I switched to 70s from the 65s keeping my 17" rims.
It seems like my gas milage has really fallen off.
It used to predict 420 mi from a tank, and I used to get close to that.
Now it predicts 380 to a tank, and I'm a little below that.
ANyone else seen this? I would have thought my milage went up.
I know my speedometer is off now, because of the larger tire, but it still seems like I'm not going as far on a tank.
I had some engine light issues, but I did a disconnect on the battery cable, and the light went out and has not come back on. Maybe something else is effecting my milage..
Just curious what everyone else is getting..
Thanks,
Jeff

 

jeff,

welcome to yotatech. what you are experiencing is normal.

Here are some of the reasons why:
1. tire is larger and therefore it's heavier (takes more energy to make your vehicle move forward)
2. tire is larger (circumference) and all calculations will be off. this includes speedo, tripo, fuel consumption, fuel calculations

What does this mean in real world terms:
you've probably lost approximately 2-5% if that in real world calculations. remember that the ecu calculations are based on the tire size being the same so the error margin is greatly amplified. either way it's not a big loss.

No clue on the cel (check engine light).

good luck and WOW 140k!

 

Did you make the tire change recently? You will always lose MPG in the winter months, so depending on how you are measuring (where you got your benchmark), this could be a contributor as well.

 

Have you corrected that 380 miles for the bigger tires. Your odometer is off as well as the speedo. Find the precentage increase in tire diameter and add that percentage to the 380.

 

I can't remember the last time I got 380 to a tank. Ah, the memories.

 

Thanks for the feedback.
I need to do the calculations to see what is really happening. I also think the colder weather is having its effect.
I was surprised, I thought lower rpms at the same speeds with the bigger tires. (Ive backed off a little going down the highway.) It just surprised me that it decreased..
Thanks

 

FWIW... I went from getting about 360miles on a tank to getting about 330miles on a tank when I made the same switch. I'm not filling up anymore, so I don't think the switch to larger (and more aggressive) tires really screwed up my MPG that much.
The computer reads about 1.5mpg lower.... Though it was always off anyway. FWIW, my watch has a Tachymeter and I have measured the spedo against mile markers and they are usually exact. of course, the mile markers probably are not very on either.

 

The speedo wont be off top much-tops 1-3mph or so. The trip odo and your odo will be off about 1.5-2 miles.

 

Well the speedo and trip odo are generally off the same, and its a percentage, not a flat number.... 65 to 70, about a 5% larger tire. MFGR websites can give you exact numbers. You will need to add 5% to your speedo, and trip odo... The 380 til empty will correspond with 380 on the trip odo, but your really traveling more like 399, its better...

Also its going to be heavier, one its larger.. two OEM tires are 4ply.. Most, if not all, 265/70/17's are 6ply rating, or 8ply rating. So that could be as much as 15-20lbs a tire....

 

What is the factory speedo error from Toyota?

 

you used to get 360miles/tank in your V8 4r? by your signature line, we have the exact same 4r. 2003 limited v8. im lucky if i get 310miles/tank and im bone stock and on avg i drive 65-70mph on the freeway (no joke, im used to driving my 91 p/u with 35s which was hella slow) and no lead foot.

 

Now that the weather has warmed up my milage has improved.
I'm closer to 370 on a tank it was as low as 330 when we were at 10 to 20 degrees.
Of course, now I'm at the shop getting my A/C checked. No cold air, and the A/C light blinks on and off.
I still think the new tires will hold up longer, although they ride a little rougher.
Jeff
I also hit 148,000 last week...