# Two questions about things seen on semi trailers **URL:** \ **Category:** Factual Questions\ **Created:** [November 21, 2024, 2:37am UTC](https://boards.straightdope.com/t/two-questions-about-things-seen-on-semi-trailers/1010541 "2024-11-21T02:37:06Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![kenobi\_65](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kenobi_65/32/13178_2.png) [@kenobi\_65](https://boards.straightdope.com/u/kenobi_65)\ **Post date:** [November 21, 2024, 2:37am UTC](https://boards.straightdope.com/t/two-questions-about-things-seen-on-semi-trailers/1010541/1 "2024-11-21T02:37:06Z")
While on a road trip on Monday, my friend and I noticed two features on some semi trailers, which neither of us were certain what they were for. I figured that the knowledgeable people here might know more. First, we saw several intermodal trailers (i.e., an intermodal container mated to a “skeletal” trailer), where there were two zip-ties, each attached to a rear corner of the trailer, very close to the mating point between the container and the trailer. We certainly _hoped_ that the zip-ties weren’t what was keeping the container on the trailer, but they were clearly there for some purpose. Secondly, we saw several trailers which had some sort of devices attached to the trailer wheels. They looked almost like big yellow streamers, about 2" wide, and maybe 2 feet long, with one end anchored to one of the wheel’s lug nuts, and the other end extending across the wheel, and to over the tire. I don’t think that they were fabric, as they seemed to hold their shape as the wheels turned (suggesting that they were metal or something like that). Any knowledge that any of you can shed on the purpose of either item will be greatly appreciated! ---
**Author:** ![Kropotkin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kropotkin/32/18045_2.png) [@Kropotkin](https://boards.straightdope.com/u/Kropotkin)\ **Post date:** [November 21, 2024, 2:56am UTC](https://boards.straightdope.com/t/two-questions-about-things-seen-on-semi-trailers/1010541/2 "2024-11-21T02:56:21Z")
Don’t know about the zip ties but the “streamers” or “wheel rotation indicators” let the driver tell if a wheel has frozen. Wheels can freeze up for any of a few reasons, and it can be hard to tell what and where the problem is. The indicators are visible in the mirrors and let the driver confirm if a wheel is not turning. ---
**Author:** ![Beckdawrek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beckdawrek/32/3647_2.png) [@Beckdawrek](https://boards.straightdope.com/u/Beckdawrek)\ **Post date:** [November 21, 2024, 2:56am UTC](https://boards.straightdope.com/t/two-questions-about-things-seen-on-semi-trailers/1010541/3 "2024-11-21T02:56:44Z")
Well, I asked my son. Hes been around a bunch of trucks to haul heavy equipment. He says the zip ties might be to hold wiring for lights and such. If the tandem trailers have their own braking, maybe brake line. He said it’s a WAG. Without seeing it himself. ---
**Author:** ![kenobi\_65](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kenobi_65/32/13178_2.png) [@kenobi\_65](https://boards.straightdope.com/u/kenobi_65)\ **Post date:** [November 21, 2024, 2:58am UTC](https://boards.straightdope.com/t/two-questions-about-things-seen-on-semi-trailers/1010541/4 "2024-11-21T02:58:29Z")
> [@Kropotkin](#): > > Don’t know about the zip ties but the “streamers” or “wheel rotation indicators” let the driver tell if a wheel has frozen. Doing an image search on “wheel rotation indicator” gave me this, which is exactly what we saw. Thank you! [![](https://skiddd.com/wp-content/uploads/2024/04/Thumbnail_HazzardFree.jpg) ](https://skiddd.com/wp-content/uploads/2024/04/Thumbnail_HazzardFree.jpg) ---
**Author:** ![PastTense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pasttense/32/14550_2.png) [@PastTense](https://boards.straightdope.com/u/PastTense)\ **Post date:** [November 21, 2024, 3:09am UTC](https://boards.straightdope.com/t/two-questions-about-things-seen-on-semi-trailers/1010541/5 "2024-11-21T03:09:10Z")
Concerning the zip-ties, there are locking pins which keep the container on the trailer and the zip-ties which secure the locking pins: > **[Securing chassis box with zip ties](https://www.youtube.com/watch?v=RAGtj1OiNKg%2F)** ---
**Author:** ![kenobi\_65](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kenobi_65/32/13178_2.png) [@kenobi\_65](https://boards.straightdope.com/u/kenobi_65)\ **Post date:** [November 21, 2024, 3:16am UTC](https://boards.straightdope.com/t/two-questions-about-things-seen-on-semi-trailers/1010541/6 "2024-11-21T03:16:43Z")
> [@PastTense](#): > > Concerning the zip-ties, there are locking pins which keep the container on the trailer and the zip-ties which secure the locking pins: Thank you! Looking at the video, that looks like what we were seeing on the rear corners of the trailers. ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [November 21, 2024, 3:59am UTC](https://boards.straightdope.com/t/two-questions-about-things-seen-on-semi-trailers/1010541/7 "2024-11-21T03:59:51Z")
> [@kenobi\_65](#): > > Doing an image search on “wheel rotation indicator” gave me this, which is exactly what we saw. Thank you! That tire looks like it is having an issue. Tread separation? ---
**Author:** ![kenobi\_65](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kenobi_65/32/13178_2.png) [@kenobi\_65](https://boards.straightdope.com/u/kenobi_65)\ **Post date:** [November 21, 2024, 4:02am UTC](https://boards.straightdope.com/t/two-questions-about-things-seen-on-semi-trailers/1010541/8 "2024-11-21T04:02:04Z")
> [@Irishman](#): > > That tire looks like it is having an issue. The front of the two wheels with the rotation indicators? I think that there are two wheels (and two tires) there, and the gap between the two may be what you’re seeing. ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [November 21, 2024, 2:32pm UTC](https://boards.straightdope.com/t/two-questions-about-things-seen-on-semi-trailers/1010541/9 "2024-11-21T14:32:37Z")
I’m taking about the white spot and bulge. ---
**Author:** ![John\_DiFool](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_difool/32/19543_2.png) [@John\_DiFool](https://boards.straightdope.com/u/John_DiFool)\ **Post date:** [November 21, 2024, 2:53pm UTC](https://boards.straightdope.com/t/two-questions-about-things-seen-on-semi-trailers/1010541/10 "2024-11-21T14:53:18Z")
Oh, I have one: “Warning: High Cube” on the back of some semi-trailers. #1, a trailer isn’t a cube, it’s a rectangular prism (cubes of course are subsets of same). #2, yeah, a trailer can be high, but everybody knows that as a default, so what’s the point? It’s not like the ones which are higher than the others get the warning pasted on the back (they look the same as the others to me in any event). #3, who are they warning? The truck driver himself? Fellow drivers? The guys who remove and unload the trailer? ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [November 21, 2024, 3:00pm UTC](https://boards.straightdope.com/t/two-questions-about-things-seen-on-semi-trailers/1010541/11 "2024-11-21T15:00:29Z")
> [@Irishman](#): > > I’m taking about the white spot and bulge. IMO … The white spot looks like simple scuffing where they ran over something white, like spilled white powder or a hunk of drywall. Or even from ops in a gravel lot. That’s a triple tandem axle set, and some sideways scuffing happens to every tire on every turn. Triple tandem setups are also IME more common on dump trucks or cement trucks than on over-the-road box vans or tankers. So the tires picking up color from the dirt, gravel, etc., they roll over at construction sites and whatever is the other end of their trip is commonplace. I’m not seeing the thing you’re calling a bulge. There is a darker area just clockwise from the white area, which I take to just be different amounts of dirt / dust stuck to the tire. YMMV of course. ---
**Author:** ![Just\_Asking\_Questions](https://avatars.discourse-cdn.com/v4/letter/j/ba9def/32.png) [@Just\_Asking\_Questions](https://boards.straightdope.com/u/Just_Asking_Questions)\ **Post date:** [November 21, 2024, 3:05pm UTC](https://boards.straightdope.com/t/two-questions-about-things-seen-on-semi-trailers/1010541/12 "2024-11-21T15:05:33Z")
> [@John\_DiFool](#): > > It’s not like the ones which are higher than the others get the warning pasted on the back But they are! By about a foot. Standard trailer height since the dawn of time (or at least the 60s) is 13’6". All interstate highway bridges, and most other bridges, are designed to clear a 13’6" trailer. The ones that aren’t are old, and have signs and barriers and still peel the tops off trucks on a regular basis. But by that fact, most interstate bridges are designed with extra clearance, like 14’8" for example. Hi-cube trailers take advantage of that. This also applies to railroad cars. In ye olden days, railroad cars were limited in height so they wouldn’t get stuck in tunnels. As railroads improved higher car heights were allowed. Box cars with hi-cube heights, as they were called (cubic feet, not geometry), have the “extra height” portion of each end painted white. Next time you see a train, look for it. [https://modeltrainmarket.com/cdn/shop/files/275204-006jpg\_19b96513-73f9-49a7-8bc5-f00e8f93c5eb\_2000x.jpg?v=1731031618](https://modeltrainmarket.com/cdn/shop/files/275204-006jpg_19b96513-73f9-49a7-8bc5-f00e8f93c5eb_2000x.jpg?v=1731031618) ---
**Author:** ![Just\_Asking\_Questions](https://avatars.discourse-cdn.com/v4/letter/j/ba9def/32.png) [@Just\_Asking\_Questions](https://boards.straightdope.com/u/Just_Asking_Questions)\ **Post date:** [November 21, 2024, 3:15pm UTC](https://boards.straightdope.com/t/two-questions-about-things-seen-on-semi-trailers/1010541/13 "2024-11-21T15:15:37Z")
PS this is what holds containers to the train, trailer, ship, and each other. This simple lock makes containerized shipping possible. You put one at each corner, rotate the lever, and voila! Containers are locked, and locked so well, they can tip over and not come apart. They make these things by the millions, I expect. At least four required for ever container in existence. [![](https://www.pacificmarine.net/shop/wp-content/uploads/2021/05/container-twistlock-left-locking.png.webp) ](https://www.pacificmarine.net/shop/wp-content/uploads/2021/05/container-twistlock-left-locking.png.webp) [![](https://images-global.nhst.tech/image/ZDluWFZ3bUdiOXFUcjRiQnRqc2kvTzVkUVBscy9hVVRDOHFscDZjQVVRMD0=/nhst/binary/a6967c31e45549726c9edc37dbfe6a61) ](https://images-global.nhst.tech/image/ZDluWFZ3bUdiOXFUcjRiQnRqc2kvTzVkUVBscy9hVVRDOHFscDZjQVVRMD0=/nhst/binary/a6967c31e45549726c9edc37dbfe6a61) ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [November 21, 2024, 10:57pm UTC](https://boards.straightdope.com/t/two-questions-about-things-seen-on-semi-trailers/1010541/14 "2024-11-21T22:57:51Z")
> [@LSLGuy](#): > > I’m not seeing the thing you’re calling a bulge. There is a darker area just clockwise from the white area, which I take to just be different amounts of dirt / dust stuck to the tire. There is a gray stripe around the center of the tire. There is a prominent white patch outside the gray. That patch terminates abruptly with what appears to be a diagonal line. That looks like a bulge to me. It could just be an illusion caused by the tread curves and color patch. The white could be scuffing. I see parallel striations, especially at the outer edge. Maybe ran over a curb or something. That still looks bad.