Speedometer Not Accurate?

[CT MINI]

I have heard for a while that BMW makes their speedometers a little on the "optimistic" side. This seems to be backed up by my own experience with my MCS. Has anyone been able to verify their speedo?

[MiniMan7]

Actually I have. I was doing about 75 km/h right on the needle in a 40 km/h zone. A cop stopped me with a radar gun, and told me I was going 75 km/h. He also gave me a ticket...

But needless to say. I think the speedometers are fine.

[barnster]

I don't know what caltrans calls those roadside speed monitors - but a 52 mph (by my speedo), I always seem to be showing 49 mph on their monitor.
I believe these speedos are faily accurate, but sometimes
have very inaccurate "holes" - not mention the variables when changing the tire and wheel sizes.

[IBMiniG]

On the first drive home I thought it was wrong too. I wasnt going that fast, but then I noticed all the other cars around were gone, left in the dust. Hence my signature quote.

[BruceK]

Yes. The speedometer is inaccurate and it is actually designed that way.

I posted the info below previously, but it applies in this discussion:


An interesting article in the the April 2002 issue of Car and Driver concerning speedometer accuracy explains why European cars have speedos that read slightly high.

The article asks the question why European cars typically have speedometers that do not reflect actual vehicle speed speed as accurately as speedometers in cars from North America or Asia manufacturers (based upon years of Car and Driver test data).

The article specifically mentioned BMW and Porsche speedometers (which does seems to include the MINI). Of course having a European car with a less accurate speedometer is counter-intuitive when you consider the high speed autobahn travel possible in parts of Europe.

The upshot: A certain level of inaccuracy is designed in on purpose by the manufacturer in order to meet EU regulation ECE-R39. Mostly this has to do with making sure the speedometer never underreads true speed. This is important, the EU feels, because a car owner may fit a variety of different -- usually larger -- wheel and tire combinations to a car.

In the US, this also helps prevent lawsuits of car makers by disgruntled drivers who get speeding violations. By ensuring the speed that appears on the speedometer is higher than actual speed they can't complain they didn't know they were speeding!

Here's the real interesting tidbit: Trip Computers do not have to meet this EU regulation, so they tend to read more accurately. Meaning if your speedometer says you are going 80 mph and you maintain that speed and reset your trip computer to determine your real average speed, the Trip Computer will show the more accurate, (i.e. slightly lower), true vehicle speed. I know that on my Cooper S, 70 mph on the speedometer reads as 67.8 mph on the computer.

[BillK]

I think I'll keepmy eyes open for a AAA speedometer calibration visit in my area.

It is free (to members) and accurate. Anyone have their speedometer actually calibrated?

By the way, most patrol cars (at least in California) have their speedometers calibrated regularly and keep a card with the results inside for referance if a speeding ticket is being written. The calibration does not actually change the readings, it just maps the readings to actual speed so you can correct for the error.

[Handy Andy]

I have a GPS unit that I use in my car and my MCS speedo is right on. indicated 100km/h is 100 km/h by my GPS unit. The gps unit is acurate to within .1 mph, at least thats what they claim.

When my MCS was in for service the other day I had a 320i as a loaner and it's spedometer was out by 6km/h. indicated 100km/h was actually 94km/h.

I also took a test drive in a CVT Cooper and it was the same as the 320i, out by 5km/h, indicated 100km/h but gps indicated 95km/h.

Looks like the only way to be sure is to have it checked.
A GPS unit is the easy way to check!

[BillK]

Quote:

Originally posted by Handy Andy
Looks like the only way to be sure is to have it checked.
A GPS unit is the easy way to check!

Good tip!! Thanks! (Why didn't I think if that? )

[Rob.]

Good article Bruce K, explains the problem.
Thanks for taking the time to post it.

[retroom]

Better to show high than low. I think 5% is an acceptable figure.

retroom

[thedude]

If my GPS handheld is accurate then my speedometer is always about 3MPH high. Interesting that some are right on. Is this something the dealer can adjust/fix?