Good Sam Club Open Roads Forum: Another ‘dadgum’ post re: tire PSI…please bear with me…
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 > Another ‘dadgum’ post re: tire PSI…please bear with me…

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goufgators

Crawfordville, Florida

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Posted: 11/29/19 05:37am Link  |  Quote  |  Print  |  Notify Moderator

I know and agree with posts relevant to ‘have your coach weighed’ and I have done so although not four-corner weights. Axle weights indicate 80 psi for all tires. In the title, I said this post was about tire psi and that is, at least, partially correct. But, it’s also about that age-old problem of steering wander. Let me explain, if I can. Wandering has been a problem since the coach was new (2017). I’ve added rear stabilizer, front stabilizer, steer safe and had alignment adjusted to 5 degrees camber (not sure that’s the correct terminology for the alignment). After all the add-ons and alignment, the problem still exists. Here’s the interesting part. As you know, as tires turn they build up heat and psi increases. When I start out on a trip, the tires are at the cold 80 psi and steering at that psi is beautiful (Cadillacish good)…well maybe not quiet that good, but no wandering. No wandering continues until psi reaches about 90 psi or slightly above. That’s when the steering wheel gets a work our along with the driver (that’s me). After all of the above, here’s the question: In order to keep the tires’ psi from increasing quickly to a point of ‘wander’, would it be safe to reduce the cold psi to say 75 (remember Goodyear says, based on weight, cold should be 80). In our Florida very warm weather, the tires, starting at 75, would rather quickly heat up along with the psi and exceed the cold 80. But, in so doing, the psi might not reach the wandering problem. At least not as soon. Comments welcomed!


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Eastern Ontario

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Posted: 11/29/19 05:58am Link  |  Quote  |  Print  |  Notify Moderator

What is Winnebago's recommended tire inflation for your Motorhome? If you're not sure, you'll find the manufacturer's optimum or recommended tire pressure for your MH on the sticker on the drivers side door, or if no door, on the wall below the drivers side window.
If this is different than the 80 lbs indicated by Goodyear, I would reset your tires to the door sticker specs and see if this solves your issue.
Also, I noted that you set your tires to the same 80 lbs all around which i suspect is part of your issue. With the two Winnebago MH's we've owned, the rear tire pressure has been less than the fronts. In our current 38 ft Suncruiser, the Front tires are 100 lbs, the rear are 90 lbs. It drives perfectly when the pressures are set to Winnebago's recommendations.


Touring in our 2010 Suncruiser, beaches, site seeing, national parks, chillaxing..

way2roll

Wilmington NC

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Posted: 11/29/19 06:07am Link  |  Quote  |  Print  |  Notify Moderator

Cold PSI means just that. Lowering PSI so the tires heat up to the recommended cold psi defeats the purpose of setting cold psi in the first place. They will be under inflated. As I am sure you are aware, low psi is the primary reason for tire failure - aside from a puncture. The F53 is notorious for poor handling. It's not going to handle like a car or a DP - ever. We had 2 gassers over the past decade and both were rather exhausting at the end of a long day in the saddle. Constant corrections. I would consider different tires, cheap handling fix or another model RV. Lowering psi below the tire manufacturers recommendation is not the proper way to handle the issue. You'd be borrowing risk. That of course is my opinion and I usually err to the side of caution. I am sure there are thousands of people out there driving on under inflated tires by 5 psi and either don't know it or don't care. I am confident however your tires will generate more heat.


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Ivylog

Blairsville, GA and WPB, FL.

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Posted: 11/29/19 06:13am Link  |  Quote  |  Print  |  Notify Moderator

Last summer I went from 95° in Moab to 50° in Colorado and NO I didn’t change my tire pressures. I would not worry about 5 psi one way or another. I would temp the tires and would not have them above 140 degrees in the bottom on the tread...hottest spot. I might go with the next size larger tires when it’s time to replace the current ones so you can run less pressure in them.


This post is my opinion (free advice). It is not intended to influence anyone's judgment nor do I advocate anyone do what I propose.

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DutchmenSport

Indiana

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Posted: 11/29/19 06:18am Link  |  Quote  |  Print  |  Notify Moderator

I've never driven a MH of any kind (I'd love to some day), so here's my worthless suggestion. Why not just deflate the tires to 75 (cold) and take it out for a test drive. As you've indicated, the tires heat up quickly, so you should have your answer within a few minutes of driving. Take it out for a 20 mile spin and see what happens.

If it doesn't work, then simply air up the tires to 80 psi again. Nothing lost except 20 miles of fuel.

Is the 80 PSI the "Max" cold PSI? I know motor homes are a different animal than the family sedan, a dually truck, or a trailer, but somewhere there has to be a "sweet spot" that works for your unique rig, tires, and overall configuration.

Tyler0215

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Posted: 11/29/19 06:20am Link  |  Quote  |  Print  |  Notify Moderator

Try it and see how the MH handles, 5 psi less is not going to kill your tires.

CapriRacer

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Posted: 11/29/19 06:38am Link  |  Quote  |  Print  |  Notify Moderator

First, caster is what contributes to straight line stability, so I assume you meant that the caster was moved to 5°. That much camber is only used in racecars.

Second, too high a pressure on the fronts tends to cause the tires to follow the ruts and grooves in the road. What you didn't tell us was the tire size and the specified inflation for that size - not what Goodyear's charts say, but what Winnebago's sticker says.

I am having trouble with the rear tire pressures being the same as the fronts. That would be a bit odd.

And lastly, while this isn't the time of year to really test this out, have you looked at how much the tire pressure builds up after an hour of driving at highway speeds? Rule of thumb say no more than 10%, and at 15% you need more.

I suspect you are hardly getting any at all.

OK, one more tidbit. When calculating the pressure buildup, you need to back out the pressure buildup due to ambient temperature change. 3% for avery 10°F. That is, if you start the day at 50°F ambient and 80 psi, and measure the buildup later when it's 90°F ambient, 12% of the buildup (about 10 psi) is due to the increased outside temperature, and not due to operating conditions (load in particular.)


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Bruce Brown

Northern NY

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Posted: 11/29/19 06:38am Link  |  Quote  |  Print  |  Notify Moderator

Try this; set them to 85 and see if they don't heat up as much. Heat is caused by rolling resistance, more pressure to begin with may equal less heat build up.

It probably won't work but it'd be free to try.


There are 24 hours in every day - it all depends on how you choose to use them.
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goufgators

Crawfordville, Florida

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Posted: 11/29/19 06:38am Link  |  Quote  |  Print  |  Notify Moderator

way2roll wrote:

Cold PSI means just that. Lowering PSI so the tires heat up to the recommended cold psi defeats the purpose of setting cold psi in the first place. They will be under inflated. As I am sure you are aware, low psi is the primary reason for tire failure - aside from a puncture. The F53 is notorious for poor handling. It's not going to handle like a car or a DP - ever. We had 2 gassers over the past decade and both were rather exhausting at the end of a long day in the saddle. Constant corrections. I would consider different tires, cheap handling fix or another model RV. Lowering psi below the tire manufacturers recommendation is not the proper way to handle the issue. You'd be borrowing risk. That of course is my opinion and I usually err to the side of caution. I am sure there are thousands of people out there driving on under inflated tires by 5 psi and either don't know it or don't care. I am confident however your tires will generate more heat.
I share your concern about under inflated tires but, knowing that they would be 'under inflated' for possible no more than 10 or 15 miles...I was just wondering if that would be enough time to damage the tires. I believe you're saying yes it would be inadvisable. Thanks for your comments.

goufgators

Crawfordville, Florida

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Posted: 11/29/19 06:41am Link  |  Quote  |  Print  |  Notify Moderator

Tyler0215 wrote:

Try it and see how the MH handles, 5 psi less is not going to kill your tires.
I was hoping for a comment like your's. Let's see if anyone else agrees.

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