What's the minimum legal height above ground for tractor to trailer air lines?

No legal limit. really, but generally trailer floor is 1.3m height.

4.10 m, 13.5' in the USA and EU, 16' (5m) in UK.

Really truck makers buid 4.0 m trailers, 10 cm is the bonus to avoid ticketing on every station

 

http://fontaine.com/pdfs/documents/prop-height.pdf

 

Make sure the air lines aint touching either. Believe it or not I got dinged for that a while back. I didnt have "enough" of those little plastic dividers on my trailer airlines and I got a friggin ticket. It was on the trailer air lines that are suspended by the springs. Apparently you cant have the two airlines touching anywhere as they can rub holes in each other.

Picture is worth a thousand words right.
http://www.google.com/imgres?um=1&hl=en&sa=N&biw=1024&bih=653&tbm=isch&tbnid=_GhTOtrydlUC9M:&imgrefurl=http://www.amazon.com/Tramec-34020-Brake-Spacer-Hanger/dp/B001Q6NSX8&docid=3nFGgcUNEj9OwM&imgurl=http://ecx.images-amazon.com/images/I/21mOGYsxutL._SL500_AA300_.jpg&w=300&h=300&ei=oUA1T_vjAoWq2gW0oviNAg&zoom=1&iact=hc&vpx=101&vpy=143&dur=423&hovh=136&hovw=131&tx=126&ty=118&sig=111315946365279363795&page=1&tbnh=136&tbnw=131&start=0&ndsp=18&ved=1t:429,r:0,s:0

Thats the part I was trying so unsuccessfully to describe lol.

 

Planning to make a low rider?

 

That's nuts! I can't ever remember seeing a rig where the two air lines don't touch each other. They even sell them bundled with the electrical pigtail. They gotta rub in there!

I know you'll get slapped if your air lines touch the catwalk, but never heard about them touching each other.

 

Ooooops, I was talking about on the trailer. I misread what the OP was asking about I guess. I didnt mean the ones on the back of the tractor. These were the ones under the trailer, just in front of the trailer tires that are hung by springs. Dot cop got me, and I was even using my "yes sir, no sir I'm a good boy" voice. I probably caught the guy on an off day, or his wife kicked his butt that morning before work. But, he sure wrote me up for them. They already had spacers, he just wanted more spacers I guess. now Ive got spacers about every six inches, it looks stupid I got so many spacers on there

 

Air lines can touch each other, he maybe saw some rub marks and that is why he gave you a ticket.

 

I not sure of height, but everybody that I know of ran them out rear frame x- member and they were up pretty close to 2ft+ off ground. I don't know of anybody being measured or hassled. Just don't forget a shut off valve setup so you can keep glad hands on front in case somebody else needs to hook up to it

 

I've always been told it's 18" on the tandems, but I've never heard or seen a minimum for the catwalk...