Myth: If It's On CNN It Must Be Correct

This article is entitled 6 Gas Saving Myths. I'll give kudos to the author for correcting some popular misconceptions but some of what he says is just wrong. Let's take a look.

#1. Fill your tank in the morning

Yep, this one is pure crap. The idea is that gas is colder in the morning and therefore more dense so you get more for your money which would be true if the temperature in the underground tank actually varied more than insignificantly during the day.

The best you can do is avoid filling up on hot days while or just after a tanker has unloaded it warm fuel.

#2. Change your air filter

I agree. On modern cars this is total crap.

#3. Use premium fuel

Again, agreed. If you car will run on regular, your just wasting money with premium.

#4. Pump up your tires

Uhm, let me come back to this one.

#5. To A/C or not A/C

Really the question is A/C vs. open windows. As he even states himself, turning of the A/C but not opening the windows will save you gas. It's just a question of comfort. (I'll take comfort, thanks.)

#6. Bolt-ons and pour-ins

Very good explanation here. These are all bull. The only alternative is a conspiracy of all gas and/or car producers. Anyone that believes that should have their tires slashed with Occam's Razor.

So, back to #4. Here's what the author says:

According to on-the-road driving tests by both Consumer Reports and auto information site Edmunds.com, underinflated tires reduce fuel economy, so proper inflation is key.

But you should never over-inflate your tires. They'll get you slightly better fuel economy because there will be less tread touching the road, reducing friction. But that means less grip for braking and turning. The added risk of a crash isn't worth the extra mile a gallon you might gain.

My first issue is that he is clearly stating (correctly) that increasing your tire pressure will improve mileage even though the "myth" is that pumping up your tires won't increase your mileage. WTF?

But let's say that his point is simply that it's not worth the risk because you have less traction. That would be a great point if it wasn't wrong.

Pumping up your tires decrease the rolling friction of your tires, not the gripping friction (traction). Here's the introductory physics that show this. Suppose your car weighs 3600# and your tires are inflated to 30psi. For simplicity, assume ideal tires. you therefore have 3600/30 (pounds/pounds/inch^2) = 120 inch^2 of tire contacting the road. Each square inch supports 30 lbs.

If you pump the tires up to 40psi then you'd now have only 3600/40 = 90 inch^2 of tire contacting the road but each square inch supports 40 lbs! Your overall amount of traction remains the same!

OK. Physics lesson over. The downsides to pumping up your tires are: harder ride, louder ride. If you pump them over the safe limit then you have safety issues. Don't do that! Also, underinflated tires increase rolling friction which could overheat your tires causing them to fail. Don't do that either!

I was hoping to have some data on my experiment with higher tire pressures but I want to wait until I get down to half a tank before filling back up and that is taking much longer than usual.