[W126 Coupe] Speedo inaccuracy

[Divov]

Hi Gerry,
I tested my 500SEC Euro whilst running 205 x 65 x 15 tyres. The speedo was 
definitely optimistic.
The only car I have ever found to be spot on was a Toyota Camry 220SEI which 
was spot on even at 210km/h (130 Mph)
Surprising also is that the Lexus 400LS is about 6 to 7km/h optimistic at 
130kp/h
VW Golf's are very bad, Isuzu pick-ups are awful!
Surprisingly my 1972 Lancia Fulvia was pretty good. Only showed a 4km/h 
error at any speed. Strange that the error was a constant even at top speed?
Also I find the odo readings similarly optimistic which of course makes your 
fuel consumption figures look better!
I think the manufacturers do it deliberately.
I use a hand held Magellan GPS on a long open road to get my readings.
Regards
Alec D
----- Original Message ----- 
From: "Gerry Van Zandt" <gerryvz at mac.com>
To: <mbcoupes at mbcoupes.com>
Sent: Monday, July 23, 2007 9:30 AM
Subject: [W126 Coupe] Speedo inaccuracy



>I agree with Dan.  When I set up the speedo calibration and  adjustment 

>box, I was very careful to measure against a measured-mile  calibration 

>setup the state of Oregon has here in I-205 south of  Portland, which is 

>4-5 miles long (signs by the side of the road).   That's where I got the 

>fact that the stock calibration was 10-12 MPH  "off" with the new 3.07 rear 

>end.

>

> I simply did the ratio adjustment, programmed the DIP switches in the 

> calibration box, and that was that.  I've had numerous "roadside"  radar 

> setups tell me, at all sorts of speeds (city and highway), what  my speed 

> was and it was right on with the indicated / modified  reading influenced 

> by the adjustment box. Never had anything as  accurate as a GPS, but as 

> long as I'm at 1 percent or less, I'm happy.

>

> Other fellow owners of E500/500Es have told me that their speedos can 

> read up to 10 MPH off (GPS measured vs. indicated) at V-max of 155  MPH. 

> I think the rule of thumb is that the higher your speed  (particularly 

> over 100 MPH) the greater the difference between  indicated and actual 

> speeds.  Heck, my Honda motorcycle is even off  by around 4-5 MPH at 80+ 

> MPH.  Actually, that's saved me from tickets  more than once...

>

> Cheers,

> Gerry

>

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