Tire Operating Temperatures

[Rocinante]

Hey thanks for the sanity check. Yeah, the door sticker on my 2014 Ram 1500 Laramie says the tires are P275/60R20 and that the pressure should be 39PSI cold with a GVWR of 6800 lbs.

[SteveSueMac]

Originally Posted by Silvery Moon

Hey thanks for the sanity check. Yeah, the door sticker on my 2014 Ram 1500 Laramie says the tires are P275/60R20 and that the pressure should be 39PSI cold with a GVWR of 6800 lbs.

Oops! I mad bad assumptions here about 3/4 ton w/LTs....my bad! Call it an insanity check :-)

[Action]

Would that recommended tire pressure for a truck be in an unloaded condition? Or all manners of load?

>>>>>>>>>>>Action

[Rocinante]

I dunno. Some door sticker expert will have to tell us. I'm assuming they recommend 39psi across he board, all the way up to the GVWR, but i'm happy to learn different based on a citation that explains how to interpret door stickers.

[Phoenix]

Assuming Silvery Moon is running the OEM tires specified on the door sticker (which are low-profile, P-rated, passenger car tires that most likely have "44 psi maximum" printed on the sidewalls), 39 psi sounds about right. Many pickups come with P-rated tires now, for a soft car-like ride. (Our Tundra came with "P" tires in 2008.)

I used to run 44 psi in all of our "P" tires when towing. After switching to "E" rated LT tires, I now run 55 psi front and 65 psi rear, when towing. However, the appropriate inflation pressure depends on your individual TV's tires, engine, equipment, etc., and the tongue weight of your Airstream.

[switz]

Our 2012 Dodge 2500HD diesel wanted 60 psi front and 70, psi rear (tire load capacities equaled axle rating) except when unloaded. Then the rear pressure could be dropped to 45 psi. That made a huge ride comfort difference for my full figured wife

[CapriRacer]

Originally Posted by dznf0g

Capri, I have noted and studied my pressures with TPMS on the TV as well as the AS. I had always lived by the 10% rule and accepted it at face value. The TVs (many of them) all are well within the 10% rule when pressured according to load.

However, on the AS (Michelin LTX MS) it doesn't matter whether I have 70psi, or 75psi, or 80 psi in the tires, I am always between 10% and 12% pressure rise. Last scale reading I was right at 4100 - 4200# per axle.

Speed makes a difference, but I can't figure why pressure seems not to. TPMS accuracy? But it is consistent day to day.

Infra red temps taken at edge of tread at side wall as well as in between tread blocks never gets above 123* or so....even in AZ last summer.

What gives?

You sent me scurrying to my calculator to answer this one!!

If I raise the inflation pressure from 70 psi to 80 psi, I am increasing the load carrying capacity by about 20%. That should result in a 20% drop in temperature build up.

So if someone is experiencing a 7 psi pressure build up at 70 psi, then he should experience a 6 psi build up at 80 psi. (Please be aware that I am rounding.)

That's not a lot of difference - and certainly within measurement error using those cheap tire pressure gauges.

[SteveH]

Originally Posted by CapriRacer

You sent me scurrying to my calculator to answer this one!!

If I raise the inflation pressure from 70 psi to 80 psi, I am increasing the load carrying capacity by about 20%. That should result in a 20% drop in temperature build up.

So if someone is experiencing a 7 psi pressure build up at 70 psi, then he should experience a 6 psi build up at 80 psi. (Please be aware that I am rounding.)

That's not a lot of difference - and certainly within measurement error using those cheap tire pressure gauges.

I'll have you know I paid $3.95 for my Slime digital tire pressure gage at Walmart!

[interstateflyer]

Originally Posted by Silvery Moon

Hey thanks for the sanity check. Yeah, the door sticker on my 2014 Ram 1500 Laramie says the tires are P275/60R20 and that the pressure should be 39PSI cold with a GVWR of 6800 lbs.

Same on my 2013 Dodge RAM 1500 Outdoorsman.

[interstateflyer]

I'm contemplating going with 15 inch Sendel wheels with Michelin LTX M/S 2 P235/75R15 108 XLs. They are rated at 50 psi. Does anyone have hot weather temp readings for these tires?

I checked the sidewall temps of the 14 inch Goodyear Marathons on my two week old 2014 International 23D with my infra-red digital pyrometer. It was 92F outside and we were on a rather rough section of US 101 near Camp Roberts, CA. I took readings as soon as I hit the rest stop.

I was rather shocked by these readings: LR 134, LF 133, RR 142, RF 143.....shade side...sun side.

Tire pressures were set at 50psi cold (62F) and again checked the next day they were at 50psi cold (65F).

These readings are at least 10 degrees higher than those taken of the 16 inch Michelin LTX M/S tires (78F cold) on my International 19 in even hotter conditions.

[r carl]

ST tires run hotter than other tires because of their inferior design. They need to be discontinued and redesigned.

[Al and Missy]

interstateflyer,

If you are going to replace wheels and tires, why not go to the 16"? With the 16" you will have the same specified load carrying capacity as the GYMs. With the P225 tires you will not. While the rated capacity of the tires is in excess of the GVW, the extra margin of the 16" helps mitigate the additional stresses that exist in a tandem axle trailer. That said, many on here run the P225 tires with apparent success.

The GYMs at 65 psi are rated at 2540, 4 gives you 10,160#. 4 P225 15" tires at 50 psi/1980# = 7920# while 4 LT225 16" tires at 75psi/2560# = 10,240#.

I struggled with that tradeoff when I was considering keeping my original wheels, but purchasing new wheels would seem to make the price difference to go to 16" small in comparison to the extra capacity.

Al

[interstateflyer]

Originally Posted by Al and Missy

interstateflyer,

If you are going to replace wheels and tires, why not go to the 16"? With the 16" you will have the same specified load carrying capacity as the GYMs. With the P225 tires you will not. While the rated capacity of the tires is in excess of the GVW, the extra margin of the 16" helps mitigate the additional stresses that exist in a tandem axle trailer. That said, many on here run the P225 tires with apparent success.

The GYMs at 65 psi are rated at 2540, 4 gives you 10,160#. 4 P225 15" tires at 50 psi/1980# = 7920# while 4 LT225 16" tires at 75psi/2560# = 10,240#.

I struggled with that tradeoff when I was considering keeping my original wheels, but purchasing new wheels would seem to make the price difference to go to 16" small in comparison to the extra capacity.

Al

I'd use 16 inch wheels but the 23D's 14 inch hubs are 5 bolt. 16 inch trailer wheels are typically 6 bolt.

Sendel makes 15 inch trailer wheels with a 5 bolt configuration.

The Michelin LTX M/S 2 P235/75R15 108 XLs are derated for trailers to 1985 lbs. at 50 psi.

The GYM ST215/75R14s on the trailer are rated at 1870 lbs. at 50 psi (the recommended pressure).

The trailer has 3000 lb axles, a GVWR of 6,000.

Your point that 'additional stresses exist in a tandem axle trailer' is one of the issues that I've yet to resolve. I'm wondering how the sidewall construction of the Load Range XL Michelin LTX M/S 2 P235/75R15 108 XL compares to the supposed purpose built Load Range C GYM ST215/75R14s.

Another issue is putting 15 inch wheels on 10 inch brake hubs. All other A/S
brakes are 12 inch. Would I be over stressing the 10 inch brakes/hubs?

[Rocinante]

The Michelin LTX M/S 2 P235/75R15 108 XLs, derated for trailers to 1985 lbs. at 50 psi with total capacity of 7,940 lbs. are pretty attractive. The max weight for our 27FB is 7,600, so those tires should be up to the job. If we don't go for 16" wheels at some point, we'll probably just move to these for our 15" wheels to get away from the ST tires.

[DKB_SATX]

Originally Posted by interstateflyer

~~

Your point that 'additional stresses exist in a tandem axle trailer' is one of the issues that I've yet to resolve. I'm wondering how the sidewall construction of the Load Range XL Michelin LTX M/S 2 P235/75R15 108 XL compares to the supposed purpose built Load Range C GYM ST215/75R14s.

Another issue is putting 15 inch wheels on 10 inch brake hubs. All other A/S
brakes are 12 inch. Would I be over stressing the 10 inch brakes/hubs?

I have over 8k miles on those Michelins on my tandem-axle Argosy, and I know people who have more than that with them on heavier trailers. The only problem I've had with them so far was one bad valve stem, and I'm fairly sure it wasn't made by Michelin.

That's towing in Texas heat around 70 mph, too. They run cooler than my truck tires! However the construction compares, the tires perform quite well on a tandem-axle Airstream in my experience.

I don't think the larger wheels will bother the brake drums at all, and if you had enough brakes with 14" wheels you'll have enough with 15s (and will be able to use more of it before they slide, too!)

[SteveSueMac]

Originally Posted by Silvery Moon

The Michelin LTX M/S 2 P235/75R15 108 XLs, derated for trailers to 1985 lbs. at 50 psi with total capacity of 7,940 lbs. are pretty attractive. The max weight for our 27FB is 7,600, so those tires should be up to the job. If we don't go for 16" wheels at some point, we'll probably just move to these for our 15" wheels to get away from the ST tires.

That's exactly what we did on our 27FB which on the scales fully loaded for camping has about 5800-5900# on the trailer wheels (so with about 8k# derated capacity I'm at about 75% - feels like plenty of headroom). I recently scuffed the curbside pair pretty badly on some construction in NH and replaced them :-(

But they've served me pretty well on some long trips (CT to TN, CT to OH) and even in 90 degree weather only a 10% rise in pressure and 30 degree rise in temp (consistent in all conditions) according to my internal TPMS monitors.