Determining best tire pressure

[jadatis]

Cold pressure is as simple as that, when temperature in the tire is the same as outside, so Ambiënt temperature.
This is the only reliable measurement, because , what speed used so higher temp, severe braking gives heat, and howmuch has it already cooled down since you stopped and tanked.

Pressure advice is given for 18degrC/65 degr F.
Some write 20degr. C/68degr. F, but difference is marginal in pressure, so no discussion necessary.

When colder > lower pressure > more deflection> more heat production.
But also then more cooling down because of the more temp.difference between rubber and in and outside air.
And that is the goal, that the rubber does not come above a certain temp at wich it hardens and crackes irreversible.

So you dont need to heighten up to advice for safety, but may do so for fuel-saving, more deflection gives more rolling-resistance.

The other way around, you certainly must not lower the pressure to advice, when outside 35 degr C/95? degr F, then the tire needs that lesser deflection the higher pressure gives to produce lesser heat, because cooling down is also lesser , because of smaller temp differences. You may experiënce a harder ride then.

I made lists for the pressure temp relation , assuming no volume Chance, which it is for a already filled tire. Use it like this.
note the outside temp when you measure the cold pressure or fill up cold.
then look in the line of that temp for the pressure you measured or filled.
Go in that colom to 18 degr C/65 degr F , and that is the pressure you have to compare with the advice pressure.
Interpolation is allowed and nescescary mostly, and gave 3 lists , so there is always one you can use for your pressure.

Once read that tires are tested to can stand 2 to 3 times the reference-pressure ( pressure behind AT , that 65 or 80 psi here).
If you would fill at freesing point with 140% of reference, and incidentially the temp in tire rises to boiling point of water, the pressure rises to a small 2 times the referencepressure ( that is 160 !psi for a AT 80 psi tire), so still within the testing standards.

Also valves are given cold pressure as standard, and extra for temprising is calculated in that cold pressure.

Rimms mostly also have a maximum load or pressure, so if you chanche tires, you also have to look if rimms are allowed that higher load or pressure.
Difficult to get information about rimms.

so dont be affraid of a bit higher pressure cold and the pressure rising above reference-pressure , its all calculated in the cold advice.

The 140% of AT , I read from old PDF of Semperit, at that pressure , when standing still so no speed, the tire was allowed 2 times the given maximum load . Nowadays for C- tyres/LT-tires the tiremakes dont allow a cold pressure above AT anymore, in earlyer days they did.

Only Brands of the Continental Group give in Europe 2 pressures on sidewall.
After the service descriptions they give referencepressure in psi without At in front of it, and thats the pressure you have to use for pressure calculation.
On other place behind maxload information they give "maximum inflation pressure of 10 psi above reference.
Then they allow that higher pressure , and if pressure calculation gives it, for rear axle , you better use that to cover overloading and unequall loading R/L.
The tiremaker though dont support this higher then maximum load.

[booster]

All good advice and explanations in the above posts.


I will point out that, nearly all of the tire pressure changes on our class b vans are done to improve handling characteristics and secondarily to improve ride smoothness. It is pretty rare for us to see anyone increasing tire pressure to get better mileage as only the front tires can be increased for many of us as the rears are at max already.


I think all of it can be put, simplified, by saying that as long as you stay between the minimum pressure needed to carry the load and the maximum pressure of the tire rating you can choose whatever pressure you want. Whether it be for handling, smoothness, mileage, or just "feels better" doesn't matter, as it all is very subjective.



Minimum pressure to carry the load can be found normally on the vehicle tire sticker and max on the tire itself. Minimums can also be found with the calculator that has been provided or from the Michelin chart or other chart.

[Roadtrek Adventuous RS1]

Originally Posted by booster

All good advice and explanations in the above posts.


I will point out that, nearly all of the tire pressure changes on our class b vans are done to improve handling characteristics and secondarily to improve ride smoothness. It is pretty rare for us to see anyone increasing tire pressure to get better mileage as only the front tires can be increased for many of us as the rears are at max already.


I think all of it can be put, simplified, by saying that as long as you stay between the minimum pressure needed to carry the load and the maximum pressure of the tire rating you can choose whatever pressure you want. Whether it be for handling, smoothness, mileage, or just "feels better" doesn't matter, as it all is very subjective.



Minimum pressure to carry the load can be found normally on the vehicle tire sticker and max on the tire itself. Minimums can also be found with the calculator that has been provided or from the Michelin chart or other chart.

You wrote;

I think all of it can be put, simplified, by saying that as long as you stay between the minimum pressure needed to carry the load and the maximum pressure of the tire rating you can choose whatever pressure you want. Whether it be for handling, smoothness, mileage, or just "feels better" doesn't matter, as it all is very subjective

Probably true.... and mileage is not a key factor , although, it's certainly the best you're going to get on a small RV...

I think that the tire shop said it would be better MPG with a little higher pressure and less rolling resistance....

I'm just staying within the pressure ranges. My biggest concern is that I don't want a blowout.

[booster]

Originally Posted by Roadtrek Adventuous RS1

You wrote;

I think all of it can be put, simplified, by saying that as long as you stay between the minimum pressure needed to carry the load and the maximum pressure of the tire rating you can choose whatever pressure you want. Whether it be for handling, smoothness, mileage, or just "feels better" doesn't matter, as it all is very subjective

Probably true.... and mileage is not a key factor , although, it's certainly the best you're going to get on a small RV...

I think that the tire shop said it would be better MPG with a little higher pressure and less rolling resistance....

I'm just staying within the pressure ranges. My biggest concern is that I don't want a blowout.

If you are mainly concerned about blowouts, I think most tire experts would say to use pressure at the higher levels of range rather than lower. Low pressure generates more heat and temp rise is a major cause of catastrophic tire failures. I will take high pressure over high heat anytime. This is contrary to logic, I know, but some stuff works that way.



I would also suggest that anyone with tire monitors that display temp to do a comparison of the monitor reading to actual tire temperature. A low end infrared temp gun works fine in most cases and will be accurate enough. I have found that the monitors can be way off of actual, especially with valve stem mounted sensors (which we have) which always seen to read quite low on warm tires. The internal ones seem to be closer, but do a lag in behind actual tire temp changes and can also read high from brake heat.