Superdumps: Innovative Dumptruck Designs for NorCal Freeways

  • Context: Automotive 
  • Thread starter Thread starter berkeman
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Discussion Overview

The discussion revolves around the innovative designs of dump trucks, specifically the Superdumps used on NorCal freeways. Participants explore the mechanics, benefits, and implications of these vehicles, including their axle configurations and legal weight limits.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note that the extra wheels on Superdumps allow for increased payload while adhering to weight-per-axle limits on public roads.
  • Others mention that similar designs, such as drop axles, are common in Europe and serve a similar purpose of load distribution.
  • A participant suggests that the extra axle is not just for the truck's support but also benefits the road by distributing weight more evenly.
  • Concerns are raised about the implications of varying tire pressure based on load, affecting driveability and tire wear.
  • Some argue that the design may also enhance stability when tipping the truck on steep slopes.
  • Participants discuss the legal aspects of axle configurations, including how they can extend the "outer bridge" length to increase legal load limits.
  • There are mentions of challenges in sourcing parts for these specialized axles, with some sharing experiences of local repair shops providing solutions.
  • A participant describes a more complex rig seen in Texas that utilizes a trailer to increase axle count and legal weight capacity.
  • Discussion includes references to bridge laws that affect total gross vehicle weight (GVW) based on wheelbase and axle placement.

Areas of Agreement / Disagreement

Participants express a range of views on the functionality and design of Superdumps, with no consensus reached on the best configurations or practices. Multiple competing perspectives on axle design and legal implications remain evident throughout the discussion.

Contextual Notes

Some participants highlight limitations related to regional availability of certain truck designs and the complexities of legal regulations governing axle configurations and weight limits.

berkeman
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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

http://www.canamequipment.com/wp-content/uploads/2009/09/KH-California-Super-Dump.jpg

http://www.rightawayredymix.com/images/rockSuperdump.jpg
 
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I've seen this on ready-mix cement trucks for years.
 
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
 
AlephZero said:
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

Interesting! Thanks for that. I'd seen vehicles with extra wheels underneath but not touching the pavement, and wondered what they were for. :smile:
 
berkeman said:
Interesting! Thanks for that. I'd seen vehicles with extra wheels underneath but not touching the pavement, and wondered what they were for. :smile:
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.
 
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!
 
DaveC426913 said:
Then bingo!

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

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.
 
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.
 
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.
 
  • #10
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.
 
  • #11
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.
 
  • #12
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.
 
  • #13

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