The OS GIKEN OSTCD SPEC-S 1.5WAY, OS-TCD-SPEC-S-E6061, is essentially a high-performance mechanical limited-slip differential (LSD) designed around the BMW E60/E61 M5/M6 driveline and S85 V10 application.
OS Giken lists the E60/E61 M5/M6 with the S85B50A and SMG drivetrain as a rear-differential application, and describes TCD as an evolution of its Super Lock LSD intended to retain high traction while improving smoothness and street comfort.
🧠 What is actually happening inside?
Think of the differential as a torque-management computer made entirely from gears, ramps, springs and clutch plates.
When the BMW enters a corner:
Normal differential
**With the OS TCD:
The important component isn’t simply the gearset. The clutch packs and pressure/ramp mechanism determine how strongly the two axle shafts are coupled.
OS Giken says its Super Lock architecture can progressively move toward 100% locking, while its TCD system adds oil circulation through passages in the discs to keep the friction surfaces lubricated and make the transition between open and locked states smoother and quieter.
🔥 Why 1.5WAY is interesting on the S85 M5/M6
“1.5WAY” doesn’t mean 50% locked.
It describes the different LSD response between acceleration and deceleration.
Accelerator ON — strong LSD action
When you accelerate out of a corner, the LSD increases coupling between the two rear wheels.
That is particularly useful for the S85 because the engine produces its power at very high rpm: 507 hp and 383 lb-ft according to BMW M Registry’s technical summary, with an 8,250-rpm maximum engine speed.
The result is:
less inside-wheel spin → more usable traction → earlier throttle application → stronger corner exit.
🏁 The “0.5” part — deceleration
This is where 1.5WAY becomes more interesting than a conventional aggressive 2-way LSD.
On throttle:
HIGHER locking tendency
Off throttle:
LOWER / more progressive locking tendency
OS Giken describes its 1.5-way configuration as providing LSD action both ON and OFF throttle, but with a smaller deceleration-side cam angle so corner entry remains comparatively mild and controllable.
Conceptually:
That is an excellent characteristic for a powerful FR car.
⚙️ The clever part: TCD lubrication
This is where TCD differs from simply installing an aggressive mechanical LSD.
OS Giken explains that TCD retains the basic Super Lock mechanism but incorporates oil holes/passages through the discs, keeping the friction surfaces wet.
This helps the LSD transition more smoothly between differential action and locking while reducing the characteristic noise/shock associated with mechanical LSDs.
Think:
That is a big deal for an E60/E61 M5, because you’re dealing with a car that can be both a grand tourer and a serious performance machine.
🆚 Comparison
|
Characteristic |
BMW conventional/open-type differential |
OS Super Lock LSD |
OS TCD SPEC-S 1.5WAY |
Aggressive 2-WAY LSD |
|
Straight-line cruising |
⭐️⭐️⭐️⭐️⭐️ |
⭐️⭐️⭐️⭐️ |
⭐️⭐️⭐️⭐️⭐️ |
⭐️⭐️⭐️ |
|
Inside-wheel traction |
⭐️⭐️ |
⭐️⭐️⭐️⭐️⭐️ |
⭐️⭐️⭐️⭐️⭐️ |
⭐️⭐️⭐️⭐️⭐️ |
|
Corner exit |
⭐️⭐️ |
⭐️⭐️⭐️⭐️⭐️ |
⭐️⭐️⭐️⭐️⭐️ |
⭐️⭐️⭐️⭐️⭐️ |
|
Corner entry |
⭐️⭐️⭐️⭐️⭐️ |
⭐️⭐️⭐️⭐️ |
⭐️⭐️⭐️⭐️⭐️ |
⭐️⭐️⭐️ |
|
Throttle modulation |
⭐️⭐️⭐️⭐️ |
⭐️⭐️⭐️⭐️⭐️ |
⭐️⭐️⭐️⭐️⭐️ |
⭐️⭐️⭐️ |
|
Street refinement |
⭐️⭐️⭐️⭐️⭐️ |
⭐️⭐️⭐️⭐️ |
⭐️⭐️⭐️⭐️⭐️ |
⭐️⭐️ |
|
Track capability |
⭐️⭐️ |
⭐️⭐️⭐️⭐️⭐️ |
⭐️⭐️⭐️⭐️⭐️ |
⭐️⭐️⭐️⭐️⭐️ |
|
Mechanical complexity |
Low |
High |
High |
High |
|
Character |
Neutral |
Aggressive |
Fast + progressive |
Very aggressive |
OS Giken specifically positions its TCD system around combining strong traction with a milder, smoother operating character.
🥊 TCD 1.5WAY vs BMW M5/M6 stock differential
This is probably the most important comparison.
**Stock BMW system
The E60/E61 M5 uses the S85 V10 with SMG III; BMW’s documentation/technical references identify the rear drivetrain and final drive arrangement for this platform.
The factory setup is designed around:
comfort + electronic stability + predictable road behaviour.
**OS TCD
The philosophy changes toward:
mechanical traction + predictable locking + driver-controlled corner exit.
So:
The OS Giken BMW catalogue confirms the E60/61 M5/M6 S85B50A application as a rear LSD application.
🧩 Why it suits the S85 V10 particularly well
The S85 is unusual.
It isn’t a low-rpm torque monster. It is a high-revving naturally aspirated V10.
That means the differential needs to cope with a very different power-delivery character:
4,999 cc → V10 → 8,250 rpm → high-rev power delivery.
Imagine exiting a medium-speed corner:
CORNER EXIT
FRONT
↑
┌─────────┐
│ M5/M6 │
└─────────┘
↙ ↘
rear wheels
↑
throttle opens
↑
S85 V10
↑
6,000→8,000 rpm
↓
huge wheel-speed
difference
↓
TCD responds
↓
clutch coupling rises
↓
BOTH tyres work
↓
HARDER EXIT
That’s where the hardware starts making sense.
🏎️ The 1.5WAY sweet spot
For an E60/E61 M5 used for spirited road driving + occasional track driving, I’d characterize the three philosophies like this:
1-WAY
Very friendly, primarily concerned with traction on power.
1.5-WAY
Acceleration ███████████████
Deceleration ███████
The compromise.
Strong corner-exit traction while retaining more natural corner-entry behaviour.
2-WAY
Much stronger differential coupling on both sides.
Great for specialized circuit applications, but potentially less natural for a road-driven M5.
OS Giken explicitly describes its 1.5-way configuration as a balance between sport driving and controlled corner-entry behaviour, whereas its 2-way configuration is more aggressive and oriented toward experienced circuit users.
🧠 The really important distinction
Don’t think:
“OS TCD makes both wheels spin together all the time.”
That’s the wrong mental model.
Think:
“OS TCD progressively decides how strongly the two rear wheels should be coupled according to the driving condition.”
That’s much closer to what makes it sophisticated.
NO LOAD
│
▼
differential
action
│
▼
┌────────────────┐
│ DRIVER INPUT │
└───────┬────────┘
│
┌──────┴──────┐
▼ ▼
ON THROTTLE OFF THROTTLE
│ │
▼ ▼
stronger milder
locking locking
│ │
└──────┬──────┘
▼
PROGRESSIVE LSD
│
▼
predictable rear
axle behaviour
🏆 The Verdict
For an E60/E61 M5/M6 S85, the OS TCD SPEC-S 1.5WAY is a particularly sophisticated choice because it doesn’t simply pursue maximum locking.
It pursues usable locking.
Stock BMW:
Comfort → electronic intervention → predictable
OS Super Lock:
Mechanical traction → extremely strong locking → performance
OS TCD 1.5WAY:
Mechanical traction + progressive locking + improved lubrication + better street refinement
That last combination is what makes the TCD concept so interesting for a V10 M5/M6 that still needs to behave like a road car.
OS Giken itself describes TCD as retaining Super Lock’s traction/response while improving smoothness and comfort through its lubrication system.
One important note: OS Giken’s public BMW catalogue confirms the E60/61 M5/M6 S85B50A application, but the exact public page I found does not independently expose every specification associated with the exact OS-TCD-SPEC-S-E6061 suffix.
So I would treat dimensions, preload, plate count, oil capacity and exact ramp angles as unverified unless supplied by OS Giken/dealer documentation, rather than relying on generic LSD specifications.
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