i called my dealership about putting a bigger tire on my truck.

the service guy said things to keep in mind are that...

bigger tires=less gas mileage

bigger ties= throws off speedometer/odometer

i have an 03 stock v6 sport f150...stock 16" wheels...not sure of the tire size off hand, but its stock...was looking to put a 20" rim with 275/60/20 tire on...

how much would this impact my gas mileage? the service guy said about 5 mpg...does that sound accurate?

and how much would my speedometer be impacted?

how will this upgrade in size affect the long term life of my gears, powertrain etc?

thanks

 

To put it into perspective, if you can afford 20" wheels and the tires to go on them, then cost of a fuel economy hit is nothing to worry about.

5mpg sounds like complete BS to me.

 

That size tire will be about 33" tall. That will effect your odo/speedo calibration. The MPG difference would be due to the heavier wheel/tire combo, more rolling resistence with the wider tire and if you have anything lower the a 3.55 gear ratio, you'll burn more gas just to get moving from a stop. But, I don't think it'll be as bad a 5 mpg worse.. 1-2 mpg more then likely. The rest of the suspension will also have to bear this additional weight/resistence as well, so additional wear and tear could also be expected....

Your braking performance will suffer as well with the stock brakes.... Initially, the only reason to go to larger dia wheels was so you could fit bigger brakes. Then the larger wheels got popular because of how they looked, the brake side kinda got left behind... Don't know how many rigs I see with these huge dia wheels and then you look and they are running the puny stock brakes....

Anyway, I digress.... Good luck with the new wheels!

Mitch

 

As long as you accept the fact of driving slower than you have been, the engine shouldn't be affected.
If you drive it the same as you did with the stock setup the engine, especially the six, will have to work harder to maintain what you've been accustomed. You won't tell by the speedo if it's off but, the tach will tell you that.

 

Survey says... 5mpg BS..

 

Survey says my v6 still gets 12 mpg with stock gearing on 35's.

Stealership guy...wrong.

Since yours is an 03, your speedo and odo can be fixed by use of a chip. You can find a simple chip for like $265 if you look around. Regearing will bring your gas mileage to near stock.

 

Hey, I have the 5.4, 3:55 Rear end and 20" rims with 285/50/20 tires.

It was like this when I bought it, but I still get about 14mpg city and around 17 Interstate. I couldn't see it getting too much better than that with stock tires and wheels.

My stock brakes work fine with the 20" wheel, and I'm almost positive my speedo is correct. (Possibly could have been previously programed)