36 replies to this topic

[rando]

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. 

[klahanie]

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 !

Edited by klahanie, 01 February 2019 - 10:33 PM.

[Wallowa]

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

Edited by Wallowa, 01 February 2019 - 10:51 PM.

[Vic Harder]

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.

[Smooth B]

Wallowa - Have you done any other suspension mods besides the Hellwegs and airbags? Thinking about a Hawk for our 1 gen DC Tundra.

Thanks!

[smlobx]

I have a '14 Tundra/'05 Hawk and run 70 lbs on my E Michelin Defenders. Rando had provided the attached link from Toyo that I found very useful :
 
https://www.toyotire...es_20170203.pdf

Thank you so much for posting this table.
I have been trying to find it but couldn’t...

[rubberlegs]

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...

[Advmoto18]

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. 

Edited by Advmoto18, 03 February 2019 - 12:51 PM.

[smlobx]

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...

Edited by smlobx, 03 February 2019 - 06:00 PM.

[Advmoto18]

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.