Proper tire inflation?

[josefontao]

So I've been reading and I see people that have the PSI on their tires set between 35 and as high as 45.

Any tips as to what the proper inflation should be?

I'm in Southern California where the weather is relatively nice.

[JATR4]

So I've been reading and I see people that have the PSI on their tires set between 35 and as high as 45.

Any tips as to what the proper inflation should be?

I'm in Southern California where the weather is relatively nice.

I've been running 44psi on all my vehicles for over ten years with no problems.  With the temperature below 32 deg here that may drop to 40 or even below in the winter.

[larryh]

Tire pressure varies greatly here in the Winter.  At -10 F, the pressure is less than 35 lbs.  At 40 F, the pressure is over 40 lbs.  So I set the pressure for the lowest expected temperature. 

[Rexracer]

I've been running 44psi on all my vehicles for over ten years with no problems.  With the temperature below 32 deg here that may drop to 40 or even below in the winter.

 

What does your tire wear look like?

 

I run by factory recommended settings, and adjust if I notice the outsides wearing more then the insides or vice versa.

 

I think prematurly wearing out a set of $600 tires to save $20 in fuel does not make sense. Not to mention the ride/handling compromise.

[JATR4]

What does your tire wear look like?

 

I run by factory recommended settings, and adjust if I notice the outsides wearing more then the insides or vice versa.

 

I think prematurly wearing out a set of $600 tires to save $20 in fuel does not make sense. Not to mention the ride/handling compromise.

No abnormal wear.  Steel belted radials sit flat across the tread unlike the older bias ply tires which bubble with added inflation.  The tires are rated to 51psi so 44psi is certainly well within the recommended pressure range.  And no chance of overheating or underinflation.

 

Remember the problem with the Ford Explorer and Firestone tires in the 1990s?  Ford decided to lower the recommended pressure to 26psi which led to possible overheating, tread separation and rollovers resulting in 250+ deaths.  There were also problems with the Firestone tires and the Explorer design.  The combination of poor vehicle design, under inflated tires along with tire defects led to numerous rollovers when the tires failed due to tread separation.

 

The vehicle manufacturer wants a smooth soft ride which means a lower pressure and the tire manufacturers want a higher psi which would eliminate underinflation and overheating.  I never use the vehicle manufacturer's tire pressure recommendations.  If a vehicle has a recommended pressure of 36psi most of those vehicles will have underinflated tires since most drivers never check their tire pressure.

 

After 10 years of doing this on a Jeep, a Ford SHO, a Maxima, a Honda HCHII, a Cruze, a Ford Escape and an FFH, I have had no adverse consequences with abnormal tire wear.  With the FFH it made difference of 2-3 mpg.  I don't think it is as noticeable on the FFE.  I wouldn't be doing this if my tires were affected.

 

If I lived where there was a large amount of snow/ice I would run a lower psi during that period of time.  Since I have an AWD Escape to use in adverse weather I don't adjust the tire pressure in the FFE.  The pressure may drop to 40 or even lower as the temperature gets to 32 deg or less.  I don't add any additional pressure during the winter.

 

I recently bought an Escape in Dallas and had them add extra pressure for the 1150 mile to NC.

 

Here is an article that estimates a loss of 2.8 billion gallons of gas each year from underinflated tires:

 

http://forums.trucktrend.com/70/6681028/off-topic-automotive/billions-of-gallons-of-gasoline-lost-due-to-underi/

 

That article is based on vehicle recommended pressures. 

Edited January 13, 2015 at 07:43 PM by JATR4

[Rexracer]

So your conjecture is that if 7-10psi under vehicle recommendation = 10% loss in fuel economy, thus going 10psi over recommendation would be an additional 10% improvement?

 

I completely agree under inflated (less then the 32-35psi typically called for) is dangerous and helps lead to bad economy, but i expect that going over has diminishing returns.

[JATR4]

So your conjecture is that if 7-10psi under vehicle recommendation = 10% loss in fuel economy, thus going 10psi over recommendation would be an additional 10% improvement?

 

I completely agree under inflated (less then the 32-35psi typically called for) is dangerous and helps lead to bad economy, but i expect that going over has diminishing returns.

I learned about this years ago on the Civic Hybrid forum.  I was skeptical at first and only increased my pressure a couple of lbs at at time until I finally reached 44psi.  The recommended psi on the HCH is 32.  One of the reasons was the tires were low rolling resistance and were hard as a rock.  The ride was slightly rougher at 44 psi but not too great for me.  I went from 42mpg at 32 psi to as much as 48mpg at 44psi.  Some of that gain was learning how to drive a hybrid.  With the FFH I was able to get 46.2mpg for the time I had the vehicle--not great but not bad.

 

There are many on the Civic forum and the FFH forum who use increased pressure--some even higher than 44psi.  There are some on this forum who do also.

[Rexracer]

I learned about this years ago on the Civic Hybrid forum.  I was skeptical at first and only increased my pressure a couple of lbs at at time until I finally reached 44psi.  The recommended psi on the HCH is 32.  One of the reasons was the tires were low rolling resistance and were hard as a rock.  The ride was slightly rougher at 44 psi but not too great for me.  I went from 42mpg at 32 psi to as much as 48mpg at 44psi.  Some of that gain was learning how to drive a hybrid.  With the FFH I was able to get 46.2mpg for the time I had the vehicle--not great but not bad.

 

There are many on the Civic forum and the FFH forum who use increased pressure--some even higher than 44psi.  There are some on this forum who do also.

 

I completely agree that lots of people inflate their tires over the vehicle recommended point, and that it leads to an increase in fuel economy.

The thing I haven't seen is a controlled experiment that shows the improvement of JUST the tire inflation at different set points and driving conditions. Like you said, you also had been working on your driving technique when you started increasing your tire pressure. SO how much of the improvement from 42 - 48 mpg is attributed to technique vs tire pressure. Also, whats the driving situation that leads to the improvement? My suspicion is that increasing tire pressure will show the largest gains on freeway driving, and far less on city driving.

 

When I am on a long drive, i.e. 200 miles plus, I do increase my tire pressure, but the bulk of my driving is in town at speeds around 30 mph. So for that driving I leave it at Manufacture recommended pressures. Tire compliance, contact patch, tire wear (yes it still has a factor in modern tires, less so then in bias ply's, but still effects it) is more important to me then then processable increase in mpg.

 

I guess my argument is the placebo effect. Radio Lab has a nicely done podcast on it.

http://www.radiolab.org/story/91539-placebo/

[Hybridbear]

I've set my tire pressures to around 46 PSI when the car is warm and parked underground at our apartment where the temp is around 70. I recently took the Energi to Discount Tire to have the tires rotated. I drove there first thing in the morning so everything was warm. They let air out of my tires down to 38 lbs. After the tire rotation I went to work. When I left work after the car had been sitting out in the cold all day the PSI was down to 33. As we've driven across the country on our road trip I've watched the PSI increase as the ambient temps increased. Now here in Cali the cold PSI in the morning shows about 45. When we were first leaving MN and driving in below 0 temps the PSI showed only about 40.

[shaggy314]

I've just started setting mine to 38, so I'll be able to compare to the previous year. At this point my driving habits after 24k don't change much so I'll know more next year. Then again, I'm only going from 32 to 38.