oversized tires and speedo calibration / mpg's

i know this topic has been covered before and i have read all the threads i could find on it, but i havent really found the answer ive been looking for. i recently put slightly larger wheels and tires on my taco. i have a 2015 trd off road that had the stock wheels and tires on it. the stock wheels are 16x7 with 265/70r16 bfgoodrich tires. the stock wheels and tires weighed 243.2 lbs and were 680 rpm. my new wheels are mickey thompson classic iii's 17x9 with 265/70r17 cooper discoverer at/3 tires. these wheels and tires weigh 260 lbs and are 661 rpm. prior to getting the new wheels and tires, i was getting an average of 20 mpg, now i get an approximate 17 mpg. i realize that additional weight will effect mpg as well as having a larger tire throwing off the speedometer and odometer, but i didnt think an additional 16.8 lbs and one inch larger tires would make a 3 mpg difference, whether im actually getting 3 mpg less or if its throwing off my odometer that much. just wanted to get peoples opinions on what it could be. also, ive thought about the fact that were now just about into winter, and where i live (northern md / southern pa) its been about 12-20 degrees out the past week and a half. ive heard that he colder weather combined with the winter formula gas will give us decreased mpgs. i have seen the hypertech speedometer calibration tool for our trucks and was wondering if anyone has used it or one like it, how well it works and if it would even be worth it for me with such a modest wheel and tire increase. i know our trucks are dialed in a couple mph's less than what were actually doing, from the factory so essentially, slightly larger tires should correct this. just looking for peoples 2 cents.

 

Try this calculator:

 

Weight impacts MPG for sure. But with heavier tires you also have to mash the pedal harder to get the truck to move at the rate you're accustomed to. So you're just plain going to burn more gasoline from here forward.

I was like 19-20mpg with stock tires.

Now I'm happy to breach 15mpg.

 

just did before i posted this and it looks like im going about 1 and some change mph faster than what its showing... is that anything significant that would make a difference in my odometer?

 

yea, i was worried about that, which is partially the reason i went with such a modest tire increase, but should a total of 16 lb increase make that much difference?

 

My 33" tires, based on calculations I did using the actual radius measurements provided by the factory tire manufacturer and my Cooper ST Maxx showed about a 9% difference in actual miles driven when compared to the Odometer. That sounds very small, however, my speedo can be 4MPH off. I also have to multiply miles driven by 1.09 to get an accurate read so I can compare MPGs and when to do oil changes.

 

what is the formula to figure out what the difference?

 

I lost almost 25% of economy going from 245/75 highway tires to 265/75 all terrains, both P metric and with a difference in weight of 16-20 lbs for the set, IIRC. That's after doing the math to correct my ODO reading for the difference in tire size.

I have a 2.7, which I attributed to the issue, but lots of guys have the same experience with the V6. More confusingly, some don't or don't claim to have that issue.

 

i read a lot of guys threads that increased their tire size slightly like i did and lost less than 1mpg or none at all as well. thats why im partially confused as to why i lost 3mpg. im hoping the weather and time of year is playing a role in it as well

 

I lost 5-6.

 

can anyone with the hypertech add their experience or if it would be worth it to get

 

found it. http://www.gitout.com/wpblog/bigger-tires-and-gas-mileage-how-to-determine-actual-gas-mileage/

 

My rig, with V6, came with 245/75/16's (Dunlop AT20's). I almost immediately replaced them with 265/70/16 Michelin LTX M/S 2's. Saw zero change in MPGs even they were a wider tire (and heavier, much better quality).

But when I jumped to the Cooper ST MAXX 255/85/16's (33") it made an impact. I also threw a bunch of armor, bumpers, sliders on the truck too though. It all adds up.

 

You can actually find the Revolutions Per Mile of individual tires at times. Some manufacturer's actually release the data. If you REALLY want to get exact. lol

I did all the math. And then used my UltraGauge and GPS in my phone to determine how far my Odo / Trip Meter was off. The UltraGauge can be calibrated to show your true MPH and miles driven. After calibration it was dang close to the calculations I did.

Of course, as tread wears down things change a little too. So you'll never truly be perfect. But you can get close!

 

i actually just ordered an ultragauge before posting lol, it looks like a pretty useful tool. i did the math and it looks like my wheels are off by less than 3%... do you think thats enough to even worry about getting a spedo calibrator for?

 

I'm off by 4-5 MPH and I just use my UltraGauge for my speedo. I don't see the point in fucking with my real speedo if I know how far off it is, personally.

 

sounds like what im prolly going to do. i dont think mine is off by enough to worry about

 

I use a Dakota Digital unit to calibrate. Works great.

 

I didn't lose any mpg around town going to 33s, but on the highway and when I tow I lost 4 or 5 mpgs.

 

I would think that if a person was to take a long trip and used a gps rather than their odometer to calculate mileage it would be more accurate.