Superdumps Dumptrucks

berkeman

I've been seeing more and more of this style of dumptruck on the freeways in NorCal, and kept wondering what the extra wheels were for. I'd only seen them driving with the wheels in the up (stored) position.

So I did some searching on Google Images, which led me to Wikipedia, which led me to Superdumps.com -- turns out they put the wheels down to let them load up with more payload, and still pass the weight-per-axle limits imposed on the public roads. Pretty clever idea!

www.superdumps.com

Averagesupernova

I've seen this on ready-mix cement trucks for years.

AlephZero

This seems like an over designed version of "iift axles" or "drop axles" which are quite common on HGVs in Europe, except they retract under the body rather than overhead.
http://www.heritagetruck.com/lift-axles.aspx

berkeman

Interesting! Thanks for that. I'd seen vehicles with extra wheels underneath but not touching the pavement, and wondered what they were for.

turbo

Those are common here on dump trucks and logging trucks. I have never seen a truck with a trailing axle like the Superdumps. And they are not available in Maine, so no surprise.

DaveC426913

Yeah, I've seen lots of trucks with drop axles. I tried to deduce the logic of them just by observation, but I could not figure out why something as sturdily-built as a dumptruck would need an extra axle to support itself under a load. What's it going to do? Collapse?

Then bingo!

The extra axle isn't for the truck, it's for the road!

AlephZero

That's only one side of the story. Because the weight of the truck varies a lot from empty to full, for a fixed number of wheels and a fixed tire pressure the contact area between the tires and the road would also vary a lot. If the tire pressure was set for a full load, the truck would have poor driveability when empty, since the engine and brakes would both be hugely over-powered and the tires would be hugely over-inflated.

Tire wear and rolling resistance (and therefore fuel consumption) are reduced as well, especially when cornering.

Some heavy trucks have tire pressure adjustment systems (with an on-board air pump) but dump trucks are often used in situations where they are repeatedly filled and emptied with a cycle time of only minutes, and drop axles are quicker to deploy than changing tire pressures.

Actually I wonder if the trailing axle design is also meant to improve stability when tipping the truck on steep slopes etc - i.e. to stop the truck falling over backwards.

Pkruse

These do more than just put more rubber on the road so you can carry more weight. They extend the "outer bridge" length. That greatly increases the legal load limit because it spreads the load out when crossing a bridge.

Fahlin Racing

Lift axles or drop axles or tag axles whatever you prefer to call them. I love trying to find parts for a model the driver or mechanic doesn't even know which one it is. I haven't had the joy of getting parts for the lift axles on the truck posted here though. Pretty beefy IMO.

Pkruse

I never had trouble getting parts for similar equipment. I used a local full service hydraulic repair shop. The would often just make new parts at half the cost of getting them from the manufacture. Not cheap, but easily available.

Pkruse

I've seen an even better rig in Texas, but it was too long to be legal in most states. They put a dump bed on a trailer, and towed it a long distance behind a regular dump truck. This put 3 more axles on the ground and greatly extended the outer bridge length, more than doubling the legal weight capacity.

Fahlin Racing

I believe those would be a B-train Pkruse. Most of the people who come into my work don't necessarily have the best knowledge about their own equipment which is a fun part. I would say air system valves regardless of the system are the most common 'assumed' one is the same as the rest of them.

drdodge

many states also have "bridge laws" that limit the total gvw due to wheelbase.
tag axles (the floater axles in between the drive and front axle) actually reduce the legal limit because the truck min wheel base is shorter.
hence, put the tag behind and "have your cake and eat it two.

https://docs.google.com/viewer?a=v&q...QQyBj1kHiDRhmA

dr