bigger tire/mpg question?

so i went from 245/75 to 265/75. larger tires. on tacoma tire calculator. it says if im going 50mph im actually going 52 mph (roughly) so does that mean my mpg reading is also off? (on dash screen) since i put larger tires im getting better gas mileage? (according to dash readings) was getting 16.5 daily commute now says 17.2 i went huh?

 

Yeah I think it does. Your tripmeter won't be registering all of the miles

 

according to tacoma calculator...its the other way around. bigger tire more speed...if speedometer says 50mph im going like...almost 52mph. or your saying it was wrong! from factory with 245 tire readings????

thinking that some tacomas come with 265/70r16....wonder if toyo does a all around guess of instrument readings

 

Half right. The part in red is wrong. The sensors simply count the number of tire revolutions. Mathematical calculations are made with the trucks computer assuming factory tire circumference. When you go to a different tire size the circumference is different and both the speedometer and odometer are now going to give a different reading.

The 2nd part is probably right. In my experience when the speedometer is compared to a GPS the speedometer is usually reading 2-3 mph slower than you're actually driving with factory tires In my truck the speedometer would say 65 with factory tires, but read 62-63 on the GPS. When I moved up to 265/75/16's which are 1" taller in diameter then my speedometer and GPS were giving exactly the same readings.

265/70/16's are the same diameter and circumference as 245/75/16's. The 65's are wider, but the diameter is the same so it doesn't change the speedo. Some Tacomas come with 17" wheels, but the tire diameter is still the same as 245/75/16 so that does not change the speedometer.

Factory tire diameter is about 30.5" regardless. Your 265/75/16's are 31.5" and that isn't enough to worry about. Your speedometer and odometer will be DIFFERENT by about 3%. And most likely will be more accurate than with factory sizes. Check your speed with a GPS. You can double check your odometer by using mile markers on the interstate on a long trip. You need to drive at least 50 miles and 100 is better. If you drive 100 miles by the mile markers and 103 by the odometer then you're off by 3%. When figuring fuel mileage by hand simply add 3% to the miles driven before dividing by the gallons of fuel used. For example if you drive 276 miles multiply by 1.03. 2761x1.03=284 You actually drove 284 miles instead of 276. But the difference isn't huge. If you burned 15 gallons of gas @276 miles then you got 18.4 mpg. If you do the math @ 284 miles it is 18.9mpg.

NEVER trust the mpg readout on your truck. Always verify by doing hand calculations. Some vehicles tend to be pretty accurate. My Tacoma is old enough not to have that feature, but my Honda and Ford do. Both of them consistently are optimistic. The Honda by 3-5 mpg. The F150 is close, always within 1 mpg and often closer to 1/2 mpg, but always showing better mpg than hand calculations.

To be honest none of this is enough to worry about unless you change tire size significantly. If you went from a 30.5" tire to a 35" tire then you need to think about it. Going to a 31.5" tire is a non-issue. Here is why. Your new tires are 31.5" tall with 1/2" of tread on the top and bottom. As the tires wear they get smaller in diameter. Once you get 40,000 miles or so on them and most of the tread is worn off you're now going to have a 30.5" tire. Same as the factory size when they were new. And none of this is new. Speedometers have always been off. It is just that before we had GPS no one knew it. If you're within 5% that is as accurate as possible. Car makers have no control over what tire size buyers put on their vehicles. And cannot account for tire wear changing the diameters.

 

marshall......wow ;0)

 

Yes speedo and mpg are off.
The dash calc is not very precise, more of a trend. Do the math on 5 tanks.

 

well....i measured my speed with my local radar signs in my area....speedo says 30mph. radar says 30mph...so i guess bigger 265 put speedo where it should be...

 

Go through it at 65 mph and report back.

 

I went to 265/75 16 last week and brought my gps along for a ride. Was surprised to see there wasn’t a difference in speed comparing dash and gps like @Marshall R states. This was at both city speeds and highway speeds. I think I drove about 45 miles round trip checking.

As for mpg, made the first long trip this week. Wife drove the truck because I met up with them after work. Truck only got 15 something mpg on a 180 trip. I’ll dive the truck back home and drive in S mode to see if there’s a difference. Won’t be the exact same conditions, but just to see what I can get.

 

I changed mine last year from 245’s to 265’s and lost about 1-2 mpg, no big deal and yes the speedometer is off by less than 3%, no worries...

 

Love it! I do math good....

245/75 16 is 30.47" calculates to a 30.47" tall tire. 265/75 16 is a 31.65" tall tire. 3.7% taller. If your speedo says your Taco is going 50 when your GPS says your going 52, its a 3.8% difference. Close enough.

You can calculate your MPG by resetting the trip at fill ups. Take that mileage traveled on the next fill and multiply it by 1.04, then divide by the number of gallons pumped in.

 

i went faster on local police radar. speed limit is posted 30mph. but after 30mph radar flashes slow down...no speed reading....