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[Hoist!]

the speed measured by the Zumo, or the "Certified" HD Speedometer?

On my trip, the Zumo consistently measured 2-3 MPH less than the HD Speedo. My bet would be on the Zumo, as matched by them highway speed indicators that tell me I'm going over the speed limit. Them things always flash, right?

Just thought I'd see if anyone knew if our stuff accurately measures our speed. 2vrolijk_21:

Hoist!

[murphy]

I'd go with the Zumo... its doing a distance over time calculation, if the spedo works like any of the other moco parts it should start leaking any day!  

[spydglide]

My speedo is the same 2-3 mph faster than the Zumo, also Hoist.  So, at least we've got 'consistancy' going on here.  har!  spyder

[sadunbar]

the speed measured by the Zumo, or the "Certified" HD Speedometer?

On my trip, the Zumo consistently measured 2-3 MPH less than the HD Speedo. My bet would be on the Zumo, as matched by them highway speed indicators that tell me I'm going over the speed limit. Them things always flash, right?

Just thought I'd see if anyone knew if our stuff accurately measures our speed. 2vrolijk_21:

Hoist!

The Zumo is accurate.  When I ran the T-Max, my speedo matched the Zumo.  When I switched to the Power Commander, the speedo read 2-3 more then the Zumo.  Not because of anything the Power Commander does, rather it is the ECM.  The T-Max corrected the error, the Power Commander doesn't correct the error...  With the Zumo in my Seville, the Cadillac speedo matches the Zumo...

[Twolanerider]

At 75 mph reported by the Garmin 2820 the GPS unit is about 5 mph faster then the speedometer on the red bike.  The 2620 reported identical to the 2820 when I still had it.

The 2820 almost exactly matches the speedometer on the other red bike though.  Since the GPS can't change with tire wear I trust its consistency.

[Bubba]

Howie, mines the same was as well the Garmin 2720 is 2-3 mph SLOWER than the HD speedo....

[spydglide]

It does appear that the HD speedos are like most vehicle speedos and read a tad fast.  Also, I notice that the optimistic error becomes greater as the speed increases.  The 2-3 mph error is at 60 to 70 mph........it becomes more at higher speeds (at least on the '04 SEEG).  spyder

[Capo]

It does appear that the HD speedos are like most vehicle speedos and read a tad fast.  Also, I notice that the optimistic error becomes greater as the speed increases.  The 2-3 mph error is at 60 to 70 mph........it becomes more at higher speeds (at least on the '04 SEEG).  spyder

In all seroiuness do we really care?

[porthole]

Consumer GPS units typically are capable of .1 (one tenth) mph accuracy. Obviously that would make for an erratic mph display so most units average your speed and update the display every 1 or 2 seconds.

Unless your unit is defective you can take the GPS readout to the bank, it is that accurate.

Sometime ago Power Motoryachts magazine did a "road test" comparing a Garmin 276C (predecessor to the 478 some of us are using), a $20,000 survey grade GPS and a police laser. Through out the test teh 3 units consistently displayed the same results.

FYI - Survey GPS units are capable of 1 CM accuracy. 
Believe it or not, the Russians have a more accurate GPS system with fewer satellites (GLOSNASS)


Providing it is working correctly you can trust the displayed speed on the GPS

[spydglide]

Consumer GPS units typically are capable of .1 (one tenth) mph accuracy. Obviously that would make for an erratic mph display so most units average your speed and update the display every 1 or 2 seconds.

)

Is this why I notice a 'lag' in my Zumo speed indication?  spyder

[porthole]

Is this why I notice a 'lag' in my Zumo speed indication?  spyder

Most likely. Your GPS is calculating speed many times per second, and then averaging it for the display. 2 seconds isn't very long, but it can seem so if your watching the GPS display while twisting the throttle.

[EGUC7]

I've had the Zumo (550) on the bike, in the Honda Pilot and the Honda CRV.  The Honda's and the Bike Zumo agree at just about the entire speed range.  Also, have gone thru two or three of those portable radar spots and the speed flashed up on the display agrees with the speedometer on the Honda's.  On the bike, the H-D speedometer and the Zumo agree between 35 and 45 mph.  Above that, the H-D speedometer starts to get faster than the Zumo.  At 60 on the Zumo, the bike says 63-64.  At 75 on the Zumo, the speedometer is showing about 79.  Hum.  Wonder what the difference is at 105 mph?  Oh, never mind.

Ride Safe.
Walt

[JCZ]

Using my GPS on my bike, it's accurate with my speedometer until I reach 60 mph.  From there on up, it gets gradually off with the speedometer gradually reading more than my GPS.  In other words, at 65 mph (per the speedometer) my gps may read 63.8........at 80 mph on the bike the gps reads about 75mph.  I think HD engineered this into the speedometer intentionally.  Just my thinking......no facts to back it up.

[Chief]

Using my GPS on my bike, it's accurate with my speedometer until I reach 60 mph.  From there on up, it gets gradually off with the speedometer gradually reading more than my GPS.  In other words, at 65 mph (per the speedometer) my gps may read 63.8........at 80 mph on the bike the gps reads about 75mph.  I think HD engineered this into the speedometer intentionally.  Just my thinking......no facts to back it up.

I've thought about this before, and since by rule, the speedo reads less than the GPS's, three of them, I came to a similar conclusion. I'm sure there is a certain tolerance in the speedos so the units are designed to read fast on average so when you do get one that reads on the slow end of the band, it is accurate at worst. This way, they're not responsible for tickets when a speedo reads 70 and you're really doing 75 or 80.

I look at it as a CYA move and a direct result of allowing a wide tolerance to reduce the rate of rejection.

Garbage in => Garbage out.