Please Explain this Oppo

"zeontestpilot" (zeontestpilot) 08/03/2016 at 08:04 • Filed to: Question

0

10

I see a lot of trucks, such as this concrete mixer, and it’s been bugging me; they have a lot of tires, some are up and others are down...why?

I figure it’s one of three things. The first idea is that they perhaps rotate which tires are used (if it was down its now up, and vice versa) because the strain and weight of the cargo kills tires quicker than the front does. But I have never seen a truck like that.

The second and more plausible idea, is that the heavier the load, they drop more tires. But again, I have never seen that either.

The third idea is that if any of the road-contacting tires explode, they can drop an unused tire to help support the load.

How close am I? I've thought about this a lot and these were the best answers I could come up with. Help quench my thirst of knowledge Oppo!

McMike > zeontestpilot 08/03/2016 at 08:06

3

(checks box #2)

The other two aren’t required.

random001 > zeontestpilot 08/03/2016 at 08:07

5

It’s the second option in there, sorta. If you get up close, you can usually see a set of airbags in there, though sometimes they are hydraulically actuated (especially if the truck already has a hydraulic system). This allows them to distribute the weight, typically used when driving on softer ground which is maybe why you won’t see it on the road since it won’t sink.

Bourbon&JellyBeans > zeontestpilot 08/03/2016 at 08:08

2

Those are called tag axles. They’re lowered via air suspension when the truck’s carrying a heavy load. They support the frame and the main axles by evening out the load.

xyzabc > zeontestpilot 08/03/2016 at 08:10

3

Actually, it’s for when they’re on the verge of running something over.

They put the other wheels “down”. Ensures they don’t have to back-up and run it over again.

Saves Diesel fuel.

zeontestpilot > McMike 08/03/2016 at 08:30

0

I’m glad I was on the right track with my hypothesis.

zeontestpilot > random001 08/03/2016 at 08:31

0

That makes a lot of sense actually. I'd imagine they have to drive across dirt roads to get to the construction site or whatever.

random001 > zeontestpilot 08/03/2016 at 08:35

0

Yep, that’s the theory.

Wacko > xyzabc 08/03/2016 at 08:51

2

so the next mustang will have 16 wheels then.

Cé hé sin > zeontestpilot 08/03/2016 at 09:50

1

In the case of on-road trucks it’s due to legislation. The more axles you have, the more you can carry. Conversely if you’re carrying less you can save on tyre wear by lifting one or more axles.

Regulations vary according to where you are but my local ones are:

Six axles: up to 46 tonnes

Five axles: up to 40 tonnes

Four axles: up to 38 tonnes

If you have a six axle combination hauling between 38 and 40 tonnes you can therefore lift one axle like this:

So if you’re grossing less than 38 tonnes you can lift one of the three axles on the trailer as well, if so equipped.

E90M3 > zeontestpilot 08/03/2016 at 10:21

1

This thing weighs something like 100,000 lbs and drives on unpaved oil field roads, that cement truck must be really heavy.