MaineFusion Report post Posted November 10, 2013 So on a long road trip a couple weeks ago, I came to an observation thanks to the TomTom app on my smartphone. What I discovered is that my FFH's speedometer was registering one mph slower than what my GPS was recording and this was consistent through a range of speeds. For instance if I set my cruise control at 55mph, my GPS was consistently reporting a speed of 54mph. Along these lines, prior to the PCM update I could set my cruise control at 63mph and still reliably go into EV mode. Of course the problem with all of this is it is based on what my cruise control is keeping the car at. The speedometer itself is an analog dial that can be hard to read with great precision. Being a computer geek, I'm kind of obsessive about precision, and the thought of setting the cruise control at say 55mph and to be really doing 54mph is an annoyance. Now I realize that factors like tread wear and tire inflation plays a big role in the accuracy of the speedometer, and I'm thinking one mph shouldn't be an insurmountable error to correct. To this end, I'm thinking just a couple PSI difference in tire pressure might be just the fix I need. The key will be to figure out what the exact correction is needed. Of course I don't want to put in too much air and cause poor tire wear just to get accurate speed readings. One would think that this day in age where cars have built in GPS, cars would have some sort of self correcting mechanism to improve the accuracy of the speedometer so that we could stop entirely relying on a calculation method that was so dependent upon something as unreliable as the diameter of the tire. 1 hybridbear reacted to this Quote Share this post Link to post Share on other sites
MaineFusion Report post Posted November 17, 2013 So I'm back from a 1,500mi road trip to Virginia, and made an observation. Before leaving, I had inflated my tires to 38psi and was carrying a much heavier load than my normal one person commute. There were three people in the car plus a full trunk of stuff. On the trip, my set cruise speed more closely matched my TomTom GPS speeds than normal. I also had much better fuel economy than I was expecting given the extra load and constant highway speeds. My last three Fuelly fuel-ups were for this road trip. Quote Share this post Link to post Share on other sites