I'm in the same boat. I put 285/60/18's on my '97 4.6 and lost a little hp. Hopefully I'm getting the filter/chip/exhaust combo soon. I'm expecting to get the hp back and then some.

Is your tire height going to stay the same? If so, you wont lose much hp at all. My tires are 2.5 inches taller than stock which is the main contributor of the lose of power.

Let me know how it turns out if you get the /chip/exhaust.

josh

 

I've heard that switching to 285's makes the truck slower because of the overall ratio change. I have a 5.4 with a K&N FIPK, if I switch to 285's (from 255/70) and add a superchip and exhaust at the same time, will that erase some of the performance loss from the larger tires?

If so, how much?


------------------
2000 F-150 XLT, 5.4L, 4x4, auto, Extended Cab, Deep Wedgewood Blue, 3.55, Towing Package, Sliding window, CD player, 4 wheel abs/discs, 255/70/16's, build date 11/99, bedmat, K&N Filter and more to come

 

What is the new tire aspect ratio; 285 is tread width in mm. Overall "height" will be the performance factor that changes.

------------------
2000 F-150 XL,RC,LB,5.4,4R70W,3.55LS,
Class III tow/Payload #3/Convenience pkgs.,
4-wheel disc/ABS,Chestnut/Parchment 40/60,
Ford bedliner & gas/wheel/spare locks,
3" cold air box modification, Superchip,
Dynomax ultra-flow welded 3" cat-back,
3" exit Y-pipe, Hellwig rear anti-sway bar.

 

You have not lost any power from the engine. You are just losing torque basically. It is like installing taller gears. You need some shorter gears to offset the larger tire size.