On a semi, on the other hand, turn radius is not an issue.
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On straight trucks, it is indeed to reduce turn radius, by moving more of the total length to the overhang behind the rear wheels, as well as reducing tire drag. Steering on a rear lift axle is fairly common on straight trucks, but never seen on tractors / semis. That's why in my country we said that "curiosity killed the cat" But damm it! I can't sleep well when some doubt remains knocking on the door of my brain. It's probably a subtle detail and, as I'm not a real world trucker, to know it will have no impact for me. Maybe reduce the turn radius isn't so good as it seems at first glance. It has to be some inherent problem in this configuration that makes the other one (the one like modeled on the game) more usual. So, moving the driven axle forwards will reduce the distance with the steering front wheels, thus the turn radius. The turning point is on the driven axle, as the only one not steered. What vantage has put the auxiliary steering axle in front of the driven one? Because put it in the back of the truck (like your second image) will noticeably reduce the turn radius of the vehicle. Am I right? Let's say those stiffness are regulated so every axle takes the load it should to comply with the regulations. The axle with more stiffness on its suspension will take more load. What part of the load will support every axle, when both touching ground, will depend on the suspension stiffness. If the extra axle is lowered, it will take part of the load (for times and places where it should be necessary by regulations, as you said). The load on the axles on both trucks should be the same, right? If the extra axle is raised, all the weight will go only to the driven one. The only difference between them is one is configured as like on ETS2 and the other is like the second image you posted (thanks for find a graphic example!) Lets say you have two 6x2/4 trucks with the same weight and trailers and everything. But I still don't find the logic or I don't understand all what you explained. I supposed there must be a lot of maths involved in the topic, as you said, but I ignored any detail. Thanks for your answer, it solved part of my doubts. If you use a narrower tire for the steer, you would reduce the total weight you may carry on a tandem. Generally you wouldn't use such a wide tire for a steer (other than heavy haul, of course). For this example, if you're using super singles on a tandem, let's do the maths: Four 17 inch wide tires x 500 lbs = 34,000 lbs. Therefore, in order to carry up to 34,000 lbs on tandem axles, you must use twin tires, or use super singles that are 17 inches or wider. In addition to this, every inch of tire width may carry 500 lbs. Bear with me, here's some maths! Under our Bridge Formula, 2 axles ("tandem") spaced between 4 and 8 feet apart (most commonly it is actually 4 feet 4 inches) can carry 34,000 lbs.
![mod bus ets2 mod bus ets2](http://www.ets2world.com/wp-content/uploads/2019/05/VW-IDEALE-770-LB-BUS-FIXED-ETS2-1.35-BUS.jpg)
If you use a skinnier tire for the steer axle, you would actually REDUCE the total weight you are allowed to carry on a set of tandem axles under our Bridge Formula. They've done it like this for a very long time as you can see on this older Mack.Īnd you also asked why not make it a steerable tag axle. ABF for example currently has many trucks in their fleet with the tag axle lifted. However, even though it's more common to have the "pusher" axle lifted, there are some companies in the US that do have trucks configured with the "tag" axle lifted. Specifically, I believe it's 11.5 tonnes or 25,350 lbs on one axle in Europe, compared to only 20,000 lbs on one axle in the US. I'm making an assumption here but since Europe allows significantly higher axle weights compared to the US, it would seem to me that you guys have more leeway in how you guys configure your axle setups.
![mod bus ets2 mod bus ets2](https://fasrlink136.weebly.com/uploads/1/2/5/5/125513681/116222233.jpg)
Yes, you are correct that maneuvering and tire scrub would be worse but properly distributed weight on our trucks is more important because of limitations in our Bridge Formula. Lifting the front axle up (the "pusher" axle) shifts the weight rearward and thus puts more weight on the drive axle. In the context of American trucks and our Bridge Formula, it's always about weight distribution. I've responded to many questions about American truck configurations and weight laws but regardless of the question my answer is almost always the same: Weight distribution.