Check my tire pressure math??

[Gottawonder]

Originally Posted by Blackrock

No math to it. Read the sidewall on the tire and air it to the posted max psi cold and you're good to go. I run these same tires on a F550 mechanics truck.

Gottawonder

[gasman94]

Originally Posted by po 185

I went and weight my rig loaded and the rear was 17880 lb and the front was 9620,,, just wanting to know,, what should the rear be,,, I have the same tires and do they have a updated chart that one is 2005
and I was looking and on the inside of the mh it has chart for air pressure and it has 120 psi for all the tires,,, should we use the tire chart or what fr. says

PO, I thought the same thing initially, since that is what it said inside of my coach as well. When I went to Gaffney for Camp FL, I had them do a four wheel weight and they dropped the pressures from 120 psi to 90 psi rears and 100 psi fronts based on the weight that I was carrying at the time. I noticed a difference in the handling of the coach. Also, since individual axle tire pressures need to be the same, you must use the calculated pressure of the heavier side for both tires.

Rich

[jadatis]

Originally Posted by dan-nickie

Pretty fancy spreadsheet.
And it's the first time I have see actual PSI instead of 5 lb increments.
Thanks.

My spreadsheet yust calculates on 1 psi rounded up , but in small you see the PSI in 2 digits. Could also round it to 5 psi if wanted but you can do that yourselfes.

My spreadsheet goes from another point of view then the system most use.
It calculates the highest possible pressure wich still has acceptable comfort and gripp. So not the minimum but the maximum, so it leaves as much possible reserve for pressure loss in time, unequall loading etc.

But If you think you can do with less reserve, you can filll in less reserve then 10% in the dark blue field.
But that means that for instance 92 psi advice can also be used 90 or 95 psi , only for 90 a little less reserve.
Mayby in time I will add something like a minimum, so if you measure that on the road , you know it still dont damage your tires if you are lucky.

Nice to see someone use my spreadsheet himself and using it directly as it is meanth.

If you ever weigh per wheel( pair) you can use part 3 , but then you have to play with the Load% instead of the reserve-adding.
Example 10 % adding is the same as using 91 % of the weight the pressure is calculated for so Load% 91%.

[Gottawonder]

Originally Posted by jadatis

My spreadsheet yust calculates on 1 psi rounded up , but in small you see the PSI in 2 digits. Could also round it to 5 psi if wanted but you can do that yourselfes.

My spreadsheet goes from another point of view then the system most use.
It calculates the highest possible pressure wich still has acceptable comfort and gripp. So not the minimum but the maximum, so it leaves as much possible reserve for pressure loss in time, unequall loading etc.

But If you think you can do with less reserve, you can filll in less reserve then 10% in the dark blue field.
But that means that for instance 92 psi advice can also be used 90 or 95 psi , only for 90 a little less reserve.
Mayby in time I will add something like a minimum, so if you measure that on the road , you know it still dont damage your tires if you are lucky.

Nice to see someone use my spreadsheet himself and using it directly as it is meanth.

If you ever weigh per wheel( pair) you can use part 3 , but then you have to play with the Load% instead of the reserve-adding.
Example 10 % adding is the same as using 91 % of the weight the pressure is calculated for so Load% 91%.

Again, it's really well done, and thanks for sharing your efforts. Thanks for the notes above. I did look at your examples folder as well to clarify a couple things for me as I filled in the numbers.

Gottawonder

[po 185]

I want to thank all of you,, when I get my mh back from camping world I will adjust my tire pressures and see how it handles on the interstate thank you
dan

[dan-nickie]

I got NEW UPDATED weights today.
Fuel and fresh water full, me and the wife seated, loaded with all our stuff for a couple months including all of DW's makeup and who knows how many scented candles, etc.

Steer Axle 11,060 (about 1,000 lb. more than last time)
Drive Axle 18,220 (about 500 lb. more then last time)

Looks like around 100 front and 90 rear would work like others have posted.
2Goodyear 75/70R22.5

http://www.goodyearrvtires.com/pdfs/rv_inflation.pdf

[Tireman9]

Just found this thread. Some comments.

Side to side tire loading is almost never 50/50. Based on limited data I have personally collected many are in the 47/53 to 46/54 range but a few are worse than 44/56%. RVSEF has thousands of data points and they say it is not unusual to have 1000# side to side variation on large RVs.

There are worksheets available to show how to calculate the individual loads if you can find an axle scale that has enough side to side clearance as seen in THIS blog post.

Yes all tires on an axle should be set based on the heaviest end. I recommend you add 10% to the psi found in the tables so you aren't chasing a 1 to 3 psi change due to Elevation and temperature variation.

Yes all tires on each axle of any road going vehicle should be set to the same cold inflation. This is for safety reasons for bother cornering and braking.

Pressure will vary by about 2% for each 10°F change in ambient temperature. Here is mathimatical proof for those who question this.
NOTE the oft quoted 1psi for 10F is old info from Tire Rack and is aimed at passenger tires. They updated their web site after I contacted them last year.

Personally I use the published industry tables and you will find that over 98% of all tires follow the tables with only some imports being different by a couple hundred pounds load or 5psi increment. If you can find the table from your tire company you should follow that but if you can't find one it is reasonable to use the tables published by Goodyear.