Just wondering if a 4" lift 92" lift in springs 2" lift in tyres) will make much difference in millage ? also will it be harder on front end parts?

 

Typically a lift will cause mileage to go down a bit. If you get a 4" lift, you should also get an adjustable track bar or drop bracket for the track bar, and a drop pitman arm.

The lift won't be harder on the front end parts, but if you put larger, wider tires on, it can be.

 

I'm running a 4" lift. At first i was running 285 75R16s and the mileage was decent. Not as good as my 2WD PSD that I used to have (that truck got 20+ MPG consistently) but it was ok, somewhere around 17 MPG on the freeway.

Then I decided to put bigger tires on. Went with 315 75R16s and the mileage really fell off. I haven't checked it in a while but I'm sure it's down around 15 MPG or a little less.

As far as front end parts, I haven't noticed too much trouble. I've had to replace a pitman arm but since installing a Bilstein steering stabilizer that's not so bad anymore.

 

I have a fith wheeler that is not sitting level. I was going to raise the suspension 2" and then go from 33" tyres 285/75/16 to 37" tyres 255/75/22.5 (changing gearing to suit). Does anyone think this will kill the mileage?

The other thing I could do is raise the hitch pushing the front of the trailer up into the air (much cheaper) but will mess with mileage?

 

When you decide to lift your truck and put bigger tires on it the thing you'll notice is your speedo will be way off... The more it's off the worse reading you'll get. I can still get 16 mpg with my setup but average 13 and I do not baby it. My speedo is also calibrated.
Big tires like mine and high ratio gears are horrible for mileage and my truck is about the worse case scenario

 

I have a 6" lift with 325s and 4.56s and I average 11 to 12 around city and freeway, max I've see is 13 but I bought it in November so we'll see in the summer.