Journey with Confidence RV GPS App RV Trip Planner RV LIFE Campground Reviews RV Maintenance Take a Speed Test Free 7 Day Trial ×
 

Go Back   Airstream Forums > Airstream Restoration, Repair & Parts Forums > Towing, Tow Vehicles & Hitches > Hitches, Couplers & Balls
Click Here to Login
Register Vendors FAQ Community Calendar Today's Posts Search Log in

Reply
 
Thread Tools Search this Thread Display Modes
 
Old 08-09-2022, 07:59 AM   #21
2 Rivet Member
 
2020 30' Flying Cloud
Lexington , Virginia
Join Date: Dec 2020
Posts: 93
This is a very helpful thread. I’m curious to know why it isn’t sufficient to weigh just once, hitched with weight distribution set (per ProPride instruction). This tells me if each of my axle weights is under their prescribed limits. Their sums also tell me where I am in relation to GVWR.
David in Lex is offline   Reply With Quote
Old 08-09-2022, 08:32 AM   #22
Rivet Master
Commercial Member
 
Ravenna , Ohio
Join Date: Apr 2012
Posts: 1,344
Tire Inflation

Unless you are making significant (1,000# or more) changes in what you pack in your RV, I see no reason to be messing with tire inflation once you have finished adjusting axle alignment and been on a scale to learn the actual load on your tires.
The general advice for weighing is to have the RV loaded to the heaviest weight you expect to travel with. This means full of cloths, books, tools, water, fuel, food, spare parts and toys you might travel with.
There is really only one inflation number you need to keep in mind and that is the MINIMUM inflation required to support your load. We are trying to protect the tire from failure and with data from RVSEF showing that over half of RVs historically have been running their tires in overload.


Damage to the tire structure is caused by the rubber bending and stretching past an elastic limit at the molecular level. This stretching actually breaks some of the chemical bonds and once broken the resultant cracks never repair or reform themselves. They can start small as seen here
The cracks only grow. Once formed the cracks will just get larger and larger till eventually they get large enough to result in a failure of the structure which many times is in the form of a belt detachment fron the body of the tire as seen here

It doesn't take too many miles for a tire in this condition to come apart and you may end up with a nice "Blowout" unless the tire is replaced before the crack gets too big.


The inflation in the Load & Inflation chart is the MINIMUM you should run but heat, age and the tearing a tire experiences from hitting pot holes can result in the rubber cracks forming even if you are running the inflation found in the charts. Running higher than the minimum inflation, can offer some protection as the tire will run cooler and bend less which means less tearing of the rubber chemical bonds.


If you look at the tables you can see that each increase of 5 psi gives you a few hundred pounds more load capacity and conversely each drop of 5 psi decreases the load capacity of your tires.
Tandem axle trailers place some additional stress called Interply Shear, on the tires which result is more cracking and more tearing of the rubber bonds.


I would recommend against lowering tire inflation once you have learned the inflation required to support your heaviest weight.
I also recommend that you set your TPMS Low Pressure warning level to no lower than 5 psi below the minimum inflation learned from your scale reading as I can think of no reason or benefit to ever run an inflation lower that what is needed to support the load. In fact, on my RV, I run my inflation at a +10% margin over the inflation from the tables which allows me to set the TPMS low pressure warning level to the inflation requires to support my heaviest scale reading.
__________________
Retired tire engineer (50 years). Write a blog on RV Tire Safety Net. Give seminars for FMCA across the US. Tucson AZ in Mar 2024 is next.
Tireman9 is offline   Reply With Quote
Old 08-09-2022, 08:57 AM   #23
Rivet Master
 
hikingcamera's Avatar
 
2022 23' Flying Cloud
Seattle , Washington
Join Date: Mar 2022
Posts: 849
Quote:
Originally Posted by David in Lex View Post
This is a very helpful thread. I’m curious to know why it isn’t sufficient to weigh just once, hitched with weight distribution set (per ProPride instruction). This tells me if each of my axle weights is under their prescribed limits. Their sums also tell me where I am in relation to GVWR.

It does not tell you the GVWR of your trailer (which for some Airstream models is pretty important given low payload numbers). It also does not tell you your tongue weight (which can be important for tow vehicle tongue weight limits).
hikingcamera is offline   Reply With Quote
Old 08-09-2022, 09:51 AM   #24
2 Rivet Member
 
2020 30' Flying Cloud
Lexington , Virginia
Join Date: Dec 2020
Posts: 93
Again, if my axle weights on truck and trailer, hitched and both fully loaded, are all under max (well under actually), I’m still not understanding why that information isn’t sufficient. Thanks in advance for your all’s help with this.
David in Lex is offline   Reply With Quote
Old 08-09-2022, 10:00 AM   #25
Rivet Master
 
hikingcamera's Avatar
 
2022 23' Flying Cloud
Seattle , Washington
Join Date: Mar 2022
Posts: 849
CAT scales: Why three passes?

Quote:
Originally Posted by David in Lex View Post
Again, if my axle weights on truck and trailer, hitched and both fully loaded, are all under max (well under actually), I’m still not understanding why that information isn’t sufficient.
To stay within the limits of your trailer GVWR, your tow vehicle’s tongue weight limits, and 10–15% tongue weight. In order to confirm that you need to know your trailer’s undistributed GVW and tongue weight. Neither of which you get from just weighing your hitched setup.
hikingcamera is offline   Reply With Quote
Old 08-10-2022, 07:52 AM   #26
Half a Rivet Short
 
2017 30' Classic
2022 Interstate 24X
Carlisle , Pennsylvania
Join Date: May 2017
Posts: 15,742
Quote:
Originally Posted by David in Lex View Post
Again, if my axle weights on truck and trailer, hitched and both fully loaded, are all under max (well under actually), I’m still not understanding why that information isn’t sufficient. Thanks in advance for your all’s help with this.
Hi

If I hitch up my trailer to the truck with *no* WD at all, each of the axle limits will be "safe". ( Yes the truck bed would be a bit empty ). However, there is no way for me to tell if I have put more weight than is safe on my receiver. If that is overloaded, I am not safe.

Not a "safe" issue in terms of limits: With a single pass only, I don't know what I've done to the front axle of the truck. It may now be very light and thus the truck will (likely) handle very poorly. If that happens when I *need* it tho handle well .... then that's safety.

Bob
uncle_bob is offline   Reply With Quote
Old 08-10-2022, 09:22 AM   #27
Site Team
 
richard5933's Avatar

 
1994 25' Excella
Waukesha , Wisconsin
Join Date: Sep 2020
Posts: 5,580
Images: 5
Quote:
Originally Posted by David in Lex View Post
Again, if my axle weights on truck and trailer, hitched and both fully loaded, are all under max (well under actually), I’m still not understanding why that information isn’t sufficient. Thanks in advance for your all’s help with this.
Without weighing your truck alone without the trailer, you have no way to know how your hitch setup is affecting the steer axle. By getting this weight and comparing it to your weights with the trailer hitched via the WD hitch, you can see if you have returned enough weight to the steer axle.

You can be lower than the GAWR for the steer axle and also have reduced the weight on the front axle enough that you don't have proper steering control. It is possible to have too little weight on an axle.
__________________
Richard
11018
1994 Excella 25 Follow the build on Gertie!
1999 Suburban LS 2500 w/7.4L V8
1974 GMC 4108a - Custom Coach Land Cruiser (Sold)
richard5933 is offline   Reply With Quote
Old 08-31-2022, 07:44 AM   #28
2 Rivet Member
 
2020 30' Flying Cloud
Lexington , Virginia
Join Date: Dec 2020
Posts: 93
Quote:
Originally Posted by richard5933 View Post
Without weighing your truck alone without the trailer, you have no way to know how your hitch setup is affecting the steer axle. By getting this weight and comparing it to your weights with the trailer hitched via the WD hitch, you can see if you have returned enough weight to the steer axle.

You can be lower than the GAWR for the steer axle and also have reduced the weight on the front axle enough that you don't have proper steering control. It is possible to have too little weight on an axle.
Thanks for your help with this. We did the three passes yesterday. Steer axle without the trailer connected was 4100. Steer axle with trailer connected and WD engaged was 4020. Am I correct in assuming that this is close enough or is the goal to end up with exactly the same weight on the steer axle after engaging WD?
David in Lex is offline   Reply With Quote
Old 08-31-2022, 07:53 AM   #29
Site Team
 
richard5933's Avatar

 
1994 25' Excella
Waukesha , Wisconsin
Join Date: Sep 2020
Posts: 5,580
Images: 5
Quote:
Originally Posted by David in Lex View Post
Thanks for your help with this. We did the three passes yesterday. Steer axle without the trailer connected was 4100. Steer axle with trailer connected and WD engaged was 4020. Am I correct in assuming that this is close enough or is the goal to end up with exactly the same weight on the steer axle after engaging WD?
I can only tell you what I do, which is get it as close as I can without applying too much tension to the spring bars.

My thought is that you're close enough, but there are others on this forum with much more experience on this than me.
__________________
Richard
11018
1994 Excella 25 Follow the build on Gertie!
1999 Suburban LS 2500 w/7.4L V8
1974 GMC 4108a - Custom Coach Land Cruiser (Sold)
richard5933 is offline   Reply With Quote
Old 08-31-2022, 08:36 AM   #30
Rivet Master
 
1988 25' Excella
1987 32' Excella
Knoxville , Tennessee
Join Date: Oct 2010
Posts: 5,118
Blog Entries: 1
Yes. One pass tells you what you need to know to determine if your rig is safe according to the axle limits and GVWR and trailer weight.

Many of us also want to know how much weight we are transferring back to the front axle. With different WD settings. Some want to know the tongue weight. These are the primary reasons for more than one pass. You may not want or need more than one pass.
Bill M. is offline   Reply With Quote
Old 08-31-2022, 09:02 AM   #31
Rivet Master
 
hikingcamera's Avatar
 
2022 23' Flying Cloud
Seattle , Washington
Join Date: Mar 2022
Posts: 849
CAT scales: Why three passes?

Quote:
Originally Posted by Bill M. View Post
Yes. One pass tells you what you need to know to determine if your rig is safe according to the axle limits and GVWR and trailer weight.
One pass will not give you an accurate trailer weight as some of the trailer weight will be captured on your truck’s rear axle.

Quote:
Originally Posted by David in Lex View Post
Thanks for your help with this. We did the three passes yesterday. Steer axle without the trailer connected was 4100. Steer axle with trailer connected and WD engaged was 4020. Am I correct in assuming that this is close enough or is the goal to end up with exactly the same weight on the steer axle after engaging WD?

As I learned here recently your manufacturer will have specific details on how to distribute the weight. Ford has a tow guide which for my F-150 indicates redistributing 50% of the weight back to the front axle. Other vehicles (especially SUVs) say to distribute 100% back. So it depends. I’m also still playing with what feels right while towing.
hikingcamera is offline   Reply With Quote
Old 08-31-2022, 11:00 PM   #32
Half a Rivet Short
 
2017 30' Classic
2022 Interstate 24X
Carlisle , Pennsylvania
Join Date: May 2017
Posts: 15,742
Hi

There are two *very* different things being looked at as you do the CAT scale stuff:

1) Are you "under limit" on the axles? If you are not, then you must to something. There is no choice. Staying under limit ( for most of us ) is something you must do. The fact that you see a lot of folks chugging down the road over limit ... ignore this. If they go into the ditch that's their problem.

2) Are you reasonably set up to prevent sway? Oddly enough you can be in spec on the axles and be highly likely to get into sway issues. Getting load onto the front axle is part ( but not all ) of what helps make the rig stable as you go down the road.

Since there are two very different constraints, there isn't going to be one single answer. This is one of many reasons why just getting to the point that "payload is ok" does not make sense. There are a lot of things that can put you in the ditch.

Bob
uncle_bob is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
visited CAT scales - the numbers are in... 2airishuman Towing, Tow Vehicles & Hitches 143 08-23-2015 02:55 PM
Took a trip to the CAT scales phbarnhart Towing, Tow Vehicles & Hitches 48 07-26-2015 06:50 PM
Maiden Voyage - First time on CAT Scales DanielB Tow Vehicles 3 05-10-2013 05:14 AM
results of CAT Scales and WD hitch adjustments funkill Hitches, Couplers & Balls 10 07-11-2009 06:35 PM


Featured Campgrounds

Reviews provided by

Disclaimer:

This website is not affiliated with or endorsed by the Airstream, Inc. or any of its affiliates. Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.



All times are GMT -6. The time now is 12:27 AM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.