I'm driving a 1998 Blazer LS, but I keep getting told that you can actually increase gas mileage with larger tires. And multiple friends actually have done it. Wanting to know if they are just bluffing or if it's true. Also, what kind of lift would I need to fit 32's-33's?

 

Keep in mind that any gains are offset by an out of calibration speedo.

 

Yes, check out this tire comparison tool: https://tiresize.com/comparison/

Between 235/75R15s and 32/11.5R15 there is a 11% difference in circumference. Your speedometer won't know this. You can confirm by using a GPS.

 

With larger diameter tires you MAY increase cruising/highway mileage, but you'll likely lose MPG in the city due to reduced torque turning larger tires, making the engine work harder to get your truck up to speed while accelerating. The extra rolling resistance of heavier and wider tires will also reduce MPG.


I went up to 31" tires on my Sonoma, and have about a 50/50 mix highway/city driving and I saw 0 net change on my calculated MPG. I did have my speedometer/odometer calibrated for the taller tires, and am reasonably confident that my measurements are accurate.


On my Blazer I ran 32" tires and did about 80% highway driving on average. There I saw a 1 MPG increase vs stock tires. On tanks where I did mostly city driving I had a noticeable decrease in MPG vs stock tires.

 

It's physics. Takes more power to change the rotational velocity of a heavy tire/rim - both accelerating and slowing down.

 

"With larger diameter tires you MAY increase cruising/highway mileage"
The odometer will register less miles traveled for the same amount fuel, worse mileage by calculations, Actual mileage will be slightly better

 

Why so many responses on not being able to calibrate the speedo???

A simple tuner can be used to calibrate a change in tire size and also if you change gear ratios. I've been doing it for years as I went from the stock 31's to 33's and now I have 32's that I run during the winter.

So, yes, you CAN calibrate for the change in tire size and have your speedo read correctly and be able to compute you MPG. I do it twice a year at home with my tuner.

 

You've completely missed my statement that I did have the odometer (Via the ECU) calibrated to compensate for the different tire size and gear ratio. Simply done with an ECU flash or calibration tool. I've done this on all my vehicles where I've changed the tire height. My Odometer and speedometer are both accurate. therefore my fuel economy calculations were accurate. When I was doing the testing, I even travelled the same route, same distance, same driving style, filled at the same pump to the same level each time, over a period of 5 weeks.

 

[QUOTE=El_Beautor;688868]You've completely missed my statement that I did have the odometer (Via the ECU) calibrated to compensate for the different tire size and gear ratio.
I stand corrected, I must be blind.

 

Compare your tire sizes on this website, and multiply your total mileage by the percentage difference to get your actual miles traveled. https://www.miata.net/garage/tirecalc.html