I was wondering if any of you 4x4 guys have ran before and after a tire swap.

I swapped out my stock tires 265/75/16? for a set of 285/75/16 which are wider and taller by about an inch or more and the truck is getting worse gas milage (fixed tire height in HPP3) and feels slower. I have not G-Tech'd it after the tire swap to see if my ETs are the same or not but I plan on going to the track tonight and have a feeling my ETs are gona suck with these new tires. <img border="0" title="" alt="[Frown]" src="gr_sad.gif" />

 

the tire diameter changes your overall gear to the ground the 1" or so bigger tire gives you a higher gear ratio. ive seen the mathematical formula for determining your overal gear ratio (transmision in each gear,rear end,and tire diameter)but i cant remember what the site was if you do a search im sure you will find it.

 

Ugg,

These things killed my ET!

I ran 2 G-Tech runs before i went to the track and netted a 15.76 and a 15.82. On the same streach of road I usually run at. Temp is about 15deg warmer and more humid but not enough of a diff. to run 3-4ths slower than normal.

I went to the track afterwards and ended up running 15.91@88mph 2.4 60'. This thing will not get out of its own way off the line. I also noticed I cross the traps about 300rpm or so sooner than I used to.

I am assuming the higher effective gear ratio and the extra weight of the tires (rotational mass) is what killed it. So suffice to say I will be selling these tires and buying a stock sized set before my converter and headers come in. <img border="0" title="" alt="[Frown]" src="gr_sad.gif" />

 

The 285s look better on a Z71, but they sure take a toll in the performance division. I too noticed a loss of gas mileage when I went to 285s (from stock my 245s). I am down to 265s now and am pleased. I cant say that they are much faster though. With the 285s, I would regularly get 2.5 60's and 10.4s in the 1/8th.