Towing Tire Pressure (1 Viewer)

[chilibit]

I am hoping that this thread title will drawn gaijin out of the woodwork.

Typically I have towed with a 5.7 Tundra. I am taking a track car over the mountains for 500 miles using the LC200. The total towed load is less than 4000 lbs using a double axle trailer with electric brakes on both axles. It is open trailer and wind load should not be an issue.

The 200 is using 17" RW running Toyo ATX 2 in P-METRIC rating. Based on load tables and my experience I use 33lbs all around and it works in terms of wear patterns. The tongue weight on the back of the unloaded 200 is 410 lbs.

The operator's manual does not address tire pressures for towing. My load is not really an issue but I feel like raising the rears by 3 lbs just on gut feel. If I were using an LT rated tire I would not. Ambient temperatures should not be an issue and I can monitor tire pressures in route. Rationally I should not have to increase pressures. But then there is gut feel.

Thoughts?

 

[TeCKis300]

Whenever I tow, I personally up the pressures. Partially because it's safer for the tires to avoid too much heat in them, but also because I find it more stable. Depending on what I'm towing, I'll go between 35-40 PSI. Depends on your specific tire as well, and how much load capability (and pressure capability) they have.

I'll defer to our in house pressure expert gaijin, who I'm sure will comment shortly.

 

[rubicondon53]

Ive been towing trailers my entire 45 plus years of driving experience. Started out pulling two axle livestock trailers with F200 then 250 pick ups, then big stuff IH loadstar dumps dragging all kinds of heavy equipment, then 18 wheelers. Now I'm retired and drag an off road trailer behind my 80. 33-34 is a perfect pressure for your rig when empty. Loaded down and pulling a trailer I'd up them to at least 38-40 lbs. If you feel your rear tires rolling out around tight turns or if they are running hotter than your front tires ( palm on sidewall test) up em some more. But I think you'll be fine at 38-40lbs.

 

[Romer]

I run at 42psi when I am not towing. Based on the weight of the vehicle that seems appropriate. I haven't thought about increasing for towing

 

[chilibit]

I do a palm-on-tire walk around every stop. Once when I arrived in NC I mentioned my rear trailer tires were slightly warmer than the fronts and the trailer was dead level. Dead level is not as easy as it sounds. Turns out the rears pick up heat front the front axle tires and are shaded from cooling air flow by the front axle tires. So perfectly normal but new to me. Thanks for your thoughts everyone. The P-metric sidewalls are flexy but my windscreen header is 3 feet lower than the 200 so my side profile is decently low WRT side winds.

 

[gaijin]

I am hoping that this thread title will drawn gaijin out of the woodwork.

Typically I have towed with a 5.7 Tundra. I am taking a track car over the mountains for 500 miles using the LC200. The total towed load is less than 4000 lbs using a double axle trailer with electric brakes on both axles. It is open trailer and wind load should not be an issue.

The 200 is using 17" RW running Toyo ATX 2 in P-METRIC rating. Based on load tables and my experience I use 33lbs all around and it works in terms of wear patterns. The tongue weight on the back of the unloaded 200 is 410 lbs.

The operator's manual does not address tire pressures for towing. My load is not really an issue but I feel like raising the rears by 3 lbs just on gut feel. If I were using an LT rated tire I would not. Ambient temperatures should not be an issue and I can monitor tire pressures in route. Rationally I should not have to increase pressures. But then there is gut feel.

Thoughts?

For starters ... what size are your P-Metric tires?

 

[chilibit]

P285/70R17

Toyota specifies LT though.

 

[gaijin]

P285/70R17

Toyota specifies LT though.

Toyota specifies a Load Limit of 2,512 pounds for P-Metric tires on the LC200.

At the 33psi you are currently using, you have a Load Limit of 2,774 pounds in your P285/70R17 tires - 262 pounds more than spec per tire.

If you like 33psi, then go ahead and stay with that. The added 524 pounds of Load Limit per axle you have with the extra pressure is more than enough to cover the 410 pound tongue weight you mentioned.

Bottom line: Stick with the Cold Tire Inflation Pressure of 33psi F/R for normal road use and for towing.

P.S. If you ever want to play around with the specified pressure for those tires onroad, it is 27psi F/R. This will bring the Load Limit down to 2,527 pounds which is still above the 2,512 pound spec. This will change the "spring rate" of the tires, however, and make them feel softer. If you don't like the softer ride, or simply feel more comfortable running 33psi instead, that's no problem - do whatever you want.

HTH

 

[chilibit]

Toyota specifies a Load Limit of 2,512 pounds for P-Metric tires on the LC200.

At the 33psi you are currently using, you have a Load Limit of 2,774 pounds in your P285/70R17 tires - 262 pounds more than spec per tire.

If you like 33psi, then go ahead and stay with that. The added 524 pounds of Load Limit per axle you have with the extra pressure is more than enough to cover the 410 pound tongue weight you mentioned.

Bottom line: Stick with the Cold Tire Inflation Pressure of 33psi F/R for normal road use and for towing.

P.S. If you ever want to play around with the specified pressure for those tires onroad, it is 27psi F/R. This will bring the Load Limit down to 2,527 pounds which is still above the 2,512 pound spec. This will change the "spring rate" of the tires, however, and make them feel softer. If you don't like the softer ride, or simply feel more comfortable running 33psi instead, that's no problem - do whatever you want.

HTH

Your comments sync fairly closely with our (my local tire guru and me) assessment of the load tables. I do find that at 29 I am getting more wear at the outer edges of the tires as opposed to 33 where it is fairly even across the entire tread. Some of this is driving style but I have many other vehicles for raucous driving and my use of the 200 is fairly sedate. I do thank you for the input and it does ease my mind a bit. I plan to run 37 on the way down and see what the tires tell me. Ciao

 

[gaijin]

I plan to run 37 on the way down and see what the tires tell me. Ciao

According to my tables, the Load Limit for those tires maxes out at 2,833 pounds @35psi. Toyo allow for pressures up to 44psi, but the Load Limit remains the same from 35psi - 44psi. You are not gaining anything by running at 37psi. All you are doing is decreasing the tire's Spring Rate which would dramatically reduce the tire's capability to deal with transient shock (e.g. potholes) without sustaining damage.

Again, at 33psi you are already above what is required - even when towing.

FYI

 

[Markuson]

According to my tables, the Load Limit for those tires maxes out at 2,833 pounds @35psi. Toyo allow for pressures up to 44psi, but the Load Limit remains the same from 35psi - 44psi. You are not gaining anything by running at 37psi. All you are doing is decreasing the tire's Spring Rate which would dramatically reduce the tire's capability to deal with transient shock (e.g. potholes) without sustaining damage.

Again, at 33psi you are already above what is required - even when towing.

FYI

Hey @gaijin, I wonder how many read your numbers not realizing how incredibly varied the numbers are based on teh specific tire. Maybe you need to add a disclaimer to your sig...that your PSI pressure recommendations are SPECIFIC to each tire type/size in these discussions. For example...my pressure is 41-42 on my 285/70/17 KO2 E's...where this one would be as low as 27. I, for one, still feel a bit mystified by how you arrive at your figures...and I suspect most average Joes hear a number and tend to apply it universally to the vehicle--just as the door tag seems to if you don't know any better...

 

[gaijin]

Hey @gaijin, I wonder how many read your numbers not realizing how incredibly varied the numbers are based on teh specific tire. Maybe you need to add a disclaimer to your sig...that your PSI pressure recommendations are SPECIFIC to each tire type/size in these discussions. For example...my pressure is 41-42 on my 285/70/17 KO2 E's...where this one would be as low as 27. I, for one, still feel a bit mystified by how you arrive at your figures...and I suspect most average Joes hear a number and tend to apply it universally to the vehicle--just as the door tag seems to if you don't know any better...

You don't have to look any further than this thread to find good examples of your point - there were 3 different users recommending specific tire pressures when they didn't even know the size of the tires under discussion

BTW, the recommended Cold Tire Inflation Pressure for your LT285/70R17 KO2's is 40psi F/R.

Science drives the numbers, and I've explained it many times.

But hey, I'm not the tire pressure police - folks can run whatever pressures make them happy. I am the bow and users are the arrows; all I can do is provide guidance and then ... you're on your own.

 

[Markuson]

You don't have to look any further than this thread to find good examples of your point - there were 3 different users recommending specific tire pressures when they didn't even know the size of the tires under discussion

BTW, the recommended Cold Tire Inflation Pressure for your LT285/70R17 KO2's is 40psi F/R.

Science drives the numbers, and I've explained it many times.

But hey, I'm not the tire pressure police - folks can run whatever pressures make them happy. I am the bow and users are the arrows; all I can do is provide guidance and then ... you're on your own.

Oops! Ya...40. That's actually where mine are at right now... It's just that when I'm driving, they tend to warm up to 41-43...so I get that visual in my head from the dash readout. Amazing how much it can fluctuate due to conditions and sun, etc.

You aren't the tire pressure police?? Ahaha! OK, then I officially nominate you for that position.
I like to think of you as the PSI Ninja, myself....

We clearly need the guidance. Anyway, thanks for always being so helpful.

 

[Dan Higgins]

Yeah. It doesn't help that my TPMS reads 2 PSI lower than what is real. So first thing in the morning my TPMS readout says 38. By afternoon it can be 42.

 

[TeCKis300]

I likewise am a bit perplexed about the process by which these pressure recommendations come about. While I'm sure load ratings are a good first approximation to pressures, I believe there's other considerations as well. I think we all agree that at a minimum, whatever pressures are identified, that they must at least meet the load handling requirements of the setup.

Beyond that, I would believe stability to most definitely be a criteria. While this is somewhat subjective, the dynamic lateral loads while towing really has a big impact to handling feel. Not just a comfort thing, but stability in a turn and resistance to sway. I have to ask gaijin if he's actually ever towed? There's other parameters to tire pressures that are not discussed for lateral stability, such as tire size to wheel width, sidewall height, tire build, etc. More pressure gives more load capacity yes, but it most definitely gives more lateral stability. Especially for higher profile or P-metric tires.

 

[Markuson]

Yeah. It doesn't help that my TPMS reads 2 PSI lower than what is real. So first thing in the morning my TPMS readout says 38. By afternoon it can be 42.

4 degrees can easily happen simply due to sunlight on one side of the vehicle parked. Add friction and road heat, and it will move all over the place throughout the day. That's why the PSI Ninja (gaijin always says to base pressures when cold.

My 200 can add 3 degrees even in these mild days when parked with sun on one side, and even more when the sun really beats down hard in the summer.

 

[gaijin]

I likewise am a bit perplexed about the process by which these pressure recommendations come about. While I'm sure load ratings are a good first approximation to pressures, I believe there's other considerations as well. I think we all agree that at a minimum, whatever pressures are identified, that they must at least meet the load handling requirements of the setup.

Beyond that, I would believe stability to most definitely be a criteria. While this is somewhat subjective, the dynamic lateral loads while towing really has a big impact to handling feel. Not just a comfort thing, but stability in a turn and resistance to sway. I have to ask gaijin if he's actually ever towed? There's other parameters to tire pressures that are not discussed for lateral stability, such as tire size to wheel width, sidewall height, tire build, etc. More pressure gives more load capacity yes, but it most definitely gives more lateral stability. Especially for higher profile or P-metric tires.

You're correct, there are many factors involved in arriving at a recommended Cold Tire Inflation Pressure. OEM pressure recommendations are critical for determining a reference Load Limit, but then one must evaluate LT vs P tire type, GAWR (Gross Axle Weight Rating) and what percentage that is in relation to the combined axle tire Load Limit, GVWR (Gross Vehicle Weight Rating) and how the total Load Limit relates to it; specific tire ratings like Load Index, Max recommended inflation pressure, Min recommended inflation pressure, etc. Search my posts to find more detailed step-by-step process description.

Since you asked, yes I have towed. But I have to ask, is that how you would choose a doctor? Doc, I've just been shot, but I don't want you treating me unless you have the experience of being shot. I hope you wouldn't delay treatment waiting for a doc who met your arbitrary criterion.

Just for the record, in the LC Owner's Manual, Toyota is happy with 33psi for towing up to the limits of the vehicle - with the stock P-Rated 285/60R18 tires. To be fair, they also recommend using a WDH for anything more than a single axle utility trailer (I'm exaggerating, forgive me). Towing, like anything else one attempts beyond the envelope of the vehicle as delivered, demands personal responsibility. IOW, tow at your own risk.

HTH

 

[linuxgod]

@gaijin, here's a trickier one - what's your recommendation on the best pressure for 205/75R14 ST trailer tires? Or at least more generally is it better to run at a high psi (is there a higher margin for error?) even if you don't need the extra load capacity. Or are you better off inflating it correctly (and gaining any margin of error by not overloading?)

Load C is 50psi max. I recently acquired a set of Load D tires (65psi max) when one of my Load C tires blew out. My original Carlisle ST tires were "unrated" for speed (supposedly 65 mph). My new ones are M rated to 81 mph. I have a dual axle trailer with a 5200# GVWR, so I don't need the Load D for weight, but was hoping to optimize the pressure to avoid another blowout.