For the record, my post above assumes a constant velocity. This is due to some older units having a 2-3 second lag. Newer units with fast processors are closer to 3/4 second lag.

 

You may also take into consideration that the GPS reading my be skewed due to coverage and reception signal.

 

Thats not correct. I have never heard of anything like that. But i have heard of human error, so maybe our boys down in Osaka screwed things up??

Those are pretty bad figures if G35 is right

 

I really don't think that is a problem Dan, with these units waas enabled and all. They are pretty darn accurate.

 

?? A multi-channel GPS using WAAS should be extremely accurate, no?

 

Do you guys have a place in your areas that specialize in Calibrating speedometers? In Calgary we have Mr. Speedometer, the guy has a deal with the local prosecutor and gets tons of customers from people looking to get out of some points. He told my dad, a chronic speeder, that most new cars aren't even close to properly calibrated often times they are off by as much as + or - 5MPH.

 

Thats total BS.

 

hahaha yea i know right

 

Cars are NOT overestimated from the factory, unless you own a Honda.

Honda just settled a huge suit because their speedos were 3.75% off, causing warranties to expire 3.75% sooner, and excecssive mileage pentalities on leases.

For the record, the SAE requests that speedometers be within +/-4%, but there is no requirement.

There is supposedely a class action lawsuit against Nissan based on the Altima speedo, but I haven't heard anything about any other car.

There are a lot of different factors that could play in to speedo readings, and I'm guessing that the tires are the biggest factor in this case.

EDIT: The Honda information is about odometers, not speedometers. I would think that the two would be directly related, but I found some information that makes me think otherwise.

 

That's way to much of an error. Have the dealer check it and make adjustments for you.
C.

 

Checked mine on the way to the airport (how do you figure tenths when looking at your speedo???). At a noted 75 on the speedo, right on the line, GPS read 74. Will have to do it with my other Garmin tho, this one doesn't show tenths.

Pretty close tho.

 

Nothing wrong with that. I would say yours is close enough.
The only reason I have my mph in tenths is because I used a conversion program to change from km/h. This one :Conversions

 

This topic has turned into a GPS debate but the culprit is probably still the actual tire size. Just try your GPS in another car or two and you will see they are pretty accurate. I've had mine up to about 550 MPH accurately?.. oh wait, that was in a airliner.

PS: Mine shows tenths. My speedo was off about 1.4 MPH on average over several days at a constant speed.

 

Anyone ever run two GPS's side by side in the same car to see if GPS's are accurate?

 

My Garmin Nuvi 660 does the same thing and almost the same %'s as the OP.

Is there a way to fix this? Can the dealer do anything?