Tire pressure ???

[M Baxter]

I just came from the tire shop. A brand new tire was only 20 dollars. Now I have two exact towing tires and they are both brand new. Im getting the other C rated tire mounted as the spare. The 35 dollar total is very much worth the piece of mind. Thanks again. MB

[austinado16]

I just came from the tire shop. A brand new tire was only 20 dollars. Now I have two exact towing tires and they are both brand new. Im getting the other C rated tire mounted as the spare. The 35 dollar total is very much worth the piece of mind. Thanks again. MB

Now you're talking!  There's nothing like fresh rubber on the road and the peace of mind it promotes.  Now run off and have a care free camping weekend tooling down the road with your family on board........amongst a hailstorm of intoxicated drivers!

Cheers!

[AustinBoston]

Now run off and have a care free camping weekend tooling down the road with your family on board........amongst a hailstorm of intoxicated drivers!

While I'm not interested in mixing it up with intoxicated drivers, encountering intoxicated campers is what I'd be more worried about.  We seldom camp on holiday weekends any more.

Austin (camping NEXT weekend)

[zamboni]

If the 60 & 90 PSI tires are the same physical size, then you're not as bad off as you think.  At 60 PSI, both tires should be rated to carry close to the same amount with the same "softness".

The pressure you should use is NOT NOT NOT what is printed on the tire, but the pressure that is on your camper's vehicle rating tag - should be on the driver side near the front, that has the GVWR, axle, etc on it.

The "C" tire needs 90 PSI in order to support its max weight = 990

The "B" tire needs 60 PSI in order to support its max weight = 780

However, if you put less than 90 PSI in the C tire, it can still carry the correct weight for that PSI.

That is why all vehicles have a manufacturer's label with the PSI.  What does your camper's label say is the recommended pressure?

For example, my Explorer has tires rated for 45 PSI on it.  However, the label says 35 PSI is what the manufacturer requires, and what my warranty is rated for.  Over-inflating a tire (ie, over the recommended amount, but under the max) will cause your tires to wear in the middle badly, because they are not being compressed enough to wear evenly.  Over-inflating can also make them more susceptible to road-damage from potholes, etc.

National Highway Traffic Safety Administration says to inflate your tire to the manufacturer's recommendation.
http://www.usatoday.com/money/consumer/autos/mauto849.htm

[austinado16]

I've always aired up according to the tire's ratings and never had a tire wear out in the middle first, or suffered from pot-hole damage.  I find that the air pressure recommendations by the auto manufacturer generally leave the tire way too soft for either good performance, or good gas mileage.

I run the PUP tires at the tire's rating, 80psi. They survived 12hrs in 100+*F temps, 70mph and 135*F tread temps on our trip to the Grand Canyon.

That's just how I role....

[wavery]

If the 60 & 90 PSI tires are the same physical size, then you're not as bad off as you think.  At 60 PSI, both tires should be rated to carry close to the same amount with the same "softness".

The pressure you should use is NOT NOT NOT what is printed on the tire, but the pressure that is on your camper's vehicle rating tag - should be on the driver side near the front, that has the GVWR, axle, etc on it.

The "C" tire needs 90 PSI in order to support its max weight = 990

The "B" tire needs 60 PSI in order to support its max weight = 780

However, if you put less than 90 PSI in the C tire, it can still carry the correct weight for that PSI.

That is why all vehicles have a manufacturer's label with the PSI.  What does your camper's label say is the recommended pressure?

For example, my Explorer has tires rated for 45 PSI on it.  However, the label says 35 PSI is what the manufacturer requires, and what my warranty is rated for.  Over-inflating a tire (ie, over the recommended amount, but under the max) will cause your tires to wear in the middle badly, because they are not being compressed enough to wear evenly.  Over-inflating can also make them more susceptible to road-damage from potholes, etc.

National Highway Traffic Safety Administration says to inflate your tire to the manufacturer's recommendation.
http://www.usatoday.com/money/consumer/autos/mauto849.htm

Sorry, you are mistaken on this one.

Trailer tires are different than car tires. They should be inflated to their max pressure.....cold.

When a trailer tire is not inflated to it's max pressure, it will ride on the side wall and quickly damage the tire. A tire that is rated at 90PSI could get away with slightly less but certainly not 60PSI as the tire may well blow out in a short period of time.
http://www.discounttire.com/dtcs/infoTrailerTireFacts.dos;jsessionid=FvxW3ZBHVFRY7BVpLC69PQNK7d52L91WWghQK30FM0Hj9ZzN

[AustinBoston]

Trailer tires are different than car tires.

Boy, isn't that the truth.  More than once, we've been hooked up to go, and I've noted that the van tires are way bigger than the trailer tires in every dimension except pressure.  Then I remember that the van runs around 1,000 lbs. per tire, while the trailer is over 1,600 lbs per tire.  :yikes:

Not only are they different, but they are asked to do a lot more.

Austin

[mike4947]

Please do not confuse advise listed for P (passenger) grade tires and ST (special trailer) tires.
ST tires have a different construction than P grade tires and the same rules do not apply. ST tires are designed to only be run at the maximum inflation pressure listed on the sidewall. That's from at least 3 makers of ST tires.

[zamboni]

From the Trailer Manufacturer's Association

Wheel and tire manufacturers recommend adjusting the air pressure to the trailer manufacturers recommended cold inflation pressure, in pounds per square inch (PSI) stated on the vehicles Federal Certification Label or Tire Placard when the trailer is loaded.
http://trailermanufacturersassociation.org/regulations/regulations4.html

Trailer tires are different than car tires.

They are?  American Institute standards are just that - measurable, repeatable, calculated values.  The same tests are used on all tires.  Why would a trailer tire be different values from a vehicle in terms of calculations of weight ratings?

When a trailer tire is not inflated to it's max pressure, it will ride on the side wall and quickly damage the tire. A tire that is rated at 90PSI could get away with slightly less but certainly not 60PSI as the tire may well blow out in a short period of time.

Are you smarter than all manufacturers?  Why on earth would they even bother putting values on the vehicle labels, then?

All tires, trailer or TV or big rig or car, should be inflated to the manufacturer's specs.  PERIOD.  Even the NHTSA says so.  Sorry, but I believe them, and all auto manufacturers, over Discount Tire.

An over-inflated tire will NOT compress the necessary amount when under-loaded.  Imagine a tire that could hold up to 2000 lbs, but you only have 1000 lbs (but still max pressure).  That means when you hit a pothole, there is not enough weight pushing DOWN on the tire to compress the tire and make it absorb the shock.  Instead, the strong, over-inflated tire says "neener-neener", and you bend a rim or break a spring instead.

A trailer tire will only "ride on the side wall" if there were sufficient WEIGHT to compress it.  If the tire could hold enough weight, then a lesser amount at a lesser pressure would ensure that the tire DID compress to the "ideal" amount.

We are talking a difference between 780 & 990 lbs per tire.  Assuming you want the tire to compress say 8%, then if you put 90 PSI into a 990 lb tire, without sufficient load, then it might only compress 3% - making it WRONG.

http://www.discounttire.com/dtcs/infoTrailerTireFacts.dos;jsessionid=FvxW3ZBHVFRY7BVpLC69PQNK7d52L91WWghQK30FM0Hj9ZzN

Doesn't say anything about not following your manufacturer's standards (they sidestep it and say inflate to tire, but do not say "ignore manufacturer").  It does say something about different SIZED tires, but not different weight rating (but does say do not mount trailer tires on cars).  It also says the combined carrying capacity should exceed the trailer by 20%.  It doesn't say you can't use different rated tires, FYI.

My trailer's tires are rated for 1480 lbs each @ 50 PSI.  There are 4 of them.  That makes 5920 lbs.  My manufacturer label also recommends 50 PSI, but the GVWR is 4947.  However, the NHTSA says the pressure should be 20% over GVRW.  Thus, 4947 * 120% == 5936.  OK, so this is 16 lbs over the theoretical perfect tire rating.

It is highly likely that the manufacturer had 4933 (the perfect ratio to the tires) as the target weight, and tweaked their manufacturing to get as close as they could.

Quotes from Canadian gov't website:
"The pressure recommendations molded into the side of the tire are maximum pressures for maximum load. Using these pressures at less than maximum load can adversely affect tire and tractor performance."
"Follow manufacturer's tire pressure recommendations when inflating tires"

The Auto Channel:
"When asked where a vehicle's proper tire-inflation pressure information is located, 67 percent of men and 45 percent of women said on the tires' sidewalls. In fact, that's wrong. "Proper tire pressure is vehicle-specific," Ferner said. "Tire sidewalls list the maximum pressure recommended by the tire manufacturer. Proper tire pressure information for a vehicle is found on a decal typically in the vehicle's door jamb or in the vehicle owner's manual.""
http://www.theautochannel.com/news/2006/05/10/006266.html

AAA and Goodyear also agree:
http://www.theautochannel.com/news/2001/08/29/028414.html

Towing World:
"Always follow the tire manufacturers recommendations on inflation, rotation and balancing"
http://www.towingworld.com/articles/steeringcontrols.htm

Web Bike World
"Make sure you follow the trailer manufacturer's recommendations for tire pressure"
http://www.webbikeworld.com/motorcycle-trailer/motorcycle-cargo-trailer/

[austinado16]

Hey Glen,
That's some great research, but seriously......tires do just fine when inflated past what the sticker says in the door jamb or in the cabinet.  And no, you're not going to dent a rim or destroy a tire by hitting a pot hole.

First, remember that when a car is built, there is quit a bit of thought that goes into the overall ride characteristic.  Since automobiles have to be dumbed down to the lowest common denominator of the American buying public, they are built to ride a certain way.  Tire brand choice and inflation has a big part in that.....and it's why a lot of people jump ship and install better tires, better wheels, better shocks/struts, springs, sway bars, etc.

Some interesting things about recommended psi on the manufacturer's decal.
1) That info is based on when the vehicle was built and could be very outdated comprared to current tire construction and other "things."
2) That info is to provide a certain ride quality.
3) That info doesn't tell you to increase the tire pressure in order to raise the hydroplaning speed of the vehicle.
4) That info doesn't tell you that an increase in tire pressure will improve gas mileage
5) That info doesn't tell you that an increase in tire pressure will stiffen the sidewalls and help the vehicle handle more crisply.

If I buy a Goodyear Assurance Triple Tread for my Audi Quattro and it's rated at 44psi, but my decal says 29psi, I'm gonna be rolling around on $400 worth of marshmallows.  Not my cup of tea, and guess what?  The car rides, drives and handles better with the pressure up at 42psi........18,000mi a year like that and we've still not hit a pot hole and dented a rim or destroyed a set of tires by prematurely wearing out the centers.

And speaking of this whole dent-a-rim theory.  Remember that tires are rubber.  When you hit a curb or pothole or rock in the road, the tires do not transfer that force as if they were solid material.  It's dissapated all over the tire and a harder tire is going to withstand the impact much better, because it is firm enough to dissapate the energy.  Drive around on a soft tire, and that is a tire that will smash out under an impact and have more potential for the actual tire beads to come into contact with the offending object.....and bend the rim.

Sometimes it's easy to get all wrapped around the axle of "This is what they tell me to do, so I better do it."  May I suggest that you go out and try some real world testing of your own and then make an opinion based on that?  But don't take the Explorer.  That whole "roll if upset, land on the roof, cave in and kill the occupants" thing isn't worth the risk.  We'd like to have you and your family around for more camping fun and discussions here!

[dupreet]

Hey - one more thing to think about MB ---

How old is your spare tire?  If it is original to your camper and is the ripe old age of 10, you probably don't want it on the road.  While it might be in 'new' condition and look okay, it is likely to be dryrotted and prone to blowing under weight/speed/usage.

Sorry Dude - good luck,

Todd

[AustinBoston]

They are?  American Institute standards are just that - measurable, repeatable, calculated values.  The same tests are used on all tires.  Why would a trailer tire be different values from a vehicle in terms of calculations of weight ratings?

Because they don't do the same things.  Does your trailer steer?  Mine sure doesn't.  Does your trailer have a drive axle?  Mine doesn't.  Does your trailer cary passengers?  Mine doesn't.

Are you smarter than all manufacturers?  Why on earth would they even bother putting values on the vehicle labels, then?

Because in the United States, they are required to do so.  If you look carefully at the label, the pressure they give is for a SPECIFIC TIRE.  On every trailer I've seen, when you go to that specific tire, it is the maximum pressure for that tire.

All tires, trailer or TV or big rig or car, should be inflated to the manufacturer's specs.  PERIOD.  Even the NHTSA says so.  Sorry, but I believe them, and all auto manufacturers, over Discount Tire.

That's why you included this link:

Towing World:
"Always follow the tire manufacturers recommendations on inflation, rotation and balancing"
http://www.towingworld.com/articles/steeringcontrols.htm

The tire manufacturers say inflate trailer tires to the max pressure.

An over-inflated tire will NOT compress the necessary amount when under-loaded.  Imagine a tire that could hold up to 2000 lbs, but you only have 1000 lbs (but still max pressure).  That means when you hit a pothole, there is not enough weight pushing DOWN on the tire to compress the tire and make it absorb the shock.  Instead, the strong, over-inflated tire says "neener-neener", and you bend a rim or break a spring instead.

I'm at a loss for how to respond to this.  

First, tires don't absorb shocks, they add a time delay to them.

Second, an over-inflated tire will only bend a rim if an under-inflated tire was going to totally smash the rim beyond all recognition.  Under inflated tires bend rims, over-inflated tires reinforce them.

Third, with a lighter trailer, less absorbtion is necessary, so less compression is necessary.

A trailer tire will only "ride on the side wall" if there were sufficient WEIGHT to compress it.  If the tire could hold enough weight, then a lesser amount at a lesser pressure would ensure that the tire DID compress to the "ideal" amount.

I'm glad you put "ideal" in quotes, because there really is no such thing.

We are talking a difference between 780 & 990 lbs per tire.  Assuming you want the tire to compress say 8%, then if you put 90 PSI into a 990 lb tire, without sufficient load, then it might only compress 3% - making it WRONG.

I can tell you're not a tire engineer.  We're talking the difference between perhaps 8% and 7%.

Doesn't say anything about not following your manufacturer's standards (they sidestep it and say inflate to tire, but do not say "ignore manufacturer").  It does say something about different SIZED tires, but not different weight rating (but does say do not mount trailer tires on cars).

I wonder why...perhaps because trailer tires are, um, different?

It also says the combined carrying capacity should exceed the trailer by 20%.  It doesn't say you can't use different rated tires, FYI.

My trailer's tires are rated for 1480 lbs each @ 50 PSI.  There are 4 of them.  That makes 5920 lbs.  My manufacturer label also recommends 50 PSI, but the GVWR is 4947.

Big clue here, but you miss it.

However, the NHTSA says the pressure should be 20% over GVRW.

It says the tire's rating (meaning weight rating) should be 20% over GVWR.  Keep in mind that that is not the axle weight, since another 10-15% is supposed to be on the tongue.

Thus, 4947 * 120% == 5936.  OK, so this is 16 lbs over the theoretical perfect tire rating.

It is highly likely that the manufacturer had 4933 (the perfect ratio to the tires) as the target weight, and tweaked their manufacturing to get as close as they could.

So these tires are still at maximum pressure by everyone's recommendation, even though they are at 30-35% less than the rated load...the tires Wayne said to inflate to Max had a weight rating difference of 27%. (990-780)/780x100%=26.9.

Austin

[zamboni]

Wow.  Where to begin...

Because they don't do the same things.  Does your trailer steer?  Mine sure doesn't.  Does your trailer have a drive axle?  Mine doesn't.  Does your trailer cary passengers?  Mine doesn't.

No, but my trailer, just like my car, categorically:
a) Carries MASS, designed to do so at an optimum setting.  PERIOD.

No, my trailer does not steer or drive, but nor do most cars' rear axle (all front-wheel-drive).  Sorry, dumb argument.

Tires are designed to primarily do one thing:  Suspend mass over a traveling distance at a pre-determined ratio of compression to rolling resistance, and primarily to smooth out shock.

Please look up the benefits of a pneumatic tire, and how they are superior to a solid tire (which is what an over-inflated tire approaches to acting like).  Note, the critical importance of the cushion - if it is overinflated, the cushion properties diminish.

Because in the United States, they are required to do so.  If you look carefully at the label, the pressure they give is for a SPECIFIC TIRE.  On every trailer I've seen, when you go to that specific tire, it is the maximum pressure for that tire.

Not me.  At rallies, I've carried my digital pressure gauge around and checked friends' tires to compare them to the labels (and found that about 80% have under-inflated tires).  The labels on trailers, just like cars are designed by the manufacturers to support a correct weight.

The tire manufacturers say inflate trailer tires to the max pressure.

True, what I left out was that the tire manufacturer has no idea of the trailer it is installed on.  Given that, their only leeway is to use the tire label - because if the trailer says 80 PSI, but you put a 60 PSI tire on it, and inflate to 80, you may have a very bad situation.  Thus, all tire manufacturers say to inflate to their tire labels, because that is the only way THEY can protect them self.  I included that link in the wrong section (meant to bolster the argument where of course Discount Tire will say to use the tire labels).

First, tires don't absorb shocks, they add a time delay to them.

Tires "absorb" shocks by instead of transferring all those pounds-of-force IMMEDIATELY to the vehicle's shock absorbers, they instead bounce the force around inside the wheel and this enables the force to be spread out over time.  Not a time delay - huge difference.  (Illustrative example, not accurate--) Instead of 1000 instant pounds of force on the frame in 10 milliseconds, it does 100 pounds of force spread over 100 milliseconds.  This means that a shock absorber that can withstand 300 lbs of force can easily withstand the shock with a suitably "bouncy" tire.  If you have a "solid" tire (one that is at max PSI without much load), in physics, it acts as a SOLID tire.

Second, an over-inflated tire will only bend a rim if an under-inflated tire was going to totally smash the rim beyond all recognition.  Under inflated tires bend rims, over-inflated tires reinforce them.

True; the over-inflated tire destroys shocks & bends frames.  They act as if you have a solid piece of cement you are "rolling" on.  You left out quoting my "they break a spring".

Third, with a lighter trailer, less absorbtion is necessary, so less compression is necessary.

Not true at all.  The rating of the axle is designed such that the tire absorbs a specific amount of the jolt of the gross mass of the trailer and spreads it out over time such that the axle can handle it.  If the tires were solid blocks, the first pothole would smash the axle or springs.  This is high-school physics (force over time).

I can tell you're not a tire engineer.  We're talking the difference between perhaps 8% and 7%.

So?  I used illustrative numbers (because I do not posses the specific compression ratio numbers for the unknown types of rubber in the tire).  I am, however, a mechanical engineer.  The physics of tires is based on one simple thing: PHYSICS.  I can tell that you are not.

It says the tire's rating (meaning weight rating) should be 20% over GVWR.  Keep in mind that that is not the axle weight, since another 10-15% is supposed to be on the tongue.

Sorry, but the manufacturer must create a vehicle that can support its entire weight.  Period.  If you are going uphill, and your TV hits a bump, the entire weight (and more, some of your TV, hence the 20% leeway) can, and does get transferred to the trailer.

Additionally, just because you are supposed to have 10-15% on the tongue, does not mean that everyone does.  Thus, the manufacturer must factor in the chance that 100% of the trailer weight will be carried by the wheels.  That is why the axle must also be rated to carry the GVWR.  Again, see the issues surrounding Rockwood Roo campers from before about 2005-6 (where the tires, hitch, frame - everything BUT the axle could easily carry more than the GVWR).

It would be incredibly foolish and fatal not to assume that all the mass may be on the wheels/axles.  How many trailers out there have under-recommended tongue-weights?  I'm sure many do, since people may have a load of firewood in the back of the trailer, things on the back bumper, full black & grey tanks with empty fresh, etc (or vice-versa, whichever puts the most load on the back).


Last, simply one thing to consider about trailers...  There are 3 weights for a trailer:
1) Trailer Mass (weight)
2) Axle weight
3) GROSS vehicle weight

Very coincidentally, the GVWR for most campers may well be the tire's max PSI, because that is the LEGAL MAXIMUM you can carry!  If the tires are rated for 2880 lbs (2 tires at 1440), then the GVWR cannot exceed that, and the manufacturer puts that on the label.  On most campers, the frame and axles can support more, but the tires are the limiting factor.  Usually, however, the tires are closely matched to the axle, making BOTH the limiting factor.  Replace both of those, and then you branch into how much can the frame support.

However, if the tires are beefier than other parts (NOTE: SEE ROCKWOOD HYBRIDS FROM 2+ MORE YEARS AGO), then the limiting factor is not the tire, so is not labeled to be at the max PSI.  No, in some cases, the max rating is the AXLE capacity.


If you put tires on your trailer that are different from the trailer manufacturer's rating, then simply contact the tire manufacturer and ask for the correct PSI to support the trailer's GVWR.  Thus, you ensure you have the correct "bounce" (shock absorption) in the trailer tire for your camper.

[flyfisherman]

They are?  American Institute standards are just that - measurable, repeatable, calculated values.  The same tests are used on all tires.  Why would a trailer tire be different values from a vehicle in terms of calculations of weight ratings?

Weavery is quite correct when he posted that trailer tires are different than passenger car and light truck tires.


Of course, here's a trailer manufacturer and parts supplier that says trailer tires are different, but then, what do they know?  You might try emailing them and seeing if you can straighten out their folly, too!


http://www.championtrailers.com/tire_art.html



Fly

[austinado16]

Good grief!  I've never seen a thread get so wound up.

"over inflated tires acting as solid objects......walking around checking the tire pressures in other peoples tires......delay in transmitting shock isn't really time delay"

Pass the popcorn. This is starting to get interesting.