Question TIRE PRESSURE ADVICE?

[Jabber Jaw]

My 2020 Canyon Star has 255/80R 22.5G Michelin tires. The coach has been corner weighed and has 3910# on Left Front, & 3725# on Right Front.
The Michelin tire chart shows a capacity of 4300# at 80 PSI. So each tire is under that capacity. This leads to my question.
Would you be comfortable running 80 PSI in the front tires? At 80 PSI, I will be 390# under on the left front, & 575# under on the right front.
I had been running 88 PSI in the front, and rear.
I feel that the lower pressure should enhance the ride quality.
By the Michelin tire chart, I can run 85 PSI in the rear, and have about a 500# capacity cushion. And the 3PSI less per tire, should help the rear ride quality too.

What say you?

Thanks!

 

[TJ&LadyDi]

Given your weights and capacity numbers, I think I would go 85# all around. That makes life pretty simple and should provide you with a little softer ride while maintaining a good safety cushion.

TJ

 

[BGMAC]

The higher the pressure the better mileage on the tire, lower tire temp, less hydro planning possibilities, meter fuel mileage. Maybe a little rougher ride.
i run my tire pressures to the max in all my vehicles cars, truck, planes, and RV. Tires have to be tested to 100% over the rating of the tire so you set the pressure when the tire is cold.

 

[Neal]

Going by tire charts is your minimum. The reason for lower pressure is a more comfortable ride. If you can stand a higher pressure it has its benefits and can improve life of the tire, sidewalls, etc. Experiment. Increase as you wish such as 5 or 10 psi and see how the ride is or if you even notice a difference.

 

[OkieRed]

Tire pressure discussions can get passionate to say the least. I'd like to share some of my findings and relay the recommendations from Michelin as related to RV tire pressure and maintenance.
Neal's comment to experiment until you find what works is good advise. While keeping in mind the absolute worst thing you can do is have underinflated tires.
Here is the process to find the minimum pressure for your tires based on the actual 4-corner weight of your coach while fully loaded with fuel, water, you and all your stuff. You say you have front left (3910#) and front right (3725#), therefore you go to the Michelin chart and find the closest weight (round your actual up) and land on 4070# on the chart below. This weight corresponds with a minimum pressure of 75 psi for the front left. For simplicity I would say 75 psi is a minimum for the front L & R. Now for the back tires, your comment about the rear weights leads me to believe your back weights are close to 4000#. If so, I'm rounding up to 4300# with a corresponding pressure of 80 psi. It appeared in your original message that your are using pressure first then looking at a resulting load on the chart. Michelin recommends that you go with weight first to find the minimum recommended pressure. And finally, in order to properly maintain your tire pressures you should always set your starting pressure while the tires at at ambient temperatures and not in direct sunlight. Best is early morning or late evening after being off the road for a few hours.

Now for the physics of pressure and temperature. The tire pressure will increase or decrease approximately 2-2.25% per every 10*F internal temperature change. Now you may not have internal temperature sensors so I've created a table for you which will predict the internal tire temperature as related to tire pressure. As you drive, the tires will heat up and the tire pressures will increase. It's not unusual for the internal tire temps to increase by 60-70*F. This is fine and you should not worry about the increasing pressures as the tires are designed for this environment. When the tires cool down your tire pressures will follow the chart. Diligent tire pressure monitoring is very important. Especially if you are travelling from cool to hot or hot to cool locations. Remember, your starting tire pressures are what matter most.

Please take this information as I intend which is to be educated about tire pressure and the dynamics of the pressure/temp.
And finally, you can easily err on the side of starting with higher pressures with no harm done. Just make sure you stay on top of the tire pressures and understand the dynamics. But your original question was asking about a more comfortable ride. You can start with the recommended minimum pressure and be safe and it should result in a softer ride.
I hope you find this information helpful and educational.

 

[Jabber Jaw]

Okie Red......
Thanks for the information.
Think I kind of worked backwards!
Started at 95PSI in each tire. Used the Michelin chart, & backed the pressures down from there.
Currently have 88 PSI in each tire. I know the lesser pressures will improve the ride, as I have already experienced it.
At 85 PSI in each rear tire, it should help ride & still have a comfort zone relative to weight on each.
As for the front, the 80 PSI will also give me a comfort zone relative the weight. My only concern at 80 PSI would be potential temperature build up. Do you think that the tire temperature at 80 PSI would be substantially greater than at 85 PSI? And could it be an increased risk?

The goal is to help improve ride quality, but not at the risk of a potential tire problem!

Thanks to each of you for your responses!

 

[TJ&LadyDi]

I may have missed this detail, but are you using a Tire Pressure Monitoring System (TPMS)? If yes, then you can monitor your tire temperature and pressure while underway. If not, then you are flying blind! Personally, I would never again (I did for a while) drive any motorhome without one. They are not all that expensive and provide a wealth of information. I consider a TPMS an essential safety tool.

TJ

 

[Jabber Jaw]

I may have missed this detail, but are you using a Tire Pressure Monitoring System (TPMS)? If yes, then you can monitor your tire temperature and pressure while underway. If not, then you are flying blind! Personally, I would never again (I did for a while) drive any motorhome without one. They are not all that expensive and provide a wealth of information. I consider a TPMS an essential safety tool.

TJ

I have a TST 507 TPMS w/ 10 sensors to monitor the coach and "toad"!
Just set it up yesterday, getting ready to go to Newmar, the first week of August.
Had an RVI TPMS to go with the RVI brake system, but the sensors were not reliable, as they would lose contact. So not very reliable, even with the repeater connected.
Like the brake system, as it's interchangeable with the Terrain & Colorado.
Think the TST system will be much more reliable!

 

[AbdRahim]

The higher the pressure the better mileage on the tire, lower tire temp, less hydro planning possibilities, meter fuel mileage. Maybe a little rougher ride.
i run my tire pressures to the max in all my vehicles cars, truck, planes, and RV. Tires have to be tested to 100% over the rating of the tire so you set the pressure when the tire is cold.

I do likewise. I am 100 lbs under max weight, w/ full few tank.

 

[OkieRed]

Jabber Jaw....
Based on the Michelin charts your tires are designed to run safely in this range of starting pressure (based on your weights): Front: 75 psi (min) to 110 psi (max), Rear: 80 psi (min) to 110 psi (max) based on your ride preference as discussed in this thread. Just to re-emphasize the most important point is to make sure you never run the tires underinflated. It is very wise to have a tire monitoring system on both your bus and toad. Keep an eye on them and learn as you go. You never need to let air out while on the road as the tires heat up regardless of which pressure you choose to use as a starting point.
If you want a softer ride it requires more attention to tire pressure monitoring and maintenance. Your call. If you want to worry about other stuff then you can have starting pressures closer to the maximum and have a harder ride. No worries.

One note on the TST TPMS is to determine if the temperature reading is at the valve stem or can it read internal tire temps. My coach has pressure/temp sensors inside the tire (photo below) which are mounted to the rim. In 2018, I added the TST TPMS sensors to my toad and to the bus wheels (I know, I didn't need them on the bus but redundancy is good). What I realized is the valve stem sensors (TST) I have are worthless for reading the temp because they don't give internal tire temps.

 

[BGMAC]

@OkieRed, I do a tire pressure check at the start of the trip (the old fashion way). I am not to worried about tire temp so much as they would be related to low pressure issues. As long as my pressures are up, my temps should be down.

 

[TJ&LadyDi]

While the external sensors will not accurately measure internal tire temperatures, they will not be too far off as wheel and sidewall temps will be close to internal tire temps. The sensors are in close proximity to the wheels and sidewalls.

As do many, we carry an IR temperature gauge to check tires and wheels. In checking both wheel and sidewall temps, I have found them to be within 10 degrees or so of my EEZ Tire TPMS sensors.

TJ

 

[Jabber Jaw]

This is the reply I got earlier today from TST, regards the measurement of "tire temperature"!

Hi Alan,

The sensors have a tiny hole that allows the air under pressure to be pushed in to the the temperature switch for reading. It is reading the temperature inside the tire.

Enjoy your system and have a great Sunday!

Safe Travels!

TST Customer Service

And I do have an "infra-red" temperature measuring device, & use it each time I stop, to check tire temperatures.

The trip to Napanee will be the first trip using the TST "TPMS" unit; & I'll be curious as to how close the temperature readings between it, and the infra-red device.

When checking tire pressures yesterday, the TST & the built in TPMS in the Terrain were the same. I was pleasantly surprised!

I'll test it, the TST, before leaving for Napanee, against my digital tire pressure gauge which I use for the coach, and compare accuracy!

At this point, I think I will be very happy with the TST system!

 

[TJ&LadyDi]

It looks to me that you have all the right tools to set your tire pressure and monitor tire pressure and heat parameters. Well done!

TJ

 

[Jabber Jaw]

THANK YOU!
Thanks to everyone for the replies. Great information!