Monday, July 28, 2008

Hypermiling Update - Nitrogen Tires

I haven't posted on Hypermiling for a little while, for a couple of reasons. The first is that my telecommuting on Wednesdays has cut down on my weekly fuel efficiency somewhat. 5 long round trips a week grants better average miles per gallon than 4 round trips plus scattered city driving on the off days. The second reason is that my wife filled up my tank, and instead of resetting the trip-ometer, she reset my average mpg gauge. I had to start from scratch on the hypermiling. I think ultimately this was good, as it now only reflects my driving, and not the previous owner. I am almost back into the 25s again, so it seems it was fairly accurate the first time.

I am writing now to tell you about something new I am trying. Ultimately hypermiling is a cumulative thing. It takes a combination of behaviors and tactics to get optimal results. The latest tactic I am trying is the replacement of standard air in my tires.

The Oxygen in a typical tire fillup contributes to a number of problems. One, it is combustible. This means it can explode. Two, it causes oxidation on the metal rims and other parts of the wheel. This means rust. Three, it causes the tires to run at a hotter temperature, which contributes to tire breakdown and pressure loss. The solution? Fill your tires with Nitrogen.

Nitrogen is the most common molecule in the air we breath. It is a larger molecule than Oxygen, so if your tire does leak it is harder for Nitrogen to escape. Nitrogen does not heat up as quickly as Oxygen, and apparently is not as combustible. This means a safer experience all around.

Where Nitrogen fits into the hypermiling mold is the consistency of tire pressure. As a typically-filled tire begins to lose air, the car has to work harder to get from point A to point B. When Nitrogen enters the tire, it leaks 3-4 times less quickly, so you maintain a consistent tire pressure for a longer period of time. The better your tire pressure, the better the mileage per gallon.

Today was my first day of commuting on Nitrogen-filled tires. I will report next week how things go, and if I notice a tangible difference.

Until then, happy hypermiling.


Vixen said...

My van came with green caps on the tires, which they said meant the tires were filled with nitrogen. But where the heck to you get them filled up?


fwaggle said...

@vixen: many tire places will be able to fill them up for you - they'll often have big signs "fill your tires with nitrogen".

you can also purchase bottled nitrogen yourself, and along with the correct regulator(s) and fittings, i'd imagine you could fill them yourself in the workshop. not sure how many fills it'd take before you'd start to see cost savings, with the cost of the regulators (i think if you have two, one to step the bottle down to say, 50-100, and the other for setting your desired tire pressure, then you can just connect it and let it equalize out, the second regulator will have an easier time - but my experience with high pressure gasses is pretty limited) and the deposit on the bottle, it might be cheaper just to find a tire place and cruise over there for a pressure check every so often.

Vixen said...

Thanks for the info Fwaggle. I haven't been able to find a shop that has it in my area yet, so maybe I will see about buying a bottle and doing it myself.