Limited slip diffs

J

James_G

Member
 Guildford, Surrey
Another day, another article in the motoring press about how, if you're any kind of enthusiast, you must spec an LSD on your next car, in this case relating to an Audi S4

http://www.pistonheads.com/news/default.asp?storyId=25886

Why? In all the time I have had my M I have never turned the DSC off, mainly because it'll happily wag its tail with it on and quite frankly I can't afford to bin it with some heroics. I know what an LSD does, I just can't see how it's feasible to exploit that kind of behaviour that it allows in every day life.

My 02 plate MX-5 had an LSD and other than it making a few grumbling noises in reverse I can't say I ever noticed it. Equally I tracked my 944 S2 and although it didn't have an LSD I can't say I ever missed not having one.

So other than carrying out road tester smoky drifts a la Chris Harris, or if you are doing a lot of track days looking for that last 1/10th sec, what possible advantage does an LSD give in the real world? Somebody help me understand it.
 
I can tell the difference compared to my non LSD 2.5si I had although as you say under normal driving you can't feel it due to the variable set up. The MX5 I tested 5 years ago (latest model) was very noticeable when going round a roundabout as it wanted to go in a straight line as it had a fixed LSD.

I notice mine when pulling away at pace and overtaking on single carriageways where again the car is more inclined to try and go in a straight line.

Probably doesn't help but for me it's like trying to explain torque.
 
not really sure...had an m3 with an lsd and a zed with none, can't say as i noticed masses of difference..as i understand it it helps with more powerful cars going round a band, as the inner wheel tries to push the car 'straight' cos of the lesser distance it has to travel. i am happy to be corrected on that..politely. :)

like how you get the honest answers on here, wack it on PH and you'll get a barrage of numpties who drive to work like jenson button on amphetamine. so they say.
 
I've driven an Impreza in the snow with LSD on front and rear. You really notice it in those conditions. Other than that I can't see the real world benefit for 90% of drivers, under 90% of driving conditions.

However I understand the benefit of the LSD and its use in track conditions


Sent from my iPhone using Tapatalk
 
Yep in snow I can definitely see the benefit, but that's never why road testers insist that as customers, we must have them.

They must think we all should be driving around holding a perfect 15 degree slip on every roundabout. Unfortunately the rather annoying presence of "other road users" makes that a rather risky approach..!
 
Adamski said:
Other than that I can't see the real world benefit for 90% of drivers, under 90% of driving conditions.
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But that's true of many things on modern cars. Not many people will utilise their engine up to red line 90% of the time. Not many people will invoke their ABS 90% of the times that they brake. I bet there are Z4 owners who have never seen their DSC light come on. Not everybody hits Vmax every time they take their car out.

But it's when you are exploiting the full capability of the car that these things can make a small, but useful, difference. An LSD is especially useful when the driven wheels are on surfaces with different traction - for example, when one wheel has gravel under it (as you might encounter when taking a racing line through a bend, rather than the cleaner line that most other traffic will have taken).
 
ZedFourM said:
Adamski said:
Other than that I can't see the real world benefit for 90% of drivers, under 90% of driving conditions.
Click to expand...


But it's when you are exploiting the full capability of the car that these things can make a small, but useful, difference. An LSD is especially useful when the driven wheels are on surfaces with different traction - for example, when one wheel has gravel under it (as you might encounter when taking a racing line through a bend, rather than the cleaner line that most other traffic will have taken).
Click to expand...

In this scenario if you don't have an LSD then the wheel with least traction will spin up compromising traction, albeit briefly. Given enough forward momentum though that's unlikely to pose a serious risk, or is it likely to drag you into the hedge/other side of the road? I've never heard of LSDs being touted as a safety measure particularly.

I suppose the point I'm getting at is this. What can a car fitted with an LSD do that is better than an identical car without one fitted? Does it make it feel better on turn in? Does it improve overall stability? Does it make a car more fun, because the suggestion is that it does but I've never thought "my my, that car is great to drive,it must be the diff"
 
Once you've had a good play with it and done the smokey road test drift though you realise it's one of the most genius bits about the car :oops:

Sure enough you can buy a 3.0si and get virtually all of the performance but this is about extracting that extra tenth & rewarding the driver, & it does it so so well :D
 
James_G said:
I suppose the point I'm getting at is this. What can a car fitted with an LSD do that is better than an identical car without one fitted?
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It gives you traction at both driven wheels, rather than having traction at one and having the other spinning on gravel/grass/ice. So the car fitted with an LSD will be faster over a section of road in these conditions than the one without.

It's not something that's going to be exploited all the time, and you'll need to be getting towards the limits of the car's performance to fully appreciate it.
 
This is quite a cool explanation:

[youtube]lpf2pK-gGKk[/youtube]


& this is what it lets you do in practice:

[youtube]ZvIeBbLceig[/youtube]

:driving:
 
Andy said:
& this is what it lets you do in practice:

[youtube]ZvIeBbLceig[/youtube]

:driving:
Click to expand...

Makes me think that having an ///M in Milton Keynes at 3am could be quite a lit of fun :evil:
 
I guess on an M you would only notice if it was possible to turn the LSD off which I don't think it is unless I am mistaken.

Doesn't DSC on just try to keep the car in the the direction you want with braking and perhaps engine management?

With it off isn't this just disabled? I don't think DSC effects the LSD.

Could be talking s**t so feel free to comment 8)
 
My point about the DSC is that I daren't turn it off for fear of bining the car. As a result I didn't believe that I'd get the benefits of the LSD since the DSC would be intervening first, but based on posts above re traction on different surfaces perhaps there is a benefit.

As for the video of the Z4MR, that's all well and good but I will never ever drive like that on the road. And neither should anybody else quite frankly. That's not to say that I wouldn't probably enjoy it immensely on a closed track with somebody else paying for the tyres.
 
Apart from the aforementioned slip conditions an LSD helps with traction while exiting turns. It helps put down power on exit.
 
+1 ga41

This is why I think if you could turn it off/on with an M you would see quite a different feel to the car and appreciate what the LSD does.
 
On our M's it's a completely mechanical device though. Can't be turned off or on. Always there, always works and provides for endless amusement on wet (QUIET) roads!
 
James_G said:
My point about the DSC is that I daren't turn it off for fear of bining the car. As a result I didn't believe that I'd get the benefits of the LSD since the DSC would be intervening first, but based on posts above re traction on different surfaces perhaps there is a benefit.
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TBH learning the car a bit more with DSC off is a brilliant experience - it's quite a bit different & let's not forget you have nice chunky rear wheels for a small light car, so grip on the whole in the dry is excellent.

I'm not suggesting you go for a midnight donut session, but perhaps try switching it off on a usual journey when it's dry & back on when you reach 50mph+ish (for peace of mind).

Certain things like pulling off from an island quickly can be transformed and if you're used to driving the car with the DSC not cutting in (ie smoothly) you won't break traction unless you force it to. Even then, the point of the LSD if really called to function is to allow slip without spinning the car, so again unless you're really wringing it's neck or you're on part-lock, you'll get a tiny bit of slide, probably ease off, your heart will be racing & you'll have a huge grin.

Clearly the guy on a track wouldn't do that on a road, but he's really sliding.. slide the rear sideways by even a centimeter on the exit of a quiet island and there's no fuss at all, except it might make you book a track day :D :driving:
 
Andy said:
TBH learning the car a bit more with DSC off is a brilliant experience - it's quite a bit different & let's not forget you have nice chunky rear wheels for a small light car, so grip on the whole in the dry is excellent.

I'm not suggesting you go for a midnight donut session, but perhaps try switching it off on a usual journey when it's dry & back on when you reach 50mph+ish (for peace of mind).

Certain things like pulling off from an island quickly can be transformed and if you're used to driving the car with the DSC not cutting in (ie smoothly) you won't break traction unless you force it to. Even then, the point of the LSD if really called to function is to allow slip without spinning the car, so again unless you're really wringing it's neck or you're on part-lock, you'll get a tiny bit of slide, probably ease off, your heart will be racing & you'll have a huge grin.

Clearly the guy on a track wouldn't do that on a road, but he's really sliding.. slide the rear sideways by even a centimeter on the exit of a quiet island and there's no fuss at all, except it might make you book a track day :D :driving:
Click to expand...

It's an excellent idea but unfortunately, for this exercise at least, I've just sold my car and it was collected today.

http://www.z4-forum.com/forum/viewtopic.php?f=41&t=38624

I have done some more research and there's some interesting stuff on the Birds Auto website about their Quaife diff options and how it improves traction on the UK's roads. It does appear though that, in the case of their E92 install, they could achieve much the same effect by softening the rear springs, something I think the Z4M would also benefit from.
 
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