Semitrailer with spinning tires

[micky]

Today at an intersection, I saw a semi-tractor-trailer and the rear of the trailer had probably 3 sets of wheels, and the front one was off the ground, and even while the truck was not moving, the front rear wheel was spinning, not just vibrating spinning but under power. It also looked like the wheel behind it was spinning, even though it was on the ground. I couldn't see the rear tire if there was one, and then the light changed and the truck started moving, so of course the tires were turning.

First, I didn't think there was ANY power in the wheels of trailers. ?? Second, if there is, shouldnt' they know when the truck isn't moving and save their energy for when it is? Third, isn't it hard on the tires to spin them when the truck is not moving?

[Bob F]

Sounds like those hubcaps on a bearing that keep spinning long after the wheel stops turning.

The extra axle probably had smaller tires, and is designed to be lowered to lessen the weight on each axle to not exceed legal limits.

[invalid unparseable]

I have seen those also. It creates the optical illusion of the tire spinning while stationary.

[Ben Verified - ✅]

It's only 4:39pm and your posts are becoming slurred.

[invalid unparseable]

Considering what today is, he should be a hoot late in the day.

[micky]

Maybe it was an illusion but it was an impressive one. It wasn't the hubcabs that appeared to be spinning but the actual tires, especially the one that was off the ground. I wish I'd had time to pay more attention other tire and to the hub and the space in between. The truck was abou5 50 feet away, on the other side of the intersection with the traffic light, in the oncoming lane.

I tried to google but just found one that only applied when the truck was moving, but mine was standing still.

[invalid unparseable]

micky wrote on 3/17/2024 1:28 PM:

It was a fad many years ago. I saw quite a few, but they were on fancy modded cars, not on tractor trailers. I haven't seem them in the last few years.

This car's front tire seems to be stationary when the car is moving, but the rear tire seems to rotating when the car is stationary.

[Snag]

Those things were popular with a certain crowd in Memfrica a fwe years back . Don't know if they still are , we fled to the woods about

12 years ago . I live somewhere now that I don't need to take a vacation from ...

[Clare Snyder]

The wheels are not powered. They are free spinning from having contacted the road while in motion. They are lifted to allow the trailer to turn without scribbing the tires off or tearing the bogeys off. The inertia of those very heavy wheels combined with really good bearings can keep them spinning for a LONG TIME!!!

[Clare Snyder]

They are called "TAG " axles if trailing and "MID LIFT" axles if leading the main load axle. They can be on the tractor or the trailer and are used to spread the load - particularly on load restricted roadways where per axle load is limited (as is common in the spring in the north) Sometimes TAG axles are passive rear steer - and can generally be left down in normal cornering but on tight turns mid lift and tag axles are often lifted from the road before coming to a stop - and they are not generally "braked" axles - so they continue spinning. The mid lift may go up 8 inches or so, while the TAG axles often just clear the road surface. If they are let down with the truck not in motion they can "lay a patch" - or at least let out a good "CHIRP" when they hit the pavement - or scatter some gravel stones on a dirt surface.

[Ben Verified - ✅]

True! The "micky" never disappoints.