Trailer and cargo masses.

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Cadde
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Re: Trailer and cargo masses.

#91 Post by Cadde » 28 Oct 2019 11:51

Center of mass determines the "tippyness" of a trailer. Having it high up means it will want to go bottom side up.
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GT182
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Re: Trailer and cargo masses.

#92 Post by GT182 » 30 Oct 2019 00:36

I believe the cargo mass CG was recently changed with a physics update by ATS, and was moved a bit too high. Now certain loads that have a lower center of gravity, now causes a great deal of pucker power on corners I used to be able to take at 65mph. Could a mod be made to lower it back down a bit?
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Re: Trailer and cargo masses.

#93 Post by Arayas » 12 Apr 2020 21:30

The problem is not the cargo or masses but the way SCS implemented that into the game.
IRL a 20 tones cargo brakes your motor uphill (480-500HP) and you must be very careful to adjust to the corect gear to finish climbing that hill. Changing gears uphill? Possible but not recomended because you must go 2 gears down instantly.
Downhill, the oposite story: the trailer is pushing you hard, the retarder will lose the battle pretty fast (that's for nice inclinations anyway) and if you are too hard on brakes you will lose direction. If you decide to slow down your truck just late, in the middle of the curve downhill...bye bye.
You have to keep the truck in control all the time to avoid later surprises.

In ETS2 everything is nice and peachy, you go up and down with 20 tones like you have wings or ultimate brakes. And i'm not talking from books, but from real experience.
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Re: Trailer and cargo masses.

#94 Post by GT182 » 12 Apr 2020 21:45

I don't think anyone at SCS has ever driven and 18 wheeler. If they had then they'd understand why we ask these questions. After all, they say they support realism, but in they long run they don't. As in real life SCS needs more private scales in-game and more truckstops with scales. But then again there's no fines for over weight loads.
Gary - CB code name: CW
Formerly from Northern NY on the Ontario/Quebec borders.
I've hauled ass down the road to deliver new cars and trucks, fuel, freight, and produce. Now I'm addicted to ATS doing the same thing in a simulation. :roll:
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Re: Trailer and cargo masses.

#95 Post by Max » 13 Apr 2020 08:31

not exactly 18 wheeler, but few people here has lot of experience with trucks. i must admit all those experience are with european trucks and those are technically build as very safe ones (you can drive it with almost no skill, really).

inaccuracies are rather math and physics ones. we are missing few mechanisms in physical simulation and fake it by tweaking of other params. which logically make sub-perfect behavior. some of such simulations are quite a burden to CPU as it might be really complex math. and last, we need the game to be playable for majority of people. no one would buy unplayable game, they wont accept it just because he/she do not understand truck technicalities. so we have to carefully balance gameplay and simulation level.
but we are still working on improvements in both.
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Re: Trailer and cargo masses.

#96 Post by dahaka » 13 Apr 2020 15:55

@Arayas Downshifting uphill is completely normal. I've never seen a trucker slow down and put the truck in a certain gear to climb a hill. Standard tactics include approaching the hill at the maximum possible speed, then downshifting all you need to till you reach a point at which your truck steadily climbs at a certain gear and a certain RPM. This point varies according to the weight of your cargo, and the incline you are climbing, and is near damn impossible to calculate beforehand, that is why no trucker slows down and shifts down to the "right" gear beforehand, but during the climb.
I've been lucky enough to drive a manual truck, a euro 6 DAF 460, and found the best thing to do under maximum load is to shift half a gear down (12th to 11th), as I approach the hill, which puts the RPM at around 1800, then as the RPM drops during the climb to about 1200 shift down a whole gear (11th to 9th) and then rinse and repeat every time your RPM drops to 1200. The optimal RPM which is 1000-1500 on most trucks is better ignored during hill climbs, as you have to account for the loss of momentum while shifting down. If you wait for the RPM to drop to 1000, by the time you downshift you will have lost enough momentum that the RPM will be only 1100-1200, instead of 1500 if you would have shifted earlier, which then will force you to downshift one more time, losing even more momentum.
Most automatic transmissions make this exact same mistake, which is the reason why I despise them, among other ones.
As for going down 2 gears, I definitely wouldn't recommend that. unless you are using the wrong definition. Most trucks have 6 gears, with a splitter, from 12 to 11 is only half a gear, and its roughly 300 RPM of difference between the optimal range. a whole gear would be 600 RPM of difference, and 2 whole gears would be about 1600, accounting for how gears work. If you downshift 2 whole gears at 1000 RPM (minimum RMP before the engine starts to lose torque) you would end up at 2600 or more, where the engine again doesn't have too much torque to offer.

Going downhill the retarder can help you hold a steady speed even at maximum weight, as long as you are in the correct gear, and you use the retarder the right way. Please note that a lot of drivers are confused about the terms here also, there are three types of continuous breaks, the retarder (could be electromagnetic [mostly a thing of the past] or hydro-static) the jake break AKA valve break, and the exhaust break.
Not every truck is equipped with all 3, in fact, most trucks come with one or two of these systems. For example the Mercedes Actross I was driving came with an adjustable jake break, and an exhaust break.
These continuous breaks function best when the engine is running at high RPM, which is why trucks with automatic transmission will shift down as soon as you activate them, and put the RPM to about 2000 or more. Retarders are adjustable, so when you go downhill, you switch them on and increase their power as much as you have to, to help you keep a steady speed downhill. If you reach the maximum retarder efficiency, and the truck is still accelerating downhill, you are supposed to switch on your exhaust break, which usually only has an off and an on mode, and it will do the trick on most inclines. Currently we don't really have huge inclines in-game, so the way retarders work is quite realistic. If all else fails, you are supposed to use your normal break to help your retarder out. Retarders are not meant to replace regular breaks, only to reduce their use downhill and prevent them from overheating from continuous use.
Best tactic I found was to approach the downhill section, and immediately downshift a whole gear, which puts the RPM at about 2000-2200, then start gradually activating the retarder. Then if I have to activate the exhaust break, I've ascended and descended mountains in Greece, Austria, Switzerland, Spain, France and Germany with no problems whatsoever, and that only with 460 HP. And sometimes overloaded with hanging meat as well.

There is also a huge difference between an experienced driver who knows his trucks inside out (gear ratios, rev-matching etc.) and one who doesn't. You'd be shocked how many "drivers" nowadays have no idea about shifting a truck and using a clutch, as most European companies opt for automatic trucks.
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Re: Trailer and cargo masses.

#97 Post by Some newbie driver » 13 Apr 2020 17:05

dahaka wrote: 13 Apr 2020 15:55Most automatic transmissions make this exact same mistake, which is the reason why I despise them, among other ones.
One bus company chief mechanic told me a few years ago they program the automatic gearboxes of every bus depending on the profile of their route. Because some lines have a very plain profile on the main part of the city where others are constantly climbing up and down strong hills on the outskirts. By the way it explained that, I understood that they change the points where the gearbox ups and downs gears to avoid those problems you mention.

I understand that isn't feasible to do on a truck unless used on a very regular line. What I would had expected is, with all the electronics that vehicles have actually, that the trucker could switch between different "gear change maps" pre-loaded. Wouldn't that help to avoid those problems with automated gearboxes? Or is that already a thing but not on most older and maybe still widespread gearboxes (that you could be referring to)?

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Re: Trailer and cargo masses.

#98 Post by xXCARL1992Xx » 13 Apr 2020 17:12

trucks these days "know" when they approach a slope and shift according to it to get up with ease and the moment they are on the highest point they start to shift again and use the retarder to get down without too much speed, ofc when you use cruise control
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dahaka
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Re: Trailer and cargo masses.

#99 Post by dahaka » 13 Apr 2020 17:41

Modern trucks have an option to switch to semi automatic mode, but a lot of companies have that mode disabled, because they either don't trust their drivers one bit, or that 0.2 cents they will loose in fuel is deemed too much by them. Last new truck I drove was a Mercedes Actross 450 euro 6, I believe it was 2017 model. The gearbox was abysmal, the truck supposedly is equipped with a special GPS map that knows and reads exact geographic data like how steep inclines and descents are etc. but while my fully loaded DAF with just 10 more HP could climb a hill at 50-55 km/h the Mercedes with its fancy automated systems would slow back down to 30km/h. Granted it burnt about 1 liter per 100kms less than the DAF, but was massively frustrating to drive. (not to mention all the creaking and rattling of plastic of which the truck cabin is entirely made off)

I'm not sure about city buses, but I've never seen a manual city bus. even really old 25-30 year old city buses I've ridden had an automatic transmission. Understandably so, because operating a clutch for 9-10 hours a day inside city traffic every day is not something anybody want to go through. Not sure how they are ordered and configured either.
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Re: Trailer and cargo masses.

#100 Post by Arayas » 13 Apr 2020 18:34

dahaka wrote: 13 Apr 2020 15:55 @Arayas Downshifting uphill is completely normal. I've never seen a trucker slow down and put the truck in a certain gear to climb a hill.
Who said something about slowing down? You use the momentum to go up until that momentum is gone, then use the gear box to continue. If we talk about "half-gear" gearbox, try passing from 6 to 5.5 when your truck it's already loosing force going already 1200RPM and tell me how that goes.
Two speed down means in this case from 6 to 5 (jumping 5.5) not from 6 to 4. But manual gear boxes are in plenty of forms and configurations. The disscution was not about technique of driving a truck IRL, it was about unreal masses in ETS and about SCS missing totaly how a truck "feels" when you are behind the wheel.
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