Hacker News Reader

Comment by ams6110 | Hacker News Reader

Most people that spend their full salary do never put more than 20$ of gas at a time. At the end, they spend around the same amount than others, but they seem to prefer to go the gas station many times instead of just filling up the tank.

When gas prices are volatile this actually makes sense. It's the same principle as "dollar cost averaging" when you buy stocks. Purchase a fixed dollar amount, and you end up buying more when the price is low, and less when the price is high, which is what you want to do. Therefore when I buy gas I stop at $25 unless I have a coupon or I'm somwhere that prices are significantly lower than where i normally buy (prices vary by $0.50--$0.75/gal within a 50 mile radius).

View on HN

This is a fair point, but more often than not people living paycheck to paycheck aren't as familiar with dollar cost averaging and are probably just buying in $20 amounts because that's how much cash they have at that time.

The OP also said it was based on 5+ years worth of data which probably means it is less about gas price fluctuations and more about buying habits.

I apologize for being dense, but what data exactly is the OP crunching here?

Internal private data. We don't know exactly what it is and he can't say.

Really, in the end, this is little more than a moderately well-sourced anecdote.

Thanks jerf, I have no idea why this made the front page. Clearly I have a lot to learn.

It has a pretty graph at the top and the guy presumably really did crunch real data, so it gets upvoted. Also it's Brazilian, so it gives you a little taste of 21st-century BRIC economics. Hits a lot of buzzers.

That would a case of people doing this to counter volatile prices if people also took advantage of the quite low gas prices they chance upon to fill it their car up completely.

But what the article says is that they don't put more the $20 at a time, period.

Such a behavior wouldn't see any advantage given volatile prices, because in the end you end up paying the same (you pay lower at some times, higher at other).

Which is the article points too: that they see the guys doing that end up paying the same amounts as the guys filling it up normally.

So it's not the volatile prices that get people doing that, it's perhaps a false idea of saving money, or that they infact do not have that much lying around and try to get to the end of week accounting for any emergency.

DucktourDreams: Your account is disabled and very few people can read what you wrote.

You should either sign up with a different account or email pg and ask for your account to be reinstated.

I've been there, and that was the case for me. You just don't commit resources to a full tank of gas, you never know what might come up. Sucks.

I had a very difficult period* years ago while trying to finish a masters in NY (never finished it), I did something similar. I would never spend any cash, I would keep it until the last moment because it gave me options.

I believe people do this because, in case of an emergency, they can switch to public transportation and use that cash for something else.

*Difficult period: I had money for one meal a day. Didn't have money to pay for two subway rides so I would walk 6 miles a day to walk from the campus to the place I was living (which was a garage's attic).

Also if the probability that your car is going to breakdown before the tank is empty is significant it doesn't make sense to fill up. At a certain point the fuel may be worth more than the car.

The scrap value of a car is several hundred dollars, a street legal car that runs is always at least a grand.

sadly it depends on location, i understand that a 'street legal running car' in the rust belt can go for $250.

This has another benefit as well - you're not burning more gas just to carry around gas that you're going to use later. If you had a 20 gallon tank and put 7 gallons in at a time, that's 13 gallons (x 6 lb/gal) you are carrying around needlessly - 78 pounds at its peak.

Or as xkcd puts it, "a fundamental and central problem in rocket science: Fuel makes you heavier." [1]

[1] http://what-if.xkcd.com/21/

An interesting idea, but I would be amazed if even 1% of the population took that into consideration. I'd never even though of that before.

Besides, a car weighs about 2500 pounds (more in the case of a van or SUV). That 13 gallons would only increase the weight of the vehicle by 3%. I'd be willing to bet you would get more fuel efficiency by just slowing down 3 mph than you would get from keeping your tank only partially filled.

It has a downside too. When your tank is full of gasoline, due to gasoline's tendency to absorb water, the walls of the tank are not exposed to air or water. This helps prevent rust. When your tank is empty, the walls are exposed to water vapor and air, and can rust.

Another downside: if your tank is always half-full, you'll need to burn more fuel making more frequent stops at the gas station.

Been there done this. As a college student, when I only had $20 to my name didn't spend 50% of my capital on gas. I spent enough to make it to the party.

Reply on news.ycombinator.com