Tire Pressure

[creativepart]

One thing I've found, by taking weights and using charts to set my tire pressures within range and improve ride quality I found it necessary to have to worry about cold weather pressures.

I'd weigh and check the charts and do my settings in the relative warm of a South Texas winter and then travel to the cooler higher altitudes of New Mexico and Arizona and find my tire pressures far too low on very cold mornings.

To accommodate the cold temps I'd need to add air in the morning before leaving a campground and that's just not a pleasant thing to have to do.

When I got home this past Feb I spent time adjusting all my tires higher off of the aggressively low pressures I had used hoping for a smoother ride. Now I'm about 1/2 way between the placard tire pressure and the tire charts pressure based on RV weight.

[Goodspike]

Originally Posted by BobC

Is it a safe practice, yes, is it a necessary practice, no.

I'm not saying it would be unsafe, but that there could be handling or tread wear concerns going below the vehicle manufacturer numbers. Isn't all the tire manufacturer is going by is the weight on the tire and the minimum pressure that is safe for that weight? They don't now anything about front/rear weight distribution, suspension or the steering geometry. They're just saying: "To not have your tires blow up on you, use at least this much air pressure." They might also be considering tread wear, but for cars and trucks I've never found a little extra pressure to cause abnormal wear. Not sure that motorhomes would be different. But I don't see how they could possibly be considering handling or ride quality on a vehicle they know nothing about.

Now if they were posting maximum pressures for certain weights that were below the maximum pressure listed on the sidewall, that would be entirely different. But from the links posted I'm not seeing any of them are doing that. If I'm missing that, please point it out.

[Tireman9]

Originally Posted by firemangk

I have found that the tire door sticker info is primarily applicable to the original tires . How would the sticker know what brand or type of tires are on the vehicle? Your tire shop guy is likely the best source of advice.

Unless you change size (the numbers) or Type i.e. ST to LT the load and inflation for tires does not change based on brand. All ST tires follow the same published data for load & Inflation. As far as I know all LT tires also follow the same Load & inflation numbers. Some 22.5" size Michelin tires may be different by 5 psi from other brands.
Your MINIMUM inflation should be based on the scale reading and the tables.

[Tireman9]

Originally Posted by creativepart

One thing I've found, by taking weights and using charts to set my tire pressures within range and improve ride quality I found it necessary to have to worry about cold weather pressures.

I'd weigh and check the charts and do my settings in the relative warm of a South Texas winter and then travel to the cooler higher altitudes of New Mexico and Arizona and find my tire pressures far too low on very cold mornings.

To accommodate the cold temps I'd need to add air in the morning before leaving a campground and that's just not a pleasant thing to have to do.

When I got home this past Feb I spent time adjusting all my tires higher off of the aggressively low pressures I had used hoping for a smoother ride. Now I'm about 1/2 way between the placard tire pressure and the tire charts pressure based on RV weight.

Yes if you travel between locations of large temperature swings (like 30°F) you may want to balance the change. Just be sure you are never operating with inflation lower that the tables say for your measured load. Being over the inflation in the tables is almost never an issue.

[Tireman9]

Originally Posted by Goodspike

I'm not saying it would be unsafe, but that there could be handling or tread wear concerns going below the vehicle manufacturer numbers. Isn't all the tire manufacturer is going by is the weight on the tire and the minimum pressure that is safe for that weight? They don't now anything about front/rear weight distribution, suspension or the steering geometry. They're just saying: "To not have your tires blow up on you, use at least this much air pressure." They might also be considering tread wear, but for cars and trucks I've never found a little extra pressure to cause abnormal wear. Not sure that motorhomes would be different. But I don't see how they could possibly be considering handling or ride quality on a vehicle they know nothing about.

Now if they were posting maximum pressures for certain weights that were below the maximum pressure listed on the sidewall, that would be entirely different. But from the links posted I'm not seeing any of them are doing that. If I'm missing that, please point it out.

You are correct the wording on tires can be a bit confusing but the inflation shown is for the load shown and that load is the maximum you should ever place on your tires. If you have lower measured load on a tire the inflation can follow the tables. An exception I would comment on is for multi-axle trailers that need to address the "Interply Shear" problem unique to multi-axle trailers that should run the inflation on the tire sidewall.
I have covered the Maximum / Minimum questions in a post on my RV tire blog.


One final point is that whenever you adjust tire inflation all tires on any individual axle should be inflated to the same level which is based on the tables and the load on the heaviest loaded tire.

[Wyatt]

This is from my Ford F53 manual giving THEIR definition of when a tire is “cold”.

[Fletcher0077]

I had the 4 corners of MH weighed and set tire pressure with that information. Using that weight and the chart for my TOYO tires the required pressure is 75 PSI. I set the tires at 90 PSI. That gives me 15 PSI for leaks or colder temps. I set the TPMS (EZ tire) to alarm at 80 PSI. That gives me 5 PSI to pull over in case of an alarm. Also regular tire inspections at rest stops. My life on the road is much easier. I turn on the TPMS in the morning and by the time I finish coffee the tire PSI are displayed. I check tires once in awhile if on a long stay at CG and when on the road. Before each trip I do check tires with a calibrated tire pressure gauge to make sure all is well with TPMS. Great for peace of mind.

[Wyatt]

Originally Posted by Fletcher0077

I had the 4 corners of MH weighed and set tire pressure with that information. Using that weight and the chart for my TOYO tires the required pressure is 75 PSI. I set the tires at 90 PSI. That gives me 15 PSI for leaks or colder temps. I set the TPMS (EZ tire) to alarm at 80 PSI. That gives me 5 PSI to pull over in case of an alarm. Also regular tire inspections at rest stops. My life on the road is much easier. I turn on the TPMS in the morning and by the time I finish coffee the tire PSI are displayed. I check tires once in awhile if on a long stay at CG and when on the road. Before each trip I do check tires with a calibrated tire pressure gauge to make sure all is well with TPMS. Great for peace of mind.

There’s so much I’ve learned, by reading Tiremans blog. He’s a major contributor on this board, but also has a blog, that will probably answer any questions you may have.

I know he has helped me personally with my tire inflation. But I encourage you to read his posts.
https://www.rvtiresafety.net/

[Lotus 7]

Thanks Tireman9. Quick question, is there a simple short answer to the question of adjusting pressure for higher elevations (7000’+) ? If not, I’ll go find ur safety blog.
I’d guess that barometric pressure is insignificant compared to all the other variables that come & go during the day, but I have a nerdy wife who likes to think up stuff to worry about & she’s not about to take my fragile eggshell opinion.

[Tireman9]

Originally Posted by Lotus 7

Thanks Tireman9. Quick question, is there a simple short answer to the question of adjusting pressure for higher elevations (7000’+) ? If not, I’ll go find ur safety blog.
I’d guess that barometric pressure is insignificant compared to all the other variables that come & go during the day, but I have a nerdy wife who likes to think up stuff to worry about & she’s not about to take my fragile eggshell opinion.

I think you answered your own question. The changes in tire inflation are less than 5 psi and the temperature changes easily have larger impact.


But You need to have some "Reserve Load" which means you have the ability to tolerate variations in load. elevation and tire pressure due to temperature changes and NEVER end up driving on an underinflated tire. To do this you first need to know your ACTUAL load on your tires and know the MINIMUM inflation needed to support that load PLUS have enough extra inflation to tolerate a drop in temperature which will lower the inflation.


Tire inflation changes 2% for each chang in temperature of 10F


In general I like to see at least a 10% margin in inflation which should cover you for 80 - 90% of your travels.


I run a 10% to 15% margin on my Class-C and when I took a 7 week 7,000 trip from Ohio to Oregon to Alberta to Yellowstone to Ohio I only needed to add air once when I got down to a 5 psi margin based on my TPMS readings.