Speedometers

[numbskull]

Hi guys,

Ok, a dumb question: How accurate are the speedometers on Ducatis? My '07 S2R1K feels slower than the indicated speed. For example, traveling in a 90Km/hr zone I normally go about 120 in my car (so does everyone else). Now it seems that I'm going 150 according to the speedo but so are all the cars around me. Are the speedos dialed a little high?

[Speeddog]

From running my '02 S4 with a GPS onboard, yes, the speedos read high, like 75mph when going 70mph.

Odometer is *very* good when compared with the GPS.

[numbskull]

I'm guessing that they are off by a percentage and not just set 5-7mph higher. Is this a correct assumption?
Pardon my ignorance but this means the odometers are incorrect as well? The bikes have actually travelled a lesser distance than indicated?

[DY]

I'm guessing that they are off by a percentage and not just set 5-7mph higher. Is this a correct assumption?
Pardon my ignorance but this means the odometers are incorrect as well? The bikes have actually travelled a lesser distance than indicated?

Yes, that is correct.  My GPSes(handheld and aftermarket in-dash) also shows my car going 2mph faster than what i'm really travelling at.  I always thought it was one of those manufacturer conspiracies in order to make your mileage warranty expire faster.  By law, the speedometers allowed to be off by a certain percentage... so why not error in favor of the manufacturer?

[Speeddog]

I've never specifically checked, but from what I recall when running with the GPS, it was a 'percentage' error, not a fixed 'offset'.

I've confirmed the accuracy of my odometer against the GPS, and against a route length calculated in Microsoft Streets and Trips software.
It is *very* accurate, off by a fraction of a percent.

[Rob Hilding]

My speedo is off by about 9% - checked with GPS-

My odometer is nearly spot on-

Go figure -YMMV

[numbskull]

Thanks for the info, guys. This would explain why I thought everyone around me was going faster than normal. Cheers!

[Speeddog]

Well, the electronics are counting pulses from the rear wheel sensor, doing a little math calculation, and displaying the miles, all digitally.

The electronics count the pulses, count the time, do a little math, and then send a signal to the servo that drives the needle on the analog speedo gauge.
It's that digital-analog conversion that's off.

I'm happy with a speedo that reads high, less likely to get a ticket that way.  

[Howie]

The error is in percentage.  The only vehicles I have owned with accurate speedometers were my German cars.  All others read high.  My Duc has about 10% error, as does my buddie's BMW 1100 RS.

[knightrider]

what i found, when i split my speedo open, to try and fix my trip odometer. is that the odometer is gear driven off the speedo cable, while the speedo is not. that i believe is why the odometer is correct, but the speedo is off. mine seems to be about 5mph slow at around 70mph according to the gps on my phone.

[Sgt_H]

I'm happy with a speedo that reads high, less likely to get a ticket that way.  

I heard years ago that this was something of a safety feature as well.  Not sure I buy it.  I think it has more to do with manufacturers wanting people to believe thier bikes are faster than they are. 

The DOT has an odometer check set up close to my house.  I checked the Duc's odo against that yesterday and it's nuts on.  Don't know about the speedo though.

[Pang]

The 5-7 percent "error" might come from the difference on tire. I mean the bigger the tire is, the slower it spins. That effects the reading of speedometer. May be I am wrong.

[Speeddog]

There's kinda two threads in one here... '02 and after Ducs have an electronic odo/speedo working off of the rear wheel, '01 and before are cable-drive mechanical odo/speedo.

[knightrider]

just to clarify, im the latter, 94 900 with mechanical doohikey on the front wheel.

[bigiain]

just to clarify, im the latter, 94 900 with mechanical doohikey on the front wheel.

I think you'll find the odo is quite accurate (better than 1% on mine according to the GPS), but the non linearities in the whirling-magnets-and-springs in the speedo mean it's not a straight percentage for the speed, mines reading less than 5% high at 60kmh, 7 or 8% high at 120kmh, and over 10% high above 160kmh.

I suspect Ducati spec the things to meet the legal requirements, which here in Australia say the odo needs to be accurate to plus or minus 2%, and the speedo to plus or minus 10% (yep, they let them sell vehicles that could have speedos reading 10% _below_ the real speed here, the British standard explicitly states the speed can read "plus 10% to minus zero%")

big