What size tires are you guys running? I just bought new tires today (265/70/17). I had 305/70/17 on them earlier. When I put the stock size back on the speedo was still way off.

1. Why would this be happening?

2. What kind of mileage can I expect with these tires?

Thanks,

Eric

 

Filled up this morning and did my math. I'm up to 17.43MPG's so far with the addition of pulleys, Ford Racing Lightning style exhaust, Mobil 1 10w-30(380.2 miles). I'm looking forward to see if the early AM fill up will change anything with the "cooler denser" fuel over the midday fills. I have no doubt with a few more things added/changed (newer better spark plugs, e-fan, CAI, trans flush, X-CAL 2, maybe coil packs) I will get 20+mpgs religiously.

Once again I know I have a 4.6l but the same theory applies to any engine.

 

I'M PRETTY SURE IT HAS SOMETHING TO DO WITH THE WEIGHT OF THE TRUCKS COMPARED TO THE MUSTANG.

 

I've got a '98 F-150 with a 2003 4.2L V6, Bosch platinum plugs, Ford Racing coil pack and wires, Motorcraft synthetic oil, and a very very dirty stock filter and I'm getting 18 city/22 hwy. My next in line is replace stock filter with K&N Series 77 cold air intake. Says it adds about 10 hp and increases 30% fuel economy. My cousin has a '04 Dodge Dakota with a 4.7L V8 and a K&N cheapo intake and with him doing burnouts and drag racing at street lights gets 16 but highway 22.....odd?

 

There is no way a CAI will increase your gas mileage by 30%. *MAYBE* 5% if you are lucky - if you can keep your foot out of the firewall to hear it howl - and probably not even that if you are already getting 18/22, which is 2 MPG higher than EPA both city and highway.

Mine is stock except for a muffler replacement and a K&N dropin, and I've seen 23 mpg - and also seen 13 mpg.

 

I average about 375 miles to a full tank, and I use my truck as a work truck and usually carry about 200-400 pounds of equipment in it and I have a CAI and thats it as far as engine upgrades. I am running 255/70/16 tires and I also have a cover on the bed which helps on wind drag. I also have the 3.55 rearend.