OPEN diff vs LSD vs WELDED diff - VISUALLY + In depth EXPLAINED - Version 2
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Published 2021-04-09
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This is version 2 of this video. The previous version was deleted as it had some misleading things in it. I also regret being a bit stubborn when defending the merits of my previous explanation, and although it did have some merit it was ultimately misleading and some parts were outright incorrect. I would like to thank all the commenters for pointing out the mistakes. Although some were rude and aggressive a great number of people was very constructive, mature and polite when pointing out the mistakes in the previous video, and to these people I offer my sincere gratitude. I don't shy away from admitting my mistakes, I see them as an opportunity for growth and work hard to correct them.
The mistakes in the previous video were: 1. Open diff sends more torque to slipping wheel. 2. Welded diff splits torque 50/50
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So let's start with the open differential. This is something you can find in the vast majority of cars on the road today. Especially in non-performance or „normal“ cars. The differential has one purpose. It allows you to take a corner. In other words a differential enables two wheels on the same axle to rotate at different speeds.
So what would happen if we didn't have a differential? Because the two wheels are now physically joined together they are unable to rotate at different speeds. Because of this the wheels have to make up for the difference in speed by skipping, hopping or sliding. You can experience this if you take a real car with a welded differential and try to negotiate it around a parking lot.
Of course this isn't a desirable scenario as it not only wears out your tires faster but it puts a lot of strain on your axles and other drive-train components. On top of this it can make a lot of noise and draw unwanted attention. Obviously none of these issues will be present with a normal open differential.
To better understand the limited slip differential we have to go back to the open differential. If there's one thing you have to remember about the open differential is that torque being sent to the wheels through an open differential will always look for the path of least resistance. So if one wheel is easier to turn or slip that wheel will limit the amount of torque available to the other wheel. If one wheel is on ice and the other is on asphalt and it takes only 15 Nm to break traction on the ice wheel than the open differential will prevent the wheel on asphalt to receive more than 15 Nm as well. Now let's replace the open differential with our limited slip differential. As you can see the wheel with low traction doesn't spin at all and the vehicle takes of immediately. The answer to how the LSD achieves this is in the name itself. Limited slip differential. It limits wheel slip.
So in the same scenario with one wheel on ice the limited slip differential will not allow the slipping wheel to waste the torque potential of the engine. It will not allow the slipping wheel to prevent the wheel with traction from receiveing more torque. So if it takes 15 Nm to break traction on the ice wheel the other wheel will not be limited to 15Nm as well, instead the limited slip differential will bias torrque to that wheel and that wheel will receive more torque. A torque biasing differential can have a biasing ratio as high as 4:1. This means that if it takes 15Nm to break traction on the ice wheel the LSD can bias as much as 60Nm to the wheel on asphalt which is more than enough to get the vehicle moving quickly and without slipping.
The welded differential effectively turns the rear axle into a solid common axle and the entire rear axle behaves as a single unit, which means that the low friction on one wheel becomes irrelevant because 100% of the engine's torque is available to both wheels all of the time.
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#d4a #LSD #weldeddiff
00:00 Intro-ish
02:43 Getting unstuck
11:39 FF vs FR vs MR
All Comments (21)
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Version 2 of this video. Previous version was deleted because it contained some misleading information. Please see description for details. -
I’ve been an automotive master technician for 20 years and this video does a good job of explaining a subject a lot of people have a hard time understanding. Everyone wants to weld the differential until they realize you can only drive it in a straight line to keep it from breaking.
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It is only human to make mistakes. Don't feel bad about it, because at least for me your channel has been the most informative car channel of the whole youtube.
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Who watched the entire original, but is going to watch the entirety of version 2.0 anyways? 🙋♂️
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Good on you for redoing this, I was going to suggest reworking of a couple of parts. Really appreciate you being big enough to correct mistakes, it's a great sign of your personal integrity.
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That’s true dedication to your channel posting an improved video of an already really well explained video
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I absolutely 100000% know that every car enthusiast started as a Lego builder as a kid
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Not only do I find this video factually correct, but I actually find it easier to understand :) very good job on the improved version!
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It is so nice to see people, that are not afraid of their mistakes, but they go ahead and correct them. We are all here because we like, how you explain thinks and your lego examples are great.
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The quality of the video production as well as the way a fairly complex vehicle engineering subjected was presented is impressive. I've been enjoying the channel for a while now but this one stands as one of the bests. Congrats for the hard work, really looking forward to the LSD types video and how they work!
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Differentials are probably one of my favorite car engineering things to understand, and this video does a good job of explaining it.
I have an RC car that's 4WD, open differentials front and back... until the rear diff stripped out, so I filled it with JB Weld. It's also great for explaining differentials. -
There is one element you missed when explaining the welded Differential during corner exit. With the Weight Bias shifting to the rear wheels, the traction is less on the front than both of the rear wheels so the traction can cause the Front Wheels to be the ones to slip, not the inside rear. As such the car will now understeer drasticly.
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Bro, I've been trying to understand diffs in general for years and this is the easiest video I've seen to really understand what differentials do and the implications of the different types that exist. Thanks so much!!!
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I watched the first video all the through and thought it was a little oversimplified in some places, but pretty good. This video is a significant improvement, well done.
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My jaw dropped when i saw an LSD built out of Legos...
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your channel is one of the most informative and the videos are all very well made, even if you decide to remake them. keep it up!
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This channel lives up to its name without a doubt. Thanks for the clear and concise information you bring forth. Im assuming you're building a 3sgte. The aw11 chassis will really move with this setup as its considerably lighter than the sw20. Good luck with your project 👍
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One of the best channels for understanding vehicle oriented engineering concepts. Thanks for the content and your dedication.
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I found you channel a week ago. I'm really happy that I did. You really do make awesome and highly detailed videos.
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A second video on diffs, a second like!
Thanks for your dedication!
