Hi Everyone,

I've noticed that my speedometer seems to read about 2 MPH faster than I'm actually going. It seems that the other computers know the correct speed and that it's just an issue of the indicated speed on the speedometer itself.

I've contacted many speedometer repair shops but none can calibrate this one.

Does anyone else' speedometer read high? I've never noticed this issue on any other cars I've owned in the past.

Any suggestions or pointers on where I could get this corrected?

Thanks!
Larry. 2009 Range Rover L322 Autobiography
Bournville/Ivory
Save lives, give blood.

Absolutely normal in the UK, speedo can over-read by up to 10% but must not under-read.

So you always think you're going faster than you are.

Actually a legal requirement over here. Not sure about the US. I would guess its similar.

Larger wheels will reduce the error.

Do you guys have tachographs over there for towing heavy stuff for work? That's where you'd go in the UK as they record time and distance properly so need to be calibrated.

As noted by Ian, an over-read is normal over here.

All my BMW motorcycles since 1993 have over-read their speed by 2 mph and also my 2005 Audi again by exactly 2 mph (GPS checked).

Back in the day, it cost too much to make really accurate speedometers, so only police cars were fitted with calibrated ones. As under-reading would be an issue re speeding offensives the law was set up to ensure this did not happen. The manufactures just set the speedos to over-read "a bit" and if this made their cars look faster than they actually were, well that was just a side benefit!

Of course now speedos can be made to be almost spot on, so much so that the manufactures seem to agreed to standardise on the 2 mph under-read. 2010 Range Rover TDV8 Baltic Blue Autobiography (2011 MY) - SOLD
1960 Land Rover SII SWB SW
2020 BMW R1250 RT LE
2021 Triton ST-125 (Monkey Bike)

Same in Oz, cars can read up to 10% high but can’t read low.
My 2007 Yamaha reads 110 km/h when travelling at 100 km/h by the GPS. Our 2009 Subaru (and our previous ones) do the same.

My P38A was almost spot-on. Ron B. VK2OTC
2003 L322 V8 Auto
2007 Yamaha XJR1300
Previous: 1983, 1986 RRC; 1995, 1996 P38A; 1995 Disco1; 1984 V8 County 110; Series IIA

Speedos are a mechanical device (not GPS) It’s done to allow for tyre wear, and differences between rolling radius of tyre brands etc... a speedo cannot legally under read speed in most countries in the world so they run up to 10% fast so it cannot be used as a reason for speeding. This is the same for all manufacturers and vehicles on the road.

If you calibrate your Speedo and make your Speedo accurate now it will drift again as the tyres wear down then when you Change your tyres it will be well out again... I guess like a stopped clock or watch it will be ‘accurate’ once in a while.... but you will have to judge when that is before you do exactly the speed limit 🤦‍♂️

If you want to see exactly what speed you are doing for some unknown reason (speed trials, drag races, world record top speed etc in a Range Rover 🧐) then get a calibrated GPS device.

There's a legal reason why not just your speedo, but all speedos over read............ so you can't use the excuse of a speedo over reading and blame the manufacturer if you're ever caught speeding.

And in your case, an over reading of 2mph is pretty good. A couple of my motorbikes over read by up to 10mph at higher speeds..

How are you measuring "actual" speed"?

GPS's are not necessarily accurate for speed, particularly when there is a change in elevation.

Anyhow, as everyone has said, it should over read - less chance of a speeding ticket!  Bish.

2005 110 TD5 CSW
2011 TDV8 Vogue SE (gone)

I've read a LOT of really good replies here.

I think what I need to do is, with my wife as an assistant (so I can keep my eyes on the road), set the cruise control on a level section of road and then reset the average speed setting and see if the two agree. I think I did something close to this (I've done so much since buying and learning more every day so I may have a mixed up memory) and the speed on the trip display was accurate and the speedo was a bit high.

Yes, the speedo is mechanical. But, it's just a small electrical device on the back of the cluster, not a cable being fed by the transmission, so I would hope it would be more accurate than it is.

My '06 Honda Pilot uses a same type of system and is dead on. My wife has a 2020 Mazda CX-5 (digital display) and it too is accurate. As was our old '07 Infiniti, '09' Honda CR-V and even my 1990 BMW 325. Maybe I've just been lucky and always got accurate units?

Thanks,
Larry. 2009 Range Rover L322 Autobiography
Bournville/Ivory
Save lives, give blood.

Larry, my wife has had company cars for many years now; BMW, Merc, Merc, and now Audi. All of them read exactly 2 mph too high on the speedometer but were almost perfect on the navigation / GPS systems. My last new car was a 2005 Audi A3 (sold in 2019 when I got my FF) and it too was just the same as were my 2001, 2008, 2014, 2015, 2018 and 2020 BMW motorbikes.

My view is that these Germany manufacturers all had very accurate equipment that they deliberately de-tuned for the speedo readout (for legal reasons). But use the accurate info for everything else.

It might be worth doing your test run on cruise control at an indicated 60 mph between two points know to be say 5 miles apart and checking the time taken and the distance recorded on the milometer. My guess the time taken will be longer than it should have been (by 2%) but the distance recorded will be almost spot on (subject to tyre diameter error only).

It is interesting to hear your experience of fully accurate speedos from the Japanese manufactures you listed (a bit of a surprise with the 1990 BMW).

Not sure what the answer is but look forward to hearing how you and your wife get on with the testing.  2010 Range Rover TDV8 Baltic Blue Autobiography (2011 MY) - SOLD
1960 Land Rover SII SWB SW
2020 BMW R1250 RT LE
2021 Triton ST-125 (Monkey Bike)

When I mentioned the Speedo is a mechanical device it’s was a general comment and I meant it is ‘driven’ off a gear or reluctor wheel /hall sensor as the sensor which is ‘driven’ off the transmission, diff or drive shafts and the dash cluster is electronic. To be fully electronic it would need to be a GPS device.

A mechanical device is always inaccurate as the rotation used for calculating speed is ultimately fixed to the tyres so tyre wear (the different of a new tyre with 7mm+ tread and worn out at less than 2mm is a lot) or different rolling diameters between brands and types are different by up to 10%

I still don’t get why you need to be traveling at a certain speed to 100% accuracy , a speed limit is just that a limit you need to be UNDER. And a couple of percent under speed limit means very little to the travel time of even a very long journey.

I think you should get over the designed inaccuracies and focus more on something else, this is fruitlessly

ur20v,

Why I need the speedometer to be accurate? "Need" may be too strong of word. Perhaps, "highly desire" would be more accurate .

Perhaps a bit of OCD. I'm just a bit pedantic about these things.

I'm starting to wonder if maybe this is more common in Europe. Since this forum is mostly in Europe I'll ask around to others here in the USA to see if theirs are also off by a few MPH.

Thanks!
Larry.

P.S. I have a friend who says he's "CDO." "CDO" is exactly the same as OCD but in the correct alphabetical order . 2009 Range Rover L322 Autobiography
Bournville/Ivory
Save lives, give blood.

If you have the digital dash then you can adjust the speedo “accuracy” if you like. As mentioned, there are too many variables for it to be 100% accurate for 100% of the time.

Besides a GPS consumer device is not really that accurate either.

If you know the speedo reads 2mph faster then why not just deduct it in your head when driving... or is that too difficult 😄. To be honest I only look at the big numbers, 20,30,40 etc etc , 2mph doesn’t even register in my thoughts as I wouldn’t notice a 2mph difference.

Hi steptoe,

Yes, I can subtract 2 MPH from the indicated speed. It's just that I shouldn't have to (in my opinion).

See my post above about being a bit OCD.

Thanks,
Larry. 2009 Range Rover L322 Autobiography
Bournville/Ivory
Save lives, give blood.

steptoe wrote:

If you know the speedo reads 2mph faster then why not just deduct it in your head when driving... or is that too difficult 😄. To be honest I only look at the big numbers, 20,30,40 etc etc , 2mph doesn’t even register in my thoughts as I wouldn’t notice a 2mph difference.

All true, but does not address the OP's original questions.

I thought that all vehicles from all manufactures over read a bit (at least by 2%) in order to meet the legal requirement to never under-read.

I am quite content that my cars and bikes over-read 2mph, but have to say I am intrigued that the OP's recent vehicles dd not seem to. 2010 Range Rover TDV8 Baltic Blue Autobiography (2011 MY) - SOLD
1960 Land Rover SII SWB SW
2020 BMW R1250 RT LE
2021 Triton ST-125 (Monkey Bike)