Tire pressure

[dogbert]

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

Good work! This might be a good sticky or FAQ somewhere. Tire blowouts are never good and this is important information for all of us.

Another question...do you guys run radials or bias ply?

[Domsz06]

pretty sure mine is bias ply. I just lowered mine 5 psi from max as they say the roads are hot here. I never had a problem in OK, but... guess it is a bit hotter here.

Not sure. I'll have to do the paper trick..

[Razzman]

Dog, that's a good idea. How do we make it a sticky? Should put this in the maintenance section.

Good catch! Currently i'm running bias as they still have a lot of tread left. I'll be switching to radials though as they run smoother and cooler and have a big tendancy to last longer as well. I'll add this to the post.

[dogbert]

Send a PM to Matt to see what he thinks.

[Tequilasun]

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.

Yes, but what is this Tire you speak of? I am not familiar with this term?

[jsz]

Thanks for the info Razzman. One more question for you (or anyone). My trailer tires are a few years old and look great on the outside. The inside however is starting to show a lot of cracks where the tire touches the rim. I keep them covered all year long and the whole trailer on blocks for about 6 months out of the year.

Why is the inside cracking much faster than the outside?

Have you ever noticed this before?

[Razzman]

The cracking is a byproduct of heat, pressure, age, UV exposure and infrequent use. In essence virtually everything! You'll notice that car tires used on a regular basis normally won't do that. Why it's cracking only on one side i'm clueless about though unless the inside was uncovered and exposure is the cause.

[dogbert]

Tires older than 5 years should be replaced. It's just a matter of time before they start blowing. A tire blowout from a tire that's cracking is quite spectacular and will cause a lot of damage to your trailer. I've had a couple. One time the tread came off in such a way that it bent the fender back into itself. In both cases, I had damaged lights.

If yours are the orignal tires, time for a new set. It's just a matter of time.

[Domsz06]

wow, all great info, Glad I'm reading it as I'll be looking at new tires then next year. Kinda sad as these still have LOTS of tread left, but better safe then sorry!

[jsz]

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.

I had a similar question about my truck tires. I heard to go off the psi on the tires since tires can always change but the sticker never will. I was also told a higher psi would give better MPG. So I brought them up to 44 psi. After my next oil change the GMC dealer dropped them back to 35, the psi written on the door. He said 44 would be a rough ride (I didn't notice).

I asked one of the fleet mechanics at my work and he said what seems to be a summary of the last few posts. He said, "It's a driver preference on how much you like to "feel" the road. Stay above whats on the door and stay below the max psi on the tire allowing for expansion when the tire heats up."

Make sense to me.

[dogbert]

Just remember, the more weight you put on your tires, the more critical the tire pressure becomes.

Dom, don't wait too long. You'll be kicking yourself when you have your first blowout.