Do you know where current model BMW speedometer sensors are? I am getting wider tires for my F30 335i. I want to select a size that will impact my speedometer the least, so I am shooting for diameters that are +/- 1.5% of original. However, I may fudge on this if the speedo isn't measuring speed from this wheel. Do BMWs takes speed readings from all four wheels, or just the front or rear wheels?
In the past it has always been the left rear wheel that sends the speed signal to the cluster. Not for sure if that is still the case with the F30
You might be aware of this already, but, fwiw, BMW purposely has their speedos show almost 5mph high. If your new tire size is less larger overall rolling dia. than currently, you'll be turning more less wheel rpm's & the speedo will be showing closer to actual speed. It'll be the opposite of course if you end up with a larger smaller o.d., indicated speed would be a bit further off from actual. Thought I'd read someplace there's a setting buried in the software where it can be toggled between actual speed & the default -5mph, not sure if that's the case or not, but if so, you'd have to have what equipment it takes to access those settings anyway. Comparing indicated to what a GPS or the Waze app. shows can give an idea of the difference too. This is handy for comparisons: https://www.rimsntires.com/specspro.jsp If you're running stock wheels, you can look up the offset (et) in realoem.com if you're inclined, but wheel offset doesn't affect the diameter. ET is an abbreviation for German "Einpresstiefe", translation is 'insertion depth".
Yes, I've experienced the 1-5% speedo variance on all my Bimmers. However, I've always thought that a larger diameter wheel would get it closer to actual speed because there would be fewer rotations per mile. Isn't that the case?
I think I found my own answer. BMW speedometers habitually read high; meaning that you are going slower than your speedo indicates. A larger diameter wheel will increase your speed relative to your speedometer reading, making your BMW speedo more accurate. This speedometer calibration calculator bears this out: https://tiresize.com/speedometer-calibration/.
Thank you Charlson89. There are a lot of people on various BMW sites that report the speedometer sensor is indeed on the left rear wheel only. Thanks.
Yes! Sorry, thought that through about halfway & didn't account for the change in distance covered with changing dia.!
