355 rears?

Tried slowing down to 65mph?

Calculate and track your average miles per day - if you have to run at 70 mph all day and can’t return a good profit then re-examine the business model.

 

Yes it will increase your mileage. Less RPM's equal more MPG.

 

well not exactly. it takes a certain amount of energy to overcome resistance. wind/weight ect. if your moving your rpm into a range that the engine is more efficient, you will gain fuel economy if you move it into a rpm that is less efficient you will loose mpg. lowering rpm does not necessarily mean better mpg.

i would look up what the manufactures recommended cruse rpm is for that generation of that engine. and go from there. im not sure where a 09 isx would want to be but its been a while sense the last isx i drove but i seem to remember it wanting to be in that 14-1500 range.

 

My ISX runs at 1250 to 1300 all day long. I have 3.58 rears & 10 speed. 58 MPH is about 1300 or just under. Now I spend about half my time in California, and the west coast mountain ranges, so this is very good for me. Average is about 8 MPG.

If your running East & West those tall 2.somethings are very good and he will get 8 all day and still be able to go faster.

He has a 13 so the hills won't bother him much. Yes he will climb the big hills slower, but overall he'll go way up.

 

Good cheap way to test a gearing change is to go from LP22.5's to 11R22.5's the next time you buy tires...be like putting in 3.36 gears but doesn't cost any more than the tires you were needing to buy anyway. And if you don't like it, swap back when you need tires again.

 

Interesting.

 

I'm not an expert but I wouldn't think that would truly have the same full effect as swapping gear ratios seeing that a taller sidewall would increase rolling resistance

 

Changing from lopro to tall is like changing rear ends. The smaller the tire the slower it will run at a given Rpm than a tall tire