The weight of a motorhome, or perhaps more importantly, how it is distributed, is something a lot of RVers don’t think about. We know that motorhomes are large and heavy, and drive much differently from the passenger cars and trucks we’re more accustomed to. But there’s more to consider. Virtually no two motorhomes built on the same chassis have the same weight distribution, and may be loaded differently. We see a lot of side to side discrepancies due to slide outs, washer/driers, generator placement, and other factors.
I remember a GM P32 chassis that drove great and the customer was happy. The next day, we worked on the same chassis for a well and pump service company, and it didn’t turn out so well. We wondered, why? Two of the exact same chassis, yet each had different results. We hate unmet expectations! And that’s when we really started paying attention to the front to rear axle weight ratios. We found that the magic number was 50% for most Class A motorhomes.
On Class C (van chassis) motorhomes, we found the number was closer to 45%. However, I have gotten many coaches that were Class C to handle and drive very well with a front-to-rear axle weight of 40% or less without having to add weight. I speculate the reason why is because a Class C doesn’t have the large cab on the front, which in addition to lighter weight, makes it less likely to be influenced by high winds that can affect steering.
But even when we started working on Workhorse chassis using the 50% rule of thumb, we were still not happy with the results. The motorhome still blew around in the wind and steering could be affected by road ruts. What we discovered was that the front axle was so far forward on the Workhorse chassis that we had to use a 55% ratio to help keep the front axle firmly planted. On diesel pushers, especially those with a short wheelbase and that big diesel in the rear, it was like a big kid and a little kid on a teeter-totter. The big kid overpowers the little one.
When we checked it out one of these coaches, we discovered the front axle was 1,000 pounds too light! To offset this imbalance, we added 800 lbs of steel to the front end, which is perfectly fine as long as the front Gross Axle Weight Rating (GAWR) isn’t exceeded. To our surprise, when we weighed the coach again, 200 pounds had been shifted off the rear axle. We added Koni shock absorbers, our Motion Control Units (MCUs) and a Safe-T-Plus steering stabilizer. That was more than 10 years ago and that customer is still driving that short little Beaver Patriot and is very happy with it.
On coaches with a lot of rear overhang, which caused the rear suspension to sag, we figured if we raised it, we would shift more weight to the front. In cases where that actually worked, it was only a slight amount—one or maybe two hundred pounds if that. All it really did was raise the rear back up, which isn’t a bad thing, but it didn’t significantly change the front-to-rear axle weight ratio, unfortunately.
Overhang ratios versus wheel base have a lot in common. I know that the average gas coach is about a 66% overhang ratio. The average diesel pusher is 50% and they usually have a lot more overhang in the front as well. in other words, the more rear overhang, the lighter the front end.
Another thing we discovered is, on a coach with a low rear corner, adding spacers or springs on the low side will transfer a lot of weight to the opposite front corner. We were once involved in a factory recall of a certain motorhome that was experiencing blowouts on the front tires due to improper ride height valve installation. To solve that problem, we relocated the ride height valves and put higher load range tires on the front.
If a vehicle is too heavy on left front, for example, we’ve seen it has a tendency to drift the opposite way. We saw this on the old Oshkosh chassis that was later bought out by Freightliner Custom Chassis, which is used in many motorhomes today.
In any case, the bottom line is this: If the front/rear weight ratio isn’t correct, it will cause lane wander in high winds or when being passed by trucks, and also when driving over rutted roads. This is one of the many reasons we always recommend performing our Road Performance Assessment, or RPA. This way the technician and coach owner can experience what the coach is doing over a variety of road conditions. It truly is a “real world” way to determine the handling characteristics of the motorhome, and learn what changes would be effective.
There are a variety of other instances where weight can have an adverse affect on handling. At a recent Heartland RV rally, we found that some of their fifth wheels can be as much as 1,000 pounds heavier on one side than the other. While this may not affect handling, specifically, it can cause the brakes on the lighter side to lock up more easily on a wet or loose road surface—and that can definitely cause stability problems in an emergency stop. Weighing fifth wheel trailers properly with individual wheel scales requires us to first make up a “dummy” scale the same thickness as the actual scale, or we’ll get inaccurate numbers—sometimes as much as 2,000 pounds off on the pin weight of a large fifth wheel.
On bigger motorhomes, tag axle weight is also very important. Most tag axle motorhomes have a feature that allows you to adjust the amount of load on the tag. I can remember a time when I was performing an RPA on a 42-foot Freightliner Custom Chassis motorhome. I went around some corners after stop signs and noticed a wisp of smoke and some noise coming from the rear. I can actually say that I’ve smoked the tires on a diesel pusher! As it turns out, the tag axle had too much load on it, so it was unloading the drive axle tires. This can also shift weight forward, putting too much load on the front axle.
There are so many other examples I could give about how weight can affect a motorhome or trailer. But the ones above just underscore how important it is to have your coach/trailer weighed and to perform an RPA (Road Performance Assessment) to see how weight affects your rig.