Last year I bought a Zumo 550 GPS. One of the reasons I went with this unit is it is made for motorcycles and another is that I can use it in my truck as well. I like the unit a lot.

When I'm running down the highway in my truck (2004 F150) I end up having three speedometers - the original in dash truck speedo, another in my Edge ECM programer, and the one in the GPS. There is a pretty good descrepincy between the three. If I set the cruise control at 80mph by the GPS reading my Edge reads 84 and my dash speedo reads 86 or 87 mph. I always figured the GPS was the most accurate and went by that but always wondered how it might or might not concur with DPS radar. I run an Escort Passport in the truck and the HD Escort unit on the bike to give me a head's up on where those rascals are at.

I had not run the GPS on the bike in a while until yesterday so I got a chance to compare the GPS reading with the bike's speedo. To my surprise they were dead on with no variation in reading between the two. 75 on one was 75 on the other, 80 on one was 80 on the other, 40 on one was 40 on the other.

I don't ususally run the GPS around town because it just isn't needed. But I now know just where the speedos in my truck and on my bike stand. My bike is right on. My truck is way high.

It may seem like a small thing to others but it's something I like to be on top of.

Oh, and anyone considering the Zumo 550... I recomend it highly. It is definately worth the money.

 

Strange for the speedo on the bike to be right on. Speedo's on Harleys are notorious for being "off". I know when I drive by the speed checkers that the police set up on some roads, there is a 3 mph difference on mine.

 

That's unusual. most seem to indicate about 3MPH difference between the bike speedo and the GPS. You are fortunate to have the accuracy

 

The tires on your truck could be larger than stock....thus giving you a incorrect speedo reading. (By the way on Ford trucks with the PSOM like yours, you can reprogram the PSOM for your exact tire size. It can only be done 6 times, and no tools are needed to get it done...oH BTW...PSOM=Programmable Speedometer Odometer Module). Usually when I pass one of those speed checker things its spot on with what my speedo on the bike says.

 

my Ultra and my Zumo are in sync

 

Friend and me rode couple saterdays ago set are speedos at same point i had 223miles she had 215 there always differant.

 

I've had LEO's I know check the speedo's on a number of Harley's against certified radar, and not one of the bike speedo's was "right on the money".

Most of the speedo's on the bikes read about 5% on the high side.

But it could be worse, as a number of metric bikes tested showed them to be off by 5% to 10%.

 

+1 on the tire size

 

I didn't mention - I have an Automax with AutoTune. It completely replaces the stock ECM. There is a value in there that, when changed, will make a difference in the speedo reading. I guess I have mine where it needs to be. If you have a stock ECM you can't change didly squat. That's one reason I went with the after market replacement. I didn't want to be forced to suck on the dealership's tit.

As far as the tires on the truck go - yes, I'm running BF Goodrich All Terrain T/As. IMO they are the best tire you can put on any pickup less than a dually. But the Edge programmer has a setting to change the truck's ECM and I've set it according to the tire size and still get this discrepency. Obviously somethings wrong there. I just haven't taken the time to jack with it.

The Edge tells me I'm getting 15.5 MPG running 75 and 80 down the highway too. That's about 20 percent better than I got before I installed it. I'm afraid if I screw around with it too much it will tell me something I don't want to know! I'd loose my bragging rights and all so I just leave it be and put my time into the bike.