Ferrugenfish Posted October 26, 2017 I replaced my stock tires (245/70/17) with much larger tires (285/70/17... BF All-Terrains). I'd like to get accurate gas mileage at the pump, and it seems I can no longer get the correct speed/gas mileage due to having significantly larger tires. My question is, is there something I can do in order to correct for the speedometer, so that I can 1) see the correct speed, and 2) correctly calculate my gas mileage? I'm not a "car guy" per say, so any help would be much appreciated. Thanks! 2013 Nissan NV 2500 HD V6 high roof. ps, yes the 285 tires work. There is a little bit of rubbing on the sliding door, but not enough to annoy me. I also replaced the wheels themselves at the same time, but kept them at the same 17" wheels so i can still have lots of soft side wall for a smooth ride and more grip when off road for the lack of 4x4. I forgot what the offset on the wheels was... Quote Share this post Link to post Share on other sites
radin2son Posted October 27, 2017 Accuracy is not a strong point with speedometers and gas gauges. Most vehicles will show you traveling +5 mph. Also, how accurate is each tank “fill?” Too many variables. (I’ve mentioned this before; our 2012 shows mpg, and it will be as much as 1 mpg more per tankful than manual math. That’s a lot considering the 8-21 mpg range others have posted.) Look for a mobile scan app that shows current and average mph/mpg. Quote Share this post Link to post Share on other sites
radin2son Posted October 28, 2017 I always thought tachometers with automatics were only needed to balance the look of the dash. But, you can use your tach to determine speed. Our V8 on a fairly level interstate: 75 mph at 2200 rpm, 80 mph at 2500 rpm and 85 mph at 2700+ rpm. Google Using a tach to determine speed. There has to be a formula or curve... Quote Share this post Link to post Share on other sites
ASD Dad Posted October 30, 2017 What Rad said. Dont sweat it too much, factory speedometers are notoriously bad. If your speedo read 60 MPH before, you are now going almost 65 MPH. Factory speedos always err on the fast side of things so it could be more accurate now. Before if your speedo read 60 you may have been going 57. If it was 5% slow before your tires now make it 7% fast. Some companies do sell speedo calibrators but those are normally for the offroad guys running really large tires. Hypertech was one company that is popular but you would need to check compatibility with Nissan. 1 Ferrugenfish reacted to this Quote Share this post Link to post Share on other sites
radin2son Posted October 30, 2017 Out of curiosity, I checked to see what was on line regarding using the tach to determine speed. Lots out there but the best was a post by a new driver, maybe yet to be licensed driver, requesting help so she could become a NASCAR driver. Oh if it could only be that easy... 1 Ferrugenfish reacted to this Quote Share this post Link to post Share on other sites
