I would like to see a palace to set a percentage deviation for cars running altered tire sizes. I have one that's equipped with 12.1% taller tires, and this would make the calculation much simpler. Is anyone else running different size tires than normal and in need of such a feature? Is this something that might be added later?
I used my Yaris with a bit smaller tires for a while (got it this way). I replaced them soon with factory sized ones. I did manual correction until I did so.
I do manual correction for Teresa (BMW F650CS) too. She runs on default size tires, but still underestimates distance by about 2% (I often check it via my commute distance and our other bike). Sometimes I glide down our hill with the key turned off, so I have to add these distances too. What's more, sometimes she loses some distance when restarting after an engine off glide , so there's one more element in the formula.
So I don't really need such a feature, it would be too simplistic for my needs, but I think I'm a special case...
I think this might work well for some who do not want to be bothered with doing their own corrections, I think it would be better to do an actual correction for both tire size and actual deviation of speedo readings. Most speedos are off some amount even with correct sized tires installed.
Speedos do usually have different calibration than odometers, though - almost all speedos speedos deliberately show more than your actual speed. But odometers tend to be more accurate, at least all our vehicles (2 bikes and a car) are like this.
I don't have a working GPS and I can't really justify buying one - but I still can rely on road (km) signs along known uninterrupted roads (especially motorways), google maps (surely has its own inaccuracy), and can compare our vehicles on identical routes.
I've brought up this topic a couple of times mainly because my scooter's odometer read 12% more kilometers than I actually go. They admins don't want to add this because it would add complexity to the site.
The best you can do is hope for a reasonable average, remember that as your tires wear they decrease in diameter, hence they will indicate more mileage for the same distance as they wear down since it now will take more revoloutions of the tire to go the same distance. For some knobby truck tires this can be significant, my son's GMC Jimmy's mud and snow tires have probably 3/4 of an inch of tread on the tires that can wear before they get to the wear indicators, that would work out to 1.5 inches in diameter difference from full tread to nearly bald, over miles that will make a statisticlly relevant change in mileage. It still is true for even high performance tires with relatively small changes between full tread height to worn out but again you're still dealing with averages. If you want to track the difference add in your multiplier and adjust your trip or odometer number accordingly, assuming that you know the proper and correct adjustment figure. Don't forget that if you're using odometer tracking here on fuelly, that you'll need to remember what adjusted number you used last time and start from there for the next fuel up, which will become quite complex very quickly.
True. This is why I check my commute length time to time. I couldn't catch this effect in work so far, it seems that those few millimeters were immeasurable (ok, a 160/60-17 tire should be over 500mm in diameter, so I can imagine). Even less than that 1% then 2% difference I correct for.
But my new Michelin Pilot Road 2 rear had ~5.5mm until the wear indicator. This 5.5mm should show in the measured distance before I wear it down!