Tire Pressure ?

[LB'sTremor]

Man I miss Doscount Tire that's my favorite tire shop. I wish I had one closer!

LB

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[OrangeStreak]

I know, old thread.
The question was asked earlier why a larger tire would need less psi.
There's more to it than I know, but just using straight numbers -
Let's take 30 pounds per square inch.
If there is 10 square inches of tire surface area on the road, then that's 300.
A bicycle tire often takes 90 psi.
But if that little tire has only 2 square inches of surface area on the ground then that's only 180.
Take a woman's high heels.
If she is 80 lbs and her heel only has 1/2 inch of surface area, her heel is exerting 160 lbs per inch.

My bike shop recommended 50psi (the rating on the tires is 35-60psi) Like you say some bike tires are rated even higher than that. Run more in them than In the KO2's on the Ranger!

 

[OrangeStreak]

Dang!
Where'd you find an 80lb woman? You need to immediately run and get her a couple of cheeseburgers or she'll blow away the next decent breeze that comes up!

1 large cheeseburger X 2 should keep her on the ground!

 

[Joeiconic]

My truck came originally with Bridgestone Dueler 255/65/R17's and the door sticker recommended 30psi cold. I experimented and found 32-33psi cold gave the best ride. I upgraded to Ford OEM charcoals with BFG K02's 265/70/17's. I called BFG corporate, and they ran a calculation factoring in the weight of the Ranger with the K02's and they recommended 35psi cold. Experimented and found that 36psi cold gives the ideal ride. Have the tire pressures checked monthly at Discount..

You go to discount tire just to get your pressure checked?

 

[Zaph]

I like the chalk test. Even tire wear is important.

My input, PSI is nothing more than pounds per square inch, so it all has to comes down to vehicle total weight per wheel and contact patch size. There are a few other small factors but in general, a taller tire and/or a wider tire = more contact patch and that is going to equate to lower pounds per square inch given the same vehicle weight.

And you don't want to create more complexity by saying more weight creates more tire contact patch... and what about sidewall stiffness... and what about tire's design load rating... This is why the chalk test is good. It kind of covers all that.

Looking at bicycles and taking the concept to extremes, it's why your skinny tire road bike takes 120 PSI but your fat tire mountain bike takes 10 PSI.

I suspect people will also find after having done the chalk test that different pressures are optimal for different tire designs even if all are 265/70R17 to get even tread loading.

That video about the chalk test posted a while back - the difference for me is I do the test with the tires hot. I go for a nice long ride then do the test. When I get the chalk test right, I let the tires cool and then note that cold pressure as the goal. And I will have different summer and winter cold pressures. Take it from an old race nerd - you should see some of the PSI data I had for some race tires - Cloudy? Time of Day? Ambient temp? Track specific suspension settings? ?

 

[AzScorpion]

1 large cheeseburger X 2 should keep her on the ground!

One thing's for sure, it'll keep you at the cardiologist office. ?

 

[OrangeStreak]

One thing's for sure, it'll keep you at the cardiologist office. ?

Right...not much nutritional value only weight to keep her from floating away

 

[Fordup]

I made the mistake of reading this thread and saw where posters said the went with 32 psi on the 18 inch tires. So I went out in the garage and cranked my pressure up 2 psi cold to 32 from the recommended factory 30. Well the truck rode like crap with bobble head ride quality plus the handling did not feel good on a 90 mile trip. Can't believe how it screwed up the ride. Back to 30 psi and a great ride. I have to stop reading these threads because I am finding Ford must have test data when they write the specs for a stock truck.

 

[AzScorpion]

I made the mistake of reading this thread and saw where posters said the went with 32 psi on the 18 inch tires. So I went out in the garage and cranked my pressure up 2 psi cold to 32 from the recommended factory 30. Well the truck rode like crap with bobble head ride quality plus the handling did not feel good on a 90 mile trip. Can't believe how it screwed up the ride. Back to 30 psi and a great ride. I have to stop reading these threads because I am finding Ford must have test data when they write the specs for a stock truck.

I think with the stock tires the recommended psi is what you should stay with. I know mine (Nitto Ridge Grapplers) which are one size larger ride much better at 32 psi cold. Chaulk testing them is really the only way to find that perfect psi but stock tires should stay at the specs Ford has on the door sticker.

 

[LostMy65]

Toad:
"What a babe! What a bitchin babe"

 

[JACKSMYDOG]

I like the chalk test. Even tire wear is important.

My input, PSI is nothing more than pounds per square inch, so it all has to comes down to vehicle total weight per wheel and contact patch size. There are a few other small factors but in general, a taller tire and/or a wider tire = more contact patch and that is going to equate to lower pounds per square inch given the same vehicle weight.

And you don't want to create more complexity by saying more weight creates more tire contact patch... and what about sidewall stiffness... and what about tire's design load rating... This is why the chalk test is good. It kind of covers all that.

Looking at bicycles and taking the concept to extremes, it's why your skinny tire road bike takes 120 PSI but your fat tire mountain bike takes 10 PSI.

I suspect people will also find after having done the chalk test that different pressures are optimal for different tire designs even if all are 265/70R17 to get even tread loading.

That video about the chalk test posted a while back - the difference for me is I do the test with the tires hot. I go for a nice long ride then do the test. When I get the chalk test right, I let the tires cool and then note that cold pressure as the goal. And I will have different summer and winter cold pressures. Take it from an old race nerd - you should see some of the PSI data I had for some race tires - Cloudy? Time of Day? Ambient temp? Track specific suspension settings? ?

The problem with the chalk test is that it's accurate to the current wear on the tires. Meaning, if you run over-inflated tires for 10,000 miles, then do a chalk test, it will show to keep them over-inflated, which will continue to wear the center tread. The same with under-inflated, continuing to wear the edges.

The same effect will come from chalk testing tires just before rotation is due. Front tires have more edge wear after 10,000 miles, and a chalk test will show to under-inflate them.

That's not to say it isn't a worthwhile source of information, but there are many factors to be considered.

 

[Zaph]

The problem with the chalk test is that it's accurate to the current wear on the tires.

Oh, definitely. Really only applicable to new tires. But once done you're just that much more likely to get even wear for the life of the tire. Generally better traction also.

 

[JACKSMYDOG]

Oh, definitely. Really only applicable to new tires. But once done you're just that much more likely to get even wear for the life of the tire. Generally better traction also.

Exactly. It's great resource for new tires.

 

[Shoran12]

I made the mistake of reading this thread and saw where posters said the went with 32 psi on the 18 inch tires. So I went out in the garage and cranked my pressure up 2 psi cold to 32 from the recommended factory 30. Well the truck rode like crap with bobble head ride quality plus the handling did not feel good on a 90 mile trip. Can't believe how it screwed up the ride. Back to 30 psi and a great ride. I have to stop reading these threads because I am finding Ford must have test data when they write the specs for a stock truck.

Yeah anything at all above 30 and mine ride like total crap. I originally deflated the tires to 32 psi cold since the dealership has them near 40. Truck rode like crap and could feel every road imperfection. Went out yesterday and dropped the tires to 30 psi and this mornings ride to work was much better. I have the stock 17s with Bridgestone Dueller’s.

 

[LostMy65]

My stock tires are 255/65/17. Why would a bigger tire take less air pressure?

Old thread, but I wanted to add a little more.
Larger tires have more surface area.
Per Square Inch. PSI
1 square inch at 35 PSI has less load capacity than 2 square inches at 30 PSI.
Skinny bike tires may need 90 PSI, and big wide tires may only need 25 PSI.
100 lb woman on a ¼-in Stiletto heel: Exerts 1,600 pounds per square inch (psi)

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