It is not 'lowering the tire pressure' or using the 'minimum safe pressure' in your vehicle. Both of those are misleading terms.
What you are doing is using the correct pressure for the weight the tire is carrying, plain and simple.
TPMS is not required to do this.
2000 Sea Breeze F53 V10 - CR-V Toad
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Garym114 has it exactly correct! The tire manufacturer knows the correct pressures for optimum performance. I have stated before on this forum, some years ago I took someone's advice and inflated to maximum pressures and it made the motorhome almost undriveable. At the manufactures reccomended pressure - smooth as glass.
Ron
ClassAGeek wrote: Manufacturer load tables assume nominal warming due to driving but they do NOT account for an increase in ambient temperature at the same time. I suspect this causes many blowouts when drivers think they are being safe. If you do nothing else: Don't use maximum tire pressure unless you can realistically expect small changes in ambient temperature. Your coach will thank you.
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While it is best to use the tire manufacturers load inflation charts, it is still safe to use the maximum PSI stated on the tire itself. "The maximum load capacity allowed for the size tire and load rating and the minimum cold inflation needed to carry the maximum load are located on the tire's sidewall." (Source: Michelin RV Tire Guide, page 2, top of page.). In other words, the Maximum PSI rating on the tire can be used without worrying about the increase in ambient temperature, provided you check and adjust your tire pressure every morning, which is the accepted practice among RVers. It will not be bad for the tire or make the tire more susceptible to blowing out. But, one should never let air out of a hot tire at midday in a attempt to adjust the tire pressure!!!
But the correct tire psi is not going to make your ride be "as smooth as glass"!! And in some respects you do not want your ride to be as smooth as glass, because you as the driver, want some feedback from the road surface for safety reasons.
CharlesOK wrote: I believe that your experiences are right on. In 20 years of driving these units, I have religiously watched and cared for my tires. Nearly 200K miles now with NO blowouts and no failures. I also have a F53, late model with 22.5 tires, Michelin XRV's, OE Ford install. I watch the tire pressures daily, carry a functioning air compressor, and use only guages which have been calibrated at a good truck tire place. Running the correct pressures for the load and road temps anticipated will reward with a much better ride for sure. Running 110 PSI ever is a sure way to damage the coach and everything and everyone on board. I use AWeigh We Go at FMCA rallyes for acurate 4 corner weights as well.
Well thought out and logically presented.
I'm curious about the "gauges which have been calibrated at a good truck tire place." statement.
For years I have wanted to find a way to calibrate my tire gauge. The way I did it was compare the readings of five different gauges on the same tire and use the ones that came up with the same pressure reading. I have found online pressure calbrating equipment but it is up in the thousands of dollars.
Every tire place I've inquired about calibrating has said they trust the gauges they use and have no idea how to calibrate a gauge.
Could you elaborate on your findings?
2004 Monaco La Palma 36DBD
Workhorse W22 8.1 Gas Allison 1000, 7.1 mpg
2000 LEXUS RX300 FWD 22MPG 4020 LBS
US Gear Brakes
Nothing is either good or bad, but thinking makes it so.
Like someone recently posted with a F-53 chassis we find our P30 chassis rides about the same even at stamped max PSI BUT the handling control is MUCH better.
We perfer the better handing and reduced risk of a blow out so we run at or near max PSI now since the ride is about the same either way in our case. This also gives us a 20 PSI margin before hitting inflation chart values. With the TST TPMS we know the PSI and temps at all times so when our PSI works down to say 85 we just keep on trucking where if some loss 2 PSI they are abusing their tires perhaps.
The 65 PSI stamped on our placard reads 65 PSI just because it shipped with D load rated tires and we run and the PO ran F load rated tires.
Some go to the troblem to do corner weights BUT forget to multiply by 1.2 before looking at the inflation chart to help prevent blowouts.
I kept myself busy with calculating tire-pressure, with use of the same formula that the European tyre-makers have used for decades ( ETRTO), and the American TRA also uses since 2006.
Came to about the same conclusions as topicstarter, but dont agree with all his conclusions.
Introduced myself the load-percentage ( L%) and that is, the percentage what the real load is of the load you calculate the pressure for.
Example: say you have 8500 lbs on an axle, and you want to calculate with a L% of 85%, then divide 8500 by 0,85 (= 85%) to get 10000lbs.
then calculate the advice pressure for 10000 lbs.
I concluded trough reactions I had about bouncing (and loose teeth-fillings )
that under 85% L% discomfort begins by bouncing.
Over 100% tire-damage begins.
The lower the L% the less comfort and gripp. The higher the L% the more gripp and comfort, but never go over 100% for savety .
Made a spreadsheet a while ago and translated it to English from Dutch. It can be used to first calculate the needed pressure, with L% called gripp-Percentage there. In part 2 you can play with the temperature and see what it does to the pressure. Normal inside-tire-temperature is about 45dgr Celcius and is filled in in Fahrenheit.
Idea is to see what you have to fill cold for other then normal conditions , to get the same warm pressure as under normal conditions would have.
The lay out of skydrive of hotmail has chanched recently, so now click on the document you want at the end at I then you get at the right side the things you can do with it. Download and open the spreadsheet in Excell or compatible programm to work with it.
I am interested what topicstarter can do with it. It means that you dont have to use fist-rules , but calculate it exactly, and see how many deveation you can give it.
Sorry for strange words and miss-spellings, English is not my native speech. give me the right spelling or words and I use it furtheron.
Greatings from Holland
Peter
* This post was
edited 07/04/11 12:16pm by jadatis *
That is very close to the 80% rule used by many in the states especially for trailer tires. I can see 85% for MH's being a great value.
Some do not understand the need for a margin to be safe due to load shift in part to roads having a slope from the center (crown) in most cases.
In our MH case where our gas tank/water tank/holding tanks are full or empty greatly determine the weight on the front axle and the rear to a lesser degree.
If you want a more precise method for checking the accuracy take the gauge to a local tire dealer or fleet truck maintenance facility and ask them to check it using a master gauge. A master gauge is a gauge that is certified to be accurate. But I caution you there are lots of tire dealers who don't have their own tire pressure gauges calibrated.
So many people read part of the sentence on the tire "Maximum pressure 110 psi" they fail to read and understand the entire sentence
Proper pressure is a function of the load the tire is carrying, The lower the load the lower the pressure. If you over inflate to 110 PSI when you should, for example, be running 90, the tires will wear in the center, the ride will be way rougher and the driver's control will generally be reduced in the event he has to do any "Serious" driving.
Likewise when you run at 80 when you should be runnin 100, the tire will wear faster on the edges, the driver has less control, and there is greater danger of side wall failure as well.
When you run at the PROPER pressure, the tire lies flat on the road, the side walls have some give, but not to much and you enjoy both the longest tire life AND the best control when you need it.
so, how to you find out the proper pressure.. Weigh the rig, wheel by wheel, of course.
Nothin adds excitment like something that is none of your business
Kenwood TS-2000 housed in a 2005 Damon Intruder 377
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