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Tires/tire pressure

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Question
Hi Barry,

2500 short I have a 2016 Pleasure Way Ascent RV on a Mercedes frame Sprinter (144 inch wheel base). Empty weight is 7163. Gross weight is 7957. GVWR is 8550. Recommended tire pressure is 47 PSI front and 70 PSI rear. The way the RV is designed, it is likely a bit heavier on the left (drivers) side.

After driving at 55 -- 65 MPH for 20 - 30 minutes, the on-board tire pressure monitor indicates that the pressure has risen thus: front right 2 lbs. rear right 2 lbs. left front 3 lbs. left rear 6 lbs.

I see where up to a 10 percent increase is considered normal, but I'm curious why the increase is different for each tire and if I should do something to fix that, such as add air to the tires that are increasing pressure more than the others.... or, if there is something else going on.

Meanwhile, on a possibly related issue, an alignment indicated that the camber on the left rear wheel is -0 025 which is 0 005 out of spec (+/- 0 020), and that it is non adjustable because it is a solid axel.  The Mercedes folks say no worries, but with the extra high pressure in that tire, I'm wondering.  What say you?

Thanks for your help!
Skip

Answer
Skip,

Let me answer your second question first.

Yes, I think the increased pressure in the LR is because of the camber.

1)  I am going to disagree that the alignment is not adjustable.  Even solid axles can be bent.  It's a difficult thing to do right, but it can be done.  

But is it enough to worry about?  It depends on what is causing it.  If it's simply a matter of uneven weight distribution, then No!, it doesn't matter.  If it's a matter of the axle being bent, then Yes!, it does matter.

2)  The pressures aren't bad to begin with and it is probably not a big enough issue to try to fix - unless there are other symptoms.

So the answer to the second question becomes dependent on what is causing the camber - and I think it might be worthwhile to weight each corner to see what is going - and if rearranging how you load the vehicle can be effective in evening out the weight distribution.

Barry

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Barry Smith

Expertise

I have over 30 years experience in the design, manufacturing, and testing of tires. I have served as the technical advisor to the "800" number. I have authored or co-authored many publications - usually without credit. I can answer almost any technical question, but please don`t ask me to compare brands. I probably have prejudices because of my work experience.

Experience

Member SAE (Society of Automotive Engineers) Member Tire Society (Tire Technical Organization) SCCA Regional Competiton License holder Authored many training manuals on tires, their care and use.

Organizations
SAE (Society of Automotive Engineers) SCCA (Sports Car Club of America) Tire Society

Publications
You may want to visit my web site: http://www.barrystiretech.com/index.html

Education/Credentials
I am a graduate of the University of Dayton, Dayton, OH - BME, 1971 I attended graduate school at the University of Akron - but did not complete my PhD - something I regret.

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