How accurate is your speedo?

[muleears]

I have a GPS in my car which can also tell me my speed and it says my speedo is off by 5 mph. Indicates 60 when actual (according to GPS) is 55. With GPS in my other car, which has an digital speedo and stock tire sizes, both GPS and speedo match. What is your knowlege of the accuracy of your speedo? Mine seems to be 5 mph off at 35, 5-6 at 60 and 6+ above 70.

[rg2098]

Mine is off just slightly under that. 3-4 off at 35, 5-6 off at 75. Stock tire size. When I looked back at an original spec sheet for my 250. It actually listed the speed error (just a few MPH off).

[Ara T.]

Pretty accurate, I believe it reads 2 mph slow.

[BobK]

My GPS has shown most of my cars to be close. The SL indicates faster than it is going by about 6 percent. The '76 300D is just off by about 4-5mph at any measureable speed. Not gonna tell the family about the error factor. Keep them out of trouble. Of course this doesn't help the wife who never looks for speed limit signs anyway. Rest of the cars are pretty well on the money-within window of measurement error.

[autobahnauto]

mercedes spec is + or - 2.5%, so it can be up to 5% different than another car. I went through this after replacing a cluster on a C-class.
Dave

[vstech]

my 82 SD is dead on. for now, ... I am putting in the 2.47 rear soon I may swap out the speedo for a 380 to get it back correct, or I may just ignore the dif.
both my TD's check out dead on with the laptop GPS also,
my Suburban is off by about 3mph high readout. also according to the gps and those speed readouts they put on the side of the road.
John

[pawoSD]

My 82SD is also dead on.....I've gone past the radar things and its exact....it also matches the speedo in our minivan perfectly when driving behind/in front of it at the same time.

My dad's is 7mph fast....because he has the 160mph speedo calibrated for the 2.47 differential, but his car has a 3.07.

[Biodiesel300TD]

My TD is pretty much exact. The 240's odometer is about 2% slow which means the speedo is about that much off as well.

[babymog]

190Dt: Reads 76mph at actual (GPS 75mph). Error seems linear, 70% OE size Michelins & Fuel Flap pressures, dry roads. Probably accurate at full-tread.

[networkboy]

Exact, again based on road-side radar.
-nB

[Mr. G]

1986SDL, speedo has less than 1MPH variance at 60MPH compared to my GPS. The odometer is within 1%

I find my cars/trucks to all be pretty close. My motorcycles are consistently optimistic. They read 5% to 12% faster than I am actually traveling yet their dodmeters are much closer. I have heard that motorcycle manufacturers purposely set speedos to read fast.