AWD vs LSD

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Sat 1 Jan 2022 14:10
AWD vs LSD - movilogo

Many SUVs come with AWD but rarely come with FWD/RWD but with LSD (limited slip differential).

Am I correct to say FWD/RWD with LSD is as effective as AWD?

By AWD means where rear wheels come into play when sensing front wheels lost traction, which excludes proper 4WD with transfer case and locking diffs.

How manufacturers determines when to put LSD vs AWD?

Typically LSD comes with some expensive cars (like Maserati Levante etc.).

Is LSD vs AWD decision is an engineering one or marketing one?

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Sat 1 Jan 2022 14:30
AWD vs LSD - Falkirk Bairn

LSD allows more power to the road when cornering - really only applicable to performance engines and RWD cars

AWD allows power to all 4 wheels - all the time with the likes of Subaru Outback or on demand when wheelspin is detected on the normal FWD/RWD wheels (CRV, Rav4 etc)

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Sat 1 Jan 2022 14:40
AWD vs LSD - RT

LSD allows more power to the road when cornering - really only applicable to performance engines and RWD cars

AWD allows power to all 4 wheels - all the time with the likes of Subaru Outback or on demand when wheelspin is detected on the normal FWD/RWD wheels (CRV, Rav4 etc)

Unlike its sibling Subaru Legacy estate, the Subaru Outback has AWD and rear LSD.

Many modern cars use vectored thrust instead of LSDs where the ABS is used to momentarily brake a slipping wheel to maximise the available grip on the other side.

It doesn't apply on tarmac, but when off-road there's nothing worse than diagonal wheels with all the grip as the AWD just sits there spinning the other wheels UNLESS there's LSD, diff-locks or vectored thrust.

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Sat 1 Jan 2022 15:01
AWD vs LSD - thunderbird

LSD's of my youth were noisy rattley things that used clutches that needed occasional maintenance, not really suitable for high mileage road cars, more for rally cars etc. On Minis they made the cars pretty much undrivable on tarmac.

Some road cars have LSD's these days but pretty sure they contain electrical devices and not clutches that do the wizardry which make them far more cultured.

No substitute or 4WD and diff locks if you plan to off road.

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Sat 1 Jan 2022 15:21
AWD vs LSD - mcb100
+1 to above. I used to rally a Mini with a Salisbury LSD - even set quite ‘loose’ it meant the car sometimes had a mind of its own as it came on cam at about 3000rpm. A day’s competition usually resulted in arms like Popeye.
It did allow you to drive out of a special stage on one wheel drive as it (frequently) broke drive shafts.

Edited by mcb100 on 01/01/2022 at 15:50

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Sat 1 Jan 2022 18:16
AWD vs LSD - badbusdriver

Many SUVs come with AWD but rarely come with FWD/RWD but with LSD (limited slip differential).

They don't need to. All but the most basic modern 4WD SUV's will have fairly sophisticated (compared to LSD) traction control which sends drive to whichever wheel needs it. This is much more useful and effective in most situations for most drivers.

Am I correct to say FWD/RWD with LSD is as effective as AWD?

No, if it was, rally cars wouldn't have moved from RWD (with LSD) to 4WD. In its very first rally outing, still an unofficial entry at this stage, the Audi quattro finished nearly half an hour(!) in front of the official winner (RWD + LSD).

By AWD means where rear wheels come into play when sensing front wheels lost traction, which excludes proper 4WD with transfer case and locking diffs.

I wouldn't get hung up this as the two terms mean the same to most folk. Cars have 4 wheels, therefore if all are driven (AWD) it means the car is 4WD, which in turn also means it is a 4x4. If you want to know what kind od 4WD system a particular car has, look into the specs of that car, not whether it is labelled AWD, 4WD, or 4x4.

How manufacturers determines when to put LSD vs AWD?

Most manufacturers are not going to bother with an LSD when modern electronic traction control systems do a better job for less cost and give better efficiency. But if a car is aimed at a particular kind of driver, analogue, old school, hardcore, a mechanical LSD would appeal to them. For the vast majority of drivers, they just wouldn't care (and neither should they)

Is LSD vs AWD decision is an engineering one or marketing one?

Marketing (see above).

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Sun 2 Jan 2022 10:31
AWD vs LSD - John F

Our FWD Peugeot 2008 has an interesting and allegedly advanced traction control system with a multiposition knob for snow, mud or sand. I have no idea how it works - presumably it is some sort of LSD with different thresholds of engagement? Or braking a spinning wheel at different speeds? Or a combination of both? Anyway, never used so far in its two years of existence in the benign climate and tarmac roads of central England.

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Sun 2 Jan 2022 10:46
AWD vs LSD - mcb100
It’s a traction control system with different parameters. There are videos showing Peugeots driving up indoor ski slopes with Grip Control on and off.
The snow setting allows minimal wheel spin to keep the tyre treads full of snow (snow grips best to snow), whilst the mud mode allows a bit more slip to keep the treads clear. Cars with Grip Control come as standard with all season tyres.
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Sun 2 Jan 2022 10:57
AWD vs LSD - badbusdriver

Our FWD Peugeot 2008 has an interesting and allegedly advanced traction control system with a multiposition knob for snow, mud or sand. I have no idea how it works - presumably it is some sort of LSD with different thresholds of engagement? Or braking a spinning wheel at different speeds? Or a combination of both? Anyway, never used so far in its two years of existence in the benign climate and tarmac roads of central England.

Presumably the same system used in PSA/Stellantis vans. They can be identified by a raised ride height and I believe they come with mud and snow tyres.

I have read that is pretty effective in most situations, though ultimately no match for 4WD in extremis (with proper tyres). Quite a few of these used by Royal Mail in my neck of the woods (Aberdenshire).

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Sun 2 Jan 2022 11:02
AWD vs LSD - mcb100
Yes, I’d imagine it’s the same kit. I’d take a FWD car with Grip Control and the right tyres over an AWD car on Sumner tyres.
youtu.be/H77FMgJrgmo
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Sun 2 Jan 2022 12:39
AWD vs LSD - Manatee

The old logic is not quite as relevant now with all the permutations of what you might loosely categorise as ESP/traction control/ASC.

Braking individual spinning wheels somewhat negates the need for an LSD for that purpose (racing applications are different). I can't work out quite what the Outlander does. It's definitely electronically controlled, and my MoT man says it just clutches in the rear diff when the front wheels spin, but quite how that relates to three switchable options, 4WD ECO, 4WD AUTO, and 4WD LOCK, neither of us can work out, On the previous model I had, I think the hardware and probably software were the same but 4WD ECO was called 2WD. Whatever it is it seems to work, presumably combined with TCS/ASC

I speculated that the Outlander might have some sort of pseudo-Haldex system but MoT man says not, and tbh I would expect something more agricultural or at least simpler on a Japanese-engineered car.

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Sun 2 Jan 2022 14:41
AWD vs LSD - RT

The old logic is not quite as relevant now with all the permutations of what you might loosely categorise as ESP/traction control/ASC.

Braking individual spinning wheels somewhat negates the need for an LSD for that purpose (racing applications are different). I can't work out quite what the Outlander does. It's definitely electronically controlled, and my MoT man says it just clutches in the rear diff when the front wheels spin, but quite how that relates to three switchable options, 4WD ECO, 4WD AUTO, and 4WD LOCK, neither of us can work out, On the previous model I had, I think the hardware and probably software were the same but 4WD ECO was called 2WD. Whatever it is it seems to work, presumably combined with TCS/ASC

I speculated that the Outlander might have some sort of pseudo-Haldex system but MoT man says not, and tbh I would expect something more agricultural or at least simpler on a Japanese-engineered car.

4WD Lock usually just engages the front-rear transfer clutch completely - and disengaging automatically above a set speed, eg 30 mph

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