What is a "cold tire pressure" and what temperature is "cold"?
I don't know if this has been discussed before, but here is some food for thought for snow birders and those of us that live in areas with wild temperature swings.
Most RVers have heard the same mantra,"under inflated tires cause blowouts"! We also know tire manufactures recommendation to inflate trailer (ST) tires to the maximum "cold tire" temperature pressure to achieve the best load rating. Additionally, as most driver's know, as the temperature drops, so does the pressure in our tires and during the fall and early winter, we should
check the pressure in our tires to maintain the correct tire pressure. Which brings up the question, what temperature is the 'cold temperature' the manufacturers are referring to?
I was always told, cold inflation pressure is the inflation pressure of tires before the car is driven and the tires are warmed up; generally less than a mile. One would think the solution is simple, inflate the tire to the maximum pressure indicated on the sidewall of the tire before driving and you are good to go.
, inflating a tire to the maximum pressure at 32°f (0°c), might sound like a great idea in Minnesota, but driving it down to sunny and warmer Florida, Texas or Arizona, could well cause problems.
As a general rule of thumb, for every 10°f (5.5°c) temperature increase, tire pressure will increase 1-2 psig., The reverse is true for temperature decreases.
So, tires inflated in Simpson, MT (south of Medicine Hat,AB) yesterday with a low of -11°f (-24°c), then driven to Palm Springs, CA with a high of 95°f (35°c), would see a pressure increase of between 10 - 22 psig, just from temperature alone. Just as a tire driven from Palm Springs to Medicine Hat would see a pressure decrease of 10 - 22 psig over the length of the trip.
It can be seen that inflating your tires (including your tow vehicle) to the max pressure before setting out on a long trip is a good idea, however if you plan to travel from an area with very cold temperatures, to very warm temperatures, unless you check and adjust your tire pressure frequently, you will could exceed your tire's maximum cold pressure sometime during your journey.
That said, traveling from an area with extremely warm temperatures to an area with very cold temperatures can be worse. A ST225/75*15, load range (E) tire rating drops from 2830lbs @ 80 psig to 2620lbs @70 psig*. A 20 psig drop lowers the load rating almost 500 lbs per tire!
As tempting as it is to put a snarky comment here about how RV manufacturers are always putting a good safety margin in for the load capacity of their tires they install on their new RVs, I'll refrain.
It doesn't have to be a long trip either, a weekend camping trip from Palm Springs,CA to Bear Mountain Ski Resort,could have serious consequences when starting out after a nice weekend of skiing. It should also be mentioned, an altitude change of 5000 ft will lower tire pressure about 2.5 psig.
As it turns out, there is no magic "cold" temperature, and while not everyone can afford or even needs a Tire Pressure Monitoring System (TMPS), frequently checking your tire pressure during long trips or significant temperature changes is a good idea.
If you are interested in a good TMPS, Ray has good video on the one he (and I use):
The manufactures of the tires set the max pressures at 70F or about 20C. This allows for expansion at higher temps and for contraction at lower temps. Most vehicle and trailer manufactures will specify what maximum pressure is required under normal conditions.
We check our tire pressure in the morning (preferably before the sun has got to the one side) and adjust accordingly. Every travel day the same routine regardless of a lateral travel or a cold to warm or vise versa travel as you outlined.
Towable RV tire inflation tends to get a plethora of comments, but we keep it simple. Inflate cold to max tire pressure, check regularly while traveling, definitely check every morning of a travel day. We run Hankook 14 ply and are at the end of set #2 since September 2011 and over 80,000 miles on the RV with never a tire issue.
We have a TPMS on our truck, RV and 2 spares. The manual recommends stetting hi alarm at 20 psi over cold pressure and low at 10 psi under cold. During the summers trips out west the psi are typically 15 psi over cold. They recommend leaving temp at default, 155 Deg F. I have only twice approached 20 psi over cold. I don’t normally air tires until say 5 psi low or bleed when 5 psi high.
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