Tire pressure

[jsz]

I know that going way over or under the recommended tire pressure is bad but I'm still curious to see what pressure you guys run at. My tires say 50 psi but I just checked them and they're all at 40.

[FIC]

I run my tires at what they spec at on the sidewall , if you run lower than spec you risk the sidewall flexing and coming apart.

[mtnsmith]

My trailer also has a tire pressure spec on the plate that states the GVWR and whatnot. I use this, which happens to be a little less than on the sidewall as I remember.

[whitlock87]

I run at 50 psi
(same as the sidewall)
why make it harder to pull?

[jsz]

I just cant remember if I had them at 40 for a reason or if they leaked from 50 to 40 over the year.

[chpthril]

Aways check cold

Cold temps causes the air to contract, thus the pressure drops. As you roll down the road, the tires heat up and the air expands and the pressure goes up. It's best to check and add, if needed, before you hit the road. If you check after they are hot, the pressure may be 'over inflated' and letting some out would only leave the under-inflated when cool again.

[jsz]

I called Extreme trailers and they recommend 4 psi under whatever the tire says.

[G-MONEY]

I called Extreme trailers and they recommend 4 psi under whatever the tire says.

I think they recommend that in so cal because it gets so hot on the way out to the river.....

[evil0ne]

My tire pressure question is about my truck. According to the sticker on the door the stock 16" wheels and tires should be at 50 front and 80 rear but when the previous owner but the 18" wheels on the tires are only rated for 50. All numbers seem a bit high but I've never owned a 3/4 ton before.

[chpthril]

My tire pressure question is about my truck. According to the sticker on the door the stock 16" wheels and tires should be at 50 front and 80 rear but when the previous owner but the 18" wheels on the tires are only rated for 50. All numbers seem a bit high but I've never owned a 3/4 ton before.

The after market tires would supersede the factory sticker IMHO.

[spharis]

Sidewall over door sticker always......

FYI (evilOne) a wider tire of the same height and load will need less pressure which is why you see the difference.

Here's a cool experiment you can do with kids to find out how much a car weighs.

Put some construction paper under the edges of the tire so you can measure the footprint.
Get the sqaure inches of the footprint on all four tires.
Take the PSI of each tire and write it down by that tires overall footprint.
Multiply them to get the total psi*sq.in. for each tire.
Add them together.
You should be within 10% of the door tag.

[Razzman]

Tire facts courtesy of 15 years in the tire industry.

Hot Inflation: When a tire heats up it will gain on the average 3-4 pounds. I say average because depending on brand, materials used and construction technique that can vary.

Tire Inflation Pressure: Automotive tires are virtually never run at max cold capacity psi. Read the sidewalls of your car tires. The average passenger car tire is 40psi max cold. The average inflation for automotive tires is 32psi, sometimes less depending on the weight of the vehicle. Are there exceptions? You bet and my boat/trailer is one of them, read on to see why.

Overinflation, the biggest issues running tires overinflated are reduced tire life or wear and a reduced contact patch (more on that later). Running a tire at max inflation pressure when cold can result in reduced tire life of up to a third less and you'll wear the centers out of the tread. Factor in trailers have built in camber and you can end up wearing out the tire way earlier!

Underinflation will cause just the opposite affect, you wear the outside edges right off of the tire and again reduced life will be the result and the reduced contact patch. Running the tires 5-6 psi less than the sidewall max cold will not over flex the sidewalls and cause sidewall seperation. Running them 20 psi less might.

Load Capacity. Trailer tires are all load rate C or 6ply tires. Using my 14" tires as an example, they have an average max capacity of 1750-1800 pounds. Multiply that by 4 and you have a maximum load capacity of 7000-7200 pounds. REMEMBER that this also includes whatevers IN your boat at the time. If you have a 40 gallon fuel tank and are carrying 200 pounds of stuff in the boat for your week long vacation you could be OVER EXCEEDING your weight limit capacity depending on how much your boat and trailer weigh!

Tire Construction or style of tire does make a difference. Bias -vs- radial? I'll pick radial every time! Radials run smoother, quieter and cooler. Radials will also last longer and are less prone to premature wear patterns as bias ply tires are.

Don't buy that? Here's proof, my boat weighs 3420 lbs trailer included. I have a single axle trailer with load rate C tires rated at 1750 each or 3500 lbs max load. I have a 80lb buffer if i follow the rules. If i add the spare to the trailer with a mount bracket i've just added 35-40 lbs and my buffer is even less. Do the math. I carry my spare in the truck bed and i don't fill up until i'm near my destination. So in my situation do i want to run at max cold psi? You bet!

Contact Patch is a term not many drivers are aware of. The contact patch for the uninformed is the amount of rubber in contact with the driving surface at any given time. This has various affects on the tire as well as driving/towing ability. Overinflation will cause the tire to run on the center of the tread with less or no contact on the edges. Underinflation will cause the tire to run on the outsides with less contact in the center. Both will reduce tire life, both can be dangerous! Reduced contact patch can promote less braking surface contact resulting in longer stopping distances as well as promote hydroplaning in wet conditions.

BTW, overinflating or running at max cold psi to reduce rolling resistance is not always the best idea as you may be reducing your contact patch!

Want to know if your tires are inflated correctly? Here's a couple of tricks that will let you know. Place a piece of white paper in front of each tire. Slowly roll across the paper and stop. Look at the papers, if your contact patch is correct you'll see the full tire tread and width across it. If not you'll either see the center (overinflated) or the edges (underinflated), adjust your air pressures accordingly. You can also use talcum or baby powder on concrete to get the same result.

Ok, so that's it for this weeks lesson. I'll be back in an hour to administer the written test.

[Razzman]

That was the LONGEST post i've ever done here, or anywhere! Jeez my hand is cramped!

[Domsz06]

thanks for the info razz. that's awesome!! NO wonder all the boats are going to tandom axle now.

[chpthril]

Awesome tutorial, thanks Razz.