Community Forums

Erik_Laura · 10-01-2018, 12:32 PM

Finally taking time to find the inflation charts for our Toyo 265/70/R22.5 and wanted to verify with more experienced people that I am reading this chart correctly!

Here is the zoomed in pic of the inflation chart, with my tires at the bottom:
http://www.irv2.com/forums/attachmen...1&d=1538418643

from the weigh station, our weights fully loaded are:

steer axle: 8900
drive axle (with duals): 15360

my amateur attempt at reading this table leads me to believe:

steer axle - divide weight by 2 for 2 tires carrying that load =4450 lbs
in the single column this gives me 85 lbs.

drive axle - divide weight by 4 and use the dual column = 3840lbs
in the dual column this gives me 80 lbs

am I doing this correctly? per the previous owner, we have been running 90-95 lbs, so I believe I can lower the pressure some. will that improve the ride some having the tires be a little softer?

thanks in advance!

Vectraguy · 10-01-2018, 01:12 PM

I go by the motorhome/chassis specification and not the tire spec. Also, keep in mind that lower PSI can create more heat, and on a hot day that can be an issue.

Ray,IN · 10-01-2018, 01:56 PM

Without individual wheel weights how can you be sure you aren't overloading one wheel using the chart? Use the Federal Tire Placard listed pressures until you obtain the individual weights. Keep in mind those pressure/load charts show the minimum acceptable tire pressure for the corresponding load.

paddler1954 · 10-01-2018, 02:05 PM

I agree with Ray, In. On our coach there is a 600 lb difference between the front left and right tires. I highly recommend getting a 4 corner weight.

veraken · 10-02-2018, 05:47 AM

To determine what the right tire pressure is for you, you need to weigh your MH. Load your MH as you would for travel, fill your gas and water tanks and then get your MH weighed.

If you can't do 4 corner weighing, this is the procedure to follow:

1. Weigh the coach axles
2. Add 5% to account for possible uneven weight side to side.
3. Divide by the number of tires on each axle.
4. Look to tire chart for your brand to find tire pressure.
5. Add 5 psi for safety

Mudfrog · 10-02-2018, 08:46 AM

You state that your front is 8900 total. Your chart shows that 85psi is good for loads up to 4440 lbs per tire, or 8880 total. That's lower than the existing weight right off the bat. Airing up to 90 psi would cover the total weight but like others have stated, there still might be an overload issue if one side is heavier than the other. For now, it would probably be good to hit the 95psi mark in the front tires until you verify corner weights.

For the rear, 80 psi barely covers the total. Again, it would probably be better to add more air to cover the likelihood that one side of the rig is heavier than the other.

boyland · 10-02-2018, 09:11 AM

Quote:

Originally Posted by Vectraguy

I go by the motorhome/chassis specification and not the tire spec. Also, keep in mind that lower PSI can create more heat, and on a hot day that can be an issue.

I always did the same until i noticed with the new 16 ply tires the wear pattern was working the outside edges(originals where 14 ply). I called the Maker they said they could not recommend doing something outside of the limits of the wheel maker but this sounds like under inflation. The wheels were rated for 120psi the chassis called for 100 in rear and 105 in front. They recommended adding 10 pounds across the board. 110 in rear and 115 in front. I did this and wear pattern ended. They said the side walls are stiffer on the new tires and likely with the weight needed additional psi.

I did notice any ride difference with either pressure setting.

Erik_Laura · 10-02-2018, 07:32 PM

thank you for the replies! I agree with everyones analysis.

I will track down corner weights asap, and keep it at 95psi until I get more accurate numbers (then add 5+ for a buffer).

thanks for the post about the wear pattern, I will monitor that more closely!

thank you all for taking the time to respond. we have an amazing community here!

EZRider800 · 10-03-2018, 07:50 AM

One thing I've noticed is that if you ask 10 guys about how to figure the correct tire pressure you're going to get 10 different answers. And EVERYBODY is an expert!

The tire store will give you an answer, but it will be different from what the owner's manual says. The tire placard in the coach will say something altogether different too.

About the best you can do is to weigh your coach with all the tanks full and all your camping goodies on board. Then look at the tire chart, the sidewall of the tires, the tire placard in the coach and the owners manual. Then get a range of air pressures based on all those sources. This should get you real close. I would err on the high side as was pointed out above, low tire pressure on a hot day is a no-no.

Lastly, keep an eye on your tires. Like someone pointed out your tires will tell the story about if they are happy or not. Look for tread wear. Excessive tread wear down the middle means too much pressure. Excessive tread wear on the edges usually means the air pressure is too low.(if it's on the front tires it could be an alignment issue also).

Good luck and keep an eye on the tread wear for a while and you should be good. Remember to err just a bit on the high side with the air pressure if you're unsure. Low air pressure can ruin a nice trip real quick with a blow out. Air pressure that's a little high (5-10 lbs) will only wear out the center of your tires over time.

Erik_Laura · 10-03-2018, 10:48 AM

thanks EZ. Good points all taken.

Wbonsell · 10-03-2018, 11:47 AM

Anyone ever checked heat across the tread via an infrared temp gauge. Always worked racing to verify under or over inflation.

Mudfrog · 10-03-2018, 11:56 AM

Quote:

Originally Posted by EZRider800

One thing I've noticed is that if you ask 10 guys about how to figure the correct tire pressure you're going to get 10 different answers. And EVERYBODY is an expert!

The tire store will give you an answer, but it will be different from what the owner's manual says. The tire placard in the coach will say something altogether different too.

About the best you can do is to weigh your coach with all the tanks full and all your camping goodies on board. Then look at the tire chart, the sidewall of the tires, the tire placard in the coach and the owners manual. Then get a range of air pressures based on all those sources. This should get you real close. I would err on the high side as was pointed out above, low tire pressure on a hot day is a no-no.

For me, this is simple with no guess work. All I need is two things, the weights of each corner and the tire chart. Heaviest corner on the front rules for pressures up front and the heaviest corner on the rear rules for tire pressures in the rear.

For example, left front weighs 4200 lbs, the right 4000. The 4200 is the number that matters. Going with chart posted in this thread, 80 psi is needed to carry that weight. That pressure would be fine as long as the coach weight never changed.

But since we know that coach weight does vary at times, it's always good to add additional pressure to cover those times when weight might be higher. Some say 5%, some say 10%, depends really on how much variance is going on. For us, 5% or the next 5psi increment works since our rig stays loaded pretty much the same on all our trips.

Gary RVRoamer · 10-03-2018, 01:06 PM

Corner weights are ideal, but not always so easy to come by. It's not a perfect world we live in...

It is my opinion that you can divide the axle weight and make an estimate to cover the probable imbalance, i.e. the load is NOT 50/50 across the ends of the axle. My working assumption is that one end of the other may be 10% high vs the 50/50 average and I set psi for the higher weight. If you worry that isn't enough extra allowance, use a larger percentage.

Tireman9 · 10-04-2018, 01:23 PM

Quote:

Originally Posted by Erik_Laura

Finally taking time to find the inflation charts for our Toyo 265/70/R22.5 and wanted to verify with more experienced people that I am reading this chart correctly!

Here is the zoomed in pic of the inflation chart, with my tires at the bottom:
http://www.irv2.com/forums/attachmen...1&d=1538418643

from the weigh station, our weights fully loaded are:

steer axle: 8900
drive axle (with duals): 15360

my amateur attempt at reading this table leads me to believe:

steer axle - divide weight by 2 for 2 tires carrying that load =4450 lbs
in the single column this gives me 85 lbs.

drive axle - divide weight by 4 and use the dual column = 3840lbs
in the dual column this gives me 80 lbs

am I doing this correctly? per the previous owner, we have been running 90-95 lbs, so I believe I can lower the pressure some. will that improve the ride some having the tires be a little softer?

thanks in advance!

Yes you are doing the math correctly. Please remember that the inflation in the chart is the Minimum needed. That is why I recommend adding 10% to your numbers so you are not chasing your tail every time the temperature drops 10F which will cause the pressure to drop 2%. 10% margin gives you some flexability so you could wait till you have dropped say 5% then you can look for truck stop with high pressure air.

Also the chart assumes perfect side to side load balance which only a very small number of coaches have (probably less than 5%)
I suggest you use 53% of the scale axle weight as a partial compensation. "4 corner weights is best but if you must lower your pressure then do the above.