Just bought this '08 R56 and noticed that the speedometer is off by 4:5 mph; is this common?

Thanks,
C@tle56

 

3-5 mph is the norm.

 

Mine seems to be about 2mph compared to GPS readings.

 

The faster you go, the higher the error. Mine is off about 5mph at an indicated 79-80 mph.

I've been told that MINI does this because they are fined if the speedometer shows a speed less than the actual speed.

 

Mine is off 3mph at 70ish range. It's a BMW thing. If you check the speed through OBDII the car knows the correct speed, but the speedo reports high. The rumor is it's to appease a euro law and our US cars have inherited it.

 

It is possible to disable the overcorrection by setting up and using NCS Expert. Just do a search on the forums to learn about the program. It also lets you enable a lot of other cool little hidden features on your car.

 

Yup they err on the high side. But the spedo is in the middle so your passenger gets to enjoy the inaccurate measurement also.

 

I've figured out that mine consistently reads 4% high according to the GPS, so at 50 MPH it reads 52, at 75 it reads 78 and at 100 it shows 104.

 

mine was off 1.9 mph at all speeds, so it is not a % error, but a fixed error

i changed out the 225/45R18 rfs for 225/50R18 michelin pss and now the speedo reads exactly correct

 

Mine is off by three at all speeds according to my Garmin.

 

I have one of those LED speed readouts at my corner and if you're above 45 MPH it starts flashing to indicate you're speeding. It never matches what my speedometer is showing.

 

Mine is off by about 5mph as well. Found this out by going by one of the radar things the police set out to have people slow down. So now I go faster hahaha.

 

I would not trust that speed readout ... the displayed speed can be adjusted by the cops

I used an aviation GPS that reads in .1 mph increments vs 1 mph in auto GPS

I also used a stopwatch snd mile markers on the I-state (3600 ÷ time in seconds to go 1 mile = speed on mph)

 

An other great size for the R60/61 in the Michelin PPS is 235 45 18, I'm running 245 45 18 Bridgestone S04 and my speed and odometer is also dead on now.

 

Not possible. Changing tire diameter changes indicated speed by a percentage. It will not eliminate a fixed error, except at one specific speed.

That is math, not an opinion.

Fail, again.

Traffic radars can not be "adjusted" or recalibrated by the user.

If a traffic radar goes out of calibration (which may be checked by the user), it must go back to the manufacturer or to a calibration lab for adjustment. They rarely need calibration, although some states require that radars be periodically tested and certified in order to be used for traffic enforcement. I got one radar that was built in the 1960s, and probably hadn't seen a calibration lab since the Gerald Ford administration. It was as accurate as radars nearly 50 years newer, which is to say, "It was dead-on."

 

scott

my oem 225/45R18 tires had an od of 25.9"
my replacement tires 225/50R18 are 26.9" od
my winter tires are 205/70R16 withn od of 27.3" and my speedo reads a CONSTANT .6 mph lowerr than actual from 10 mph to 100 mph

 

FACT: It doesn't matter if it is a mechanical/analog or a digital system. It is still measuring tire rotations. It is a mathmatical certainty that changing tire size, without changing anything else in the system will change the indicated speed by a percentage. It does not induce or eliminate a fixed error. Your observations (I am sure they were flawless ) can not change that.

You're like the guy who once tried to argue with me when I said that half the people in the world are below average. He refused to accept a statistical certainty. Of course he also lost thousands of dollars trying to get rich in Vegas, so...

And I haven't see a radar speed sign where the speed readout was adjustable. The displayed speed range and operating range, yes. But not actual recalibration of the of the speed readout. But as long as a cop told you...

 

you are wrong

the difference in speed between different size tires variues with speed, the percent difference is constant



and just for completeness are my observed speeds with different tires

 

You just agreed with him. The tire changes the entire range by a fixed percentage. A 1% change in OD changes the speed by 1% at all speeds. The speedo doesn't know your tire size.

Mine is off by more like 8%. I use the phone GPS readout through torque which gives to .1

 

Yes but both the digital speed display in the tachometer and the analog speed display in the central gauge are driven by a computer. The computer need not be exactly linear in the relationship between tire rotation rate and indicated speed. And in fact it seems to subtract a constant from the indication regardless of the tire rotation rate.

 

Linear or not, a change in tire size is a fixed percentage that will adjust the curve by that percentage at each point.

I do not see a fixed amount but rather about 8% off at all speeds.

 

http://www.miata.net/garage/tirecalc.html

fun to play with.

And, I believe you can fix the overspeed error VIA NCSExpert coding.

 

Damn! 8% is a lot. Still acceptable by manufacturer standards, though.

 

What about when the car is stopped? Does it read -5 MPH at that point? Or does it read 0 MPH when you are driving at 5 MPH?

 

With some 50 years of computer experience I think I would be able to arrange things so that the reading never went below zero.