[xxxjecxxx]

Found this amazingly simple video explaining how and why a differential works! Obviously technology has changed a bit since then but the foundation is there.

[kent11202]

Originally Posted by xxxjecxxx

Found this amazingly simple video explaining how and why a differential works! Obviously technology has changed a bit since then but the foundation is there.

Inasmuch as most people have no idea whatsoever how they work, this actually is a very informative video (once you are into it about 2 minutes).

[itrocks4u]

great explanation!

[spuntyb]

Also some great black and white videos out there from the same era on how automatic transmissions work. Spoiler: Magic and unicorn tears

[chums]

I was into 1/10 scale RC cars and was always impressed by the tech and materials they used.

Ball differentials have been in RC cars for decades but never understood why they never made it to full scale cars as ball diffs work smoother than gear diffs.

The red pointer represents the direction of the car.

[ka24682468]

awesome video, thank you for sharing it

[mike@x-ph.com]

Very interesting video, thank you for sharing

[Aatish]

lol, they used this video in every mechanical engineering course I took.

[xxxjecxxx]

Originally Posted by Aatish

lol, they used this video in every mechanical engineering course I took.

Electrical and Computer engineering here... All I saw was semiconductor production and I think that was the ONLY video lol.


Glad you guys find it as interesting as I did!

[casualDIYer]

If you want to try a vehicle without a diff, try a go kart. Lots of fun but there wouldn't be a single auto insurance company in business if all cars drove that way. Diffs are great but a solid rear axle is tops for fun!

[tony176000]

I love simple explanations this this. It really leads to deeper understanding.

[casualDIYer]

Now that you've had an education in what a differential is, do a Google search on TORSEN differentials and Limited Slip Differentials, for a mind blowing experience.

I believe the video shows an 'open' differential, which at first glance seems to solve all of life's problems. Unfortunately, because open diffs allow one wheel to 'slip' (rather than drag) the normal distribution of torque (50/50) among two wheels becomes more like 50/0. This happens even when going around a turn. Racers call this phenomena 'Last Place'.

The 50/0 complex of Open Diffs is a complete barrel of laughs in all sorts of situations: Wheel up in the air? Send torque to wheel spinning the fastest (i.e. the wheel least resisting). That will fan your burning hot anger. One wheel stuck on ice? Great, an open diff will spin that wheel too so everyone can now peer out their window to see your misfortune and secretly mock you as 'The dumbass who should have got snow tires'.

If you want to performance mod your car, as tempting as 'flames' on the side of your car or a wing bigger than that found on most modern passenger jets might be, go for a limited slip diff (LSD). Instead of one-wheel drive around a curve at 50/0 power with an open diff, you get 2 wheel drive at 70/30 (or some other ratio adding up to 100%). Most modern BWMs use an Electronically Limited Slip Differential (eLSD). Now, it's hard to say exactly how eLSD and LSDs differ. One might infer that if an eLSD is in a 320i and an LSD is in an M3 LSDs are better but Ferrari uses an eLSD. Probably has a few more features I'm guessing. But even a cheaper eLSD will out perform the lowly open diff. Have access to a non-M e46? (open diff) and an F30 (eLSD). Drive them back to back and you will likely notice the F30 tends to scoot around a corner a bit quicker than the e46 even if the F30 has a bit less power. There are a few reasons for this but a critical difference is in the differentials. Swap out that eLSD with an LSD and your car will almost be in a different league of performance and you haven't even melted a piston with Bob's Gogo Juice or SlagMyEngine Power Performing Chips.

Diffs make a BIG difference.

[SFM2C]

Thanks!

[oceanview]

menncars great post so far, just two adds:
1. the E46 also has eLSD (at least mine had), but eLSD of F30 has improved.
2. eLSD as on the F30 non-M is a marketing phrase. All it does is braking down the spinning wheel. (Regular brake is beeing used). So the Diff is plain open, compared to the eLSD on an F30 M-Car.

[casualDIYer]

Originally Posted by oceanview

menncars great post so far, just two adds:
1. the E46 also has eLSD (at least mine had), but eLSD of F30 has improved.
2. eLSD as on the F30 non-M is a marketing phrase. All it does is braking down the spinning wheel. (Regular brake is beeing used). So the Diff is plain open, compared to the eLSD on an F30 M-Car.

Hey Oceanview, did you have a 330i? I had a 2005 325i and I was told it was an open diff. I know the 330i had a bit more kit (besides power) over that of the 325i or 320i.

You are right, the non-M F30 uses braking to send a bit of extra torque to the wheel spinning fastest (so instead of 50/0 you get 70/0 around a turn). I couldn't believe how fast I wore out the inner rear pad of my current f30. I don't know if the F30's eLSD is clever enough to figure out what to do if a wheel gets lifted or stuck on a slippery surface. Although we get (or used to get) winter, with snows even my RWD rarely gets stuck and never to the point of needing assistance. I chocked up the reason for never getting stuck to the tires (X-Ice3), not the eLSD (= elcheapo LSD). I wonder if it made a difference?

I'd love an LSD in my current f30 but I wonder if the M LSD would fit or I'd have to go after market.

[rking117]

Originally Posted by chums

I was into 1/10 scale RC cars and was always impressed by the tech and materials they used.

Ball differentials have been in RC cars for decades but never understood why they never made it to full scale cars as ball diffs work smoother than gear diffs...

I suspect it has to do with weight of the vehicle.

[oceanview]

Originally Posted by menncars

Hey Oceanview, did you have a 330i? I had a 2005 325i and I was told it was an open diff. I know the 330i had a bit more kit (besides power) over that of the 325i or 320i.

I had a 330i E46 (as now added to may signature).
Both E46 and F30 have an open diff. With "eLSD" I ment actually the DSC and DTC which is part of both of those cars as well.

Originally Posted by menncars

You are right, the non-M F30 uses braking to send a bit of extra torque to the wheel spinning fastest (so instead of 50/0 you get 70/0 around a turn). I couldn't believe how fast I wore out the inner rear pad of my current f30. I don't know if the F30's eLSD is clever enough to figure out what to do if a wheel gets lifted or stuck on a slippery surface. Although we get (or used to get) winter, with snows even my RWD rarely gets stuck and never to the point of needing assistance. I chocked up the reason for never getting stuck to the tires (X-Ice3), not the eLSD (= elcheapo LSD). I wonder if it made a difference?

On the RWD DTC will brake down the faster spinning wheel. The other wheel will get more power. I assume other factors like car speed, steering wheel angle and others will also influence how the DTC regulates.

That's where a mechanical LSD acts just based on wheel torque or wheel speed differences. And you can feel the difference (especially on dry or wet roads. Probably less on snow, when wheels are spinning anyway)

Originally Posted by menncars

I'd love an LSD in my current f30 but I wonder if the M LSD would fit or I'd have to go after market.

If you are talking about the LSD which is part of the F80/F82 M-Cars. It has also electronic components. It will probably be very difficult and expensive to get the M LSD and all electronics into a F30.

My experience with the E46 DTC is, that after an intensiv drive on snow roads, the (rear) brakes gets hot and the DTC will be deactivated. (Error shown in the dashboard)
From that point on, car has just an open diff. Even with snow chains on, the spinning wheel will get all the power.
I've not had that situation yet with my F30. But in fact, also those rear breaks will get to hot at some point, causing the same situation as in my E46.

DTC is a good helper, but it's not making an mechanical LSD obsolete (Also if BMW marketing would like to make us believe so.)