Fuel saving tips that just don't work - May. 13, 2008

The two that surprised me
#2) air filter affects mileage/performance (false)
#3) use premium fuel if the mfg suggests it (false)

 

Good find!

 

i never really thought about putting premium in for better gas efficiency, most cars that call for it are because of the performance factor (high compression, or f.i.)

 

#1 IS a myth... because gas at a gas station sits in a tank, which is underground, where the temperature is more constant. The only related situation I could think of that would affect the density of fuel would be right when the tanker truck is filling the tanks. The tanker has been exposed to conditions that would affect the temperature of the fuel.

Almost all of the rest are a wash... They're saying 'This DOES get you a little, but you shouldn't do it anyway'. They're not really pointing out myths, they're pointing out reasons not to use these practices.

I will add about the octane rating of fuel - It is NEVER a good idea to use higher octane fuel than your car requires. You get nothing out of it. However, if your car REQUIRES mid or premium gas - USE IT. When I bought my Boxster from a used car dealer, he filled it with 89. I didn't complain, since I knew I wasn't going to be wailing on it right away. After I burned that off and started putting 93 in it, I DID notice the engine ran smoother.

 

I am not sure about the temperature thing...........have you ever been in the South around summer time? It can be 50-70degrees in the morning and 80-100 in the after noon. Sure the tanks are in the ground but in the evening(after sunset) is when the tanks could reach their maximum temperature in the ground. I have no data on this but I am skeptical that the temperature in the tanks don't increase throughout the extremely hot days.

 

Once you dig deep enough, temperature becomes a near-constant.

You dont really need to get very deep either. Here is a quote from an article I found on geothermal heating/cooling:


Here is the article.

 

I like #5... in the 3 weeks i've been in this forum i've seen numerous people say they fill there car tires to 45+ PSI... that is dangerous and not worth an extra 1 mpg in my book. Car tires heat up when you drive, no myth there and if your overfilling the tires, your asking for a major problem like a tire bead failure or like the story says, reduced traction and braking control.

 

I knew about the gas. I have been stating that forever on this forum and others. But not so intelligent people cannot get that through their minds.

 

51psi is the max. for our Fits, so 45psi would not be "over filling" would it??

 

But the article said you can put 89 into a premium car. My coworker drives an X5 (agg) and she said she recently added regular, and I said she shouldn't because the engine will hiccup due to premature ignition due to higher compression. But according to that article, it detects you're using the wrong gas, and will detune itself's horsepower/spark plugs so it won't hiccup.

 

Their blanket statement of '1MPG' is a pure ASSumption. The affect on ALL cars will NOT be the same.

I always recommend running tires 'a few more pounds' than the recommended... not the MAXIMUM sidewall pressure.

 

It is not dangerous at all... 51 PSI is the max COLD pressure you can use. Full tires also do not heat up as much. Modern steel belted tires will also not wear unevenly. Tranction and tire performance is guaranteed at the max cold PSI, otherwise it would be lower. The difference between 45 and 50 PSI in the Fit is most certainly noticable.

 

Did you notice very few had any data to support the rule?

This is like the tank 1/2 empty and pump in the AM and a few others. My guess is they are bunk and not tested in the real world.

 

Max PSI is generally determined by the tires (written on them), not the car.

If you read the side door sill it clearly says for 195 tires to use 32PSI, this is the recommended optimum PSI that suites your vehicle weight to give you the best combination of traction and mileage. Going more or less than this will impact traction, tire roll and mileage; more importantly the safety of your vehicle is also affected as a direct result of some of those factors. However it has been brought up that people don't care about safety when it comes to gas mileage anyway so I won't waste my breath

With wider tires that displacement may change, easiest thing would be to calculate the percentage of the difference and adjust your tire pressure to match.

 

32 is manufacturer recommended for ride and not much else. Handing is MUCH better at 40 than 32. There is no safety concern at all unless you are running well over the max PSI when cold.

 

I wouldnt waste your breath... if they want to run 50+ psi and ruin their tires/handling, let'em. Like you said, saving 1 more gallon of gas is more important...

 

You have no evidence supporting that claim... handing is much better now, and my tires are wearing just fine.

 

You are actually correct about handling to a point; for instance in AutoX it is common to run slightly higher pressure (usually between 5 to 15lbs) on street tires more than the rated amount so your tires don't roll over too much.

However with that said, this practice is only done on a closed course and people will then deflate the tires to the recommended pressures when they leave to avoid a few problems such as getting dings in the rim from hitting pot holes, changing the ride to be more comfortable and increasing the vehicles ability to stop in emergency situations more quickly.

Getting even more technical, the advantage quickly fades if you over inflate even a few more lbs then you need in your tires. Too much pressure can leave your car floundering all over the course.

On the course we use chalk to determine how much pressure is required to maximize handling. The chalk will show how much the tire rolls. Keep in mind, this is under extreme cornering highly unlikely in daily driving. My tires operate best at around 8psi higher, anymore more and they start getting useless. This is good for corners, not so good for stopping.



50lbs is way too much for the Fit IMO, it will vary from tire to tire but a safe margin such as 36psi might be better to maximize your economy and still stay safe on the roads.

Anyway, that was my breath. Take it or leave it lol

 

I roll at 50psi and that is still with in the limits. Everything has tolerances, therefore, ranges. The ride is more harsh than 32psi meaning you feel bumps in the road more and possibly nosier. I have my tires rotated and balanced every 5k also. Keeping up with vehicle maintenance is a must. I currently have about 27k on my fit and the stock tires that come with the sport. I do believe I have achieved better mpg with the increase psi. I think I demonstrated the increased mpg in one of my threads on here(buried somewhere in a thread).


The ground temp is a good thing to know........so, it really doesn't matter what time of day you fill up.

 

Yeah there is no doubt that rolling on 50psi is going to give you better mileage, I don't think anybody is going to dispute that.

However (come on you knew the counter point was coming lol) there are disadvantages at that PSI; your handling is NOT better than lets say 40psi and your car will not stop as fast as the recommended 32 PSI. Comfort and ride is really a personal thing so I won't touch on that.

Now you are also at a much higher risk of denting your rim in the event you hit a pot hole or curb. If you do, well you can kiss your jar of gas savings goodbye your tire wear is going to be a bit weird. I would imagine that the center of the tire (as it is bulging slightly) will experience much more wear rather than an even wear across the face of the tire. Probably the side of your tire is going to look new all the time at that PSI. As your tire has less surface area on the road, the surface that is touching will wear faster... you guys can argue... but it's physics

Just looking at your tire from the side is going to be deceptive, I would almost suggest you pick up a tread wear indicator and keep tabs on the center. If I had to guess I would say your tires will be done about 20-30% sooner... running at 36psi would probably have negligible wear in comparison to stock. Now if you factor in that you have to buy 3 sets of tires rather than 2 for the same mileage I think it would outweigh the amount of gas it would save you.