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Open Roads Forum  >  Class C Motorhomes

 > Tire PSI

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n4nsl

Hoover, Al.

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Posted: 04/04/02 04:58pm Link  |  Print  |  Notify Moderator

Hello All,
Stupid question but newbie. Have Class C Itasca Spirit. The tire PSI "stamped" on tires shows 80 PSI.......have duals in rear. The "vin" sticker in door shows rear tires at 80PSI and the front should be 65PSI. So which should I go with?
Thanks for any replies!
Dale Harden

richmondmj

St. Cloud, Fl , USA

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Posted: 04/04/02 06:35pm Link  |  Print  |  Notify Moderator

The 80psi stamped is the maximum psi for the tire. The vin sticker shows the psi to carry the maximum rated load for each axle. Weigh the coach first after you load as you would normally and then inflate the tires to the tire mfgs chart for psi requied to handle that load. Every tire mfg has one for their tires, many list it on their internet site.

You'll also want to get the wheels aligned with that weight. Alignment changes with added weight and Ford and other chassis mfgs align them as a cutaway. The modifier, in your case Winnebago, is supposed to align it again before it leaves but many don't. The reason is you'll be adding weight of water, fuel, propane, passengers, gear, etc and that will change the alignment anyway.

Good Luck!

wolfe10

Texas

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Posted: 04/04/02 06:50pm Link  |  Print  |  Notify Moderator

Good answer, richmondmj. But until you do weight the axles (and even better the individual wheel positions), go with what is on the door unless you may be overloaded. If you had adequate CCC (from the manufacturer's sticker on all newer coaches) and have not added much, until you weigh, go with the 65/80. 80/80 would be too high in front. After weighing, as outlined above, go with the tire manufacturer's recommended pressure for each axle. If you weigh the individual wheel positions use the heavier weight on each axle to look up the correct pressures. All tires on an axle to have that same higher pressure.


Brett Wolfe
2003 Alpine 38'


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g241b

Wilmington,NC

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Posted: 04/05/02 04:11pm Link  |  Print  |  Notify Moderator

Another opinion:
Talked to Ford and Winnebago,about my rig.The results are as follows:
lower front pressure=good ride
max pressure=harder ride
I run 80psi in all tires hot
I put 76psi in them cold,this will give me 80psi hot.They say this is good tire maint.But to watch tire wear. If the tire wears in the middle the pressure is to high.(reduce pressure a couple of lbs. at a time)If tire wear is on the sides of the thread, the pressure is to low.(add a couple of lbs.at a time)I consider my tires hot after about 30 miles highway.Loaded alignment is a good idea. My rig is not close to max. weight. But i still maintain the pressure at 80psi hot

richmondmj

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Posted: 04/05/02 05:13pm Link  |  Print  |  Notify Moderator

Don't ever trust Ford for correct tire pressure, look at the Explorer pressure they suggested! If Winnebago gave that advise they're just as bad. Too much pressure is as dangerous as too little. The tires wear uneven because they aren't riding on the entire footprint and that is dangerous for many reasons, beside being a rough ride on top of it. Use the tire mfgs weight/pressure scale only! They test the tires and know what the pressure should be for the given load. Ford and Winnebago don't have a clue if that's the advise they give!

Brent (Wolfe10) is correct that you need to get the weight of each tire and use the heaviest per axle to determine correct pressure for the axle.

Ghost9mm

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Posted: 04/06/02 03:55am Link  |  Print  |  Notify Moderator

To richmondmj:
I agree with your post whole heartly,I called ford and got one answer and called Winnebago and got another answer agree that is is correct that you need to get the weight of each tire and use the heaviest per axle to determine correct pressure for the axle.This is really important because of weight factor in most class C
Thank You & Hope This Helps
Gary & Pat


richmondmj

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Posted: 04/06/02 06:08am Link  |  Print  |  Notify Moderator

There is one more important point regarding LT tires. Many aren't speed rated and therefore when driving at higher speeds precautions must be taken. Most warranty pamphlets will tell you if you will be driving at sustained speeds of 66-75mph you need to add 10psi cold inflation to the standard psi for the weight being carried. If that brings you over the rim/tire max you must lower the weight on that axle or take your chances at driving with that load at high speed and improper psi, that could cause serious problems for the tires! When driving at 76-85mph sustained in addtion to the 10psi you must decrease the load by 10% of the tires rated value.

Both of these are important issues and could account for some tread seperations on tires since many people travel at the posted highway speed that in many states is 65-70mph on highways. You get much better MPG at 55-60mph often losing 1-3mpg as you go faster, speed is the #1 factor in fuel economy followed by weight. It will only take a little more time to get where you're going driving at a lower speed and you'll save a lot of gas in the process.

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