Fuel Economy: Tire Changes & Engine Changes Affect MPG

With the cost of gasoline almost triple what it was just a short time ago, there have been a rash of folks freaking out about how crappy their Vanagon's MPG is. Many comments have come from our customers that have installed GoWesty 15” or 16” wheel packages, and/or have gone to a higher output GoWesty engine.  Now they are second guessing the wisdom of making changes to their Vanagons that may have reduced the vehicle’s efficiency. Let me take the opportunity here to put these issues to rest.

Wheel and Tire Change

Changing from 14” wheels to either the GoWesty 15” or 16” wheel/tire package:

When this change is made, the odometer on your Vanagon started registering much more accurately than it did with your old 14"s. It is typical for the odometer on a Vanagon with 14” wheels to read anywhere from 4% to 8% TOO MUCH. With the GoWesty wheel package, it is reading about 0-2% TOO LOW. So, if you add up the worst case, you can attribute as much as 10% of the change between your old MPG and the new MPG to simply the change in the actual odometer reading. So, if with your old set-up you were able to get, say, 300 miles on a full tank (yeah, in your dreams!), now you get only 270. No, the vehicle is not getting worse mileage, the odometer is just reading more accurately. That is, you never really went 300 miles on that tank of gas, and you never really got 20+ MPG.

So what about the new tires? Aren’t they heavier and wider? Does that not cause more drag? This must cause a decrease in mileage, right? Answer: NO. First of all, the increase in weight is pretty negligible. We are talking maybe 20% more, max. Furthermore, whatever more the tire and wheel weighs makes them consume more energy when accelerated to speed. But once there, the energy is stored in the rotating assembly as kinetic energy and takes no more energy to maintain at a given speed. When climbing a hill, the energy stored is transferred back to the entire vehicle’s kinetic energy, and actually helps keep the vehicle moving, reducing what is needed from the engine. With respect to the width of the tire and whatever more aerodynamic drag they may create: Come on! We are talking about a brick on wheels here, after all. Compared to the poor coefficient of drag (CD) of the Vanagon’s shape, and its sheer size, the increase in air drag that the wider tires makes is totally negligible.

The fact about the switch to the our recommended tires is that there is no down side. We offer only the most cutting edge, longest lasting tires on the market, and there is just no way the change to a 15” or 16” tire from ANY 14” tire rated for a Vanagon can possibly cause a decrease in overall efficiency. None.

Engine Change

Changing from the anemic 2.1 or even more anemic 1.9 to a GoWesty 2.2, 2.3, 2.45, or 2.7 high output engine:

There is nothing about any of our larger displacement, higher output engines that would cause them to be less efficient. All of these engines are more efficient than the original design due to the fact that all have higher compression ratios (CR). The larger the engine, the higher the compression ratio, the more fuel efficient it is. It is a basic principle of any reciprocating piston, internal combustion engine: efficiency is directly related to the engine’s CR, all other things equal. The 2.2 liter has a CR that is only 2% higher. The 2.3 is 5% higher, the 2.45 is 9% higher, and the 2.7 has a CR that is 16% higher that the original 2.1 liter design.

The problem is that most people don’t understand what efficiency means. More efficient does not necessarily mean that one engine can produce a higher output and use less fuel. Higher efficiency means that one engine can do the same amount of work and use less fuel. That is, if asked to do the same work, any of our engines will do that and use the same—or even less—fuel. The main reason folks get less MPG is because they ask the engine to do more work than they asked of their original engine: faster acceleration, higher speeds.  It is easy to get used to power. Anybody who has experimented with tuning a vehicle knows that whenever better performance is achieved, in short order it just does not seem as drastic an improvement as originally opined. One takes for granted the ability to get going faster, and keep up higher speeds, especially climbing hills. And, that takes more fuel.

Beyond those excuses, we are finding people are actually starting to bust out calculators much more often, and are now accurately figuring out their MPG precisely. It’s like when you get a HUGE bar tab: “How many beers did I drink?” Now that it costs $75 to fill that tank, and, what, “That only got me 225 miles!” There is a major freak-out about the cost to run a Vanagon, and it is valid since they are and always have been quite the gas hog when compared to regular cars in general. But considering their extreme usefulness and function, they are quite efficient.

For more on fuel consumption, please read this article.