Every spring I see a lot of people asking many questions about fuel ratings, nitrogen air filled tires, vortex generators, etc...
I wanted to start this thread to educate people (It's what I do for a living) and provide solid, reliable, and applicable scientific evidence to help people navigate some of the sales pitches we get. If you have more information to add, please feel free, but be prepared to back up ANY claims with reputable sources.
Here we go:
#1 - "I want to 'treat' my car/truck/RV to some special fuel and buy premium gas"
This is a VERY common myth. Premium fuel has higher octane and costs more money. This in turn causes people to think it's 'better.' In the U.S. Octane ranges from 85 octane - 97 octane with a few degrees in between. The PRIMARY function of octane is to prevent pre-ignition. That means that a higher octane fuel will ignite at a higher temperature and compression. What does this mean for you? Your Toyota Corrolla does not need high octane fuel. It has a regular engine that does just fine with lower octane. A high performance vehicle however, has a higher compression ratio and requires higher octane to prevent the fuel igniting before the spark plug ignites. If you put low octane fuel in this kind of vehicle, you'll burn holes in the tops of pistons.... this is bad. If you hear pinging while going over a pass while pulling a TT or in an RV, fill up with higher octane and it SHOULD get better.
Another thing to note. There is no such thing as 'mid-grade' fuel. When you see the typical three grades of fuel at the pump, the middle one is just a mixture of premium and regular gasoline. HOWEVER, it's mixed at a 3:1 ratio of regular
remium. Which means that it's the WORST value for money at the pump. You're better off either buying regular or premium.
If in doubt about which to buy, consult your owner's manual.
More reading material
Selecting Gas
#2 - "I want the highest cetane for my diesel"
This is VERY similar to octane for gasoline, and performs nearly the same function. However, modern diesels require a higher cetane content. Also, if you live in the great frozen north, you'll need high cetane content to prevent your fuel from freezing in the winter.
Cetane Ratings
#3 - "They want money to put nitrogen in my tires.. that means it MUST be better!"
Nope. Nitrogen provide next to zero advantages over regular old air. Common statements are:
---- "It's a dry gas! It won't let things corrode inside your tire!"
While it is technically a gas that does not dissolve water vapor readily, wheel corrosion on the interior has not been an issue for 40 years.
---- "It keeps your pressure more steady when temperature changes!
This is just completely false. ALL gases expand and contract at the same rate over the same temperature changes. (
Guy Lussac's Law)
---- "The molecules are bigger so it will leak less!
While technically correct... the difference between sizes is so small that effect is negligible.
The fact is this. Air that you breathe is the same stuff that gets pumped into your tires is 78% nitrogen. Unless your tire has been mounted in a special room that is 100% nitrogen, it's impossible to have your tires inflated with 100% nitrogen. The tire itself has a volume of air in it when it's mounted and the amounted of compressed nitrogen that's added is only a percentage of the volume that's already there. Suffice it to say, it's a scam.
Please feel free to post more common myths, but make sure to have sources and data to back up your claims!