4 corner weight ? inflation

[PushedAround]

Originally Posted by VanDiemen23

Crasher has it right. His method was what I was trying to describe in my post above. In the car shown in my avatar, the rear spring rate is 1000 lbs/in. A 1/10 in difference in rear ride ht translates to 100 lbs of cross weight in the front. On that vehicle, as little as 50 pounds of cross-weight (5% of total weight) makes the car spooky.

I have some racecar engineering experience as well, but these behemoths do fascinate me. With most cars, the side to side balance is fairly equal (on a percentage basis) and the chassis are reasonably stiff so that changing the ride height on the heavy corners will properly balance the car. A motorhome chassis is 30~40 feet long, and I surmise fairly flexible with respect to it's overall weight. Add in the fact that there could be significant side to side weight differences due to tank placement and loading variables. Before I got too crazy about perfect weight balance, I think that I would want to know whether or not I was twisting the chassis to accomplish this. With a car it's easy. Not quite sure how you could do this practically in something so big.

[Crasher]

Originally Posted by jimbo2013

Ok had time this morning before all the holiday stuff starts to check ride height.

Rear was on 9 3/4, so that's ok.

wheel well heights were equal L&R

----

Front which there are two not one ride height adjusters, was off.

It should be 10" it was a little over 9"

So I'll need to fix those two soon.

Are you saying that both sides were a little over 9" or is only one side low? Do you have only one ride height valve on the rear or two there also? If both sides are low in the front, I doubt that there will be any change when you get them up to 10".

[Crasher]

Originally Posted by PushedAround

I have some racecar engineering experience as well, but these behemoths do fascinate me. With most cars, the side to side balance is fairly equal (on a percentage basis) and the chassis are reasonably stiff so that changing the ride height on the heavy corners will properly balance the car. A motorhome chassis is 30~40 feet long, and I surmise fairly flexible with respect to it's overall weight. Add in the fact that there could be significant side to side weight differences due to tank placement and loading variables. Before I got too crazy about perfect weight balance, I think that I would want to know whether or not I was twisting the chassis to accomplish this. With a car it's easy. Not quite sure how you could do this practically in something so big.

I think the chassis manufacturers take that into consideration when they specify no more than 1/4" + or - from the recommended height. I was told that the range can be used to balance the corners, but not to go beyond that range.

[jimbo2013]

Originally Posted by Crasher

Are you saying that both sides were a little over 9" or is only one side low? Do you have only one ride height valve on the rear or two there also? If both sides are low in the front, I doubt that there will be any change when you get them up to 10".

I didn't stay on the cold pavement long enough to get the exact #'s I say it was off so I know it needs to be done,

In looking at the coach on the scales which are pretty much dead flat, the drivers front looked a little bit lower, but hard to say how much.

What I think I'll try is 10 1/4 on driver, and 9 3/4 on pass fronts.

That way I'm still in the 1/4" tolerance.

It may not need that much?

I'll then measure the wheel well to ground on both sides to see what the numbers are.

[ahicks]

Originally Posted by Crasher

Are you saying that both sides were a little over 9" or is only one side low? Do you have only one ride height valve on the rear or two there also? If both sides are low in the front, I doubt that there will be any change when you get them up to 10".

I'm not sure what he was saying either, but taking care of the low front end, especially if it's the end with 2 valves, definitely worth the time/trouble to set up correctly. Potential for ride to become more firm, maybe a little better handling on on/off ramps and sharper corners, less wallowing in wind? -Al

[targaboat]

Jimbo, let us all know which of these assumptions are true.

[Tireman9]

Separating out the ride height issues, I would suggest you read the posts HERE on tire load & inflation.

[VanDiemen23]

PushedAround - you are exactly right. One way of finding a cracked chassis in a race car is when you change the weight jacking and it either doesn't make a differenc or it's inconsistent.

I'm guessing several hundred pounds won't twist the chassis much, but several thousand will (as those who have jacked up the coach on a 4 post system wrong and popped the windshield out will tell you). Once you take the chassis to the bump stops and keep applying load all bets are off. But, if the chassis was a complete wet noodle, it would twist severely, loosen up the interior, and pop the windows out on entrance and exit ramps. So I guess it's a matter of degree.

[targaboat]

A light weight forty foot long chassis is a noodle. Also the road surface is constantly changing since the axles are about 30 foot apart. It is really hard to estimate the amount of variation in inches during travel between the four wheels which depends on the road surface. However, it is several inches. So when we change the average alignment by equalizing the loads in the corners, we are changing the average. I suspect that after a few thousand miles the joints in the frame will have adjusted to reflect the overall average alignment and if the corner weights are measured at that time we will see similar weights we saw during the original measurements. Therefore we have accomplish nothing in adjusting the suspension height values IF WE HAVE NOT CHANGED THE WEIGHS INSIDE THE COACH FOR THAT IS WHAT WE REALLY MEASURE WHEN WE WEIGHT THE CORNERS. So level the coach, distribute loads inside as much as possible, and enjoy.

[Steve Ownby]

Originally Posted by targaboat

A light weight forty foot long chassis is a noodle. Also the road surface is constantly changing since the axles are about 30 foot apart. It is really hard to estimate the amount of variation in inches during travel between the four wheels which depends on the road surface. However, it is several inches. So when we change the average alignment by equalizing the loads in the corners, we are changing the average. I suspect that after a few thousand miles the joints in the frame will have adjusted to reflect the overall average alignment and if the corner weights are measured at that time we will see similar weights we saw during the original measurements. Therefore we have accomplish nothing in adjusting the suspension height values IF WE HAVE NOT CHANGED THE WEIGHS INSIDE THE COACH FOR THAT IS WHAT WE REALLY MEASURE WHEN WE WEIGHT THE CORNERS. So level the coach, distribute loads inside as much as possible, and enjoy.

Targaboat is exactly right with this post. Chassis flex. Some more than others. In extreme situations you can see the result. Have you ever leveled up on a really off level lot and felt the door drag a little when opening and closing? You can sometimes see some mis alignment of the compartment door. If you try to tweak the weight balance with ride height settings you are introducing another source of stress to the chassis.

The ride height settings are intended to keep the distance between the main chassis rails and the suspension components in an optimum range. Amoung other things that keeps the drive shaft universal joints in the correct range of motion.

[Crasher]

Hey guys, we are not talking several inches of adjustment here. 1/4 inch either side of the recommended height is not going to twist the frame beyond its design or result in a bad a drive shaft angle . My left rear height was only 3/8" higher than required. That had the effect of increasing the load on the right steer by 600# and lowered the left steer by a similar amount. Lowering the left rear by the 3/8" brought the steer tires with 150# of each other. The manufactures also told me that on a coach of our size (43') shifting the load in the basement will have very little effect toward balancing the corners. I suppose if one was carrying lead or gold bars, you could concentrate a lot of weight in one spot, but my basement is full and I doubt if there is more than 800# which is already spread out. I couldn't possible shift enough weight to balance either corner. However the ride height valves can do it and the frame won't be twisted beyond its designed limits.

[targaboat]

This thread reminds me of a five year boy that was fascinated with the family alarm clock about 80 years ago. His Dad had introduced him to tools, wrenches, screw drivers, etc. One day he was in his room for an extra long time and when mother went to investigate, the clock was in pieces on the floor. There was a big harangue for the clock was a major item in family life in those years. "Put the clock back together" I remember hearing as the last comment on the subject. Well, the clock was put back together but never did run again.

[Crasher]

Originally Posted by targaboat

This thread reminds me of a five year boy that was fascinated with the family alarm clock about 80 years ago. His Dad had introduced him to tools, wrenches, screw drivers, etc. One day he was in his room for an extra long time and when mother went to investigate, the clock was in pieces on the floor. There was a big harangue for the clock was a major item in family life in those years. "Put the clock back together" I remember hearing as the last comment on the subject. Well, the clock was put back together but never did run again.

That would be a valid point if we were taking the motorhome completely apart, but all we are doing is fine tuning it much like adjusting a clock to run faster when it is consistantly losing time.

[targaboat]

It is all in the category of tinkering with something which is not fully understood, and which is not broken. That is in the genes of many people. There are many other items in a 14 year RV with can and should have maintenance done such as lubing the air brake stuff on the rear wheels which is often over looked. And are the slack adjuster working properly?