gg923 Posted August 1, 2015 Report Share Posted August 1, 2015 This is not really a RV Hauler question but rather one of curiosity that I think this group can answer. We have spent the last couple of months in WA and have noticed that most of the commercial T/T combos have a LOT of axles. Being from FL & TX the typical config is a single or tandem tractor with a trailer with tandem axles. The tractors up here in WA have 3, 4 and 5 REAR axles and then the trailers have 4, 5 and 6 axles (or may not actually be axles but have support "drop down type" Tire wheels in front of the rear axles) but most have at least 4 real axles. I have difficulty believing that they are hauling loads that are that much heavier (maybe they are) - can any of you "in the know" educate me? Bet the tire business is good! thanks! Link to comment Share on other sites More sharing options...
noteven Posted August 1, 2015 Report Share Posted August 1, 2015 http://www.wsdot.wa.gov/NR/rdonlyres/DF443726-F00D-48BA-A562-8A22F172F254/0/legalweigtchart.pdf Warshington axle weight info Link to comment Share on other sites More sharing options...
Mark and Dale Bruss Posted August 1, 2015 Report Share Posted August 1, 2015 There are weight limits on the force of an axle on the pavement. More axles allow a greater load capacity and stay within the limits of the force on the pavement. There is a rather complicated calculation of axle loading called the bridge formula. Here is an example: a single axles can be up to 20,000 lbs. But it an additional axle is close enough to the first axle (about the spacing of a tandem) the combined load of the two axles is only 38,000 lbs. Link to comment Share on other sites More sharing options...
Raquel Posted August 1, 2015 Report Share Posted August 1, 2015 When I was living in Kalispell, MT, I noticed the same thing. In Montana, every Spring, The ground under the roadbed would start to thaw and become almost liquid. The roads would actually open up and start to fall apart because of the liquidation of the earth. The trucks would put down their drop axles to keep from doing as much damage to the roads by distributing the load over more area/tires. I believe that some trucks also had more axles that did the trucks where I grew up, the Portland, OR area. Link to comment Share on other sites More sharing options...
Rick & Alana Posted August 1, 2015 Report Share Posted August 1, 2015 http://www.wsdot.wa.gov/NR/rdonlyres/DF443726-F00D-48BA-A562-8A22F172F254/0/legalweigtchart.pdf Warshington axle weight info In the Midwest these regulations are commonly referred to as Bridge Laws Raquel and Mark gave very good explanations! Link to comment Share on other sites More sharing options...
G&K Posted August 1, 2015 Report Share Posted August 1, 2015 If you're in Michigan look out for what they call a Michigan Millipede. Those units are axles pretty much from one end to the other! Link to comment Share on other sites More sharing options...
gg923 Posted August 1, 2015 Author Report Share Posted August 1, 2015 Thanks! Great Info! Had not really thought about the road bed situation being so different but that makes a lot of sense. Link to comment Share on other sites More sharing options...
Darryl&Rita Posted August 1, 2015 Report Share Posted August 1, 2015 Multiple axles for weight capacity, with spread for increased capacity, as well load support. Link to comment Share on other sites More sharing options...
shorts Posted August 1, 2015 Report Share Posted August 1, 2015 Most of the weight laws are based on a pounds per inch of tire width, here in Michigan it ii something like 154000# on10 axles plus the steer tires before you have to get special permits. Lots of Mi. trains, 3 axle tractor with 2 3 axle trailers and a dolly being one of the most common configurations. the next most common is a single trailer with 8 axles, with 3 of them having lift capability so they can be drug around a corner Link to comment Share on other sites More sharing options...
adept99 Posted August 2, 2015 Report Share Posted August 2, 2015 Michigan also has a thing they do in the winter where they shut certain roads down due to temperature. You are not allowed to move your equipment (cranes, dozers, etc) over those roads regardless of wheels and axles. At $38,000 a month rent plus fines per day, and with the roads shut down for over a month, you don't miss many opportunities to move your equipment out.!! Link to comment Share on other sites More sharing options...
peety3 Posted August 2, 2015 Report Share Posted August 2, 2015 It comes from this: https://en.wikipedia.org/wiki/Federal_Bridge_Gross_Weight_Formula Aside from the classic "20k for single axle, 34k for tandem, steer tires limited by tread width", there's also a complex equation based on axle spacing as shown in the link above. I haven't done the math, but I suspect it's the reason the dump truck + dump trailers often have long, extendable "tongues". I suspect they extend to maximum overall length when loaded, and shorten up for easier manuevering when empty. Notice that the formula has to be rerun for every possible set of axles: not just axles 1-5, but also 2-5, etc. Apparently 1-3, 1-5, and 2-5 are the typical ranges that truckers exceed, so those are likely the ones they calculate. Link to comment Share on other sites More sharing options...
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