Weighing Tag Axle 42AD - Update From Freightliner

[rv rick]

I have a new, 2010 Tour 42 AD and have really enjoyed it. I have had it weighed, using individual scales, at the FMCA and Escapees rallies, and found weights that seemed overly heavy on the tag and front axles, and light on the drive axle.

I was able to have it checked out at Freightliner of Salt Lake (who did a great job, by the way) and learned quite a bit as this is my first tag axle unit. First, they found the ride height was off on both the tag and front axles (these were too low, meaning they were carrying too much of the load). Similarly, the drive axle was too high and did not carry the correct weight. They were able to adjust everything and I noticed a significantly better ride when driving back from the dealer (bumps were absorbed much better).

Finally, the shop confirmed with Freightliner Custom Chassis that the correct way to weigh the coach is to be sure it is level, then dump the air. Next, refill and then weigh. Not sure why this matters, but it probably has to do with making sure the ride height is correct on all axles.

[kjburns]

It makes sense. If the ride height is off somewhere, it would put too much weight on one or more axles. Thanks for the post. It gives us something to look out for.

[robodoc]

rick

i have suspected this on my 42 AD. can you give me any more info to figure it out.

[rv rick]

My weights from the individual wheel scales, before I knew about the right weighing method as described from Freightliner, showed our tag at almost 11,000 lbs (over the GVW of 10,000). My front axle was close to the max (14,300). Finally, the drive axle was only 11,500 (max of 20,000). We are packed for fulltime living and those weights included full fuel and water.

After my first weighing at FMCA, and reading the response from Winnebago regarding the FMCA coach review (see link in above post) I was getting suspicious of the ride height and tag loading, so at the second weighing with Escapees, we played around with the tag dump while on the scale. I found that if you dump the axle, weight went from about 11,000 to 1,200 on the tag. Then, releasing the dump switch, the tag re-filled with air and ended up in the 9,500 range. Apparently, dumping the axle allowed the two read axles to even up a bit. Now that the ride height is adjusted, this seems to be even better from a ride quality perspective, although I have not re-weighed it (they said they did at Freightliner and that we were well under the earlier readings, but I did not get the specific numbers as the tech was already gone).

Based on this little adventure, I would suggest that if your weights seem off, you first follow Freightliner's weighing procedure by dumping the air, and letting it refill before weighing. Then, I would have the ride height checked.

Hope this helps.

[cbeierl]

Something seems very odd about this. Since nobody is saying that the scales are wrong that means that the overloaded tag and front axle weights that folks are getting are real and are in fact overloaded as you drive down the road.

Dumping the air may temporarily fix things so that the weights are distributed the way they were designed to be, but it seems that in operation the weights end up distributed incorrectly. It doesn't seem to me that the ride height system with the tag is working correctly.

[rv rick]

Cbeierl asks a good question and is, in fact, the same question I asked to Freightliner.
Certainly, the overall coach weight does not change, but the weight placed on each axle does change given the ride height adjustment for that axle. While I am no chassis engineer, here is what I was told.

The key, apparently, is the fact that the coach has a tag axle and the weight is spread over three axles. When there are three axles, the air bag inflation determines how much pressure that particular axle carries. For example, if the tag axle is carrying too much air pressure, it is pressing on the ground with too much force and literally trying to lift the coach. This pressure takes too much pressure off of the drive axle and at the same time, moves weight forward to the front axle (explained to me as sort of like a teeter-toter like relationship). Thus, if the tag ride height is lowered, the air pressure exerted on the tag will be reduced and the pressure it exerts on the ground goes down. Then, more weight is carried by the drive axle and less by the tag. With the tag now not trying to lift excess weight and lift the coach from the rear, the front axle load also drops. With a 42' long coach, that is a pretty long lever from the tag axle to the front and makes a significant difference.

My ride height was quite a bit off (about 3/4" too high on the tag -meaning it was trying to lift the coach and too low - about 1/2" on the front axle). Now, the coach rides much better and the weight is correctly distributed on the axles. I also learned that you should get this done after the coach is loaded, which certainly makes sense.

I will admit that I had not really considered this before, but once the tech explained this, it made sense. The bottom line is that the ride height and axle loading are all adjustable and the adjustment is important.

[Bill Adams]

The correct way to get a good weighing is NOT to dump and fill as this can give a totally false reading. You need to have driven the coach for a period, pull into the parking area, get straightened out (the longer the run the better) and pull onto the scales. You will now have an accurate reading of your various axle weights and you can make adjustments accordingly.