misconceptions on proper inflation!

[OneEyeJack]

Originally Posted By: 4wheeldog
Originally Posted By: OneEyeJack
I run my Honda Michelin tires at 40psi. About 20 years ago this car (the one in my sig, I'm the original owner) was the subject of a friendly bet. We used a back street at an industrial park on Sunday morning and did a breaking test with the tires hot and at 32, 36 and 40 psi from an indicated 65mph. With 3 stops at each setting the best stopping distance by 9 to 11 feet was the 40 psi. We also set up a circle and drove around it. The 40 psi setting was much better but I don't remember any more how much it was. I do remember collecting the dollar from the bet and it's still taped up on the lid of my tool box. When Social Security crashes I'll be covered.



We did this testing with a couple of other cars and obtained similar results.

I get excellent mileage out of the tires at 40 psi and have had not problems beating up the suspension.



40psi hot is not the same as 40psi cold. A good rule of thumb is the tire pressure is optimum for roadholding and braking when checking them hot, they are 4psi above what was put in them cold.

Since your bet was based on hot temps, all things being equal, you should probably be running about 36psi cold. Just sayin'.


The tire pressures were set at 40 psi with cold tires. The gauge was a calibrated gauge. The tire test was run with hot tires, that is tires up to operating temperatures, also checked with a calibrated contact temperature gauge. One can't be too careful when there's a dollar at stake.

 

[Lapham3]

When radials first came out I ran 35lbs, but wore too much center tread-I've been running 32lbs ever since and had pretty even wear over many tires/vehicles.

 

[CapriRacer]

Originally Posted By: Bear
While reading a truck owners forum I came across a thread asking about proper tire inflation. I was amazed how many forum members recommended running at the maximum value posted on the tire and not per on the vehicle. And even when presented with evidence to the contrary some insisted they were correct.
While there are valid reasons for running at higher pressures such as hauling/towing and high speed driving on the Autobahn, over inflation is not the way to go. Another reason to be careful and verify what we read on the net.


Yup! I've always puzzled over why some folks can't seem to change their minds about things - especially when confronted with contradictory evidence.

I've also always puzzled over the idea that one pressure is the right pressure for every vehicle. you would think that different car manufacturers specifying different pressure ought to indicate that there is more to it - but No!

Originally Posted By: HerrStig
Racers measure tire temperature across the tread with a pyrometer
after a run looking for hot spots which would suggest an alignment, pressure
or "jacking" adjustment is needed. It's probably the only way to
insure the tire is inflated and aligned properly. Those who put 40 pounds of air in a passenger car tire "cause it says so on the sidewall" are beating their suspension AND occupants to distraction.


What is interesting is that a change in race venue changes the optimal pressure and alignment, especially camber.

 

[mclasser]

While it took some experimenting, I've finally found the optimal tire pressures for my cars, and they aren't what's listed on the tire placard. By optimal, I mean a good balance between ride quality and some MPG improvements.

 

[geeman789]

Originally Posted By: Nick1994
....took my car into Discount Tire for a rotation and they let air out of my tires

Like dude, the tires are hot. Your 32 psi hot isn't enough.


Similar situation here in the winter... I asked what they inflated some new winter tires to... the service guy said 32 psi, as per door jamb sticker... sounds good, right...

WRONG. Shop was about + 15 * c , outside was - 20* c ... about a 7 psi drop just due to temps...

When I asked the front end guy about temperature adjustments, the blank stare told me all I needed to know...

 

[97tbird]

Originally Posted By: fredfactory
I run 2 psi less than the door sill placard in the cold winters, and 2 psi more in spring/summer/fall.
This works because tire flexing generates heat, and winter cold keeps them from overheating, while they generate less heat in summer due to less flexing.

I always read here that the exact opposite was correct.??
(more air in winter, less in summer)

 

[geeman789]

Originally Posted By: 97tbird
Originally Posted By: fredfactory
I run 2 psi less than the door sill placard in the cold winters, and 2 psi more in spring/summer/fall.
This works because tire flexing generates heat, and winter cold keeps them from overheating, while they generate less heat in summer due to less flexing.

I always read here that the exact opposite was correct.??
(more air in winter, less in summer)


Lower pressures allow more tire flex, which generates heat, which on a hot highway in the summer, can lead to tire failure. Not what you want to have happen...

In the winter lower pressures can maximize the contact patch, ideal on hard pack and ice... and heat typically isn't a problem.

 

[eljefino]

Originally Posted By: 97tbird
Originally Posted By: fredfactory
I run 2 psi less than the door sill placard in the cold winters, and 2 psi more in spring/summer/fall.
This works because tire flexing generates heat, and winter cold keeps them from overheating, while they generate less heat in summer due to less flexing.

I always read here that the exact opposite was correct.??
(more air in winter, less in summer)


It takes more molecules to make the same pressure when it's colder. Fred's taking the lazy way and letting the "automatic" adjustment of 1 lb for every 10 degrees F do most of his work.

It just depends on what the temp is when you check your pressure, but, then again, Fred's happy with less when it's cold, so he's always happy.

 

[Mr_Joe]

I saw a lady driving with one tire over half flat the other day. It was the passenger side front. I tried to flag her but we just passed as she was turning.

I mostly go by the door jam, but I may adjust up a bit depending on what I am up to.

 

[fredfactory]

Originally Posted By: eljefino

It takes more molecules to make the same pressure when it's colder. Fred's taking the lazy way and letting the "automatic" adjustment of 1 lb for every 10 degrees F do most of his work.

It just depends on what the temp is when you check your pressure, but, then again, Fred's happy with less when it's cold, so he's always happy.

Yep, the 1 psi drop in pressure for every 10 deg Fahrenheit you drop is inescapable.
Say your tire placard says "35 psi cold", well go ahead and put 38 in there on a hot day, and you can go with 32 in there on a winter day (below freezing). As soon as a spring-like 70 degree day happens (and your tires haven't been sunbathing!!), you'll see the pressure be about the placard's 35 psi. (I see this all the time on my 2011 GM car with all 4 pressures displayed on the dash when I hit a button.) So a "natural" + & -3 psi is OK.

Where you might get in trouble is when your car triggers malfunction-light when the TPMS reports underinflation because its 20 degF or less outside, and you know you put enough molecules in there to meet placard at, say, 50 degF, for example. Then, as on my BMW, I'm left with no choice but to stay within the negative 2 psi tolerance of my TPMS in winter, but thats OK, just a little extra pressure is needed to avoid those malf-light warnings.