Just bought new twin axle TT. When measuring between the tires on each side there is about 3/8 in difference.Some component of the axles,tire mounts or such must be slightly out of parallel. Salesman said no problem. Is that enough to be concerned about?

Yes it is a problem. While the tires may and will flex some, it still is putting extra stress and wear on the tires, bearings and every component of the suspension. Contact the manufacturer and get a spec, my guess is 1/8 inch or less although they may measure the difference in degrees.

Unless you have the trailer sitting on a 100% level surface, the trailer itself perfectly level and perfect as far as measurements from frame to level surface, along with some other things, you can not determine alignment in any accurate way. Even with all that done you're only doing half arsed guessing. There is enough play in the suspension, movement in the equalizer, differences in the tires etc to throw of your results to the point of them being worthless. The spread on the tires changes with equalizer movement on a conventional leaf spring setup, or with travel on a torsion arrangement.The only way to determine it is accurate measurements on the frame from the center point of coupler or A frame attachment points to the spring hangers or axle attachment points.

What Cramden said was correct for aligning the axle to the trailer frame for a single axle, and then it is a matter of ensuring that the second axle is parallel to the first. In your case the axles are not described as parallel, which can be checked for potential tire cause by measuring space between axles. I just did a quick google search, and the 1/8 inch measurement appears pretty close for the axle to frame requirement, but the paralleling of the axles should be near perfect.

Cramdon is correct ! Even loading will spread and move axles .

As previous suggested, your measurement may not be "good" depending on the conditions that it was done under since the suspension may not be totally at "rest" / "neutral" position. You may need to pull it to a long flat surface and travel in a straight line for a bit to allow the suspension to "set", then measure and see if it compares, then repeat and compare once more. If it is out after that, as suggested, you should potentially get it looked at for suspension check (loose components) and ultimately an alignment.... otherwise, you may be eating tires in quick fashion down the road.

? Equal spacing of tires important? | Good Sam Community

Dr__Feelgood
Explorer
Aug 19, 2018
Thanks to all
I've got some homework to do
RCMAN46
Explorer
Aug 19, 2018
"As far as dropping plumb bobs to floors that may get you a measurment thats close to accurate, but it may not. "

I am open for a method that will give more accurate measurements.
Huntindog
Explorer
Aug 19, 2018
These are pretty primitive suspensions. They have a lot of slop in them. It is one of the factors that allows them to distort out of shape when making a tight turn, such as jacking them into a tight campsite while backing.
When under tow in a straight line, the tires/suspension take the path of least resistance. IOW the suspension sort of floats or drifts into a straight line.

I have an extreme example of how this works.
Quite few years ago, I was having trouble backing into a site. The TT just wasn't responding to my steering inputs normally.
In frustration, I got out to look over the situation.
What I found was several spring hangers sheared off at the frame.
Amazingly it towed fine on the highway. This was because the front hangers were fine. Where the broken hangers were, the frame just dropped down on the spring eyes. So long as I went forwards, everything was pulled into line. Only when backing was it a problem.
mosseater
Explorer II
Aug 19, 2018
Having had a hanger alignment issue from new, I have found that while primitive in design, there are specs for installation to opimize alignment throughout the travel. Yes, always changing. But if that change happens throughout the parameters of what is acceptable tracking, tire wear and handling will be much better. Your truck will live a long time with the front end out of whack, but tire wear will be increased, sometimes dramatically. Given that the steering geometry is affected with every bump and so is the relationship between specific adjustment points, we are only ever going to optimize measurements. Not a reason to give up and forego attempts at alignment.
JIMNLIN
Explorer III
Aug 20, 2018
One of my older GN flatdeck trailers tandem axle has 5/8" difference between the tires side to side. The trailer has over 200k miles. The tires have always worn even across the tread and the trailer pulls good.
I had it checked at the local big rig trailer shop. They said the front axle is within specs but the rear axle has been shop bent at the stubs to follow or track the front axle.
Huntindog
Explorer
Aug 20, 2018
JIMNLIN wrote:
One of my older GN flatdeck trailers tandem axle has 5/8" difference between the tires side to side. The trailer has over 200k miles. The tires have always worn even across the tread and the trailer pulls good.
I had it checked at the local big rig trailer shop. They said the front axle is within specs but the rear axle has been shop bent at the stubs to follow or track the front axle.
This is an often recommended way to fix an alignment issue.

I do not like it for my TTs.
My reasoning is simple.... The root cause still exists. If the custom bent axle should ever need replacing.(this can happen due to many things) it too will need to be custom bent. If instead the hangers are installed properly, then a replacement axle can just be bolted in place, and it will be good as new.
Ralph_Cramden
Explorer II
Aug 20, 2018
RCMAN46 wrote:
"As far as dropping plumb bobs to floors that may get you a measurment thats close to accurate, but it may not. "

I am open for a method that will give more accurate measurements.

Your method is probably about as accurate as needed or your going to get. Unless you want to find a true level and flat surface, get a bunch of jack stands, and account for unequal weight loading as well as frame camber.

All that is probably for naught as these things are junk and have a ton of flex and twist when going down the road, not to mention a good amount of both most likely built in as well.
SoundGuy
Explorer
Aug 20, 2018
Dr. Feelgood wrote:
Just bought new twin axle TT. When measuring between the tires on each side there is about 3/8 in difference.Some component of the axles,tire mounts or such must be slightly out of parallel.

Your concern shouldn't be whether the tire spacing is different (because it will be) but whether the frame is square and the hangers on each side are mounted correctly to the frame - if so, you have no issues. Spacing between tires will be different AND will vary according to load, where the load is located in the trailer, and ground surface - whether the tires are sitting on a hard flat surface such as tarmac or cement OR are sitting (and sinking into) a soft ground surface such as sand. I myself hadn't given this much thought with the various trailers we owned until I tried to fit a set of adjustable BAL Standard Tire Locking Chocks between each set of adjacent tires on our most recent dual axle trailer and found that sometimes they'd fit, other times not. Of the two sides the chock even when fully retracted to it's shortest length would most often most likely fit between the street side tires but not the curb side tires, the reason I later realized being that the weight of the slide on the street side would cause the suspension on that side to sit slightly lower, forcing the tires to spread slightly further apart than the curb side tires. Once I realized what was happening I further comfirmed by string measure that the frame indeed was square and all the spring hangers were mounted exactly where they should be. My bet is yours is exactly the same and you in fact have no issue. Much ado about nothing.
GrandpaKip
Explorer II
Aug 20, 2018
SoundGuy wrote:
Dr. Feelgood wrote:
Just bought new twin axle TT. When measuring between the tires on each side there is about 3/8 in difference.Some component of the axles,tire mounts or such must be slightly out of parallel.

Your concern shouldn't be whether the tire spacing is different (because it will be) but whether the frame is square and the hangers on each side are mounted correctly to the frame - if so, you have no issues. Spacing between tires will be different AND will vary according to load, where the load is located in the trailer, and ground surface - whether the tires are sitting on a hard flat surface such as tarmac or cement OR are sitting (and sinking into) a soft ground surface such as sand. I myself hadn't given this much thought with the various trailers we owned until I tried to fit a set of adjustable BAL Standard Tire Locking Chocks between each set of adjacent tires on our most recent dual axle trailer and found that sometimes they'd fit, other times not. Of the two sides the chock even when fully retracted to it's shortest length would most often most likely fit between the street side tires but not the curb side tires, the reason I later realized being that the weight of the slide on the street side would cause the suspension on that side to sit slightly lower, forcing the tires to spread slightly further apart than the curb side tires. Once I realized what was happening I further comfirmed by string measure that the frame indeed was square and all the spring hangers were mounted exactly where they should be. My bet is yours is exactly the same and you in fact have no issue. Much ado about nothing.

I found the same condition after a couple of trips using the X chocks. I wrote PORT and STARBOARD on them because they are a tad different. So far, after about 20k miles, no uneven tire wear. If the camper tracks fine and tires aren’t wearing unevenly, probably not a big deal.
Besides, as EVERYBODY knows, they are just junk waiting to fall apart, spewing parts down the highway. Better hurry up and enjoy it while you can.
SoundGuy
Explorer
Aug 20, 2018
GrandpaKip wrote:
I found the same condition after a couple of trips using the X chocks. I wrote PORT and STARBOARD on them because they are a tad different.

So too did I - even managed to trim the base of each chock about 1/2" and cut a bit off the ends of each threaded rod to shorten the overall length of each chock a bit but if the tires were sitting on soft sand this still wasn't enough. :M Since the street side tires (where the slide is) would consistently spread apart just a touch more than the curb side tires I too marked my BAL chocks by painting a small black band on one and a white band on the other so would always use the same chock on the same side. However, I still ran into situations where one of the darned chocks wouldn't fit and eventually gave up, instead using rubber chocks secured with hardwood spacers -

This method achieves the same result as the BAL chocks but it sure would have been simpler if Norco would offer this chock in a slightly shorter version that would fit every dual axle trailer under all conditions. :R