Surfer2001

Does anybody know if these can be calibrated? Am I looking at 500 bucks to fix this thing? Is the 2 mph difference adding extra miles to my car? ugh, I thought my car was perfect!!

Thanks Don

platinum997

Add what speed is it off. Most cars are calibrated off by 3mph @ 65 for legal reasons. If it was off the other way there could be lawsuits for tickets.

You can go down in tire size to make up for it if your seriously concerned. Taking a standard 245.40.19 to a 245.35.19 is about 2.5 mph slower.

You realize 2mph over 100,000 miles is like 3000 miles. I.e. insignificant

platinum997

..

Conan Dombroski

Seconded. I read a "study" at one point (wish I could find it) where they randomly tested a bunch of cars and found all of them off by anywhere from +3 to +10 mph. And all were OEM wheels and tires. Basically, no one makes a perfectly calibrated speedo. As your tires wear down, you're indicated mph will increase for the same real over-the-ground speed.

andy92782

Mine's off by more than that - if it reads 80mph, GPS says 76mph.

It's a German car thing. BMW, VW, Porsche, they all have wildly optimistic speedometers. It's intentional. But the mileage they log on the odometer is bang-on.

In my experience, Japanese and American cars have accurate speedometers. 80mph is 80mph.

I do understand it's a struggle. It is for me. My other car is a lifted Toyota 4Runner with upsized wheels. When the speedometer says 75 it's really more like 78. I'm constantly having to re-calibrate my brain each time I switch vehicles

81911

😂
I hope they give you a GT3 allocation for your troubles!

Tj40

This is pretty common on most car's I've owned - speedo is optimistic and mileage is bang on.


I used to test this out on the highway on my cars - set cruise to 100 kmph (Canada) and reset the average speed reading on the trip computer - average speed on the trip matched my GPS at 97Kmph while speedo resolutely said I was going at 100!

RCD

I am on my 5th 911 over a twenty year period. Every one has been ~3 mph high.

extanker

yepper...be sharin dis one 2

mike9186

My 997 speedo is dead nuts on with both Waze on my phone and with my Uniden radar detector that has a GPS function.

My Cayenne speedo is exactly 2 mph fast and it makes me crazy.

champignon

German car manufacturers, especially, intentionally set their speedometers to over read the true mph/kph. In BMWs you can actually code this out, the most common and easiest way being to buy an OBD II device with software from a company named "Carly." This company has started to produce similar products for other brands such as VW, but I don't know how far along they are in that process. Amazon sells the device for BMWs on their website, and the software can be bought through Android Play and the Apple App Store.

With BMWs, you can't code out the over-reading on the analog speedometer, only on the digital one. If you do this, as I have done now on 3 vehicles, if you were going, say, 75 as measured accurately with a radar gun or gps, your analog speedo might read 78 or 81 or even higher, whereas your digital reading would be correct. The cruise control remains similarly uncorrected, so if you set it in this example to actually go 75, the cruise control indicator would say that the speed setting was really whatever the analog speedo reads, e.g. 78 or 81 or whatever.

BMW dealers WILL NOT code this out, they will tell you that it is a "safety feature" and that they cannot code it out due to "liability concerns," more or less the same thing they will tell you if you try to get them to deactivate the seat belt chime (which can also be coded out, on BMWs, with the Carly app and with raw code, also).

I have read that this sort of coding is not available for Porsche automobiles, and I have not researched it.

VWs are reputed not to intentionally over read the speed, and in my own experience this has been correct and my VWs have been spot on.

Wayne Smith

There is a DOT requirement that the speedometer read 2 mph high.

Of course, if you buy larger wheels this can affect tire circumference and have an affect (Pam's GLA 45 with 20 inch wheels is spot on, but the same car with stock 19 inch wheels is 2 mph high ... MB isn't going to change speedometer drive gears to adjust for wheels and tires).

The odometer should be pretty well calibrated. Set your cruise control to 62, start a stop watch at an even mile, and drive for 10 minutes ... you will (probably) have gone 10 miles.

myw

are you on factory size rims and tires with proper tire pressures ? I am assuming your using a cell phone or some sort of gps device to track actual "real" speed ?

For all my cars the gps speed and instrument cluster speed are dead on unless I am running an off sized tire/wheel combo.

vern1

Surfer2001

First off, thanks everybody for the input.
I didn't know manufactures fudged these numbers. (Stress level and blood pressure) back to normal.

Secondly, Yes in my coup, I'm on stock 19" wheels. Tires - Front 235/35R/19, Rear 305/30R/19, pressures are set to factory specifications.

I used the GPS on my phone for the check, and then I used a Garmin NAV to cross check.
I'm okay with the MPH error, as long as the miles on my car are correct.