Before dismissing this “un” recommendation, read our other post about the engineering side of Springs Vs. Torsion Axles and realize it is compounded with heavier trailers and more axles. So for multiple axles, if we want our wheels to carry roughly even amounts, then the axles must interconnect somehow. Use eye-eye for lighter applications, and slipper style for the heavy duty ones. Basically, as one wheel goes up (or down), the equalizing bar pivots to offset the height of both leaf springs. Walking beam suspensions and linked airbags do this well too, and there are others. More business’ should operate with this sort of approach. This gives 5 points of contact. Same for styles like axle-less suspension, Moryde axles, and others. Maybe a comment on required monitoring and maintenance. Road surfaces are uneven everywhere. Item# 48197 ... Tandem Axle 7k or 10.4K Utility Car Hauler HD Trailer DIY Master Plan — 19 How-to Steps with Blueprint Only $ 59. For example, the trailer is 4800# with a max load of #6400. A car has 4 wheels, one at each corner. (Interestingly, they didn’t like my advise about load sharing for the axles. Firstly I want to thank you for this article. Even so, I bumped the new Lippert axles up to #2800lbs each. Many End dump trailers are added daily. Travis January 21, 2021 @ It is not, however, common with smaller trailers. In flat towing, they’ll perform well, but as soon as one axle goes over a bump, or goes into a depression, these axles become unequally loaded. It also determine how strong the trailer should be. Even though the axles don’t load share, one is capable of almost all the weight, and the other will usually carry at least some of the load (even if it’s much less). Using 3200# axles will absolutely overload one axle. It’s not a good idea — especially when you can accomplish almost the same damping with a hybrid system as shown above. Easy enough, but Why not just buy a beefier single axle? I would really like to see a correlation for axle, hub and tire failures — First to see how age affects the failure rate, and Second to see how overloading affects it. To get around the possibility of overload in such situations, you can use axles and tires that are way overrated. You want to live Tiny, but not “that” tiny? Rear steering axles – heavy trailers. The more distance between tires whether because of triple axles or spread axles, the more rubber you will leave on the pavement. Double eye spring configurations solve the same task with another type of equalizer. 11:05 AM. End dump trailers come in a variety of sizes. Independent suspension for trailers is not helpful. I like the look of the Timbren Tandem axle Silent Ride Walking Beam Suspension. He sent a bunch of images and video. Front Axles Beam Drop All Models 8-2 Front Suspension Ride Heights 4700 DDC Chassis 8-3 4800/4900/6900 WST Chassis 8-4 ... Hendrickson RT650 65k# Tandem 622-051 8-17 Hendrickson RS650 Walking Beam 65k# Tandem 622-052 8-18 Hendrickson Haulmaxx 40k# & 46k# Tandem … I have seen and experienced the damage to many different manufactures trailers that use tandem and triple torsion axles. For the single axle trailer, the bump is really no different because the wheels just carry the weight over the bump. The springs are 26 1/2″ from center hole to end with 3500# axles and the A frame tongue is 54″ out from the front frame. For the 6400# trailer example above, most applications will have 3500# axles. 99 $. No, this is not extreme. End dump trailers are made of aluminum and steel. Also, the article on axle-less suspension, and a comparison for leaf springs and torsion axles. CaseIH 330 True Tandem Turbo Disk 30' * Hydraulic Wing Fold Frame * Walking Tandem Wheels & Tires - MF & WF * Single Point Depth Control * C-Spring Cushioned Disk Gangs * Turbo Blades @ 7.5" Spacing * Single Flat Bar Rolling Harrow * Front Wing Frame Gauge Wheels * 31’ Good luck with your project. I don’t think it’s brakes. What’s your opinion and analysis? See the image below. Travis January 21, 2021 @ I just replaced the torsion axles on my 1973 Argosy (Airstream) travel trailer with tandem axles. I dislike the spread axle design because it stresses tires, axles, and the frame when turning sharp more than a conventional spread, Carl B November 17, 2020 @ If that’s you, go with a wider tiny house built with these new trailer plans! All of these situations require suspension movement — all while (hopefully) not overloading one wheel or axle. The walking beam axle adds another pivot point to the machine, helping to keep consistent seeding depth. Tire failures often happen AFTER the overload — meaning they don’t just pop as you go over the speed bump. Models include 567, 367, 348, 389, 365, 357, 379, 388, 378, and 520. Another successful interconnection is with air ride. My question, as long as the air bags are interconnected so air can flow between bags that should be enough axle equalization but I wanted to hear other thoughts. The weight means the tires continually look flat though they are properly inflated. For really heavy or really long trailers, triple axle configurations are common. Your email address will not be published. Carl B November 17, 2020 @ As the trailer rolls over a speed bump, the first wheel rises on the bump, then because there is no equalization, the back wheel may lift off the ground too. I’d love to know if failure rates are higher for single axles or tandems or triples. Think about what is happening. Choose between Slipper Style and eye-eye style. It is amazing how many people do not pay attention to the sidewall weight rating when they buy tires. It moves like a “Teeter-Totter” to adjust the relative vertical position of the wheels as they go over bumps or into dips. walking beams (tandem axle): 1 ½" x 3 x 3/16" HSS with closed, beveled ends, painted steel frame axles: 1-1/2" cold rolled round bar inside 1 ½" sch 80 pipe, fitted with a grease nipple box measures 24" wide at the base and 48" wide at the top One of the desires for using twin torsion axles (as shown above), is the vibration damping that comes with rubber. Either way, don’t set yourself up for failure. That means the wheels on the bump carry more. This allows the axles to share the load when the road is not flat and level while offering vibration damping. It’s fun and interesting research if you want to know more. My hunch is not enough engineering goes into many trailer designs. And, there should also be the advantages that airbags have: 1. variable ride height 2. variable spring rates 3. some natural damping effects of the rubber 4. suppression of a wide band of vibration frequencies, which protects both trailer and it’s load from fatigue loading stresses. Maybe it just needs higher capacity tires? The transparent wheels in this view allow us to see the torsion arm angles. the list goes on. and three axles 42,000 lbs., as shown in Figure 2. You bring up a great point, and you’re exactly right. Watch for more about trailer axles in general and tandem axles in specific — in coming posts — like this one looking at spring mounting. Overall trailer stability requires axle stability, but there is more too, including proper axle position under the trailer. As one wheel goes up, air from its bag passes to the other keeping pressure equal in both. $. Walking Beam Suspension Made For Torsion Axles in Tandem. Yes, there is a lot of wiggle room, and it’s just a rule of thumb, so consider the application. 4:24 PM. A second key to success is making the axles stable under the trailer. As illustrated above, axles must interconnect to act as one. Their effort has more focus on the upper and the interior — the things customers interact with. Some others require a lot of fabrication. I’m assuming this problem is caused by incorrect axle positioning, but could it possibly be caused by rear axle brakes? My club has a custom 28′ trailer that the builder unfortunately put the axles in the center of, and some people had no problems towing it and for others it was a nightmare. Lower:  Torsion axles in tandem on the same bump. Here are a couple keys to success. This configuration is a disaster waiting to happen IMO, and here is the engineering to support it (written in simple terms). The boat pulls exceptionally well as is but I was considering adding a second axle to re-distribute the weight. On top of the bump, the one axle (and it’s poor tire) takes all the weight. That’s why it works (most of the time) for RV’s, and tire failures are common for utility trailers with torsion axles in tandem. James Wohlford June 10, 2020 @ Since we’re talking about torsion axles, let’s look at a trailer with Torsion Axles In Tandem. In this case, the effect is more visible because of some structural issues, but it highlights changes in load for the 3 axles. A tandem axle trailer has 4 wheels, all bunched together. Do you concur? I’m currently in the market for a new race car trailer and see a lot of the tandem axle trailers with torsion axles, so as an ME myself I appreciate informed information like this that cuts through the marketing hype. No matter where that trailer goes (within reason), those 3 points of contact are stable. Why do they set their customers up for failure? When the front set of wheels are on the bump, the back set becomes unloaded. In fact, (think about tandem axles), one wheel starts up first, and there is a complex motion of suspension as all transition to the ramp, and as the trailer pitch changes with the tow vehicle going up and over. For another example, look at big trucks with tandem rear axles. I spend a few thousand dollars a year on tires and this is a significant contributor. In effect, the formula reduces the legal weight limit for shorter trucks with fewer axles (see table below). 5:23 AM. I don’t know how else to say it. 12:34 AM. These are the most common, by far, and also the cheapest — but those are not the only advantages. A small force gives small deflection. Good luck. Thank you in advance for your response, Tom. For instance, this PDF gives suggestions for Dexter axles and hardware based on each axle capacity. Think Eye-Eye type for lighter applications 4000# axles and below. This is the best equalization, and I can see why they are so proud of it. That’s an engineering failure. Brent 1084 grain cart, 20” front auger, 20.8R38 walking tandem duals, roll tarp, SN B20100109 While this is simplified for discussion, hopefully it conveys the concept. As one goes up (or down), it must NOT carry more load (or less) than the other. Triple axles are less common, but you do see them once in a while. Incidentally, that center pivot is high load, but it’s big & fat — designed to take it. Compare the equalizer rocker for the tandem axles and triple axles in this drawing below. We’ll also use the trailer above (triple torsion axle 5th-wheel) as a case study. Looking at your article, it appears what Airstream did to handle the overloading problem you mention was to totally over-engineer it. We invite your thoughtful comments below. This changed the load center of the trailer and made it unstable when tongue low or less unstable when the tongue high.) That’s one reason for the 6000# rule of thumb. Dave: One big problem with spread axles would be tire wear on tight turning/backing maneuvers. $. Extrapolate this to 3 axles, and the problem is worse. You want to live Tiny, but not “that” tiny? The bolt is much harder than the cast, so after wearing through the thick part, the thin area went relatively fast. For the tandem axle trailer it’s different because of the 5 points of contact. They interconnect for the same reasons trailer axles should interconnect. One key with multiple axles is making sure they will share the load. Nothing else. 6:32 PM. While it’s true that torsion axles handle overload conditions better than springs, the tires don’t, and frames don’t. I notice Ridewell and others offer tandem air ride suspensions, but most offer suspensions without walking beams or other equalizers. $. Heavy full trailers, heavy simple trailers and heavy pole trailers must not have rear steering axles. I like your intuition, and I don’t have much to add either way. And, it isn’t really a solution. So, let’s dive in. When they are in tandem or triple, they are almost always independent, and — as in the illustration — that’s a problem. The trailer itself weighs 3400lbs- Axles were rated at 2600lbs apiece. I’d replace with all new parts (rocker, bushings, bolts), then keep an eye on it. Utility trailers, on the other hand, are often at (or over) the limit. If the axles are the same (which they certainly should be), and if combined they are rated at capacity of the trailer (typical), then in this condition, the first axle is overloaded by Twice. Why do people do it? Tandem Axles for Capacity Load Capacity. STEVAN J WHITE September 16, 2020 @ Motion of one wheel does NOT affect motion of the others, so there is (at times) a miss balance of load. . Why not just get a single 7000# torsion axle? 1978 Mack RS600L Grain Truck, Tandem Axle, Mack 350 Engine, 5+4 2 Stick Trans, Mack Spring Ride Susp, 102”x20’x50” Box, 3pc Endgate, Shurco Roll Tarp, Hoist, 13/80R20 Fronts, 11R22.5 Rears on Spokes, Air Brakes, Mud Scrapers, VIN- RS686LST39186, plate- TM89344, feb 21 If the manufacturers do it, then it must be OK — Right? Downsides are: if you develop a leak or have un-repairable rubber tears, cracks, or rots, then road-side repairs are made more difficult, and you may not be able to safely limp home on a jerry-rigged repair. More to the point, a 1″ bump or a 2″ bump does some of the same thing. My first commercial driving ticket was for under rated tires in comparison with the scale weight of the trailer. Required fields are marked *. Next, consider a trailer with 2 axles in tandem — 4 wheels as in the image above. A Feature of Synthesis Engineering Services, Inc. As the front of the trailer rises, the angle changes, and because the axles are independent, it takes some weight off the front axle and puts more on the rearmost axle. There should be a bushing in the eye to keep it from wearing into the cast material, but I’m guessing that was not there, or bad, so it wore quickly. The Mechanic August 28, 2019 @ On the other hand, with a full load (near 6400#), failures begin to happen. I was looking at putting triple-axle air ride on my 5th-wheel. Mostly it’s the tires, the hubs, or the bearings. Thanks, The Mechanic January 28, 2019 @ Each spindle is bolted into a sleeve and can be removed by simply removing the bolt and pulling out the axle. There are several ways you can use rubber for suspension yet still achieve load sharing. Center pivot and the 2 outside brackets. The beam pivots so the wheels follow uneven ground, while each wheel keeps the same load. Of course the car goes over first, but that’s not our focus. On The Road – Rattle Traps We Call Trailers. The biggest part of stability is connecting the axles closely to the frame. It’s whether the axles work together to share the load on uneven surfaces — or not. Good comments and good observations. Mechanical Elements - Your Source For Do-It-Yourself Project Plans! In this case, the first axle is carrying all the weight, so it deflects a lot. There are vehicle scales at truck service centers, recycling centers, garbage dumps, etc. They fail later with heat or something because of the internal damage from overload. Shop Log Trailers For Sale by owners & dealers near you. OK, maybe that explains some of it, but I’m not totally embracing it. Eugene January 28, 2019 @ This is also quasi stable because movement in the equalizer actually moves the back axle fore and aft just a tiny bit. With standard leaf springs, if you place 2 axles in tandem WITHOUT an equalizer bar, then they act independent. There are some structural integrity issues too, but the big problem is the triple torsion axles. Again, I would never use twin torsion axles without some accommodation for load sharing. Kenneth Gregory August 5, 2020 @ All spindle axles are designed for easy removal and maximum strength. This is my warped opinion: They are trying to make the trailers cheaper and lighter while ignoring that trailers do not travel on even flat ground all the time. 100% of the load is shared by the 4, and the attitude (pitch and yaw) are controlled by the position of the 4 wheels. As in the article, independent suspension does not make sense for a trailer. A final choice for trailer axles should balance many factors and, of course, your situation. The big issue is that systems are not over designed as indicated above. The left side wheel. If one bottoms out, it messes up the load sharing. While the volume in one bag increases and the other decreases, pressure stays the same in both. There are, of course, many more options and variations of the above options, but we’ll suffice with this group as they are the most common and most easily available. The classic example is pulling into a gas station. You can see that they do not link in any way — meaning they are independent. This customer reports that poor road surfaces make the trailer dangerous to pull. 3.) What are your thoughts about putting an air bag on each end of the of the walking beam? Right? Maybe, to fix an existing problem, the hubs, bearings and tires can be changed to beefier versions? A reason to use slipper style springs is the pinning of the back axle springs to a more supportive front piece. (Slipper shown here, eye-eye style shown below in the image for Hybrid.) . Torsion Axles In Tandem or Triple. If the tires are rated for the axle, then they are also overloaded by Twice.