truck weights per square inch
truck weights per square inch
(OP)
how much weight per square inch is place on each tire per square inch on a tandem axel truck weighting 50,000 pounds.
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truck weights per square inch
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RE: truck weights per square inch
RE: truck weights per square inch
To get a handle on the importance of load distribution, run the calcs on the three cases I listed above.
Please see FAQ731-376 by VPL for tips on how to make the best use of Eng-Tips Fora.
RE: truck weights per square inch
First of all, completely disregard the 80/20 split, or any other ratio because it is meaningless. For design purposes, use an axle rating that would be average, or worse case. A typical axle for gravel trucks would be 46,000 lbs or 48,000 lbs. In most cases however, it is not the axle rating that will limitl loads, but tire size. The most common tire for the rears is 5,500 lbs per tire, therefore the max loading will be 44,000 lbs....on the rears only. Since you are trying to enable a design, the splitting of the weight 80/20 is not advised because it is not a realistic value.
Let's take my truck for instance. My gross vehicle weight is 58,000 lbs. My tare is 30,000 lbs (empty) and my front and rear tires limit my loading capacity. I load to about 43,000 lbs on the rears, or about 28,000 lbs of gravel/sand from the pit.
My point is that for an actual surface loading, each rear tire is loading the road contact surface to 5,500 lbs. THe psi at the tire contact is about 60 to 75 psi (depending on the tire width and contact area).
Also, tire pressure has nothing to do with it's load rating. The recommended tire pressure on my front tire is 125 psi, and it's recommended load limit is 8,500 lbs. My rear tire pressures are 100 psi and they are rated for 5,500 lbs.
For your design, use the very common rear axle split of 46,000 lbs (2 x 23,000 single axles), even though the tires will likely limit it to 44,000 lbs or so. The equals 5,750 lbs. per tire.
KRS Services
www.krs-services.com
RE: truck weights per square inch
Let's see - 43,000 pounds on the tandem axles divided by a gross vehicle weight of 58,000 pounds. That's about 74 percent of the weight on the rear, and 26 percent on the front. Fits right there between 80/20 and 70/30.
Using an 80/20 split and a GVW of 58 kips, I'd assign 0.4*58,000 = 23,200 pounds per axle - or 5,800 pounds per tire. Compare this to KRSServices's 5,750 pounds per tire. I don't mind being off by 50 pounds in 5,750...and on the conservative side, to boot.
Don't get me wrong - it's always better to have vehicle-specific loads and vehicle counts to use when designing roads. But it's also important to know what range of values represents reasonable results, too. And I have seldom had a complete traffic analysis to use in design; with no crystal ball to know what will appear on the roads in 10 or 20 years, either.
Remember - "It's better to be approximate and correct than precise and wrong."
Please see FAQ731-376 by VPL for tips on how to make the best use of Eng-Tips Fora.
RE: truck weights per square inch
LOL, don't get me wrong, the entire purpose for my rambling was to demonstrate that your rule, is not incorrect, but should be premised on realistic fugures. In a highway design, for example, I would utilize the loading based on the 46,000 lb axle rating and then compare the results to a 50,000 lb axle rating. Since 46,000 lb ratings are common today, that is a good start, however, who knows what will be allowed in the future (tandems vs. tri-axle and super-B). Anyway you get the picture. The one point that I wanted to strive for was that commonly, the axle rating should be a good start for your design premise, not gvwr's. Of course, these must then be converted to frequencies and assumed ADSL's to enable the design of the structure.
What do you do in the case where the gvw on the unit (trailers) is 80,000 or 100,000 lbs? The 80/20 does not quite work well, yet the axle ratings remain the same, there is only more of them. The loading limit on the road surface per tire remains constant as 5,750 lbs. Applying a split in this case would lead to a different design criteria. The bottom line is to utilize whichever methodolgy the designer is comfortable with. I really wanted to clarify the tire air pressure to loading comments.
KRS Services
www.krs-services.com
RE: truck weights per square inch
RE: truck weights per square inch
RE: truck weights per square inch
You're right, of course - the ratios don't apply to everything, and an 80/20 split will get you in the wrong arena with school buses, for instance. But they can help in evaluating some loadings, when you don't have anything else to go on -
Please see FAQ731-376 by VPL for tips on how to make the best use of Eng-Tips Fora.