Differentials Explained: LSD, Open Diff, and Drivetrain Upgrades | Mod Monster

The differential is one of the most overlooked components in car modification. People spend thousands on engine power, suspension, and tyres, then wonder why their car can't put the power down cleanly out of corners or struggles with traction on track. More often than not, the answer is the differential — specifically, the open differential that came from the factory.

Upgrading to a limited-slip differential (LSD) is one of the single most transformative modifications you can make to any rear-wheel-drive or front-wheel-drive performance car. It changes how power reaches the road, how the car rotates through corners, and how much confidence you have on corner exit. This guide explains what differentials do, the different types available, and when an upgrade makes sense.

What Does a Differential Do?

When your car turns a corner, the outside wheels travel a longer distance than the inside wheels. If both driven wheels were locked together on a solid axle, turning would cause the tyres to scrub and skip — the inside wheel would be forced to spin faster than it needs to, and the outside wheel would be dragged slower than it needs to.

The differential solves this problem. It's a gear assembly that sits between the driven wheels and allows them to rotate at different speeds while still receiving power from the engine. When driving straight, both wheels spin at the same speed. When cornering, the differential allows the outside wheel to spin faster and the inside wheel to spin slower, letting the car turn smoothly.

The differential lives in the rear axle on rear-wheel-drive (RWD) and all-wheel-drive (AWD) cars, and in the transaxle on front-wheel-drive (FWD) cars. AWD cars typically have three differentials — front, rear, and centre.

Open Differential

An open differential is the simplest and most common type. It uses a set of spider gears (also called planetary gears) that allow unlimited speed difference between the two wheels.

How It Works

The ring gear (connected to the driveshaft) turns the differential housing. Inside, spider gears mesh with side gears connected to each axle shaft. When both wheels have equal traction, the spider gears don't rotate on their own — they just carry the side gears around equally. When the wheels need to spin at different speeds (turning), the spider gears rotate to accommodate the difference.

The Problem with Open Diffs

An open differential always sends equal torque to both wheels. This sounds fair, but it creates a critical problem: the maximum torque delivered to the road is limited by the wheel with the least traction.

If one wheel is on a slippery surface (or lifts off the ground over a crest), it loses traction and spins freely. The open diff happily sends all the power to that spinning wheel while the wheel with grip gets nothing. You've seen this — one tyre spinning wildly while the other sits still.

In performance driving, this means:

Corner exit: When you accelerate out of a corner, weight transfers to the outside rear wheel. The inside rear wheel gets light, loses traction, and spins. The open diff sends power to the spinning wheel instead of the gripping outside wheel. Result: the car understeers, you can't put the power down, and you're slow.
Launches: Under hard acceleration, weight shifts rearward unevenly, and one wheel may break traction first. The open diff feeds that spinning wheel, limiting your launch performance.
Wet / uneven surfaces: Any traction difference between left and right wheels is immediately exploited by the open diff in the worst way possible.

Why Manufacturers Use Open Diffs

Despite the performance limitations, open differentials have significant advantages for road cars:

Cheapest to manufacture
Zero maintenance
No unusual tyre wear
Predictable, easy-to-drive handling characteristics
Quiet operation
No effect on steering feel (FWD cars)

Most economy and family cars use open differentials because the performance limitation simply doesn't matter for normal driving.

Limited-Slip Differential (LSD)

A limited-slip differential limits the speed difference between the two wheels. Instead of allowing one wheel to spin freely, it redirects a portion of the torque to the slower (gripping) wheel. The result: better traction, better acceleration, and more controllable handling at the limit.

Types of LSD

There are several fundamentally different LSD designs, each with distinct characteristics:

Clutch-Type LSD (Plate-Type)

The most common aftermarket performance LSD. Inside the differential housing, a stack of friction plates (clutch plates) is sandwiched between the side gears and the housing. When torque is applied, ramp angles on the cross-pins push the side gears outward, compressing the clutch plates. The friction between the plates resists speed differences between the wheels.

How It Works

Imagine the clutch plates as a clutch (they literally are). When compressed, they lock the two wheels together. The more torque applied, the more the plates compress, and the more locking effect you get. The ramp angles determine how the diff responds to different conditions — acceleration, deceleration, and coasting.

1-Way, 1.5-Way, and 2-Way

The ramp angles on the cross-pins control when and how much the LSD locks. This is described by the "way" rating:

1-Way LSD:

Locks under acceleration only
Free (like an open diff) on deceleration and coasting
Best for: FWD cars, drag racing, cars driven primarily on the street
Character: Puts power down well on exit, doesn't affect braking or corner entry behaviour

1.5-Way LSD:

Full locking effect under acceleration
Partial locking effect on deceleration (typically 50-70% of the acceleration lock)
Best for: Street/track dual-purpose RWD cars, circuit racing
Character: Great acceleration traction plus improved stability on corner entry under braking. The partial deceleration lock helps rotate the car into corners when trail braking. This is the most popular choice for track-focused street cars.

2-Way LSD:

Equal locking effect under both acceleration and deceleration
Best for: Drifting, professional motorsport, dedicated track cars
Character: Very aggressive. Provides maximum stability under braking and corner entry, but can feel "nervous" on the street — the car wants to go straight under braking, which makes turn-in more abrupt. Takes skill to drive well.

Ramp Angle Comparison

Setting	Acceleration Lock	Deceleration Lock	Best Application
1-Way	Full	None	FWD, drag, daily street
1.5-Way	Full	Partial (~60%)	Street/track, circuit
2-Way	Full	Full	Drift, race, dedicated track

Clutch-Type LSD Pros and Cons

Pros:

Strong, predictable locking behaviour
Adjustable (plates can be changed, preload adjusted, ramp angles modified on some units)
Progressive engagement — not on/off
Available in 1-way, 1.5-way, and 2-way configurations
Proven technology with decades of motorsport use

Cons:

Wears over time — clutch plates need periodic replacement (typically 30,000 - 80,000 km depending on use)
Requires LSD-specific differential oil (contains friction modifier)
Can produce clunking or chatter when manoeuvring at low speed (parking)
Needs rebuilding periodically (RM 500 - RM 1,500 for service)

Popular brands: Cusco, Kaaz, OS Giken, Tomei, ATS, Quaife (also makes gear-type) Typical cost: RM 3,500 - RM 10,000 installed

Helical / Torsen LSD (Gear-Type)

Helical LSDs use a set of worm gears instead of clutch plates to redirect torque. The helical gear geometry creates friction when there's a speed difference between the wheels, naturally resisting the differentiation.

How It Works

The helical gears mesh in a way that creates an inherent resistance to rotation. When one wheel tries to spin faster than the other, the gear friction redirects torque to the slower wheel. There's no wear surface — the gears themselves create the locking effect through their geometry.

The "Torsen" differential (short for "torque sensing") is the most well-known helical LSD. It was developed for motorsport and is used as OEM equipment by Audi (Quattro), Mazda (MX-5/Miata), BMW (some M cars), and others.

Helical LSD Pros and Cons

Pros:

Virtually maintenance-free — no clutch plates to wear
Completely silent operation — no clunking or chatter
Very smooth, progressive engagement
Uses standard differential oil (no special LSD fluid needed)
Excellent daily drivability — you may not even notice it until you need it
Long service life (essentially the life of the car)

Cons:

Lower torque bias ratio than clutch-type LSDs (typically 2:1 to 3:1, meaning it can send 2-3x more torque to one wheel than the other — a clutch-type can approach full lock)
Cannot provide locking when one wheel is completely unloaded (no preload)
Less aggressive overall — won't help as much in extreme situations
Not adjustable — the gear geometry determines the behaviour
More expensive than basic clutch-type LSDs

Popular brands: Quaife, Wavetrac, Torsen, Cusco RS (helical type) Typical cost: RM 4,000 - RM 8,000 installed

Quaife ATB (Automatic Torque Biasing)

The Quaife is probably the most popular aftermarket helical LSD. It's a direct replacement for the open differential in many cars and is renowned for its smooth, silent operation. If you want LSD benefits without any change in daily driving character, the Quaife is the benchmark.

Wavetrac

The Wavetrac improves on the standard helical design by adding a wave-profile washer that provides preload. This means it can still provide locking effect when one wheel is completely unloaded — the traditional weakness of helical designs. The Wavetrac is widely considered the best helical LSD available.

Viscous LSD

A viscous LSD uses a silicone-based fluid that becomes thicker (more viscous) when it's sheared by speed differences between the two sides of the differential. Discs attached to each axle shaft are submerged in this fluid. When one wheel spins faster, the fluid shearing creates resistance, transferring torque to the slower wheel.

Viscous LSD Pros and Cons

Pros:

Completely smooth operation
No maintenance required
Very gentle engagement — excellent for daily driving
Often used as OEM equipment (Honda, some BMW, some Mitsubishi)

Cons:

Limited locking capability — weakest of all LSD types
Performance degrades over time as the fluid loses its properties
Cannot be rebuilt — entire unit must be replaced
Not suitable for aggressive track use (fluid overheats)
Slow to respond compared to clutch or helical types

Best for: OEM applications, mild street driving improvement. Not recommended as an aftermarket upgrade — clutch-type and helical LSDs are superior for the same or less money.

Electronic Differential (E-Diff)

Many modern performance cars use electronically controlled differentials. These use clutch packs similar to a mechanical LSD, but an electronically controlled actuator (hydraulic or electromagnetic) controls the clamping force. The car's ECU manages the differential behaviour based on steering angle, wheel speed sensors, yaw rate, throttle position, and vehicle speed.

Examples of Factory E-Diffs

BMW M cars: Active M Differential
Porsche: PTV Plus (Porsche Torque Vectoring)
Audi: Sport Differential
Mitsubishi Evo: Active Yaw Control (AYC)
Ford Focus RS: Rear Drive Unit (RDU)

E-Diff Advantages

Infinitely variable locking from 0-100%
Adaptive — changes behaviour based on driving conditions
Can pre-emptively lock before wheelspin occurs (predictive)
Different modes for different driving situations (Comfort, Sport, Track)
Torque vectoring capability — can actually push the car into corners

E-Diff Limitations for Modification

The ECU calibration limits what the diff can do
Tuning the e-diff usually requires specialist software
Not all aftermarket ECUs support e-diff control
If the electronic system fails, it may default to open diff behaviour
Expensive to repair

For cars with factory e-diffs: In many cases, a software tune that adjusts the e-diff behaviour is more effective (and cheaper) than replacing it with a mechanical LSD. Some tuners offer e-diff calibration that makes the stock system more aggressive.

LSD Type Comparison

Feature	Clutch-Type	Helical (Torsen/Quaife)	Viscous	Electronic
Locking strength	High	Moderate	Low	Variable (0-100%)
Response speed	Fast	Very fast	Slow	Very fast
Noise / chatter	Some	None	None	None
Maintenance	Rebuild every 30-80k km	Essentially none	Replace when worn	Electronic service
Daily drivability	Good	Excellent	Excellent	Excellent
Track performance	Excellent	Very good	Fair	Excellent (when tuned)
Adjustability	High (plates, preload)	None	None	Software tunable
Durability	Moderate (wear item)	Excellent	Moderate (degrades)	High (mechanical)
Typical cost (RM)	3,500 - 10,000	4,000 - 8,000	OEM only	OEM only

How an LSD Transforms Driving

Corner Exit Traction

This is where an LSD makes the most dramatic difference. With an open diff, applying power on corner exit causes the inside wheel to spin uselessly. With an LSD, torque is redirected to the outside wheel (which has grip), allowing you to get on the power earlier and harder. On a circuit, this alone is worth seconds per lap.

Straight-Line Traction

Under hard acceleration, an LSD keeps both wheels driving together. If one wheel breaks traction (rough surface, expansion joint, paint line), the other wheel keeps pulling. Launches are more consistent and faster.

Stability Under Braking (1.5-Way and 2-Way)

On deceleration, the LSD prevents one wheel from decelerating faster than the other. This stabilises the rear end under trail braking and during turn-in. The car feels more planted and predictable.

Oversteer Control and Drift

For drifting, a 2-way LSD is essential. It keeps both rear wheels spinning at the same speed, allowing the driver to control the slide angle with throttle. An open diff is nearly impossible to drift consistently because the inside wheel just spins while the outside wheel does nothing.

Wet Weather Confidence

In Malaysia's frequent heavy rain, an LSD provides a massive confidence boost. On wet roads, traction differences between left and right wheels are amplified. An LSD ensures power goes to the wheel with grip, reducing the chance of unexpected wheelspin and loss of control.

When Do You Need an LSD Upgrade?

You Definitely Need One If:

You track your car regularly and it's RWD with an open diff
You've added significant power (Stage 2+) and experience one-wheel burnouts on corner exit
You drift or want to drift
You autocross and need consistent corner exit traction
Your FWD car torque-steers aggressively under power

It's Highly Recommended If:

You drive spiritedly on mountain roads (Malaysian touge)
You've upgraded suspension and tyres but still feel limited by traction on exit
You drive in heavy rain regularly and want more confidence
You've upgraded power and find the car unpredictable at the limit

You Can Skip It If:

Your car has a factory LSD or e-diff (already sorted)
You only drive on the highway and in traffic
Your car is naturally aspirated with stock power (limited benefit)
You have an AWD car with a centre diff (less critical)

The Welded Diff (Drift Special)

A welded diff is exactly what it sounds like — the spider gears inside an open differential are welded together, permanently locking both wheels to spin at the same speed. It's a 100% locked, zero-differentiation "differential."

Why People Weld Diffs

Cheapest possible "LSD" — costs only a stick of weld
Maximum locking for drifting — both wheels always spinning together
Cannot wear out (no moving parts)

Why You Should NOT Weld Your Daily Driver's Diff

Tyre wear: Both tyres are forced to spin at the same speed, even in corners. The inside tyre scrubs horribly. Rear tyres wear extremely fast and unevenly.
Terrible in the wet: Any traction variation between left and right causes the car to snap sideways. Welded diffs in rain are genuinely dangerous.
Parking is a nightmare: The tyres chirp, skip, and scrub during every low-speed turn
Handling is unpredictable: The car resists turning (understeer) and then snaps into oversteer mid-corner
Bearing and axle stress: The constant binding loads stress bearings, axle shafts, and the differential housing itself

The only legitimate use for a welded diff is a dedicated drift car that is trailered to events and never driven on the street in traffic. Even then, a proper 2-way clutch-type LSD is a better choice if the budget allows.

Differential Fluid Maintenance

Regardless of diff type, the fluid inside needs periodic replacement:

Oil Change Intervals

Open differential: Every 60,000 - 80,000 km (often neglected, but important)
Clutch-type LSD: Every 20,000 - 40,000 km (critical — the friction modifier depletes)
Helical LSD: Every 40,000 - 60,000 km
Viscous LSD: Not serviceable (sealed unit)

LSD-Specific Fluid

Clutch-type LSDs require differential oil with a friction modifier additive. Using standard gear oil in a clutch-type LSD causes excessive chatter, clunking, and accelerated plate wear. Always use the LSD-specific fluid recommended by the differential manufacturer.

Popular LSD fluids:

Cusco LSD Oil — RM 80-120 per litre
Motul Gear Competition — RM 90-130 per litre
Red Line 75W-90 GL-5 — RM 100-150 per litre

Typical diff fluid capacity: 1 - 2 litres depending on the housing

Signs of Depleted Diff Fluid

Clunking or chatter on slow-speed turns (clutch-type LSD)
Whining noise from the differential
Reduced LSD effectiveness (less locking feeling)
Metal particles visible in drained fluid

LSD Upgrade Budget Guide

Component	Budget	Mid-Range	Premium
LSD unit	RM 3,000 (Cusco RS)	RM 5,000 (Cusco Type-RS)	RM 8,000+ (OS Giken)
Installation labour	RM 500 - 1,000	RM 800 - 1,500	RM 1,000 - 2,000
LSD fluid	RM 150 - 250	RM 150 - 250	RM 150 - 250
Differential bearings	RM 200 - 500	RM 300 - 600	RM 300 - 600
Setup and shimming	Included in labour	Included in labour	Included in labour
Total	RM 3,850 - 4,750	RM 6,250 - 7,350	RM 9,450 - 10,850

FAQ

How do I know if my car has an LSD already?

Check your car's specifications — the option is usually listed. Alternatively, jack up the driven axle: with the car in neutral, spin one wheel by hand. If the other wheel spins the same direction, you have an LSD (or locked diff). If it spins the opposite direction, you have an open diff. Note: this test doesn't work perfectly for viscous and some helical LSDs as their locking may not be apparent at low speed.

Is a helical or clutch-type LSD better?

It depends on your priorities. Helical (Quaife/Wavetrac) is better for daily drivability — silent, maintenance-free, and smooth. Clutch-type (Cusco, Kaaz, OS Giken) is better for aggressive track and drift use — stronger locking, adjustable, and available in 1-way/1.5-way/2-way configurations. For a street/track car, a 1.5-way clutch-type or a Wavetrac helical are both excellent choices.

Will an LSD make my car faster on track?

Almost certainly yes, and often by a dramatic margin. The ability to get on the power earlier and harder out of every corner accumulates across an entire lap. On most circuits, an LSD is worth 1-3 seconds per lap on a typical 2-minute circuit, assuming the driver can exploit the additional traction.

Does an LSD affect tyre wear?

A properly functioning LSD does not significantly increase tyre wear during normal street driving. On track, it can actually improve rear tyre wear by distributing power more evenly. A welded diff, however, destroys rear tyres rapidly.

How long does a clutch-type LSD last before needing a rebuild?

Typical service intervals are 30,000 - 80,000 km depending on driving style and the specific unit. Track use, drifting, and aggressive driving wear the plates faster. A rebuild involves replacing the clutch plates and springs, which costs RM 500 - RM 1,500 in parts and labour. Many enthusiasts rebuild annually if the car sees regular track use.

Can I install an LSD in any car?

Most RWD and FWD cars can accept an aftermarket LSD — it replaces the open differential inside the existing housing. However, not every car has aftermarket LSD options available. Japanese sports cars (Silvia, GT86, MX-5, Evo, STI) and European performance cars (BMW M, Porsche) have the widest selection. Check with LSD manufacturers for fitment to your specific model.

Is a 2-way LSD too aggressive for street use?

For most street drivers, yes. A 2-way LSD's deceleration locking can make the car feel nervous and darty under braking, especially on bumpy roads. The car wants to drive straight when you're trying to turn in. Experienced drivers can adapt, but a 1.5-way offers nearly the same acceleration traction with much friendlier street manners. Reserve 2-way for drift or dedicated race cars.

My car has an electronic diff. Should I replace it with a mechanical LSD?

In most cases, no. Factory e-diffs from BMW M, Porsche, and Audi are very good. A software tune that adjusts the e-diff calibration is usually more effective and far cheaper than swapping to a mechanical unit. The e-diff can also provide torque vectoring that a mechanical LSD cannot. Only consider replacing an e-diff if it's failed, if aftermarket ECU support is unavailable, or if you're building a dedicated race car with an aftermarket ECU that doesn't support e-diff control.