Does your speedometer cheat?
Thread Starter
Senior Member
Joined: Nov 2016
Posts: 268
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2017 Mercedes-Benz C300, 2017 Mercedes-Benz GLC300
Does your speedometer cheat?
I get the impression that my speedometer (2017 C300) shows a bit (5%-10%) more than the actual speed of the car.
I haven't got a chance to measure it yet, but based on my driving habits something seems to be off.
Did anyone else notice this?
I haven't got a chance to measure it yet, but based on my driving habits something seems to be off.
Did anyone else notice this?
Member
Joined: Feb 2016
Posts: 181
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From: UK
2020 GLE 350d AMG Line Prem+
Yeah I have noticed this as well, near me there are road signs that show your speed as you drive past then, I've tried going past at various speeds and at 33 on my digital speedo the sign shows 30-31.
Thread Starter
Senior Member
Joined: Nov 2016
Posts: 268
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2017 Mercedes-Benz C300, 2017 Mercedes-Benz GLC300
Junior Member
Joined: Feb 2015
Posts: 59
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From: Canada
2015 C300 Lux 4MATIC
I have driven many rental cars in France where there are many road speed measuring signs. All cars show slightly higher speed than the measured one. Different brands, different years, so I assume this is normal.
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2016 C300
YES! I came home from work early one afternoon and caught my speedometer with my tachometer!! I always saw them together but I thought they were "just friends". I don't blame my tach though; that speedometer has always been a *****.
Last edited by Mike5215; Feb 18, 2017 at 10:13 AM.
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From: TX
2023 GLE3502W, 2024 GLC3002W, 1967 Pontiac GTO 4 sp (sold...sniff)
There are a few speedo apps for iPhone. I used one to check my GTO speedo after the trans was rebuilt. Tranny has 2 gears to turn the cable. Gears are diff colors. I had to get the right match. Never did though. Speedo overreads by about 5 mph vs the speedo app.
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From: Northeast USA
AMG CLE 53
A properly calibrated and accurate speed measuring device (RADAR or Laser), will only give an accurate speed when a car is coming directly toward it. As the angle between the RADAR or Laser unit and the car being measured increases, error is introduced. The error will always favor the driver (the RADAR unit will show a slower speed than the actual speed of the car). So, if the RADAR unit for a speed measuring sign is at the side of the road, you can expect to see a lower speed on the sign than the speed on your speedometer.
Speed signs that just show your speed and are not used for enforcement may or may not be routinely calibrated and accurate.
Speed signs that just show your speed and are not used for enforcement may or may not be routinely calibrated and accurate.
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Joined: Apr 2010
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From: Eastern Massachusetts
2021 E450, 2020 C43, 2015 C300, 2007 C280
Try GPS
Who says the road side speed measurement signs are more accurate than your speedometers? Your GPS (esp. a freestanding one) should be the most accurate measurement. Has anyone compared their speedometer with a GPS? (I have not done so yet.)
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Joined: Jan 2014
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From: Florida
2013 ML350 Bluetec, 2016 C3, 2020 Lincoln Aviator
I have a freestanding GPS that gives MPH readout and have checked it against both of my cars. My ML was dead on. My C300 speedo actually measured between one and two MPH low, so I was going faster than my speedo indicated. Measured at 70 MPH on the interstate. Seems to go against what most people are saying.
The car felt like it was on greased rails.
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Joined: Apr 2010
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From: Eastern Massachusetts
2021 E450, 2020 C43, 2015 C300, 2007 C280
Beep! Beep!
Beep! Beep! (Beep! Beep!).
His horn went Beep! Beep! Beep! Beep! Beep!
Now we're doing a hundred and twenty, as fast as I could go,
the Rambler pulled along side of me as if I were going slow.
The fellow rolled down his window and yelled for me to hear,
"Hey, buddy, how can I get this car out of second gear?"
(Donald Claps & Carl Ciccheti, The Playmates, 1958)
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From: TX
2023 GLE3502W, 2024 GLC3002W, 1967 Pontiac GTO 4 sp (sold...sniff)
Went on I-45 S to Houston this morning. Wifey driving her '14 ML350. I opened up Waze to get traffic info. Lower left on Waze shows your speed vs posted speed. I glanced over at the speedometer and it was right on. 65 on speedo, 65 on Waze. At no time did the speedometer vary from Waze by more than 1 mph.
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Joined: Nov 2004
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From: Nelson NZ
17 E220d all-terrrain, 92 SL500, 16 C250D Wagon, 16 A200 (wife)
As part of making an electronic throttle (for disabled people) we found that the Canbus reports the right speed but the dial speed reads 4kph low right from the bottom. (01 W203)
I think pretty much all do this, not really any reason in a digital world to have speedos that are not right on the correct value, tire wear even has a pretty tiny impact.
I'm sure its a deliberate policy. I always add the extra 4kph to my speed plus whatever margin over I feel like doing!
I think pretty much all do this, not really any reason in a digital world to have speedos that are not right on the correct value, tire wear even has a pretty tiny impact.
I'm sure its a deliberate policy. I always add the extra 4kph to my speed plus whatever margin over I feel like doing!
