My '97 F150 supercab with 4.6 auto trans gets only 10 mpg. I do have 32inch tires, but this seems way too low. I don't drive with a heavy foot, and I am wondering if there could be some cause to this poor mileage. With the bigger tires could the gearing be off? It also seems to bog when switching gears...especially on hills. Any advice would be much appriciated.

Thanks, Doug

 

Here's the problem. Your truck came set-up at the factory with certain tire sizes and gearing. The Engineers at Ford put the optimum tire sizes for handling, hauling, ridability, gearing, performance and mileage. Probably several more factors. When you put too small or too large a size tire, you disrupt the variables. You might substantially increase performance and handling with a lower profile but kill a smooth ride and the ability to off-road.

What you've done is like going from a stock 4:10 rear ratio to a 2:55. Should give great mileage on a flat surface but getting you up to speed is slow and taxing on the engine. Every hill requires more gas as well.

I am assuming your tires are very over-sized?

Going up a size or 2 sometimes makes the vehicle do what the owner wants. Not the Engineer! Likewise going down a size.

Its like the slow trans shifting Ford incorporates into these new trucks and Expeditions. They did t to appeal to a wider range of people...WOMEN!
Tires can be the same way. They put on sizes that are not radical in any way but appeal to most drivers!

Hey, if all Ford trucks came with 32 inch tires, they would scare-off 90% of the type of people who buy Ford trucks! The other 10% are young and like over-sized tires for looks and off-roading!

Hope this helped....

 

Forgot to mention the fact that your computer is saying WHAT THE F*CK DID THIS GUY DO????

You are confusing it. Probably over compensating by thinking your towing or something.

Hopefully another person with knowledge of how the computer works in relation to gearing. Maybe Mike T?

 

THANKS FOR THE INFO! SO YOU'RE SAYING THAT ONE OF MY OPTIONS IS PUTTING THE ORIGINAL TIRE SIZE.? WHAT ABOUT CHECKING INTO CHANGING MY GEARING TO MATCH THE TIRES. AND IS MY 10 MPG ANY REASON TO THINK THAT SOMETHING ELSE COULD BE WRONG SOMEWHERE ELSE?THANKS AGAIN!

Doug

 

Have you taken into account the difference the oversized tires will make to your speedo/odo readings. I had a boss once that had huge tires on his (boo-hiss) Dodge pickup. He was constantly complaining about poor acceleration, excessive engine noise on the highway, poor fuel mileage, etc. etc.

When I finally had a ride in the thing it turned out he didn't compensate for the speedo difference. He drove at 70 - 80 mph on the highway (indicated) which was really around 90 - 100 (true). We were passing everything in sight. With an 11" suspension lift (he did his own engineering)and the 38 or 40" mudders he had on the thing I thought I was going to die in a massive roll-over.

Needless to say - it was slow to accelerate, had extreme noise on the highway, got very poor mileage and was an amazingly scary vehicle to ride in!