I saw this strange thing on a semi Wheel

it was a small semi (that is it was a semi truck pulling one short trailer), and on one wheel, in the centre, it had a cylinder shaped object with numbers on it’s face.

The numbers looked like the numbers on a Odometer, and the whole thing must have been on bearings, because when the truck moved, the cylinder shaped object didn’t move (it moved back and forth in the plane of rotation of the tired, but not around and around like the wheel).

It was on the second set (to wards the front) of the farthest back wheels.

What was I looking at?

It’s a gauge. I can’t remember what it’s measuring though. In regards to the fact that it didn’t spin though, cool, eh? This technology was tried out on Taxi cabs a while back where the entire hubcap was an ad and it was mounted on bearings and weighted at the bottom so it wouldn’t spin. Problem was it played some serious tricks on yoru eyes. It made the taxi look like it was hovering over the ground like a land-speeder from Star Wars.

Very odd indeed.

Now that you’ve seen them, you’ll see them on almost every semi-trailer you come across. I’m pretty sure they’re used to count rotations of the axle of the trailer. That way instead of using milage, because the trailer can be used by multiple cabs…they use this as a gauge of the age/shape of the trailer itself.

I don’t have any actual authority to answer this question, but I did ask my Dad about it on a road trip. He used to drive semis a LONG time ago and for a short period of time as a non- professional.

What I was told was that it was (is) exactly what you thouht: an odometer. It is specifically for the trailer itself. How far has this trailer been towed?

CAVEAT: This is a hearsay answer.

If I can hijack a little with a related question… On most large trucks I often see plastic tabs on the front wheel lugnuts, and they are always pointing to the next lugnut so as to form a circular pattern. I’m assuming that these are just an easy way to make sure that all the lugnuts are tight with a quick visual check?

Just to pipe in, I used to see these all the time as well, when I was a passenger, I saw it was an odometer, so I figure it must register miles, or more correctly, revolutions of the tire. I then recalled that most Truckers get paid X cents per mile… I think this is where X is decided… that is, you can’t reset this meter, and its on the ‘truck’ bed itself, and not the cab… which could be taken off, taken for a joy ride and brought back, for oodles of cash.

Then again, this is what I deduced, it made sense, Advertised payment by the mile, and the meter on the trailer it self. Does anyone else have something to the payment by the mile scheme?

It’s called a hubodometer, if you’re interested (I did a little project on 'em a long time ago). There are a number of manufacturers, Veeder-Root and Engler among them. Yes, as **meeko ** suggested, they’re for keeping the drivers under the thumb of The Man, but they also help keep preventive maintenance on the rolling stock on schedule - things like regreasing the bearings every X thousand miles and such.

It’s called a hubometer. As said above, it tracks mileage of a trailer rather than the semi. From my experience working with truckers, most of them didn’t use it for anything. I have never met anyone that was paid off of hub readings. My impression was that companies with a large fleet of trucks use it as a general way to track wear and tear on the trailer and it’s tires.

As ElvisL1ves says, they are called a hubometer and their main purpose is to keep track of trailer miledge for maintence purposes. All the ones I have seen read out in miles. They are also handy for double checking that the tractor odometer is working correctly and recording trip miles if the tractor odometer is not working.

I get paid the miles that I record off the tractors odometer, but some companies pay based on what the miledge ‘should’ be according to a map quest type program to prevent drivers from padding their pay with some extra miles.

It seems to me that I have also seen them mounted on the tractor itself. Does this ever happen or am I just losing my mind?