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RV Tech Savvy: Inflation Pressure Versus Altitude

Originally Published in MotorHome Magazine

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We have a Class A motorhome. I maintain 100 psi air pressure in the rear tires and 95 psi in front (maximum is 110 psi). This is based on scale weights. I live at 9,200-foot elevation in Colorado. I normally travel in the Western states, between 6,000-10,000 feet in elevation. I’m planning a trip to the Eastern Seaboard and then down coast to winter in Florida. Will a 9,000-foot change in elevation have an effect on the tire pressure? My guess is it will be low at sea level. What are the facts?

Chris Quaderer | Divide, Colorado

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Yes, your suspicions are correct. Air density changes roughly 3 percent per 1,000 feet of elevation change. Tire-pressure gauges measure the difference between the pressure inside the tire and outside (not absolute pressure). Therefore as you descend, the internal pressure, which was filled in the mountains, becomes relatively less, compared to the external air pressure of the denser air closer to sea level. I recommend checking (and adjusting) tire pressures at least two or three times as you descend. Pressure should only be checked and adjusted when the tires are cold.


Slideout Adjustments

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My Forest River FR3 has two cable-driven slideouts. I’ve owned several motorhomes before, but none had any slideouts. I have two questions. Since cables generally stretch, how long before they need to be adjusted to make up for the slack? Also, how much difference should there be between the right and left? I seem to have a ½- to ¾-inch variation on one side versus the other when the slideout is closed. The one side is barely touching the seal, while the other side is tight.

The cable slideout mechanism seems similar to pop-up campers or boat lifts. Any information would be helpful.

Andy Carter | Elkhart, Indiana

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Cables don’t stretch much once the system is in place and adjusted, unless something has happened. When the slideout is in for travel, both ends should be as tight as possible to help deter rainwater from sneaking past the seals. In other words, the motorhome-wall to slideout-wall measurement you mentioned should be the same, instead of ¾-inch off. I recommend that you first inspect the cable-drive path for any debris, snags, bent parts or anything that’s abnormal, before attempting to adjust the cables. Also, mark the nut locations so you can go back to the original settings if needed. You didn’t mention which system you have, but I believe it is a BAL Accu-Slide. There should be an instruction manual with the paperwork for the motorhome. Fortunately, the manual is also available online at http://norcoind.com/bal/downloads/accuslide/accuslide_service-manual.pdf. You’ll find the adjustment procedure on page 6, but be sure to read the whole booklet first. Please follow this procedure and, if you are unsure how to do it, contact Forest River (www.forestriverinc.com). Bryan Knight handles the service questions for this model motorhome, and can be reached at 574-206-7611 in your town of Elkhart, Indiana.


Improving the View

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We are the happy owners of a 2010 Winnebago View. In general, we are satisfied with its road handling, even while encountering light side winds. However, in strong wind conditions, especially when combined with passing trucks, the View demands constant attention and a steady effort on the steering wheel to keep it in its lane. I would like to know what I can do to improve this situation. Through my RV magazine readings, I see ads for steering stabilizers, torsion bars, specialized shocks, air shocks, etc. In your opinion, what is my best option in terms of quality/price-efficiency ratio?

Have a tech question?Yvan Jerome | Laval, Québec, Canada

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You didn’t note if this is your first experience driving or owning a motorhome. I say that because owner expectations will vary. Motorhomes are for the most part based on large box vans or truck platforms and as such they tend to ride and handle considerably worse than an automobile, particularly modern luxury models. There is a lot of surface area on a motorhome, and the tall sides provide plenty of leverage for the wind to act on. Therefore, when there’s a strong crosswind, the forces generated are going to try to push the motorhome sideways and require steering input and correction.

Having said that, I believe the best single product for your situation would be a heavy-duty rear anti-sway bar. These resist against the vehicle lean without making the ride harsher, like heavier springs or torsion bars would do. Hellwig (800-435-5944, www.hellwigproducts.com) makes a rear replacement anti-sway bar for the Sprinter 3500. Roadmaster (800-669-9690, www.roadmasterinc.com) also sells a heavy-duty rear sway bar. A heavy-duty front anti-sway bar is available from Mercedes-Benz as an option and as an accessory through dealer parts departments. SuperSteer makes a rear track bar, an excellent hardware addition, that will also improve the vehicle’s stability by mostly eliminating any lateral axle shift and resultant body reactions under crosswind situations. A rear anti-sway bar, or both front and rear anti-sway bars, together with some new Koni FSD shocks (or equivalent), should transform your ride.


Question About Brakes

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I own a 2011 Roadtrek. Last fall the brakes warped coming down a big hill into Lewiston, Idaho. I was told by the Les Schwab folks that I had half-ton brakes on a one-ton vehicle. I was also told that mine was the third rig the shop had encountered in a couple of weeks that had this problem. Is this brake downsize customary for Class B’s?

Dean Clark | Via email

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Let me begin with a brief summary of terminology. The so-called half-ton van is denoted as a 1500 model. The commonly used name three-quarter-ton model is officially called a 2500, and the one-ton model is actually called a 3500 series. You will find that all of the 3500 models have eight wheel studs. If your truck has eight lugs, and I’m sure it does, you can’t possibly have half-ton brake discs because they simply wouldn’t fit onto your vehicle’s large hubs.

This problem of overheating brakes is not a unique problem to this model van. Getting the brakes hot, and warping, may not be able to be completely prevented in all cases, but it can be minimized. When you have brake service done, always insist on premium-quality brand rotors and brake pads. They withstand and dissipate heat better than the cheapo parts. When descending long steep grades, slow down as you crest the summit. Approach the down grade at a slow to moderate speed, and downshift to allow the engine to create more drag, which takes a large heat load off the brakes. If safety allows it, pull off onto the shoulder to allow the brakes to cool if you suspect they are getting hot.

I’m familiar with the Lewiston grade, and have traveled over it in a Sprinter van. It’s definitely a good place to apply downshifting and engine braking as much as possible.


Ken FreundRV DIYRV Tech SavvyTech topics

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