Determining best tire pressure

[Roadtrek Adventuous RS1]

Originally Posted by gregmchugh

Recommended tire pressures are always for cold tires not tires that are warmed up from driving. Usually I check in the morning.

Maximum tire pressure for my Michelin tires are 80 pounds... cold tire in front is around 61-62 and rear are 65-66. .. they warm up fast and depending on how hot it is are usually around 75 pounds rear and 71 pounds on the front.

[gregmchugh]

Originally Posted by Roadtrek Adventuous RS1

Maximum tire pressure for my Michelin tires are 80 pounds... cold tire in front is around 61-62 and rear are 65-66. .. they warm up fast and depending on how hot it is are usually around 75 pounds rear and 71 pounds on the front.

Max pressure is also a cold tire reading, they are designed to handle the higher pressures as the tires warm up above 80 psi...

[Roadtrek Adventuous RS1]

Originally Posted by gregmchugh

Max pressure is also a cold tire reading, they are designed to handle the higher pressures as the tires warm up above 80 psi...

Greg, my vehicle sticker says 55 cold psi in the front and 60 or 62 in the rear.... although, I've pushed that to 60-61 in the front and 65-67 in the rear...

After driving on the road it increases to 67 or 68 in the front and 75-77 in the rear...

[booster]

Originally Posted by gregmchugh

Max pressure is also a cold tire reading, they are designed to handle the higher pressures as the tires warm up above 80 psi...

Pressure goes up with temperature so the tire design would pretty much match max pressure with the point where heat would start to give problems. Just because your pressure is OK cold, you could be higher than OK once heated up, if the the temp is climbing too much.

[Roadtrek Adventuous RS1]

Originally Posted by booster

Pressure goes up with temperature so the tire design would pretty much match max pressure with the point where heat would start to give problems. Just because your pressure is OK cold, you could be higher than OK once heated up, if the the temp is climbing too much.

Here's my RT specs; although I'm pushing the pressure up just a bit.
I've never seen it get past 80.

If I understand you correctly, you don't want to exceed 80 psi after being heated up especially in triple digit temperatures.

I think I'm around 61 front cold and 65 or so cold in the rear. Heats up pretty fast when the mercury soars.

I don't want to cause myself problems. I have a tire pressure monitoring gauge right up front to watch that.

[booster]

Originally Posted by Roadtrek Adventuous RS1

If I understand you correctly, you don't want to exceed 80 psi after being heated up especially in triple digit temperatures.

No...



What everyone said is that the max inflation pressure is 80psi and that inflation is done cold. So you would go to whatever pressure above 80psi the tire temperature dictated after inflating to 80 psi cold.

[Roadtrek Adventuous RS1]

Originally Posted by booster

No...



What everyone said is that the max inflation pressure is 80psi and that inflation is done cold. So you would go to whatever pressure above 80psi the tire temperature dictated after inflating to 80 psi cold.

Thanks for clarifying that for me...OK, so, 80 pounds cold PSI is the maximum...

I see, so, even if it exceeded 80 pounds pressure .. even on the hottest days...it would still be OK.....

I guess I'm being conservative by just running slightly above the sticker pressures. The rig runs fine at that recommended pressure..or just above...

Thank you again for your assistance.

[D&J Phillips]

I think some of you are mixing metaphors...

"Recommended" pressures are by the vehiclemanufacturer and are usually called out as "cold" settings and they are based on engineering design limits for the vehicle, preferred ride quality, etc. - again, by the vehicle manufacturer.

"Maximum" pressures are just that, maximum and are set by the tire manufacturers based on engineering design limits and application requirements for the tire itself.

Two entirely different things. In the example above by Adventurous RS1 they set tire pressures 'cold' at 55F and 60R and after driving they get up to 68F and 77R which is still under the "max" inflation of 80 and therefore 'safe'.

You should check with the tire manufacturer if you have tires that say "max inflation 80psi" you should start at least 10 psi less IMHO…… Because I guarantee, if you start at the max, you will quickly exceed the max,. Beyond that, if you don't have a tire monitor set up, you should occasionally check them when hot to make sure you aren't exceeding the max.

Just my .02
Dave

[booster]

Max pressure is max cold, they will go higher than that when hot and that is intended to happen. If you don't go to max cold, if you are at max tire load like in many b vans in the rear, you will be overloading tires and asking for a failure.


From the Tirerack site:


Maximum Inflation Pressure

A tire's maximum inflation pressure is the highest "cold" inflation pressure that the tire is designed to contain. However the tire's maximum inflation pressure should only be used when called for on the vehicle's tire placard or in the vehicle's owners manual. It is also important to remember that the vehicle's recommended tire inflation pressure is always to be measured and set when the tire is "cold." Cold conditions are defined as early in the morning before the day's ambient temperature, sun's radiant heat or the heat generated while driving have caused the tire pressure to temporarily increase.
For the reasons indicated above, It is also normal to experience "hot" tire pressures that are up to 5 to 6 psi above the tire's recommended "cold" pressure during the day if the vehicle is parked in the sun or has been extensively driven. Therefore, if the vehicle's recommended "cold" inflation pressures correspond with the tire's maximum inflation pressure, it will often appear that too much tire pressure is present. However, this extra "hot" tire pressure is temporary and should NOT be bled off to return the tire pressure to within the maximum inflation pressure value branded on the tire. If the "cold" tire pressure was correctly set initially, the temporary "hot" tire pressure will have returned to the tire's maximum inflation pressure when next measured in "cold" conditions.
A tire's "maximum inflation pressure" may be different than the assigned tire pressure used to rate the tire's "maximum load." For example, while a P-metric sized standard load tire's maximum load is rated at 35 psi, many P-metric sized standard load performance and touring tires are designed to contain up to 44 psi (and are branded on their sidewalls accordingly). This additional range of inflation pressure (in this case, between 36 and 44 psi) has been provided to accommodate any unique handling, high speed and/or rolling resistance requirements determined by the tire and vehicle manufacturers. These unique tire pressures will be identified on the vehicle placard or the vehicle's owner's manual.
The tire's maximum inflation pressure is indicated in relatively small-sized print branded near the tire's bead (adjacent to the wheel) indicating the appropriate value. Because tires are global products, their maximum inflation pressure is branded on the tire in kilopascals (kPa) and pounds per square inch (psi). These values can also be found in the industry's tire load & inflation charts.

[Roadtrek Adventuous RS1]

Originally Posted by D&J Phillips

I think some of you are mixing metaphors...

"Recommended" pressures are by the vehiclemanufacturer and are usually called out as "cold" settings and they are based on engineering design limits for the vehicle, preferred ride quality, etc. - again, by the vehicle manufacturer.

"Maximum" pressures are just that, maximum and are set by the tire manufacturers based on engineering design limits and application requirements for the tire itself.

Two entirely different things. In the example above by Adventurous RS1 they set tire pressures 'cold' at 55F and 60R and after driving they get up to 68F and 77R which is still under the "max" inflation of 80 and therefore 'safe'.

You should check with the tire manufacturer if you have tires that say "max inflation 80psi" you should start at least 10 psi less IMHO…… Because I guarantee, if you start at the max, you will quickly exceed the max,. Beyond that, if you don't have a tire monitor set up, you should occasionally check them when hot to make sure you aren't exceeding the max.

Just my .02
Dave

Hi Dave,

I understand, which is why I only pushed up the pressure a little bit on the front and rear of the coach. I didn't want to exceed 80 PSI ...

I have a Truck System Technologies tire pressure monitoring system.... so, I can visually see the air pressure in all 6 tires..... I specifically got this because I have the dual wheels and tires in the rear.

----MARK

[D&J Phillips]

Wow, sorry about my earlier missive. Shoulda known better than post without researching first. I always thought it was max. Defies my personal logic simply because everybody's idea of 'cold' and 'hot' are different. I guess, since I have never seen a temperature listed along with the pressure, e.g. 65psig @ 60*F, I always assumed the weakest time for a tire would be when it is at it's hottest so..
Again, sorry for interrupting, carry on.
Dave

[booster]

Originally Posted by D&J Phillips

Wow, sorry about my earlier missive. Shoulda known better than post without researching first. I always thought it was max. Defies my personal logic simply because everybody's idea of 'cold' and 'hot' are different. I guess, since I have never seen a temperature listed along with the pressure, e.g. 65psig @ 60*F, I always assumed the weakest time for a tire would be when it is at it's hottest so..
Again, sorry for interrupting, carry on.
Dave

Your observation of how people see hot and cold is likely why they specify cold, as it it just ambient temp, no matter what it is. Hot would totally depend on the too many conditions like speed, sun, etc.

[Roadtrek Adventuous RS1]

Originally Posted by D&J Phillips

Wow, sorry about my earlier missive. Shoulda known better than post without researching first. I always thought it was max. Defies my personal logic simply because everybody's idea of 'cold' and 'hot' are different. I guess, since I have never seen a temperature listed along with the pressure, e.g. 65psig @ 60*F, I always assumed the weakest time for a tire would be when it is at it's hottest so..
Again, sorry for interrupting, carry on.
Dave

It never hurts to double check and restate something important...

As per tire pressure recommendations, no one was ever faulted for following instructions especially when they're on the vehicle sticker....

When I got these tires the tire shop said that I could add a few pounds and it would improve the steering, fuel efficiency and be perfectly fine. I keep a close eye on the monitor up front. I'm glad to have it, I had some defective valve stems when I got them installed and the tire pressure monitoring system alerted me to the issue.

[jadatis]

Originally Posted by Phoebe3

Thank you for doing this! I used your most recent file (I think, it said it was updated last Friday).

Here is a screenshot of the top portion.

I put the Ford GVWR and GAWR in the dark blue cells at the top.

I put the Ford GVWR and GAWR and the Ford recommended tire pressures in the light blue cells that are in the grey ovals. Since this is the maximum weight that would ever occur on the axles.

In the light blue cells below, I put the actual weights of the axles that we got from the scale.

Since the recommended tire pressures are far too low, I must have done something wrong. Can you explain it further?

The loadkind is set on lbs , and you probably filled in KG?
But you have to give the tirespecifications only in the ovals ( wheelshape)
The GAWR/MPAW belong in the dark blue above . Mostly front and rear the same loadindex, so you only have to give it once, and for the other axle is taken over from that. You overruled the loadindex dropdownlist by filling in your GAWR's as maximum load of one tire/tyre.
Also set number of tires on the axle, now set on 4 ( dual load) but probably 2 for single load axle.
You filled in the advice pressure in space where referencepressure belongs of probably 80 psi or 65 psi.

Then you set the reserves on 6 and 8 % , wich is strange, if left open, it uses my preset of 10% in case of given weights in part 2, and F5% R 18% going down scale to 10% , if given only GAWR/MPAW.

So in short, begin again.
See,looking back , you are living in California, you can set the language to American-English. not that important , for instance tire instead of tyre.
GAWR istead of GAW.
so you set the loadkind right to LBS, or it was already set that way.

[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.

[Phoebe3]

Please see my comments after each point:

Originally Posted by jadatis

The loadkind is set on lbs , and you probably filled in KG?
*** No, I used lbs.

But you have to give the tirespecifications only in the ovals ( wheelshape)
***Do you want the tire specifications from the TIRES or from the VEHICLE MANUFACTURER? I used the sticker inside the door which gives Ford's recommendations. Please specify where you want the source to be from.

The GAWR/MPAW belong in the dark blue above . Mostly front and rear the same loadindex, so you only have to give it once, and for the other axle is taken over from that. You overruled the loadindex dropdownlist by filling in your GAWR's as maximum load of one tire/tyre.
*** Again, I took this information from the GAWR on my vehicle's sticker. The GVWR is LESS than the sum of the the two GAWR ratings. It does NOT specify per tire. If the axle weight should be divided by the number of tires carrying the load, please specify that you want that.

Also set number of tires on the axle, now set on 4 ( dual load) but probably 2 for single load axle.
**** I have two tires on the front and four tires on the rear.

You filled in the advice pressure in space where reference pressure belongs of probably 80 psi or 65 psi.
***Again, this was taken from the FORD sticker. If you want the max pressure listed on the tire sidewall, please specify.

Then you set the reserves on 6 and 8 % , wich is strange, if left open, it uses my preset of 10% in case of given weights in part 2, and F5% R 18% going down scale to 10% , if given only GAWR/MPAW.
***OK, I set it to 10% although since we weighed the van with a full load, I can't imagine adding another 900 lbs.

So in short, begin again.
See,looking back , you are living in California, you can set the language to American-English. not that important , for instance tire instead of tyre.
GAWR istead of GAW.
***Thank you.

so you set the loadkind right to LBS, or it was already set that way.
***Yes.

[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.

[jadatis]

Answer to Phobe3.

Googled the tires from your " VIN plate" and the 195/75R16 107/ 105 is a 8 plyrated is D - load tire.
Those mostly have 65 psi as refencepressure, but because advice is given at 67 psi, I think it is 69 psi in this case, as often given in Europe
So as loadindex you have to select 107 front and 105 rear
The referencepressure ( where you filled in 67 and 57 psi , you have to fill in 69 psi. But on tires you can read this information.
Then you have to remove the gawr's from the maxload place , otherwise it overrules the loadindex selection.

[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.