Quote:
Originally Posted by kaisen
I only ask because a truck tire can be 15/32 tread depth. So wearing down to 4/32 can be a 22/32 inch difference in overall height/diameter. There are fewer revolutions per mile with the new tires than the old. So there can be a real difference in fuel economy with new tires (even same brand, just new).....like an effective gearing change.
If you're calculating fuel economy by resetting your GPS tracking, that's accurate. Using your odometer? Not accurate.
YMMV
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Larger diameter wheels would lead to fewer miles recorded and lower MPG. The OD on the tires is around 33.4". Tread depth is 12/32. So losing 24/32 would mean a final OD of 32.65". That is a 2% difference if you use the full tread.
The GPS reading of speed vs. the ODB-II speed reading reading is also pretty close. The actual speedometer display guage adds another inaccuracy into things. I'm not using that. My old BMW had about an 8% high speed reading on the guage, but the ODB-II speed (A scanner hooked up) was very close to GPS.