A short video showing the Discrepency between the Speedo and GPS/Ultragauge. This was on the highway between Sacramento, CA and Reno, NV. Headed to the Nevada Desert for some offroad fun! Boy is this Disco a joy to drive on the highway. Smooth, Quiet, and Comfortable.

 

So, what size tires are you running?

 

I'd believe the GPS. The SLABS averages the four ABS sensors and supplies that to the ECU for vehicle speed. Which the Ultra Gauge shows as pretty close from OBDII port. The speedo running 5 mph fast is a good thing for vehicles operated by SWMBO. Just don't tell her...

You should realize that speed radar range is proportional to the cross sectional area of the target, a big flat nose semi can be picked up further away than a Corvette with radiator inclined back 11 degrees from vertical. On I-95 this weekend I noticed our state smokies have adapted to park on side of road near a chunk of semi retread (road alligator), trunk lid up, driver door open, and they are seated so they can point and click from the open door. You think it is some poor sucker broke down.... hiding in plain sight. And doing a brisk business from what I saw.

Betcha like that 180 thermostat....

 

Still running what came on it when I bought it. Toyo A/T Open Country 255/65R16That's what I normally do on vehicles.Funny you say that. I did that for years, but slipped one day and said it out loud. From then on, she's used it to her advantage. As are most vehicles, her VW is the same.Yes, they were doing well on I-80 too. I almost got hit once by a laser, but he was just raising it up when I went by.By FAR, the best peace of mind I've bought in many years. It was a nice warm 80 degree day, and it never creeped up on me. Even slowly climbing hills and such with a full load of people, it never climbed above 195.

Also, got a good chance to try out the Hill Decent Control on a sand covered hill. It was about 1/8 mile long decent, and it worked flawlessly! I did realize that it's working the brakes pretty hard, so I didn't use it all the time, but on some of the looser stuff, it was pretty cool. Everyone inside the vehicle was blown away at how comfortably and safely they were being hauled around the mountains. I don't have mine built up, just stock so far, but it's still a very capable vehicle compared to many I've owned.

 

Mine is off at least that much (5+ mph) with stock OEM tires. Just figured it was a Land Rover thing.

 

You should also be aware that GPS units are only as accurate as the number of satelites they are connected to at the time of your test.

 

I believe it's done intentionally by the manufacturer on most cars. After all, it gives them a more dishonest MPG rating to the average unknowing driver. As if they need to be more dishonest! Their MPG test tracks are a joke, Flat, Level, no stop and go, tempurature controlled, etc... NOTHING like real world driving.

They claim it's to keep the driver safer and not get tickets, among other things.

The Odometer will tell you that you've traveled 100 miles when you've actually only traveled 94.2 miles. That's a 5.8 percent LIE! Times MILLIONS of cars, that ads up quickly!Yeah, I've gotten used to when I feel they are accurate and when they are not. Where I was at the time of that video, I was in a clearing and getting a good signal. The speed was staying within .5mph constant, so I figured it was pretty close.

When I'm downtown San Francisco, you can't even count on being on the correct street with those high buildings around you, let alone, how fast it's reading.

 

And I thought it was just me...

 

This is interesting. Explains why those "check your speed" things always sync to my speedo with 31" tires.

 

I noticed that too with mine. I am running 265-75/16's which are about 10% larger than the stock tires but my speedo is only about 5% off, reading 70 mph when I'm going 73.

This reminds me of a road test in Motor Trend I read back in the late 80's. They tested the police cruiser version of one of the last Dodge Diplomats. It had a speedometer marked as certified yet it was around 7 mph off at 60 mph. And not in our favor.