As an owner an F-53 motorhome, tire pressure matters to me more than most. I could fill my tires to the maximum load carrying capacity @ 110 PSI and then have my teeth loosened by the less than ideal ride. And as you will see in point 6 below, starting out @110 PSI can also be a bad idea. I choose instead to use a good TPMS and maintain the lowest possible recommended tire pressure year round. The result is a ride that rivals MH costing twice as much.
Maintaining minimum safe tire pressure is NOT a passive activity. You really need to continually monitor tire pressure and temperature to achieve the right balance between safety and comfort. If this bothers or scares you, fill to the maximum and ignore this posting (you will be less safe but don't let me burst your blissful bubble). I don't post often, but many of the recent tire pressure threads drive me crazy.
Here are facts I have collected and observations I have made using a TPMS to maintain the lowest safe pressure for a number of years:
1. (most important) Have your normally loaded coach weighed on a CAT scale. Determine the weight on each axle and check the manufacturers pressure tables to determine the proper cold temperature for your tire. I have Michelin 22.5 XRVs, so I use these tables: http://www.michelinrvtires.com/michelinr........tires-retreads/load-inflation-tables.jsp. I normally have 6900 lbs on the front and 12900 lbs on the rear axle.
2. Using the Michelin tables, I see I can safely use 85 PSI on the front axle and 75 psi on the rear. This is a significant difference from the 100-110 PSI that is routinely recommended by many 'experts' as a safe pressure. I can assure you that my 2008 Gulf Stream rides much smoother than coaches @ 110 PSI or even those at 90 PSI.
3. My tire pressure rises 10 PSI after 20 minutes of driving. Cold tire pressure charts take this into account by many drivers miss this basic fact: if a cold tire has weight capacity Y at pressure X then that same tire will have weight capacity Y when a tire has warmed from a colder temperature to X. That means, while I am at the low end of weight carrying capacity when my tires are cold @ 86 PSI, in twenty minutes my pressure will rise to 96 PSI and I will be at a much higher capacity. I never go below the recommended cold tire pressure yet in a few minutes I am no longer in this range. RV tire manufacturers do not provide performance curves like race tires I have used. That's too bad. If they did, more people might run at lower pressures.
4. My cold tire pressure varies daily. I routinely add and bleed air prior to most trips in anticipation of the ambient temperature that will exist when driving. During a hot spell I can plan on having cold pressure rise by as much as 5 PSI. Just this week my cold tires went from @ 86 PSI midday to 90 PSI midday. Before setting out this weekend, I bled back to 86 PSI. I will be able to potentially maintain this pressure by doing nothing until fall when I will need to add pressure to get back to my target 86 PSI midday pressure.
5. Weight capacity is reduced at higher speeds and is increased at lower speeds (including standing still). Continental tire charts show this difference where Michelin shows much less of this information. In general, your tires have more than twice their rated load carrying capacity at less than 10 MPH. So in other words, your tires are not going to blowout when standing still.
6. You will notice that Michelin has dire warnings about over inflation. If you start out a trip @ 110 PSI on a cold morning that turns into a hot day, you can easily exceed the maximum tire and/or rim limits. 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.
Do I expect many to join me and perform active pressure monitoring to achieve a better ride? No. At least F-53 Chassis owners should consider doing more research. I love the ride on my MH. Aside from investing in a good TPMS, I have had to spend nothing more.
----
Happy Ford F-53 Class A Owner (2008 Gulf Stream)
2010 Ford Fusion Toad (with 6 speed manual transmission - the only way to tow)
Brake Buddy Vantage, Blue Ox Aladdin Tow Bar,
TST RV 507 TPMS, Power Master Voltage Controller
I don't have TPMS on the Tioga.
I run the tires at the pressures recommended on the door frame placard, even though I have Load Range E tires installed instead of D.
I stop in at Tire-Rama (where I bought the Cooper tires) and have the pressures checked every year (that reminds me, I need to do that this coming week!).
The pressures on the tire sidewall are for the weight on the sidewall. Since my tires are never run at maximum weight, I don't think I need the maximum pressure.
The Tioga rides nicely, and handles very well, even in severe crosswinds.
It works for me.
CM1, USN (RET)
2002 Fleetwood Southwind 32V, Ford V10
Toad: 2006 Jeep Rubicon LJ
Other toad: '06 PT Cruiser, Kar Kaddy dolly
Toy: 1977 Dodge W100 CC SWB, 3/4 ton axles & springs
"When seconds count, help is only minutes away!"
My guess is that you've not searched and found any of the hundreds of posts here advocating that tire pressures be set based on actual "travel ready" four corner weights using the tire manufacturer's specifications plus a small "fudge factor".
I'm really kind of surprised that you have multiple recommendations on the correct pressure to run. IN most instances they have only ONE recommended pressure and that is the pressure necessary to carry the GVWR of the vehicle.
2011 F-150 HD Ecoboost 3.5 V6. 2550 payload, 17,100 GCVWR - 2004 F-150 HD (Traded after 80,000 towing miles) 2007 Rockwood 8314SS 34' travel trailer
US Govt survey shows three out of four people make up 75% of the total population
in over 200,000 towing miles we have only had minor nail punctures for tire problems, and we have NEVER inflated TT tires to the maximum on the sidewall. We use the manufacturers tire pressure versus weight table number, plus 5 psi for luck. Tires seem to wear out evenly accross the tread. Of course we've also never loaded our TT's to the max GVWR either.
For those who wonder, no, we do NOT use Chinese tires. We DO use ST tires.
Just our experience.
Chuck
Wonderful Wife
Australian Shepherd
2010 Ford Expedition TV
2010 Outback 230RS Toybox, 5390# UVW, 6800# Loaded Not yet camped in Hawaii, 2 Canada Provinces, & 2 Territories I can't be lost because I don't care where this lovely road is going
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.
* This post was
edited 07/03/11 09:54pm by CharlesOK *
Chuck&Gail wrote: Well we haul TT's, not a MH, but;
in over 200,000 towing miles we have only had minor nail punctures for tire problems, and we have NEVER inflated TT tires to the maximum on the sidewall. We use the manufacturers tire pressure versus weight table number, plus 5 psi for luck. Tires seem to wear out evenly accross the tread. Of course we've also never loaded our TT's to the max GVWR either.
For those who wonder, no, we do NOT use Chinese tires. We DO use ST tires.
Just our experience.
You are comparing apples to oranges here. When was the last time you rode in your trailer? The OP was commenting on ride quality. You really don't know how the trailer rides since you can't ride in it legally.
2003 Newmar Mountain Aire, Workhorse W22, 2008 Saturn Vue, Falcon 5250, & US Gear Unified Tow Brake
I agree with the OP, except ... you go to all this detail, yet skip the need to do 4-corner weights, not just each axle. I didn't cross-check your numbers vs. the tables, but based on your description, it sounds like you weigh by axle, and then assume that your weight is evenly distributed side-to-side. Ideally, you should be weighing by wheel position, and setting your pressures for both sides of an axle to the appropriate pressure for the heavier wheel, but if you can't, many would recommend adding a "fudge factor" of 5 lbs. to your pressures.
My only other comment is that I think all that adjusting for expected ambient temps is overkill. The tire manufacturers' tables specify cold pressures; I let it go at that.
Mike and Trish
2008 Mandalay 43A
2008 Jeep Liberty on Blue Ox towbar
Yorkiepoos - Janis and Jimi
ClassAGeek wrote: If you start out a trip @ 110 PSI on a cold morning that turns into a hot day, you can easily exceed the maximum tire and/or rim limits. 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.
Not to sound argumentative here, but I can gurantee no tire in healthy condition will ever blow due to overinflation. Almost 100% of tread seperation is caused by low pressure and / or overloading, which overheats the tire.
To actually blow a tire by pressure, you'll have to exceed the limits by magnitudes. Tests done on 11r22.5 truck tires showed blowouts at approx 500 psi! Stunt drivers routinely inflate 44 psi car tires to 110 psi and never blow them due to pressure (abuse is more likely).
Otherwise, very good advice mentioned. Us RVers are lucky enough to have a non-changing load, thus allowing us to fine tune our pressures for comfort, mileage, etc. On the other hand, imagine if a commercial bus driver had to readjust tire pressures each time a passenger got on!
Offline
