Tire pressure when towing

[Traction]

Originally Posted By: CapriRacer
The first step is to look in the owners manual. What limitations does the vehicle manual place on the vehicle? What does the manual say about tire pressures?

In this case, I'm going to guess it says that the trailer is too large for the truck - but there is the possibility that it is marginal. I'm also going to guess that the vehicle has P metric tires and the vehicle tire placard says 35 psi.

If I understand this correctly, what is listed on the vehicle tire placard is adequate for the max conditions - SO - the tires will be either overloaded or marginal - and no amount of additional pressure is going to change that.


I understand most P tires are rated for max load at 35 psi even when rated for 51 psi max. Why are some OE cars calling for 44 psi on the placard for example, if it make no difference in going over 35 in load capacity for occasional heavy loads a vehicle is capable of carrying? Even though not specifically stated in load/inflation tables, I find it hard to believe that adding a little extra air would not be a benefit

 

[CapriRacer]

Originally Posted By: Traction
I understand most P tires are rated for max load at 35 psi even when rated for 51 psi max. Why are some OE cars calling for 44 psi on the placard for example, if it make no difference in going over 35 in load capacity for occasional heavy loads a vehicle is capable of carrying? Even though not specifically stated in load/inflation tables, I find it hard to believe that adding a little extra air would not be a benefit


I think you will find that the only time values over 35 psi were specified is on older European cars - and it was a dual specification - and that's because of the higher speeds on the Autobahn. I also think the practice of displaying dual inflation pressures was discontinued a few years back on US models - and my best guess as to why that happened is because NHTSA saw this as adding confusion to the situation.

HOWEVER, there have been a couple of exceptions where a value larger then 35 psi appeared on a US vehicle tire placard for P metric tires - and my best guess on those is for handling reasons. Those are pretty rare.

And the deal about overinflating not being a benefit: I am stating that an overloaded condition will likely fail a tire EVEN IF the tire is overinflated.

 

[TiredTrucker]

Really too bad that the tire manufacturers don't provide load/pressure charts for the auto/pickup market as easily as they do for the commercial truck market. I live by those charts for my commercial stuff and they have always gotten me the best tire performance and longest life out of my heavy truck tires. Got 447,000 miles out of my last set of Michelin drive tires, still had 8-9/32 tread left, no uneven wear, and dealer gave me $150 per tire when I put on the new ones. I tried getting Michelin, BFG, and others to ante up with a recommended load/pressure chart for my pickup tires, and they just punted back to the vehicle OEM. Seems stupid, as the vehicle OEM's don't make tires.

 

[mjoekingz28]

Is that why all of our roads are in bad shape TiredTrucker? The tread is so hard to make them last 400k AND they are often overloaded. I think this is why roads crumble and get grooves that hold water and cause hydroplaning.

I think that is criminal to have a million mile tire. Somethings gotta give and it is the roads. 100-150 should be plenty. Half of yall are running recaps anyway that blow all over the interstate in the summer.


Forgive me if I am wrong, I have just been wondering why roads deteriorate so rapidly, and with finding out that heavy truck tires go over half a million miles I think I now see.


Also, is this weight distributing hitch basically just a sway bar? I looked it up on images and cannot understand the physics of what it is supposed to do.

 

[RhondaHonda]

Mjoekingz28-the roads are bad because you live in Mississippi! I couldn't believe how bad the roads were in Jackson.

The weight distributing hitch just moves some of the tongue weight towards the front of the vehicle.

 

[claluja]

Make sure he pays attention to psi of the trailer tires. Too low will go boom. Not fun. My trailer tires say 80 psi max cold. FWIW, I started today with 73 psi in them, and they got to a touch over 80 psi hot after 600 miles or so.

 

[UltrafanUK]

Originally Posted By: 09_GXP
Originally Posted By: UltrafanUK
TRY READING YOUR OWNERS HANDBOOK TIRE PAGE!

The tire pressures approved for towing should be listed and are often the same as those listed for max
weight on a highway. Never heard of using the max tyre pressure listed on the sidewall before.


Maybe the manuals are different in the UK. The F150 manual does not have any tire pressure info aside from set it to the door label.


It should be listed on both, but the door panel placards get dirty or pulled off. Never heard of an owners manual not listing tyre pressures before.

 

[TiredTrucker]

Actually, the drive tires on my semi are some of the lowest rolling resistance tires made. They impact the road less than many pickup tires. Also, even though the side walls say max 120 psi, I typically run them at between 95 -100 psi per the Michelin load / pressure chart. They are not overloaded. They are always loaded to below their max capability. No more than 17,000 lb per axle, and they are rated for much higher than that. 445/50R22.5 tires. $1100 each.

The reason the roads are bad is because highway money get siphoned off for such things as studies to understand why monkeys have feces fights in the zoo. And also that road contracts typically go to lowest bidders or cronies that know how to cut corners. The fact that it is rare, even with today's technology, to get a bridge and a road the same height should say something. Try drinking an open lid hot cup of coffee when crossing a bridge and see what I mean. And that in 1942, we built the Alaska - Canada highway, all 1500 miles, in 18 months, yet today construction outfits can't seem to get a new road intersection done in that time frame.

 

[CapriRacer]

Originally Posted By: TiredTrucker
Really too bad that the tire manufacturers don't provide load/pressure charts for the auto/pickup market as easily as they do for the commercial truck market. I live by those charts for my commercial stuff and they have always gotten me the best tire performance and longest life out of my heavy truck tires. Got 447,000 miles out of my last set of Michelin drive tires, still had 8-9/32 tread left, no uneven wear, and dealer gave me $150 per tire when I put on the new ones. I tried getting Michelin, BFG, and others to ante up with a recommended load/pressure chart for my pickup tires, and they just punted back to the vehicle OEM. Seems stupid, as the vehicle OEM's don't make tires.


The reason why car and light truck manufacturers do not sanction tire inflation pressures different than what they specify on the vehicle tire placard is that unlike big rigs, cars and light trucks handle quite differently at those different pressures - AND - those car and light truck manufacturers have only done handling studies at the specified pressures. The amount of ride and handling work they do is enormous and to duplicate that for any other set of pressures is quite expensive.

 

[440Magnum]

Originally Posted By: CKN
Originally Posted By: Kuato
Originally Posted By: 440Magnum


The data plate ON a pickup is FOR a pickup AT its maximum load (or else the door placard has multiple entries for different loadings). Put another way- if you have to inflate over the door placard in order to reduce observed pressure climb, then you have either overloaded the truck chassis OR you are using tires that aren't actually up to the job (wrong load range, or poor temperature class rating). Don't cheap out on truck tires.

Running tires grossly over-pressure (relative to the placard) is a good way to wind up with your own trailer stuffed in your radiator and the entire rig stuffed under a semi. The only exception would be if you change tire type (eg. put LT tires on a light-duty pickup where the door placard only covers P-metric tires).


Hmm interesting, because I thought my owner's manual indicated that higher pressures may be needed while towing or heavy loading.

But if your assertion is true:

Then please explain to me how several people were having sway problems with a light (4000lb) trailer, their max towing was 8000# or above, when tires were inflated to door plate numbers, but when they went to pressures closer to the tire's max, the sway problems went away. In some instances they went to HD tires, and increased inflation there.

Also, please explain to me how front tire wear on several vehicles I've owned was extreme on both edges and virtually nil in the center (classic presentation of underinflation) at the placarded pressure, which was then cured by inflating to maximum tire pressure? And by the way, this made handling much more secure in all conditions.

We may never agree on this point, just wanted to illustrate with things in my experience. IMO the placard maximizes the ride quality of the vehicle, NOT necessarily performance or load carrying capability. In fact, a lower tire pressure results in a lower carrying capacity for the tire than a higher inflation pressure.

Please see:
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=195

http://www.fourwheeler.com/how-to/wheels-tires/1407-understanding-tire-load-ratings/

http://www.f150forum.com/f82/tire-pressures-weight-carrying-capacity-221869/




Exactly!

You will get "squirm" if you don't have enough pressure in your rear tires when towing. Especially with those tires that have soft sidewalls. This MAY NOT be the pressure indicated on the placard.


I have seen many tire placards with dual entries for loaded vs. unloaded on pickup trucks. The owners' manual is the final word if the placard isn't... but most definitely NOT the tire "max inflation pressure" stamped on the sidewall. As I said, if you have to inflate close to that number, you need different tires or a bigger truck. You should always have at least some margin between your cold inflation pressure and the max pressure on the tire sidewall, IMO.

Sadly, a lot of people out there tow in configurations that their truck is most definitely NOT rated for, and they don't realize it. People will put a trailer on and may be under the max trailer weight rating, but will be over the combined vehicle weight rating, especially with crew-cab and 4x4 trucks. You have to look at tongue weight, total trailer weight, and total rig combined weight and not exceed the truck's rating for any one of them.

 

[mjoekingz28]

When you overload those rears they sure do get squirrely.

 

[Ken2]

Higher pressure, up to the sidewall max cold inflation pressure, may offer more stability. Stability when towing is good.

10% tongue weight is the bare minimum. More is better, up to the max tongue weight the truck & hitch can handle. The more trailer weight forward of the axle (thus higher tongue weight), the more stable the trailer will tow.

RV trailers and semi trailers are nothing alike. Semi trailers are made to be reliable and stable. RV trailers are made to be cheap.

 

[TiredTrucker]

Originally Posted By: CapriRacer
Originally Posted By: TiredTrucker
Really too bad that the tire manufacturers don't provide load/pressure charts for the auto/pickup market as easily as they do for the commercial truck market. I live by those charts for my commercial stuff and they have always gotten me the best tire performance and longest life out of my heavy truck tires. Got 447,000 miles out of my last set of Michelin drive tires, still had 8-9/32 tread left, no uneven wear, and dealer gave me $150 per tire when I put on the new ones. I tried getting Michelin, BFG, and others to ante up with a recommended load/pressure chart for my pickup tires, and they just punted back to the vehicle OEM. Seems stupid, as the vehicle OEM's don't make tires.


The reason why car and light truck manufacturers do not sanction tire inflation pressures different than what they specify on the vehicle tire placard is that unlike big rigs, cars and light trucks handle quite differently at those different pressures - AND - those car and light truck manufacturers have only done handling studies at the specified pressures. The amount of ride and handling work they do is enormous and to duplicate that for any other set of pressures is quite expensive.


Probably quite true.

 

[leeaspell]

Take the car tires off it and put on some real truck tires.

 

[TiredTrucker]

What would that real truck tire be? Something like the 445/50R22.5 14 ply tires on my commercial truck? I always get a kick out of what constitutes a "real truck" whatever in some folk's minds. You get the tire for the load you are working with, just that simple.

 

[leeaspell]

Originally Posted By: TiredTrucker
What would that real truck tire be? Something like the 445/50R22.5 14 ply tires on my commercial truck? I always get a kick out of what constitutes a "real truck" whatever in some folk's minds. You get the tire for the load you are working with, just that simple.


How about a non P rated tire. My wife's fusion has P rated tires, but then again it doesn't haul anything. My truck came with P rated tires, instantly changed them to LT (light truck).

My truck is rated for 14,000lbs and 3500lb payload, with my p rated tires. How heavy of a camper can I pull

 

[CapriRacer]

Perhaps it is time to explain why some pickup trucks come with P type tires.

There are basically 2 types of tires available for trucks under 10K GVW - P type, and LT type.

LT tires have large load carrying capacities, but they don't ride well, and aren't very fuel efficient. P type tires are the opposite.

So on lower capacity trucks, it just makes sense to use P type tires. You can changeover a truck from P type tires to LT type tires, but what you get is a harsher riding vehicle and worst fuel economy.

But you generally can not change a truck from LT tires to P type tires. The load carrying capacity required by those bigger trucks is too large.

 

[George Bynum]

Originally Posted By: leeaspell
My truck came with P rated tires, instantly changed them to LT (light truck).

My truck is rated for 14,000lbs and 3500lb payload, with my p rated tires. How heavy of a camper can I pull


If it wouldn't be considered rude, what is the p rated tire the manufacturer used on your 14,000lb rated, 3500lb payload, truck? I'm unaware on any.

 

[OVERKILL]

Originally Posted By: leeaspell
Originally Posted By: TiredTrucker
What would that real truck tire be? Something like the 445/50R22.5 14 ply tires on my commercial truck? I always get a kick out of what constitutes a "real truck" whatever in some folk's minds. You get the tire for the load you are working with, just that simple.


How about a non P rated tire. My wife's fusion has P rated tires, but then again it doesn't haul anything. My truck came with P rated tires, instantly changed them to LT (light truck).

My truck is rated for 14,000lbs and 3500lb payload, with my p rated tires. How heavy of a camper can I pull


The P-rated tires were capable of supporting whatever the truck was sold as being able to carry/tow. If you are running the P-rated tire pressure in the LT-rated tires, you may actually have reduced the load carrying capacity of the vehicle.

 

[PumpPusher]

Maybe I'm under thinking this, but I buy tires spec'd by the OEM. Then I run the max pressures listed on the door jamb since I have a F350 flatbed and never know what weight I'll be carrying. I know what my truck is spec'd to carry and or pull, so I stay under that. Then I just drive down the road?