What Tire Pressure Would You Run???

[Capt Joe]

Many questions and thoughts as to tire pressures to run have been brought up here on the iRV2 forum. I thought I would outline a real life scenerio and ask for the reasoning as to why a certain tire pressure might be best.

Coach: 2004 Winnebago Brave 32V on Workhorse W20 Chassis, 11766 miles
Tires: Bridgestone R250F 245/70R19.5 new in June, 2008 (mfg 1408)
Balance: Magnum Plus Balanceing Compound LTP200 6.5 ozs
Added Suspension Mods: None
Weights:
GVWR - 20,700
GVWRF - 7500
GVWRR - 13,500
Recommended Tire Pressure: 95psi front, 90psi rear
Actual Weights (unable to get 4 corner):
Gross Total (loaded w/full fuel - 18,080
Front Axle - 6280
Rear Axle - 11,780

At 95 psi, the load table allows for a single weight of 4080 lbs and dual weight of 3970 lbs. At 90 psi the weights are 3890 single and 3655 dual. At 85 psi weights are 3740 single/3515 dual. And at 80 psi it is 3640 single / 3415 dual.
(Note: Complete table is at http://www.trucktires.com/bridgeston...Truck_Load.pdf ,
Scroll to last page for the 24570R19.5 tire)

So, my question is just what tire pressure would YOU run in this case.

I have been keeping them right at the pressure noted on my placard on the drivers door as well as in the Workhorse data sheet. However, I am getting a bit of vibration through the steering wheel at the 55-60 mph speed I usually drive. Not so bad that it shakes the coach much at all, just feeling it through the wheel but I would like to get rid of it. Thinking about running a bit reduced pressure (maybe like 85 psi all around?) to see if that will help before putting some Koni's on the front. Kind of expensive to put the Koni's on just to see if that would help.

What are your thoughts????

[FLYTYER]

In your case I would divide the front and rear axle weights by 2 and apply the pressure table recommendations.

My weights are close to yours. I run 90 in front and 85 in rear and have a nice ride.

A recent replacement of all tires with Michelin XRV's gave a smoother ride and no steering wheel bounce or vibration which I had before the change.

The tire Tech said my old tires may have been "out of round" which would cause bounce and vibration.

I also had them spin balanced...no powder for me!

[Capt Joe]

Well, since I haven't been able to garner much interest in this thread, I thought I'd outline my reasoning on tire pressure for my MH.

On the front, I divided the actual weight by 2 and have 3140# for each tire. At 85 psi, the load charts say the tires will carry 3740# (single) which gives me a comfortable margin and actualy bringe the total capacity to within 20# of the GVWR front axle.

For the rear, I divided the actual rear axle weight by 4 and have an weight of 2945#. With the psi at 85 (dual), the load chart gives a carrying load of 3515#. Figuring the 4 tires on the rear axle, I should have a total capacity of 14,060# which is a bit over 500# above the GVWR rear axle.

The only thing I can see that might be done different is maybe dropping the rear to 80 psi but I'm not sure I want to my tires at 80.

So, how does my reasoning stack up with that of others when figuring the tire pressures for the best ride, performance, etc, etc?

I do realize that while there is a lot of specific information that goes into this type of calculation, there is also a bit of leeway too. I haven't really seen any figures as to how much 'cushion' you should figure for when deciding on the pressures or anything. Also, I'm sure that different setups, tolerance for vibrations, road noise, perceived handling, etc, etc will enter into an individual's choice.

I just thought this might make an interesting discussion on tire pressures.

[taipan]

The pressures on your card in the coach take into account the weight of vehicle and they give the best pressure for both tire life and handling. At all counts you do want to stay at this pressure to avoid uneven wear.
If you are feeling the vibration through the steering wheel only it is coming up off your front tires, the fact you are getting the vibration only at 55-60 MPH can be a odd wear of slight separation of the belt in the tire (which can occur when sitting too long) or you have a slight out of balance tire.

If your tire is still relatively good condition, rotate it to the rear as it will most times this will even out any strange wear.

[mfire1339]

You didn't say how many miles on these tires. I'm thinking not enough to cause unusual wear pattern. I would spend the money to remove the powder and really balance at least the front tires and while they balance they can see if one is out of round. I would run them at the recommended pressure for the weight they are carrying. Sure sounds like an out of balance front tire.

Mike

[DriVer]

I didn't have a problem running "Equal" when my rims were properly equipped with the valves that support the powder. Once the valves were compromised the powder backed up in the valves and I was experiencing my tires going flat on me. The repair was very easy, all I had to do was inflate the tire and this would blow the powder out of the valve. Just don't check the pressure in the tire because that's when the powder backs up in the valve.

Now given that complexity, I had the tires broken down, cleaned and then spin balanced. No more flats ....

A vibration in the front end is normally setup by a tire being out of balance, a rim out of round or wrapped or a defective tire. yesterday, an owner shared with me that he had a vibration issue. Here is what was done. The tire store. broke the tire down, removed all the old weights, spun the tire on the rim 180 degrees, re-inflated the tire and spun balanced it and it's been fine ever since. The process was inexpensive and apparently it worked.

[bill dean1]

Hi:

Have a 04 Monaco Monarch and had very rough ride at first then went to Rally in Tucson and spoke with Keith at Redlands T & RV. They did some work for me and for 1/2 labor they weigh each tire and recommend tire pressure. My fronts went from 110 to 85! and back went down to 90.

I thank you all for all your input BUT certain things should be left to the pro's.

[Capt Joe]

Well, I finally got my motorhome out of the shop after having my THIRD brake problem....both rear calipers failed to release....but that is a very sore topic for another thread.....

Today was the first chance I have had to get back by the tire store to see what else I could do about my steering wheel vibrations. Oh yes, right before we left on a long weekend...the trip where my brakes failed to release for the THIRD time...I had adjusted my tire pressures to 85# all around AND installed KONI FSD's on the front. Well, the vibrations were still there through the steering wheel.

I had already been back earlier when they broke down ALL of the tires to make sure the Magnum Plus Balancing Material (beads) had not clumped up or anything and my tire guy wanted to try a spin balance on them. Of course we broke the tires down, front only, and removed the Magnm before spin balancing them. Got it done and came on home. Had one section of road where I could run it up to a bit over 55 (tranny actually went into OD) and the vibrations were GONE!!! Still rode kind of like a truck but what do you expect from a truck chassis? We are headed out Sat am just for a couple of days and will have some Interstate driving so I will be able to give it a good try. I was looking at the weights they put on and they put an 8 oz on each wheel and a smaller one on the back of one of them. Anyway, I hope to be a happier camper on Sunday...except that Workhorse denied any coverage for my last brake episode and it cost me a) my rear KONI shocks and b) another $300 worth of new goodies for our MH out of pocket to get the rear brakes fixed. I'm just lucky that they only charged me warranty prices on parts and warranty labor rates and time....otherwise it would have been quite a few more $$$ out of pocket to put a temp fix on the Workhorse problem.

Sorry for the rant...not trying to hijack my own thread but as you can tell, I'm kinda frustrated.

On a brighter note, my tire store hasn't charges a single dime more to do the breakdowns, balancing, etc.....Good Folks!!! If anybody needs a good tire shop in the Panama City, FL area, drop me a line and I can give you a contact. I have no connection with this shop other than being a very satisfied customer.

Thanks for reading...just wanted to report back in on my tire experience and hopefully give someone else a little bit of info on how I hopefully have solved my tire problem.

[Batman_777]

I would run at 5 psi under the tire max as long as the tire psi max does not exceed the rim or wheel max. I don't care to reweigh and repressurize the tires every week or be concerned with load shift etc. And it's a good idea install a tire pressure monitoring system.

There is talk that all future cars, trucks etc will be required to have tire pressure and temp monitoring.

[George Z]

Quote:

Originally Posted by Capt Joe Well, since I haven't been able to garner much interest in this thread, I thought I'd outline my reasoning on tire pressure for my MH. On the front, I divided the actual weight by 2 and have 3140# for each tire. At 85 psi, the load charts say the tires will carry 3740# (single) which gives me a comfortable margin and actualy bringe the total capacity to within 20# of the GVWR front axle. For the rear, I divided the actual rear axle weight by 4 and have an weight of 2945#. With the psi at 85 (dual), the load chart gives a carrying load of 3515#. Figuring the 4 tires on the rear axle, I should have a total capacity of 14,060# which is a bit over 500# above the GVWR rear axle. The only thing I can see that might be done different is maybe dropping the rear to 80 psi but I'm not sure I want to my tires at 80.

I think you are good with your calculated pressures but I would take them and add 5 PSI as a cushion.

[DriVer]

I also favor actual pressure for the wegiht PLUS +5+ psi. This margin will afford you the luxury of time in the event you don't check your tires each and every day. Better a little over than 5 psi under.