I stand by my statement. We bought the tires right before a 2000 mile trip and I immediately noticed the difference in fuel economy and it has never equaled what the van used to get on any of the old sets of tires.
I'm not trying to start a you know what contest but the tires were the only thing that changed when the mileage dropped.

 

Please know I am not in any way disputing the MPG results you saw before and after tire purchase. See table I in link which speaks the typical 3% difference in economy between premium radials vs green LRR's (Low Rolling Resistance). This would equate to less than 1MPG. Therefore the gas mileage drop you experienced came from something else, not tire type.

http://www.energy.ca.gov/reports/200...-001CRVOL2.PDF


Tire pressure has the greatest impact on economy. Fuel economy drops by approx 0.4% per psi! This means 7 psi does more than special, high efficiency green tires.

Basically I am disputing the primitive, unscientific test method you use to compare tire economy. Any time somebody touches your wheels or tires, the first sin that gets corrected is low air pressure. I am not surprised that you noticed a change in economy after a tire change. A change in pressure of just a few pounds means a lot.

The change you saw simply can't be attributed to tire model/type. This sort of test method doesn't work . I was a lab test engineer for Gulf R&D 30+ years ago so I understand a bit about test error, repeatability and variables. A tire efficiency comparison requires a control study with all other variables removed. Tires are not the only variable, as you claim. To begin with, vehicle condition and usage is not being held as a constant when your're driving around and your vehicle has aged over 40K mi.

Tire manufacturers have published fuel economy comparisons for the various techologies and graphs showing econnomy as a function of air pressure.

Tire technology does not result in the 10+% difference you saw. The best to worst will show a single digit percentage span and we're talking bias vs best green radials, not two premium radials. I would suggest reading some tire techology articles to get a better handle on what tires can actually do beyond some wag based upon somebody randomly driving around to and fro with different oils, gas, hills, roads, weatehr, temps, vehicle condition, etc. What I'm trying to say is you don't know more about tire efficiency than Michelin or Goodyear lol.

Unscientific studies are what got millions of multi-electrode spark plugs sold to suckers based upon a half dozen "unpaid testimonies" suggested gains of 10% or more in power and economy. Lawsuits and facts finally put an end to it, but not after companies like splitfire made millions and almost put legitimate companies out of business.

Tirew pressure will have the greatest effect. You didn't even mention what the pressure was in the old tires before they were removed. In all liklihood they were low. You also probably changed the brakes more than once. They tend to stick and drag, throwing a wrench in any econnomy testing data.

 

More tire thoughts:

http://yokohama-media.unitedfuture.c...etin-final.pdf

Mileage and $'s saved claims are on the 2nd page. I would think that with the brick wall aerodynamics of the vans the air resistance is going to dominate the mpg equation. Regardless, they look to be great tires for the money and I have them on 3 of my cars now (T&C, Elantra, Spectra). Most important - keep the tires inflated on the high end of the psi range.

There are claims of tire life and mpg savings from having very well balanced tires. There are dynamic solutions to wheel balancing such as Dyna beads, Counteract beads, various low freezing point fluids and even straight antifreeze, etc. Those strategies appear to be more relevant to big trucks tires but might be worth investigating. Again, I think with these vans, you are limited first by aerodynamics and then the fundamental characteristics of the engine and transmission. I did put a K&N air filter on my van, can't say it helped mpg at all, I just like the reusable product.

 

Yesterday we made a trip to Québec city from Montréal, 263 km (160 miles). Strong winds, about 60 km/h (little less than 40 mph). I reset the computer and we saw 7.6 L/ 100 km (about 31 mpg).

Reset before going home, wind upfront : 8.2 L/ 100 km (29.7 jpg). A 8 % difference.

 

Hi all and thanks for the suggestions. On that trip I originally posted about I got over 24mpg, and that included a section of interstate that took me up and over the highest point in PA (not sure if it's that high, but it was a lot of up hill).

Seriously I think I'm looking at between a 2-4 mpg increase, if not 3-5. It was a big jump just by doing the basics; oil change, air filter, tire pressure, and a couple other suggestions, and the improvement seems to have lasted, whether around town or highway.

I'd love to get more though!

 

changing oil won't matter unless you're switching from dino to full syn. Used oil is thinner and typically results in marginally less friction than fresh.

tire pressure means a lot. This is the #1 service-related opportunity to increase mileage. Tire type from worst generic to best green type will only affect mileage 3% (less than 1 mpg).

Driving behavior means a lot. My wife gets 17 mpg on the exact same suburban drives that I see 21 MPG. She does not maintain constant speed, foot is constantly on the brake or throttle.

any misfire from leaky wires or old 100+K mi plugs will hurt mileage. Brake jobs & gas aren't cheap either. Proper brake maintenance includes cleaning and greasing floating hardware, springs and pins. Skipping these service steps when replacing pads or rotors will cause brakes to drag continuously.

Air filters typically don't create significant restriction until they see 50K mi or more. However if you live in a dusty area driving on dirt roads, the air filter could clog every 10K.

dragging brakes that wear out in less than 20K mi will definitely hurt gas mileage.

A roof-top cargo carrier will kill mileage by several mpg. Any GC owner who needs one of those has a huge family or they are packing too heavy. I used one to drive 8 hrs to the beach and camp for a week (5 people, tents, supplies plus 5 bikes). Try carrying that in an SUV lol. With rooftop carrier, mileage dropped 2-3 MPG.

Keep highway cruise speed at or under 65MPH. Above that, the GC is a brick that must work harder to push air.

 

You are not using enough fuel to get an accurate reading. There is too much variation in gas tank loading, gas station pad level, and pump shutoff point with gas in filler neck. The error could exceed 1 liter which is over 10%. You need to burn a full tank of fuel to get within 5% measurement accuracy.