Lower Gear ratio better mpg?

[Riff Raff]

Thanx PK, you're right on target. The main problem is the tires-- you're running 255/55R18 (29" O.D.) which are smaller in diameter than the OEM tire of 245/60R18 (29.5" O.D.). Thus, your current smaller diameter tires are rotating 1.8% more than OEM causing your VX to consume more fuel (less MPG) for the same distance traveled.

Instead of changing the differential ratios, a better solution for more Highway MPG is to go to a tire that meets three(3) criteria:

1. Must be "tall" in O.D. between 32" -- 35" O.D. to act like a transmission Overdrive thereby reducing engine RPM's (saving fuel) for the same given forward speed of travel.
2. Must be "narrow" in width to create less drag/rolling resistance. The skinnier, the better.
3. Must be "lightweight" to reduce unsprung weight and use less fuel from standing start/launch.

Here are some optional tire sizes that meet the above criteria (tall, narrow, lightweight):

P255/70R18 (32.1" O.D./35 lbs) - bolt-on perfect with OEM rims.
P265/70R18 (32.6" O.D./44 lbs) - slight trimming required.
P275/70R18 (33.0" O.D./46 lbs) - more trimming required. (recommended tire: BFG - Rugged Trail)

To minimize fitment problems, utilize your stock OEM 18x7 rims for the above listed tires. Use only "P"-series tires (aka Passenger/P-Metric) which are lighter in overall weight, and stay away from heavy "LT"-series (Light-Truck) tires.

For the absolute extreme gas saving tire, you could use:
35/10.0-15 (35" O.D./48 lbs) - lifting required. (recommended tire: MickeyThompson - Baja Pro, which is a Sand-Rail tire and not DOT approved for the street. Use 15" super lightweight CenterLine brand wheels to keep weight to a minimum)

Focus on changing to a taller O.D. of your tires, not the gearing in your differentials. Then drive your VX like you are hauling very fragile eggs; be featherlight on the gas pedal, and let off the gas pedal early before coming to a stop. You'll be amazed at how much your MPG will improve.

[Triathlete]

(recommended tire: BFG - Rugged Trail)

Everyone I know that has bought these tires has complained about how quickly they wear. Just a FYI.

[VX KAT]

We all know this vehicle isn't cheap on fuel. Is it just me, or are others surprised how some are willing to invest serious coin to modify something or buy a different vehicle to get a few more MPGs...have you ever calculated the break even point on that cost?

Let's assume you do some modification that costs $1,000,and it increases MPG from 16 to 20 MPG....a full 25% increase, which is doubtful.
16MPG x 22.5 gallons = 360 miles per tankful
20MPG x 22.5 gallons = 450 miles per tankful
If fuel is $2.95/gallon, you gain 90 extra miles per full tank
90 miles ÷ 20MPG = 4.5 gallons to travel that far
$2.95/gallon x 4.5 gallons = $13.27 saved on a full tank
Another way of looking at it is you save .029/mile.....

$1,000 ÷$13.27 = 75.35 tankfuls....for most, filling up every 2 weeks, that would take 3-4 yrs to just break even.....and only then would you begin saving any money

Maybe for tracking MPG, you might look into registering at fuelly.com. It's kinda fun. Here's my VX:
http://www.fuelly.com/driver/vxkat/vehicross

[Riff Raff]

Everyone I know that has bought these tires has complained about how quickly they wear. Just a FYI.

Billy--- The BFG - Rugged Trail only has 10/32nds tread depth when they're brand new off the shelf. So compared to say a General - Grabber AT2 which has 17/32nds brand new-- then yes, the BFG - Rugged Trail will have a short life right from the start.

What makes the BFG - Rugged Trail so unique is it's the ONLY "P"-series tire made in size 275/70R18 with a tall O.D. of 33" and only weighs a featherlight 46 lbs each. Take a peek at TireRack.com for all tires made in 275/70R18 (33" O.D.) and you'll quickly discover that all of the rest are much heavier "LT"-series tires easily weighing 10 lbs more in the ballpark of 56 lbs each.

Remember; for best MPG we want tall O.D., narrow width, and super lightweight all combined in one tire. Class dismissed.

[Scott Harness]

Nice thread-info...have you guys drank too much coffee?

[Ldub]

OK. Thats it! I'm getting a new ring and pinion set. Yes I know I will need two sets but mine is only 2wd unless put into 4wd manually. I get 15-17 mpg city. I'm thinking down to 3.20's any suggestions?

Thanx PK, you're right on target. The main problem is the tires-- you're running 255/55R18 (29" O.D.) which are smaller in diameter than the OEM tire of 245/60R18 (29.5" O.D.). Thus, your current smaller diameter tires are rotating 1.8% more than OEM causing your VX to consume more fuel (less MPG) for the same distance traveled.

AND...

Unless you're already factoring in 1.8 - 2% less miles on the number of miles driven per tank, you're not getting 15-17 mpg...