Tire Pressure and gas

[surfsupl]

I have been reading posts here and on other sites about tire pressure and gas mpg. I have read some people putting as much as 40-45 psi in their tires. Has anyone done this and noticed a difference besides the extremely rough ride? I keep mine at 35 psi and seem to be doing ok. I was running at 29 psi a while back but the tires looked a little low. No difference in mpg between the two I have been running. Only thing I notice is that I usually run mid grade gas but with such high prices here in so cal I went with the low grade and the mpg is worse and my engine is back to clicking really loud.

[chris4x4]

The lower your rolling resistance, the better your MPG will be. So, If you jack up your tire psi. you will get better MPG. Also going from off road tires to a more street oriented tire will increase your MPG.

[rachunter]

Just be careful with raising your pressure too high, the downside to lowering your rolling resistance is loss of traction and harsher ride. You have to check and see how your tires are wearing and let that be your guide.

If you increase your mpg but lower your tire life you have not really helped yourself any.

[Ridingontrd]

Originally Posted by rachunter

If you increase your mpg but lower your tire life you have not really helped yourself any.

Very good point.

[chris4x4]

Originally Posted by Ridingontrd

Very good point.

X2!

[Ridgerunner]

But I assume you know not to exceed the MAXIMUM PSI ON THE SIDEWALL?? Some tires have a 52PSImax. Some have a 44PSImax. Some have a 35PSImax. What does yours say? If it says "MAX TIRE PRESSURE @ 44PSI" I would go 42 or 43PSI and that's pushing it. But they test the tires to fail waaaaay beyond that but dont mess with it

[Ridingontrd]

Originally Posted by Ridgerunner

But I assume you know not to exceed the MAXIMUM PSI ON THE SIDEWALL?? Some tires have a 52PSImax. Some have a 44PSImax. Some have a 35PSImax. What does yours say? If it says "MAX TIRE PRESSURE @ 44PSI" I would go 42 or 43PSI and that's pushing it. But they test the tires to fail waaaaay beyond that but dont mess with it

While what you'd said is correct,I'd like to add there is a SECOND psi # on the sidewall.The lower psi# is the unloaded max#.I have the stock Dunlops.Max psi under full load is 50.The second # is 40psi.I keep them at 36psi for norm.

[Ridgerunner]

Originally Posted by Ridingontrd

While what you'd said is correct,I'd like to add there is a SECOND psi # on the sidewall.The lower psi# is the unloaded max#.I have the stock Dunlops.Max psi under full load is 50.The second # is 40psi.I keep them at 36psi for norm.

WOW I had NO idea there was a 'minimum pressure' indicated! I gotta go check that out now Hey so if I had YOUR tires on my truck (max 50-min 40) and I followed the advice of all these people who say "follow the manufacturer plate in the doorjamb"-which says 'max 26PSI' I'd be GROSSLY underinflated right? The tire makers put their own max tire pressure on the sidewall for a reason: they know how much air is required to properly fill out the construction of that particular tire! That's why some only max out at 35, others at 44, others at 50-etc. I'm with you on this one buddy

[rachunter]

I can promise you guys if you are running max air pressure in your tires and your driving your truck empty you are without a doubt beating yourselves to death.
Again, let tire wear be your guide but no need to run max pressure unless you are running near max weight for your truck.

A few pounds of air pressure will sure make a big difference in ride.

[chris4x4]

The best gauge I have found for getting the correct air psi for your tires is this:
Start at max. psi. Make a chalk line accross your tire about 4" wide, and from out side of tread to the inside of the tread.
Drive a couple hundred feet. CHeck the line.
Take out air until only 1/8" of chalk is left on your tires out side/in side treads. For me and my tires, this equates to 35 psi in the front, and 31 psi in the rear.

[Ridgerunner]

Originally Posted by chris4x4

The best gauge I have found for getting the correct air psi for your tires is this:
Start at max. psi. Make a chalk line accross your tire about 4" wide, and from out side of tread to the inside of the tread.
Drive a couple hundred feet. CHeck the line.
Take out air until only 1/8" of chalk is left on your tires out side/in side treads. For me and my tires, this equates to 35 psi in the front, and 31 psi in the rear.

That sounds like a smart sound method

[chris4x4]

Originally Posted by Ridgerunner

That sounds like a smart sound method

Seems to work for me, as tires, vehicle weight, and such, very from one vehicle to another. I seem to get good life out of my tires since I have been doing this.

[rachunter]

Chris,

The only problem with your method is the fact that once you run the tires for a few miles at highway speeds the tires heat up and the air inside them expands which changes the contact patch of the tires.

Don't believe me, go out in the morning and check your tire pressure then drive about 15 miles then check your tire pressure again. That is exactly why you should always check your pressure while your tires are cold.

Also at highway speeds depending on the build of the tire they can expand height wise, kind of like a dragster doing a burnout, ever notice how tall and skinny those tires get and then when they launch off the line for the race the same tire is short and wide. You will have a different contact patch at 70 mph vs. driving in a parking lot.

The way your tires wear is the ONLY way to determine correct air pressure for your set up.

You had a good plan but your signature line says it best.....

"The simplest solutions are often the most clever..........they are also usually wrong."

The chalk method is not a accurate way to determine tire pressure.

[Ridgerunner]

Originally Posted by rachunter

Chris,

The only problem with your method is the fact that once you run the tires for a few miles at highway speeds the tires heat up and the air inside them expands which changes the contact patch of the tires.

Don't believe me, go out in the morning and check your tire pressure then drive about 15 miles then check your tire pressure again. That is exactly why you should always check your pressure while your tires are cold.

Also at highway speeds depending on the build of the tire they can expand height wise, kind of like a dragster doing a burnout, ever notice how tall and skinny those tires get and then when they launch off the line for the race the same tire is short and wide. You will have a different contact patch at 70 mph vs. driving in a parking lot.

The way your tires wear is the ONLY way to determine correct air pressure for your set up.

You had a good plan but your signature line says it best.....

"The simplest solutions are often the most clever..........they are also usually wrong."

The chalk method is not a accurate way to determine tire pressure.

UH...what?? He tels you to drive a couple hundred feet-not a few miles-so the tires will still be cold. It takes WAAAY more than 200 feet to heat up the tires so what's your point? Plus YOU didnt offer your alternative. I'd love to hear it.

[rachunter]

He tels you to drive a couple hundred feet-not a few miles-so the tires will still be cold. It takes WAAAY more than 200 feet to heat up the tires so what's your point?

The point is....with the chalk method you are checking the contact patch of your tires while they are cold and at very low speed. That is the total opposite of actual driving conditions which would be a hot tire at highway speed. This method will work very good if you plan to only drive around in parking lots at low speed but it will not work for real world driving.

Plus YOU didnt offer your alternative. I'd love to hear it.

From my first post:
"The way your tires wear is the ONLY way to determine correct air pressure for your set up."

[Ridgerunner]

Originally Posted by rachunter

The point is....with the chalk method you are checking the contact patch of your tires while they are cold and at very low speed. That is the total opposite of actual driving conditions which would be a hot tire at highway speed. This method will work very good if you plan to only drive around in parking lots at low speed but it will not work for real world driving.



From my first post:
"The way your tires wear is the ONLY way to determine correct air pressure for your set up."

Yeah but the contact patch changes with heat and speed no matter WHAT your method may be. Besides, your footprint doesn't alter that much from original so his chalk thing is good for overall use I personally run 32PSI in my 35PSI max tires. I know that they can heat up to an inflation of up to 38PSI at times (I've checked) but the tire construction keeps that footprint firmly planted. If you look at my photos-those tires as of that time had almost 45,000 miles on them and they still look pretty fresh.

[rachunter]

Yeah but the contact patch changes with heat and speed

Exactly. That is why reading the tire wear is the only way to determine what psi to run in each set up.

[Ridgerunner]

Thats what Chris DID! He does the chalk method-adjusts accordingly-and his tires are wearing very well according to his post. I still dont get where you say he's wrong! So how do you "read" your tire wear? Also-when you quote somebody, quote the WHOLE sentence, not just the part that serves you.

[rachunter]

Yeah but the contact patch changes with heat and speed no matter WHAT your method may be.

There you go, did that changes anything?

Then you said:

Besides, your footprint doesn't alter that much from original so his chalk thing is good for overall use

Its ok to have a difference of opinion. All is well.

[chris4x4]

Rachunter,
Im not sure where you are going with your logic. Dragster tires are ENTIRELY different than tires designed for street use. A Drag tire is designed to get taller as centrifugal forces are applied to it. Street tires are not. I have watched street tires on a Dyno as they have been spun to over 125 m.p.h. The growth they experience is not mesureable. Street tires are designed to keep their shape under all speeds for wich they are rated. You say that you need to gauge tire psi according to treadwear. That is EXACTILLY the point of the meathod I use. It gives you a good "baseline" with wich to start and "fine tune" your psi, as the chaulk is going to "mimick" tire wear, just quicker.