is on the rear wheel and the tire calibration function is to account for different tire heights which affects the gearing ratio and most likely the traction control as well.
 

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Good idea but to make an 8% difference in speed the rear tire would need to be about 2 inches bigger in diameter. :)


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Discussion Starter #6
True, but without GPS or some other way to measure speed, what are you calibrating it to?
It's calibrating according to Ducati's algorithm based on rear wheel rpm to speedometer speed.
 

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Discussion Starter #7 (Edited)
Good idea but to make an 8% difference in speed the rear tire would need to be about 2 inches bigger in diameter. :)
I'm cognizant of that which is why I wrote "somewhat closer to true speed" in my OP.
Moreover, it's the only thing I can think of in the absence of a Speedo calibrator.
 

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Are you also aware that the difference in diameter between a brand new rear tire and a totally bald one Is 14/32”?

This is what makes the theory that the 8% allowance is there to allow for tire wear is ridiculous.

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Discussion Starter #9
Yes. it's probably marginal. But it's doesn't hurt to see if it makes a visible difference especially if you're changing to a taller sport tire.
 

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My SuperGlide speedo will be way off if I don’t wait for the gauges to do a sweep after starting but before putting it in gear. Maybe something similar exists on other brands.
 

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Oddly, on my 1260 when I used the cruise control, the cruise indicated speed would be 100% dead on accurate even thought the speedometer was 8% over. Then I got a service done, and presumably an update, and now it shows the same speed as the speedometer unfortunately.
 

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Discussion Starter #13 (Edited)
Dang, that's too bad. BTW, I just wrote to a few Speedometer Calibration unit manufacturers to inquire about a unit for recent Ducati models. HealTech (SpeedoHealer) was quick to respond but theirs is not compatible with a CAN BUS communication protocol.

An 8% tracking error is totally unacceptable IMHO in this day and ages of built-in Nav systems.
I wonder if the S1000RR (which has Nav) has such a upward speedo bias?
I would doubt it.
 

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Ducati is purposefully tacking on 8% as made evident by them saying so in the manual. It’s common practice in the motorcycle industry to tack on 5-10%. The BMW I had was overly optimistic as was the Honda. The KTM a little less so at 3%. It’s not that they can’t accurately determine speed. It’s legal CYA stuff. The only bike I’ve seen that came with a spot on speedo was a Hyosung. Go figure.
 

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Discussion Starter #15 (Edited)
I read ya but the new 2019~2020 BMW S1000RR has Nav.
I highly doubt the GPS will be out of whack? I suppose it could be but that would stand-out.
Our Jeep Wrangler with built-in Nav is spot on with any of our Garmin units.
 

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I guess I’m not tracking with how built in GPS factors in. Can you please explain your thought process? Thanks!
 

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Discussion Starter #17
My though process is sometimes outta-wack. Even more so according to my wife but I would find it odd to have a GPS reading a different speed than the speedometer within the same vehicle.
 

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Ok, so you expect the read outs to be consistent. When I set the cruise control on my PP, it matches my GPS spot on while the indicated speed on the dash reads 8% high. Its silly that it is inconsistent within the dash.

I understand where you are coming from. I think the real breakdown is you are trying to be logical.
 

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Hi all. One thing not mentioned is the odometer readings. The manual states an error of +8% for the speedometer. The odometer however must be accurate, thinking within 1-2%, due to warranty/service issues. If the odo was off by +8% you could potentially be cheated out of a warranty claim or denied a claim by not servicing at correct intervals. Not legal to do most everywhere. The speedometer could be more accurately programmed by the factory. But what fun would that be. Hay guys I topped out at "XXX" MPH. The error makes it look better.

Cheers
 

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There’s several reasons for OEM speedos to read fast.
One is there’s HUGE federal penalties for even one vehicle having a speedo that reads lower than actual speed. Second, there’s tolerances, or margins of error, in every component of the system. Third, tires have tolerances as well, affecting their circumference. Fourth, as tires wear, they get smaller and rotate faster.

So they run the tolerances of all the components, plus manufacturing tolerance of tires, and figure out the maximum error for the system, then add a safety margin.

Back in the old days of analog systems of gears, it was a percentage. So the variance changed based on speed. In modern electronically managed systems, it’s usually a fixed number of MPH.
On my cars, one is exactly 1mph high, the other exactly 2mph high. On the Goldwing, it’s 1mph. All regardless of speed.

On the Multistrada, the variance changes. Below 50mph it’s exactly one 1mph. Above 50 it’s exactly 2mph.
I think that’s why the speedo won’t show 51mph, and the cruise will not set to 51mph, with the added 1mph of variance it skips from 50 to 52.
 
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