Topic: Tested speedo accuracy on BMW 328

[Slow_lane]

Yesterday I tested the speedo accuracy on my 2011 BMW 328. I had read that they overstated the speed.

I used my GPS. I locked the cruise control in at 105 Kms. GPS showed speed of 100 kms. It was overstating speed by 5 kms/hour. Tested it a number of times with help of my wife as co-pilot and every time the speed was exaggerated on speedo.

I believe I had read somewhere that even though speedo's are not calibrated properly the odometers are still reflected proper mileage. I hope so

Not sure there is any fix available for this problem.

[Sir Osis of Liver]

You should read this:

Sorted by price, luxury cars are the least accurate, and cars costing less than $20,000 are the most accurate. By category, sports cars indicate higher speeds than sedans or trucks. Cars built in Europe exaggerate more than Japanese cars, which in turn fib more than North American ones. And by manufacturer, GM's domestic products are the most accurate, and BMW's are the least accurate by far. One other trend: Only 13 of our 200 test speedos registered below true 70 mph, and only three of those were below 69 mph, while 90 vehicles indicated higher than 71 mph. Are our cars trying to keep us out of traffic court?


http://www.caranddriver.com/features/speedometer-scandal

[Fobroader]

Ive read that in the past BMW and Porsche had optimistic speedos. Dont know of any fixes available, maybe if you went to a tuner and got them to reprogram the speedo to your exact size of tires, but otherwise......

[Spheric]

My VW Golf overstates by around 7 kms per hour. From various forums this appears to be a feature, not a defect, of German vehicles.

My previous 2007 Passat also had this 'feature'. Having driven VWs last 7 years, I've started to appreciate this as my overstated 'speeding' was given a leeway margin of 10% or so, especially when driving in places like Guelph where police don't really have much to do except sit there with a radar gun.

[Ex-airbalancer]

Yesterday I tested the speedo accuracy on my 2011 BMW 328. I had read that they overstated the speed.

I used my GPS. I locked the cruise control in at 105 Kms. GPS showed speed of 100 kms. It was overstating speed by 5 kms/hour. Tested it a number of times with help of my wife as co-pilot and every time the speed was exaggerated on speedo.

I believe I had read somewhere that even though speedo's are not calibrated properly the odometers are still reflected proper mileage. I hope so

Not sure there is any fix available for this problem.

Old news our 2000 BMW is about 6 km / hr difference at 100

[Guy]

Our Volvo XC60 understates speed by 1-2 km/hr at 100. The G37 is right on.

[mmret]

Surely if they can make ABS, ESP, etc. systems using sensor data from all 4 corners, a speedo accurate to within 1km/h is not much of a challenge*. So I can only assume that some engineers / product people have a meeting and a coffee and decide how much optimism to program in there.

* after adjusting for tire size / tread depth. If you burn 5/32 off that's 4mm less radius. 245/45/18 has a radius of 677.7mm. So over half a percent is removed. With rounding, that can be 1km error at 100km/h

[Sir Osis of Liver]

Surely if they can make ABS, ESP, etc. systems using sensor data from all 4 corners, a speedo accurate to within 1km/h is not much of a challenge*. So I can only assume that some engineers / product people have a meeting and a coffee and decide how much optimism to program in there.

* after adjusting for tire size / tread depth. If you burn 5/32 off that's 4mm less radius. 245/45/18 has a radius of 677.7mm. So over half a percent is removed. With rounding, that can be 1km error at 100km/h

As I understand it, there used to be fairly heavy penalties either at the national level or the EU level for having speedometers that read below actual, so the German makes got in the habit of building in a fairly wide margin.

[sailor723]

Probably explains why the nav system in neither the BMW or the Benz  displays speed the way a Garmin does.

[RS4Dalf]

My Audi is about 3 km/h off at 100.

[Northernridge]

I'm going to test the Berlin taxi – reminds me of Rrocket's decibel level test thread from a while back.

[tortoise]

The Mazda5 read a few % fast until I went from a 205/50 to 215/50 tires.  Now it's dead accurate.  Which probably explains why I'm always 5 km/hr faster than most people.