Speedo accuracy checked with portable GPS

[Gruntled]

Just an fyi:

I finally got around to checking my speedo accuracy using a portable GARMIN GPS unit. I did my best to hold a steady indicated 60mph and 70mph. My results were the speedo is low by 2mph; meaning GPS read 62mph and 72mph respectively. It was extremely hard to try and hold a steady 25mph (school zone speed), but when I tried, the GPS said 28mph.

And before anyone asks, no, I did not intend to check any higher speeds, as around here those higher speeds are instant citation. :frown

 

[SLF360]

And before anyone asks, no, I did not intend to check any higher speeds, as around here those higher speeds are instant citation. :frown

Would you speculate about higher speeds - Could be interesting for us Euro speed junkies here !!? :biggrin :biggrin :biggrin

 

[dbk]

I'd be stunned if the Speedo actually read low. That's a serious, serious issue with auto manufacturers. Most autos read at least 1-2mph low, cars like BMW's are notorious for reading as high as 5mph over real speed at speeds like 60-70mph. Cross 100mph and all bets are off. My Jaguar S-Type R would read 4mph high consistently at speeds in the 40mph range(wonder how far off it was when it was pegged at 155).

If your car reads to high, no harm no foul. If your car reads too low, and you get tickets, auto manufacturers are in deep, deep trouble.

 

[THE1GT]

Just got my Bentley Cont. GT out of the shop today. I determined that my speedo was reading at least 5 mph high. They confirmed it and said "its normal" and that there was nothing they could or would do. They also said don't worry, the odometer is accurate. I am amazed that a car of that caliber would have that sort of an unresolvable issue!

 

[analogdesigner]

Right on!

My GT reads right on at all legal speeds.

My NSX read about 4% high. My Honda Insight (Hybrid) reads about 4-5% high also. I think this is to make the MPG figures appear better.

Jay
http://www.fordgtforum.com/forums/forumdisplay.php?f=34

 

[w. mitty]

I checked mine the other day on a fixed radar site, one of those "your speed is..." trailers that the poe-leese set up around town.

Sign said I was going 52, Speedo said was going 50. I was very surprised-- first time I've ever seen a speedo read humble instead of proud...

Be careful out there, none of the usual buffer that we all count on (how many of us set the cruise at 80 in our lesser cars knowing it is really more like 76?)

My Lambo was the worst--like most Italian cars, the speedo was at least 7 mph proud at high speeds (90+). I know this because I checked it several times with GPS after I noticed that at an indicated 90 on the freeway, I was still just keeping even with most traffic.

 

[sharp33]

Just an fyi:

And before anyone asks, no, I did not intend to check any higher speeds, as around here those higher speeds are instant citation. :frown

Because of the offset location, I find it impossible to read the speedo at high speed. The Garmin saves highest speed and I can report that what I thought was 150 in the GT was captured at 156 with the Garmin. :cheers

 

[Neilda]

Kyle, tell your mummy you don't want to take those special pills anymore! :lol


In the UK the law allows for a ten percent inaccuracy of speedometers, all of my cars have been inaccurate when using a GPS system - by one or two MPH at legal speeds, and more at much higher speeds. The 212 I hit in my Lamborghini may have been a mere 205, I'll never know.

Speed cameras in the UK are triggered at between 10 and 15 MPH over the posted limit.

 

[SLF360]

I did my best to hold a steady indicated 60mph and 70mph. My results were the speedo is low by 2mph; meaning GPS read 62mph and 72mph respectively. It was extremely hard to try and hold a steady 25mph (school zone speed), but when I tried, the GPS said 28mph.

And before anyone asks, no, I did not intend to check any higher speeds, as around here those higher speeds are instant citation. :frown

To tease you, the higher the speed, the better the accuracy of the GPS

So go and check 200mph ! :wink

 

[Lgaruti]

I can tell you our GT speedo reads about 5 mph low at 185.

Speedo was 185, the GPS recorded 189.9. These things fly!!! Tach. around 4800 and the GT stable as a rock.