RWD + LSD, how important?

[PetrolHeadSeb]

So I'm (still) looking at switching to RWD and at the moment I quite fancy an E36 328i Sport.

As I understand, early models had LSD's fitted, whereas later ones didn't and had traction control instead.

I've driven a few RWD cars with and without LSD's in the past, but due to my inexperience of RWD and it not being the right time or place, I've never pushed hard enough to be able to tell what difference it makes.

As a FWD hatch driver, I understand the benefits of a LSD in this scenario, but what difference does it make to a RWD car with average power output?

[V8NRG]

Normal driving - you won’t notice the difference.
Hooligan mode - useless without a LSD (IMHO).

[kambites]

In a front engined car, it's quite noticeable because they tend to have more traction problems. It really depends on the kind of driver you are though, you can't easily power slide withing one.

[nonuts]

It works rather well in my M3, I'd say get one with an LSD if you can.

[Crusoe]

much better in the snow with a lsd too

[PetrolHeadSeb]

So would it be fair to say having a LSD fitted makes things more progressive and controllable?

[wolves_wanderer]

V8NRG said:

Normal driving - you won’t notice the difference.
Hooligan mode - useless without a LSD (IMHO).

This

Crusoe said:

much better in the snow with a lsd too

And this

[kambites]

PetrolHeadSeb said:

So would it be fair to say having a LSD fitted makes things more progressive and controllable?

"Progressive" yes, "controllable" I think is debatable. It's much harder to get yourself into trouble in a powerful RWD car with an open diff because it essentially acts as a form of traction control when cornering - if the inside wheel loses traction (which it will, since there is less weight on it) the outside wheel loses drive.

I'd say that for the huge majority of drivers, an open diff is more controllable.

[nonuts]

wolves_wanderer said:

Crusoe said:

much better in the snow with a lsd too

And this

However it'll still be crap if there's proper snow without winter tyres.

[WeirdNeville]

For 99% (or more) of the time it makes no difference at all. In road driving I'd say it never makes a real difference unless you play with fire the whole time.

The 328i in particular is not a light car, and it has wide rear wheels and good balance. It simply doesn't light the rears up, and I'm not sure I'd want to push it hard enough away from a track to light up the inside rear on cornering. I can't say I think the car would benefit from an LSD, especially when to get one worth having, you'd be spending £500 or doing mods to the car (M3 LSD isn a direct fit, the propshaft is different and the ratio is different IIRC).

In the 200SX however the viscous diff was needed - the car felt 'tail end light' and would wag it's tail at any opportunity. The diff just helped
maintain forwards drive even when one rear wheel was scrabbling for traction. That said, my one spin in that car probably wouldn't have happened if the car had either an open diff OR some form of traction control system.

MR cars don't really need LSD's until you get to high power and track work, IMO, as the weight of the engine keeps
both wheels in traction for the most part.

So, LSD important for a performance car, not so important for day to day use.

[PaulG40]

So how would having an LSD be more beneficial than a car that had traction control/esp/whatever it wants to be called? i.e. if it had TC anyway?

[Crusoe]

PaulG40 said:

So how would having an LSD be more beneficial than a car that had traction control/esp/whatever it wants to be called? i.e. if it had TC anyway?

In low grip when the esp/tc would be trying to stop the individual wheels spinning a LSD would spread the power to the wheel with more grip keeping your forward momentum. Difference between getting your car going in the snow and being stuck on your drive. Also stops your brakes overheating when you are fooling around and lets you power oversteer when you switch the tc off.

[JonyTVR]

nonuts said:

wolves_wanderer said:

Crusoe said:

much better in the snow with a lsd too

And this

However it'll still be crap if there's proper snow without winter tyres.

Well I would have to disagree, my E36 325i with LSD was fantastic in last years snow and never once failed to get me to where I was going, even managing to get off our driveway which is quite steep, whilst a friend couldnt even get his off a flat driveway with no LSD. I was running 245/40/17 falkerns on the rear so certainly not winter tyres.

IMO LSD makes things more controllable once you've lost control, if that makes sense.

[nonuts]

WeirdNeville said:

For 99% (or more) of the time it makes no difference at all. In road driving I'd say it never makes a real difference unless you play with fire the whole time.

The 328i in particular is not a light car, and it has wide rear wheels and good balance. It simply doesn't light the rears up, and I'm not sure I'd want to push it hard enough away from a track to light up the inside rear on cornering. I can't say I think the car would benefit from an LSD, especially when to get one worth having, you'd be spending £500 or doing mods to the car (M3 LSD isn a direct fit, the propshaft is different and the ratio is different IIRC).
...
So, LSD important for a performance car, not so important for day to day use.

Not sure I agree, I know I'm not comparing apples with apples here, but in my M3 the LSD does help a lot especially when it's pissing with rain, certainly makes pulling out of junctions etc. easier when the conditions are crap.

[RobM77]

I've not owned a FE/RWD car with an LSD, but I've owned an E36 328i Sport, as well as a 330ci, Z4C, 330ci, 325i and 320d. The Z4C at 1390kg and 265bhp was bordering on needing an LSD in the wet, but I didn't feel the 1320kg 197bhp 328i needed one at all really. I guess if you were driving on track you might need one. As I say though, I've yet to sample a BMW with an LSD, so can't comment on how effective they are. Do watch out for turn-in understeer though if you test drive one (or at least a tendency for the nose to resist turning) - this is a classic problem with LSDs.

edited to add: I was wrong above - I've driven an E46 M3 with an LSD. It was absolutely marvellous thing is, it has a lot more power than the cars I've described above. I got back in my Z4C after the test drive and drove the same roads and felt that an LSD would be nice, but not essential. A 328i? I'm not sure it's necessary at all.

Edited by RobM77 on Thursday 3rd March 11:21

[nonuts]

JonyTVR said:

Well I would have to disagree, my E36 325i with LSD was fantastic in last years snow and never once failed to get me to where I was going, even managing to get off our driveway which is quite steep, whilst a friend couldnt even get his off a flat driveway with no LSD. I was running 245/40/17 falkerns on the rear so certainly not winter tyres.

IMO LSD makes things more controllable once you've lost control, if that makes sense.

How much snow were you talking about? Mine never stopped me getting anywhere either, however it did need digging out and pushing in the office car park so I could leave, nearly stopped me getting out of a junction on a slight hill, made it take 45mins to go 200meters back to my house the evening the council decided to grit the road and make the 2-3 inches of snow / ice turn to deep slush. LSD doesn't help if there is that little grip.

Agree that is makes it far more controllable though and wouldn't want an M3 or car with similar power without one!

[WeirdNeville]

PaulG40 said:

So how would having an LSD be more beneficial than a car that had traction control/esp/whatever it wants to be called? i.e. if it had TC anyway?

We need to be clear about what systems we're talking about here:
An LSD's basic funtion is to transfer torque to a wheel in traction even if the other wheel is spinning in free air. An open diff would transfer no torque to the wheel in traction in this situation.

Traction control in it's simplest form monitors the driven wheel speed and if it exceeds more than a certain amount over a non-driven wheel, it will throttle back the engine by some means to limit the engines power and hopefully bring back traction by slowing the spinning wheels.

Advanced 'stability' control or ESP will monitor the status of the wheels, and steering inputs, and may be able to apply individual brakes to bring the one spinning wheel under control, thus transfering torque towards the wheel in traction.

Finally, really clever systems may be able to use an active differential to place more torque to the wheel with more grip even before anything starts to slip, to enhance cornering ability and stability for example.

So whilst an LSD can put more power to the wheel in grip, without Traction control that wheel itself may suddenly be overwhelmed, such that neither rear wheel is now in traction and you spin.

LSD's and traction control go hand in hand pretty well - the traction control throttles back the engine to bring total torque within manageable limits whilst a passive LSD distributes it to the grippier wheel. Modern 'ESP' systems can do away with an LSD completely, as McLaren have proved with the MP4-12C. A brake acting individually on the spinning wheel transfers torque back to the grippy wheel just fine, and can be infinitely variable where a mechanical LSD can't.

[NoelWatson]

WeirdNeville said:

e need to be clear about what systems we're talking about here:
An LSD's basic funtion is to transfer torque to a wheel in traction even if the other wheel is spinning in free air. An open diff would transfer no torque to the wheel in traction in this situation.

I think you need to be clear about which type of LSD - a torsen won't help if a wheel is spinning in free air

[Stig]

It also depends on the car. LSD can cause more understeer with the increased 'push' from the rear.

[rhinochopig]

An LSD equipped car is, IMO, more likely to leave you in a hedge than one with an open diff. An LSD equipped car is much much more likely to wag its tail than an open diffed car.

LSDs, are however, much much more fun.