Tire Pressure Carrying Hawk on Tundra w E-Coopers

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Wallowa

Double Ought
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I retired my Toyo II 6 plys for Cooper AT3 10 plies [E] and went to a narrower LT235x85 - 16.

These Cooper's have a max load rating [3,042 lbs] and max pressure at 80 psi....

My question is this: What pressure do any of you run in a similar tire size and load? Reasons?

Do you go for max pressure or adjust for the weight [scale weight wet is 3,020 lbs front and 3,780 lbs rear on my Tundra/Hawk]. Please no comments about GVW specters.

My Tundra is an '05 Access Cab SR5 and carrying a fully kitted out '16 Hawk w/Firestone airbags/Hellwig anti-sway bar rear and wheel well height fore and aft of 35" ...primary use is off road and only pavement to get there...

FYI here is the approx load rating by pressure for these Coopers:

75 psi = 2,905 lbs
70 psi = 2,765 lbs
65 psi = 2,623 lbs
60 psi = 2,485 lbs

I understand there is a balance between ride quality/handling/puncture resistance vs traction on various surfaces but what has been your real world experience?

Thanks for any information,

Phil
 
I adjust my pressure and don't go max pressure. I've only run max pressure a couple of times, and not with the Hawk (only when I was pretty maxed out hauling landscaping material). I have a different truck, but the weight ratings of the tires probably isn't that different. I might also try putting a chalk line across your tires and run a block or so down the road. See how much of the chalk is worn off. You might adjust pressure dependent on how much of the tread you're using, or something similar.
 
ACE,

Thanks great idea using the chalk to see how much of the tread is in contact with the road...understanding that lower pressure elongates the contact patch rather than widens it, but I still would like to see what part of the tire width is subject to wear..

Thanks again...Phil
 
Been a long time since I ran that size and weight ...

Myself, I would "adjust for the weight".

Meaning, scale like you have and look up the load and inflation tables like you have (?)

Even so I tend to over inflate*, in my world that has meant harsher ride off highway, more steering input need on highway (wandering) and accelerated centre tread wear.

I would be looking here at:

35 psi = 1700
40 psi = 1870
45 psi = 2030

and prob calculate down a pressure for the front axle tires

EDIT * by over inflate, I mean put a bit more air pressure than stated in the tables. Makes me feel a bit "safer" on the hwy, and maybe reduces fuel economy. Force of habit really. Besides those table numbers are max load for a given psi. Nothing saying you can't go higher psi for the same load. But there may be noticeable
consequences.

HTH
 
Been a long time since I ran that size and weight ...

Myself, I would "adjust for the weight".

Meaning, scale like you have and look up the load and inflation tables (like you have (?))

Even so I tend to over inflate, in my world that has meant harsher ride off highway, more steering input need on highway and accelerated centre tread wear.

Curious about the load ranges you listed, I would be looking here at:

35 psi = 1700
40 psi = 1870
45 psi = 2030

and prob calculate down a pressure for the front axle tires


Check page 21 on the site you referenced above...you listed the "C" rated tires.

"LT235/85R16 Single 1700 1870 2030 2205 (C) 108 2335 2485 2623 (D) 114 2765 2905 3042 (E) 120"

Again my tires are "E" or 10 ply tires....I gained about 400 lbs per tire with Cooper "E" tires over previous Toyo "D"s....plus more puncture resistance and going narrower better loose [mud/sand] off road traction.

Adjusting for weight yes, but what weight vs tire rating at what pressure for off road? I do agree on selecting a higher pressure rather than shaving the weight vs pressure load too close.

Phil
 
Check page 21 on the site you referenced above...you listed the "C" rated tires.

"LT235/85R16 Single 1700 1870 2030 2205 (C) 108 2335 2485 2623 (D) 114 2765 2905 3042 (E) 120"

Again my tires are "E" or 10 ply tires....
Click to expand...


Okay, and according to that site the 60 and 65 PSI ratings you posted (OP) are for the "D" rated tires

10 plies [E] and went to a narrower LT235x85 - 16.

...primary use is off road and only pavement to get there...

FYI here is the approx load rating by pressure for these Coopers:

75 psi = 2,905 lbs
70 psi = 2,765 lbs
65 psi = 2,623 lbs
60 psi = 2,485 lbs

Thanks for any information,
Click to expand...

Yours are "E" right ?, so if the reasoning is to only use the "E" only ratings then in that case I'd say that would put you at 70 psi for regular road use.

Adjusting for weight yes, but what weight vs tire rating at what pressure for off road?
Click to expand...
Off road is a whole different matter and depends greatly on a number of variables. I can only speak for my own experience "off highway" (FSRs) and I'm out of my depth here already for this vehicle weight class !

But, because I'm here, I would start with the load and inflation table for the tire size and the applicable tire load [EDIT scaled weight if possible] as a starting pressure. Then for off highway reduce pressure in stages, to suit desired comfort and traction. For me that has meant up to 10 psi lower than the tables, measured tires "hot" not "cold".

I consider the max loads stated at a given psi in the table for the higher tire load ratings ( E, F etc) to be an extension/continuation of the loads given for the lower ones (D,C) for the same tire size. That is, I believe the higher load ratings are inclusive of the lower load ratings. Therefore, I think the tables can still be a useful reference for loads quite a bit lighter than the tires max rated load.
 
Toyo AT2s I retired [only 11K miles] were "C"; max pressure 50 psi [6ply] not "D" [8] ply. See first post.

Yes my vehicle weights were measured on a commercial scale with full gear including all tanks full & 100 lb Warn winch in front ...wet weight.

Your last comment gave me food for thought...that the pressure/load ratings listed for a 6 or 8 ply tire were applicable by extension for my 10 ply tire...makes sense. I am with you on only dropping pressure perhaps 10 psi from normal pressure if needed off road for sand or mud...I have a good compressor but hesitate to drop pressure and chance a flat...all this of course is a crap shoot and I prefer to stay pressured up and pick my routes with care...

Measuring hot and not cold? I always have set the pressure cold initially but see the wisdom to only drop the pressure if necessary based on the hot pressure while driving off road...that way it retains a % of needed pressure.

Currently I have 60 psi and will do a chalk test suggested by ACE and then inflate to 70 psi and repeat the chalk test...not certain how I will use that information but at 60 or 70 psi my E rated Coopers will handle the weight.

Thanks again..

Phil
 
The load table doesn't vary depending on the load rating, only the maximum load changes because the max pressure for different load range (C/D/E) tires is different.

For your application, the rear tires are loaded at about 1900 lbs per tire. Go to the load table for 235/85R16 (page 21 of the Toyo document, poorly copied below) and you would see that you would need to be at least 40-45 psi in your rear tires:

Dual 35 40 45 50 55 60 65 70 75 80
LT235/85R16 Single 1700 1870 2030 2205 (C) 108 2335 2485 2623 (D) 114 2765 2905 3042 (E) 120

I run the same size tires and typically run 50-55psi in the back and 45 psi in the front. If I am doing a lot of rougher dirt roads I may air down to 35 back 30 front.

You can go higher than this number, but shouldn't go lower on the highway.
 
Thanks Rando...I know I was equating psi to max load for a given tire size and rating...

Your Fleet and Tacoma are probably lighter than my Tundra/Hawk...

I also try to balance the height of the Tundra fore and aft..if I may ask, why not run the rear pressure in the front tires? All tires at same pressure, the higher one.

As stated I do use my airbags to level out the Tundra but tire pressure is in the mix.

Thanks again...Phil
 
I don't have the numbers with me, but I have more load on the rear axel than the front axel (the camper is about the same weight as yours, but the truck is lighter than your Tundra so the front is lighter). By tailoring the tire pressure to the load, you get a better ride quality. If i have the front tires at 55 psi it seems like I can feel every pebble on the road, it is a little better at 45 psi. Based on the load tables, I could run a lower pressure, but I don't weigh the truck before every trip so it is nice to have some margin.
 
Phil,
My application, the numbers for my "E" tires are 46FR/62RR. I put another few psi in cold, for highway. This for a diesel fullsize scaling +12K. Granted, different vehicle and different tires. But when I saw your first post listing the range of 60-75 psi for <7K rig it prompted me to reply.

I get having HD tires, relative to the rig weight, I did the same size in an "E" 30 yr ago with my '86 4runner. Liked the size. Truth, it was a bit too much tire for that vehicle but nevermind. 20 yr ago had the same E size on OE my F250, with and with out the FWC. Better match, still liked the size. I hope you enjoy yours. Sorry too long ago to remember the weights and pressures, and in those days, who cared !

Thing is, having a HD tire, it doesn't always follow you need a HD pressure. I think your Coopers will take the weight at a much lower psi than that original range, and that doing so will give you a better driving experience all round. That's the only reason I posted - simply food for thought.

If you or anyone else is happy at 60 or 70 or whatever, great. Roll on !

I've never done the chalk test (no chalk !) but have read it's the way to go. I'd also suggest you pick up a basic tire depth gauge and keep an eye on the evenness of wear across the tread width as you put some miles on them.

Off highway pressure for me, lower is better (more cushioning) but of course, I have to air back up. Hot reading 'cause it's all I have at the time. I know there's a temperature rise, more at lower pressures off highway. If I air down too much I notice under steer - not good in corners or avoiding a fat-boy log truck. Too low and the tires get hot as an indicator. Slower speeds can go lower, faster travel required more air.

For any real "off road", sand etc, I wouldn't want to lower to min right away, just in case we get stuck, then I'd still want some room to air down a bit for traction. Anyway, lots of variables but keep a log and you'll soon figure out whats best for you.

That's me. Good luck !
 
Klahanie....good stuff, thanks. As to size, I went to a smaller tire tread @ 235 [so called 'pizza cutters'] but kept the same diameter [31.7 "]...knowing I am adding a little unsprung weight but using a tire that should take more "abuse-use" off road and offer more pressure options.

Will get that tread gauge and will complete the chalk exam...thinking back if my "C" tires worked fine at 50 psi then my "E"s should do the same...and I will log my experiences..thanks good idea.

Thanks again...Phil
 
I went through this exercise two years ago. E rated tires with 2500HD and Hawk. I was surprised at how low I could go according to the tire tables referenced above. I run 50 psi front, 55 rear.
 
Wallowa - Have you done any other suspension mods besides the Hellwegs and airbags? Thinking about a Hawk for our 1 gen DC Tundra.

Thanks!
 
Something about these high tire pressures doesn't make sense. Educate me. Here's my thoughts:

  • Stock tires, placard pressure is 35 psi in our truck.
  • Then we add a heavy camper on the back. Front axle load barely changed, 2700 lb. Rear axle was way lower, but went way up to 3300 lbs.
  • OK, leave the front pressure at 35 psi. Up the rear pressure by the ratio 3300/2700 = 43 psi. (Stock tires rated at 51 psi max)
  • Now replace the stock tires with E-rated. Why would the pressure change to such big numbers? The load is really carried by the air. And the E-rated tires are probably stiffer (likely a second order effect), so maybe even lower the pressure.
Or replace all those complicated steps with the chalk test...
 
Prior to the Ford-Firestone tire debacle in 2000, nearly every light truck tire manufacturer provided recommended PSI based on vehicle weight.

As Ronin linked, Toyo is one of very few tire manufacturers still publishing such data. Further, Toyo provides some of the best information in a single document regarding tire data. I've referenced the doc in several previous posts on WTW and consider is a key travel doc.

I refer to the guide whenever I load/laden my truck and note the data on the doc. If I have a new, heavy load, I weigh my truck and develop a new tire psi. Invariably, it seldom changes more than 15 psi. I keep a printed copy of the doc with my notes in my glove box.

Load is indeed adjusted for weight and handling characteristics.

A major misconception is that your vehicle's tire max load rating is what is stamped on the tire. That is not correct. The max load rating is what is published on the placard attached to the vehicle. It may be equal to the load stamped on the tire's sidewall, but, I suspect the placard figure will be much less.

When you alter tire size from OEM installation, you're on your own. Yes, you should absolutely adhere to the stamped rating on the tire sidewall, but, also the tire inflation tables of the manufacturer. As mentioned, most manufacturers provided such information prior to 2000. Now you have to sort of interpolate such data from any source available.
 
Bill- thanks for chiming in.. Let’s say for the sake of conversation that having weighed the truck and referring to the table the reccomended tire pressure should be 60 psi for the given load. As I in derstand it that is for traveling on a road/highway.

My question is if you go off-road (and are now driving much slower) can you / should you further reduce your tire pressure if the conditions warrant? I would think so but then the question becomes how much can you reduce the pressure before you risk tire damage etc. I’ve had our pressures as low as 25 psi on our F-350 srw while at the beach without the Hallmark on but at some point I anticipate going to Portsmouth Island with the camper...
 
Eddie...

You are indeed correct, the Toyo inflation charts are for tarmac, normal highway driving.

Off-road is certainly different. And of course, vehicle weight and terrain will ultimately determine how low you will want to go.

Airing down actually increases the tire's resistance to puncture and traction.

I have had no issues airing down to 20F/25R psi in outer Banks beach sand with my ~1400# FWC Hawk (wet). Of course, I am driving slow, max speed 10 MPH.

I use 35F/40R psi on gravel and rocky roads. I do not drive faster then 35 MPH.

Hard pack dirt roads, 50F/55R psi at 45MPH.

Once you reach tarmac, it is critical to air back up if going more than a few miles. Under inflated tires will heat up very quickly on tarmac and fail without notice. Under inflation, driving highway speeds on tarmac is the easiest, fastest way to kill a tire.

With your F-350 long bed, Hallmark and aux fuel tank, I'd be inclined to add 3-5 psi to my numbers above. You can always decrease psi in 2-3 psi increments to see how your ride improves.

I'm not too worried about tire damage with low psi off-tarmac. I started 4 wheeling in the early 70s and have yet to damage a tire due to low psi. The real concern IMO, is popping the bead with low psi. And I have popped quite a few beads with 5-10 psi; all in the days before bead-lock wheels.
 
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