My speedo is off by 2% on OEM tires/rims. I bought it new, so it’s like this from factory. When my speedo says I’m doing 100km/h, it’s actually 98km/h. I’ve verified this via gps apps (Google maps) and also driving through radar digital speed signs.

what are my options? Can I do this myself? Is this a warranty claim?

normal... ish :

Just my opinion, but I think 2% is far more accurate than the older mechanical speedometers.

Also, tire wear will make slight changes in the diameter of the tires which will affect the calibration. Your true speed will decrease a bit as tires wear from new to worn out.

Facts from our experience: There is a roadside radar speed indicator at the change from 55 MPH state highway to 35 MPH main city street on a route we travel daily. My wife’s ‘21 GLB250 always gets 35 MPH on both the roadside and her speedometer. My ‘23 GLA250 always gets 36 MPH on the roadside at 35 MPH indicated on my speedometer. That’s about 3%. This may be the tolerance to which the system is built.

On the bright side, if your indicated speed is less than actual, then the indicated odometer mileage should be less than actual, and your warranty coverage will be a bit longer. 🙂

Appreciate all the comments. I suppose 2% isn’t much after reading other comments. It’s not the end of the world, just a bit annoying for this perfectionist.

In the last 10 years I owned 2 Mercs and 4 Volvos. Both this GLB250 and my R350 were 2% under. All the Volvos were bang on. I’m also aware the Volvos can be adjusted in the software. I figured that in today’s digital age where we can send satellites into space with 100% accuracy that we could calibrate a wheel 😂

Wasn’t sure what was possible on the Mercs, but I’m glad I asked. There are YouTube vids showing how to adjust, but they didn’t seem to work for me. If I do find a way, I’ll update here.

For sure

The speedometer is electronic, so it’s in the software somewhere. Whether it’s accessible is another matter. Some of the older MBs from 12-15 years ago did have wheel size options in the engineering menu. Haven’t dug that deeply into these as ours are all ‘21 and newer.

There is an app for our Ford trucks and GM trucks include tire size selection in the onboard menu. If I find anything asking MB techs I know, I’ll post it here.