Tire Pressures

[K & K]

Hi all,

Kevin here. My wife and are getting our FWC installed tomorrow! We bought a Fleet to fit on our 2017 Tacoma TRD off road.

I apologize for this question as I'm sure it's been covered ad nausuem, and if so, please post a link to previous discussions.

I am curious as to what tire pressures to run with the camper. I have seen many different thoughts on this and I know it is generally a trial an error thing, but I'm just looking for a good starting point, being the newbie camper owner that I am! I would appreciate thoughts from those of you who have a FWC on a Tacoma.

My tires are E rated 265/75/16 and they show MAX cold pressure at 80 psi. Some have said that is the pressure you run all the time loaded or not, which doesn't seem right to me. I can't imagine running that pressure in an off road situation. Do I need to bring the tires up to pressure before the install, or can I do it afterwards? Currently the pressures are at are around 35 psi for normal driving.

Any thoughts are appreciated as it's all about the safety factor for me...

Thank you.

 

[buckland]

Generally I run 60 in rear and 50 in front (I have a mini diesel) on the midsized Colorado....with the camper on. Without camper I run 35 rear 45 front.

 

[daverave]

I have similar E-series tires and run about the same pressures as buckland above but I have my Hawk on an F-150.

Beware that when you have any kind of tire service (rotation, flat repair, etc.) that tire shops (and sometimes even mechanics) will generally default to the OEM pressures unless you tell them you prefer the higher numbers.

 

[K & K]

Thanks for the replies. Much appreciated. It gives me a starting point!

 

[Advmoto18]

Best thing to do is load your truck and camper as if going on a camping trip. Fill up the gas tank, then head to a truck stop with scales and get your truck weighed. You then have your axle weights.

Since the Firestone/Ford tire debacle back in the late 90s, only Toyo (to my knowledge) still offers tire inflation data based on load.

Even though you may not running Toyo's, the data can give you of idea of optimum inflation based on load.

 

[rubberlegs]

I have nearly the same setup, and settled on 45 front, 55 rear. But it could go higher in the rear depending on axle weight. We leave the camper on full time, but if not we'd use 45 front and rear with an empty truck. Here's more:
http://www.wanderthewest.com/forum/topic/17823-tire-pressure-carrying-hawk-on-tundra-w-e-coopers/?p=211582

Off road we've gone down to 15 front, 20 rear.

 

[K & K]

Wow, that's perfect. Thanks. I will do that...

 

[Andy Douglass]

I am not even close to an expert but I feel like with E-rated tires in good shape, you can worry a little less about what PSI to be at. Your risk of a problem is lessened with the stronger tires. I run my tires at 60 front/80 rear or a little less. This is on a 3/4t diesel with/without a loaded Hawk, so my axle weights are going to be a little heavier than yours. I actually lowered the psi in the field 2 weeks ago driving across a desert highway because my rear tires were up to 91 psi, which made me nervous. I would obviously lower pressure on any sharp or soft surfaces as needed, but other than that I don't really worry too much. But again, this is just based on my thoughts, not any expert opinion.

 

[rubberlegs]

The 45/55 pressures I use are based on industry recommendations for my tire loads and highway speeds.

If pressure is too low, you can overheat the tires which reduces their life and can lead to failure. (But it seems heating will raise pressure and help alleviate that to some extent...). Cornering can be worse due to sidewall flex.

If pressure is too high, the ride can be too harsh. Grip can be worse.

Both over or under pressure can reduce tread life, either in the center or the edges.

Meanwhile, on the internet you can find very strong opinions, not necessarily based on tire engineering. Some opinions even are published on tire sales websites that, to me, are just plain wrong. Anyway, some of the posts in the link I referred to have links to good data, with tables for tire sizes, speeds, loads, pressures, etc.

Off road, the story changes. There, we travel very slowly and need more grip. So overheating is not a big concern. At first it seemed strange to ride at 15 psi, but in this case the anecdotal evidence is strong that it works better.

 

[Wallowa]

Interesting how the opinions on tire pressure vary so much...but not mentioned is that off road when you lower pressure for better traction you also increase the chance of cutting a sidewall or punctures...or in extreme cases of breaking the bead..

I guess in the real world there are no free lunches and either too high or too low for conditions can bring negative results.

Oh, remember that inflation figures are stated for "cold tires"...prior to driving on them...the increase in pressure from the heat generated while driving varies dependent on many factors but the pressures will go up above the recommended cold pressures.

Phil

 

[Andy Douglass]

Another offroad consideration is that is it a lot easier to plug a tire than to reseat it.

 

[nevaska]

Interesting how the opinions on tire pressure vary so much...but not mentioned is that off road when you lower pressure for better traction you also increase the chance of cutting a sidewall or punctures...or in extreme cases of breaking the bead..

I guess in the real world there are no free lunches and either too high or too low for conditions can bring negative results.

Oh, remember that inflation figures are stated for "cold tires"...prior to driving on them...the increase in pressure from the heat generated while driving varies dependent on many factors but the pressures will go up above the recommended cold pressures.

Phil

In my experience reducing tire pressure actually increases puncture resistance. Cooper's testing seems to confirm this

 

[Wallowa]

OK...this 'test' done in OZ on Coopers is valid for the speed of the contact on this single spike...a slow crawl over sharp objects may allow the tire to conform and not puncture...but you note that the tires eventually did puncture...even assuming that the contact point was identical each pass over the spike...why then did they puncture? Probably due to tire temperature at that point of contact...rubber temp is another factor to add in...not that each pass cut further into the tire..Scott Brady does a good job of explaining some of this [https://expeditionportal.com/the-lowdown-off-road-tire-pressures/] but note that the sidewalls will bulge and this increases the chance of a sidewall breach which can not be plugged...also tire temps go up with lower pressure making the rubber 'softer'; throw in heavy loads and things get worse..losing the bead on a tire is also a game stopper and lower pressures even at slow speed can cause the loss of the bead from the rim..rough rocky terrain will throw all the "gotcha" items at you even if you are driving at less than walking speed, which we seldom do..

So this is kind of like an oil thread...we all decide what best works for us...to each their own; as it should be.

But I do recommend Tom Sheppard's and Chris Scott's books on off-roading...these guys have been there; time and again.

Oh, not on trucks/cars but on my off road motorcycle low pressure produces "snake bites' when the rim pinches the tube on an impact and ruins the tube...why we carrying extra tubes! We trade a larger contact patch for not having a flat and potentially ruining a tube or tubeless tire.

But hey, I could be wrong...

Phil

 

[nevaska]

Watch the video again, the point of contact with the spike more or less remains the same and there is no way this was a temperature induced tire failure. The video also shows that you don't have to lower your tires to rock crawling pressures to achieve increased puncture resistance, just going from 38 to 28 psi double the amount of passes over the spike. There is a lot of area for increased comfort, traction, puncture resistance between crawling and highway pressures, and losing a bead is not going to be a concern above 15-18 psi.

IMO match your intended speed and terrain to your tire pressure, balanced by how often you want to futz with your tires. If I'm on dirt for less than a few hours I'll keep highway pressures (40/50), on gravel/trail most of the day and don't need any help with traction I'll drop to 25-35, crawling up angular rocky trails and worried about my tires I may drop to 18 or 20.

 

[Wallowa]

Watch the video again, the point of contact with the spike more or less remains the same and there is no way this was a temperature induced tire failure. The video also shows that you don't have to lower your tires to rock crawling pressures to achieve increased puncture resistance, just going from 38 to 28 psi double the amount of passes over the spike. There is a lot of area for increased comfort, traction, puncture resistance between crawling and highway pressures, and losing a bead is not going to be a concern above 15-18 psi.

IMO match your intended speed and terrain to your tire pressure, balanced by how often you want to futz with your tires. If I'm on dirt for less than a few hours I'll keep highway pressures (40/50), on gravel/trail most of the day and don't need any help with traction I'll drop to 25-35, crawling up angular rocky trails and worried about my tires I may drop to 18 or 20.

Not at all challenging your premise or methods you use....but there is a lot more to preventing punctures than just lowering pressure..

What still is unanswered is why the tire eventually punctured after repeated trips over the spike..flex rubber, or anything, and heat is generated...but unless the spike is slowly separating the tire carcass belts with each pass, the failure must be in the rubber tread..

I have no firm idea why the tires eventually punctured...something structurally failed, but what? I would like to have had the demonstration include various speeds....and regardless of treads, sidewalls become more vulnerable to cuts as you lower pressure.

Anyway...good discussion, but as in life no definitive conclusions...I guess in the end, one size does not fit all..

Phil