Hi all.

The speedo in my 2003 L322 is showing speeds approximately 10% faster than the actual road speed - 30 indicated, 27 actual / 60 indicated, 54 actual etc. Is it possible to re-calibrate?

Cheers. QUID FACIUM TIBI
ANTEQUAM ALIIS

2003 TD6 VOGUE Zambezi Silver
tows 2006 Lunar Delta 540/2

First of all, are you using a smartphone app to get your speed? Use at least two different ones, and are you sporting standard wheels tyres?
Is you needle steady?
Had a few dicky speedos in older cars, but, on the l322, there are pifalls to research before throwing in a secondhand speedo, as the mileage can be wrongly added to your actual car, (permanently,) from the older higher Mileage donor speedo.

generally speedos do read slightly more than actual speed, about 5% i think...as above, get some other readings .. ... - .- -.




Y. O. L. O.
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What bugs me though is the car knows it's speed accurately enough , mine over reads by the usual little bit but my speed warning bongs on the money and I have checked with multiple GPS and Glonass devices . 2008 MY Supercharged
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Well I just brought a my10 ffrr. It's come with 22" wheels. Now I'm looking to get a set of 20"s for winter. Will that make a massive difference?

axle wrote:

What bugs me though is the car knows it's speed accurately enough , mine over reads by the usual little bit but my speed warning bongs on the money and I have checked with multiple GPS and Glonass devices .

Hmb wrote:

Well I just brought a my10 ffrr. It's come with 22" wheels. Now I'm looking to get a set of 20"s for winter. Will that make a massive difference?

Can none of this be adjusted though? The speedo is electronic, not cable driven like antiques from the 80's. Somewhere in the ECU subsystem there must be a calibration for this ?

I was contemplating fitting the L405 20 inch tyres with a 55 profile rather than a 50 to overcome the small percentage that mine over-reads. There has to be a better way. I get 67 actual for an indicated 70.

EU law really isn't up with the times. A vast amount of cars have GPS on board now so it's not exactly tough to take readings from multiple sources in the name of ensuring accuracy.

A speedometer, whether mechanical or electronic, is a mandatory fitting to an EU registered car. GPS is not.

Furthermore, GPS is not sufficiently accurate unless its algorithms can compensate for turns and gradients. Also, GPS uses and average speed calculation. Try this; accelerate to 60mph and then brake very hard to a stop. I confidently predict that there will be a noticeable time lapse before your gps speed reads zero.

If you get your speedo to be more accurate by fitting different profile tyres, don't forget that the rolling radius will change as the tyres wear. Moving away from the Type-approved sizes also means you need to tell your insurance company of the change

As I posted above, it's not worn/new tyres that are going to affect the speedo, were only talking something like 6mm x2 from new to legal limit, I meant has he got some giant mud pluggers, or more so, some RRS lower profile wheels. Though I think we are talking here about huge oversize.
I've got some oversize tyres, (285 50 20) and somehow, they read dead on correct, with two different speedo apps at 50 and 70mph. But they are about 20mm diameter bigger, if I remember.
I wonder if, the easiest thing, would be to disconnect the battery, and leave it for an hour, and replace, just so everything get a shutdown. Before you start pulling your wallet out.

Sounds about right to be honest. My disco was reading about 6mph over all the way down the autoroute to Le Mans. As I was on a fairly straight road and on cruise for hours at a time the Tom Tom speedo was pretty accurate and concurred with my phone speedo.

Pretty sure it is a conspiracy to make us all drive more slowly...... just remember that at 70 your speedo will be reading 75/6 and you will be all right. There is nothing that can't be fixed with a hammer😜😜
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Your gps may be more accurate than your speedo but you cannot rely on gps to be accurate either.You need 'Measured mile',drive it at a steady speed and time it accurately,then calculate your actual speed.The percentage difference will give you actual speeds for different speeds .A simple way it travel at 60 if you can ,it should take exactly 1 minute.

Im running everything std - tyres wheels etc and I first noticed there might be a problem when I went past one of those roadside speed displays. Not too accurate, but it made me check my Garmin closely when recently did a 140 mile run. It didnt make any difference road type or speed - the Garmin consistently disagreed with the speedo by 10. I can compensate, but I do like something to do its job properly if possible...... QUID FACIUM TIBI
ANTEQUAM ALIIS

2003 TD6 VOGUE Zambezi Silver
tows 2006 Lunar Delta 540/2