RE: Ask the expert: All you want to know about differentials

[Yorkshirepud]

As there is little cost difference between manufacturing a normal diff and a limited slip diff, why doesn't everyone just fit one as standard? Are there some drawbacks that car hacks never mention?

[BarnatosGhost]

Yorkshirepud said:

As there is little cost difference between manufacturing a normal diff and a limited slip diff, why doesn't everyone just fit one as standard? Are there some drawbacks that car hacks never mention?

For Carol Normal, spinning away excess power through an unweighted wheel might be the safest course of action?

And cost savings...

[Chunkychucky]

Why does BMW insist on fitting it's active M differentials as opposed to a conventional mechanical LSD with a fixed locking action, as was the case with the older M cars (E28, E30, E34 etc)?

[Marf]

Chunkychucky said:

Why does BMW insist on fitting it's active M differentials as opposed to a conventional mechanical LSD with a fixed locking action, as was the case with the older M cars (E28, E30, E34 etc)?

I believe the active differentials are able to alter the ramp angles on the fly, i.e. you can adjust the LSD from pretty inoffensive to full on lock.

[rikkiseddo]

Is McLaren's limited slip differential-less MP4-12C the future for sports/supercars? And is mechanical Torque-Vectoring (a la Saab XWD and Audi's sport-diff) better than electronic ABS based torque vectoring?

[jellison]

jmjo88 said:

Will brake-steer systems replace mechanical diffs in the coming future?

Er no.

[V8mate]

Strawman said:

Dagnut said:

3) Do sheep get really heavy when it rains?

They get heavier, but not as heavy as you'd expect due to water repelling oils in the wool.

Surely the fact that they shrink compensates for the additonal weight?

[Captain Muppet]

V8mate said:

Strawman said:

Dagnut said:

3) Do sheep get really heavy when it rains?

They get heavier, but not as heavy as you'd expect due to water repelling oils in the wool.

Surely the fact that they shrink compensates for the additonal weight?

ROFL

[Dagnut]

V8mate said:

Surely the fact that they shrink compensates for the additonal weight?

I got caught in the rain in a woolly jumper and it weighed a ton..from personal experience I think they would....I could go in a field and try picking one up when it's raining but it may look a tad suspicious...I don't think anyone would buy it.

[engineer666]

Why don't F1 cars have diffs (as we know them) anymore or flywheels for that matter...b-----ks missed the boat.........

[dot1989]

My Megane R26 has a Mechanical LSD however, through regular "commuting" daily use does it provide much benefit? Or do I need to take it along to my local track? FWD FTW!

[RenesisEvo]

engineer666 said:

Why don't F1 cars have diffs (as we know them) anymore

They do have differentials, they are packaged tightly in the gearbox.

[freecar]

kedaha said:

This might make me sound stupid, but for a long time I found it hard to actually fully grasp how and diffs do.

A 1930's video helped me figure it out
http://www.youtube.com/watch?v=K4JhruinbWc&lis...

This video should be compulsary viewing for anyone purporting to be a petrolhead!

[Triumph Man]

freecar said:

This video should be compulsary viewing for anyone purporting to be a petrolhead!

Well I'm going to spit my dummy out, I posted it first I did!

Anyway, more spokes!

[jagfan2]

Marf said:

Kozy said:

For a FWD racing car, is a helical or plate diff a better option?

Do Quaifes/Torsens/helicals work under braking?

Helicals require both wheels to be loaded in order to work, i.e. if one wheel is in the air, then no power is being transmitted to either.

Plate type diffs do not have this little foible.

Plate diffs have the same issue, but get over it with preload (a base level of locking). Torsen did develop a preloaded unit for racing, but as its less tunable and heavier, everyone stuck with plate diffs

Torsens are generally better for road cars as they are more predictable, and dont wear out as quickly. And you can easily fix the unloading issue by applying brake torque to the lightly loaded issue when it starts to spin up again. Audi us this principal a lot, and have taken it further with brake torque vectoring, as have Porsche

No one has asked anything about Torque vectoring diffs, this is the future and where the clever stuff happens

Edited by jagfan2 on Thursday 23 February 22:49

[jagfan2]

jatinder said:

I've heard you can knacker your diff, if just messing about in the snow?

Is this true or rubbish? I heard it the Integra forums.

I think rubbish, but still just wondering….

Its not, torsens can overheat (as they use mechanical friction to lock the diff) with prolonged and high speed differences between the wheels. If it gets too hot the oil breaks down and they start to grind metal on metal. This does take a lot of time, and requires some grip on the wheels, so its rare but is possible, know at least 2 people it happened to though, but both exceptional circumstances. Its possible to do with excessive track use with tight corners and poor/used oil too

[Kawasicki]

jagfan2 said:

Marf said:

Kozy said:

For a FWD racing car, is a helical or plate diff a better option?

Do Quaifes/Torsens/helicals work under braking?

Helicals require both wheels to be loaded in order to work, i.e. if one wheel is in the air, then no power is being transmitted to either.

Plate type diffs do not have this little foible.

Plate diffs have the same issue, but get over it with preload (a base level of locking). Torsen did develop a preloaded unit for racing, but as its less tunable and heavier, everyone stuck with plate diffs

Torsens are generally better for road cars as they are more predictable, and dont wear out as quickly. And you can easily fix the unloading issue by applying brake torque to the lightly loaded issue when it starts to spin up again. Audi us this principal a lot, and have taken it further with brake torque vectoring, as have Porsche

No one has asked anything about Torque vectoring diffs, this is the future and where the clever stuff happens

Edited by jagfan2 on Thursday 23 February 22:49

From my experience it works great for sub limit agility, but (so far) I've been unimpressed with the results of torque vectoring on limit driving.

For limit driving how is it logical to add to the vehicles kinetic energy? You've gone in too fast? Here is some more speed(energy)!

Linking active steer seamlessly to the DSC package is, for me, where the clever stuff happens.

[rhinochopig]

Kawasicki said:

jagfan2 said:

Marf said:

Kozy said:

For a FWD racing car, is a helical or plate diff a better option?

Do Quaifes/Torsens/helicals work under braking?

Helicals require both wheels to be loaded in order to work, i.e. if one wheel is in the air, then no power is being transmitted to either.

Plate type diffs do not have this little foible.

Plate diffs have the same issue, but get over it with preload (a base level of locking). Torsen did develop a preloaded unit for racing, but as its less tunable and heavier, everyone stuck with plate diffs

Torsens are generally better for road cars as they are more predictable, and dont wear out as quickly. And you can easily fix the unloading issue by applying brake torque to the lightly loaded issue when it starts to spin up again. Audi us this principal a lot, and have taken it further with brake torque vectoring, as have Porsche

No one has asked anything about Torque vectoring diffs, this is the future and where the clever stuff happens

Edited by jagfan2 on Thursday 23 February 22:49

From my experience it works great for sub limit agility, but (so far) I've been unimpressed with the results of torque vectoring on limit driving.

For limit driving how is it logical to add to the vehicles kinetic energy? You've gone in too fast? Here is some more speed(energy)!

Linking active steer seamlessly to the DSC package is, for me, where the clever stuff happens.

These chaps disagree.

Watch from about 5:50m http://www.youtube.com/watch?v=0YJ-9GE0Re0 or skip to the end to see their conclusions.

[enneffo]

That Chrysler video is brilliant - especially the nutty bit at the end when they're dancing on the wheels

There seems to be perpetual confusion about differentials, which is odd since all cars have one (until someone welds it up for mad drifting yo!). I think the way motoring journalists write about them doesn't help - 'mechanical diff' is something of a tautology.

Did anyone ask about 1/1.5/2-way limiting action?

[Marf]

jagfan2 said:

Plate diffs have the same issue, but get over it with preload (a base level of locking). Torsen did develop a preloaded unit for racing, but as its less tunable and heavier, everyone stuck with plate diffs

Torsens are generally better for road cars as they are more predictable, and dont wear out as quickly. And you can easily fix the unloading issue by applying brake torque to the lightly loaded issue when it starts to spin up again.

Thanks, that's interesting, I've had both plate and torsen type diffs in FWD turbocharged hatches, both were effective but the road manners of the torsen(was an ATB copy) were far far better.

You didn't really know it was there until you threw the car at an apex and it just stuck and pulled you through the corner.