"These build journal entries are part of a Special Series on the development of the E60 M5 & M6 Carbon Fiber Driveshaft by YFCM Composites. 

In this entry, I take a dive into the SMG: what makes it uber fast, harsh, atrocious, and totally awesome.

Should we all give up and swap manuals - and keep chasing the DCT hopes and dreams?

These entries are written in collaboration with M Lee: lead engineer and patent holder to YFCM's innovations."
- Matt

The SMG3 was peak something. 

Evolving from the SMG1 found in a few rare European E36s, we know the SMG2 from its use in the E46 M3. 

The SMG3 was the latest, greatest development of the SMG gearbox concept back in 2006.

It was also the last. 

SMG got most famously controversial with the E60 M5: it was the only available transmission at launch and for most of the world except a few lucky Americans during the entire production run. 

How it works.

It's like a manual that makes you think, I swear!

The hydraulics replace your left foot. 

The SMG is an automated manual with an hydraulic pump strapped to its side. 

The black casing is the accumulator, building up the pressure to do the clutch in/out operations.  

The actuators replace your hand. 

The "pump" as BMW M calls it, are actuators that replace the shifter linkage. They connect to the cogs that swap gears. 

The actuators sit in these casings, where shift linkages usually reaches the transmission to swap cogs in standard manuals.

Notice how the casings all have cracks? They were pre-determined failure points by BMW and Getrag to save the pump just in case - that case happened due to a clutch failure. 

It has a dual mass flywheel.

Aka, the anvil. 

[...] and a twin disc clutch

More friction surface, more torque capacity. 

A slave cylinder! Find that in an automatic. 

[...] and an oil cooler. 

The oil cooler sits on the passenger side and has NACA ducting integrated into the undertray. They built the SMG to take a beating. 

Using a suite of sensors across the car, it replaces your brain, sort of. 

The SMG3 made use of Drivelogic to allow the drive to have an influence over the gear shifts. The secret is actually still in one of your feet.

It was extremely fast

The SMG3 had the not-so-secret S6 mode to the Drivelogic. Turn off DSC, and an another level appears on the Drivelogic display between the gauges. 

The M5/M6 in Drivelogic set to S6 take about 150 ms to complete the complete power transfer to the wheels. BMW M famously quoted 80ms, leaving out the clutch in/out action. 

This was in line with exotics of this era such as the F430 and Gallardo. The latest development of this gearbox found in the Aventador can supposedly knock out shifts in 50ms. 

Knowing Lamborghini's inflated marketing numbers, we can assume this compares to the 80ms from BMW M. 

[...] in an extremely small operational window. 

The hydraulics build up pressure as you climb RPMs and will only release max pressure at max RPM and max Throttle input. 

For most of us, we spend 99% of our time driving these cars below the redline. 

The DCT was a multi-generation leap. 

Introduced in 2007 with the E92 M3, the MDCT made the SMG feel like 2 generations back. 

The MDCT at full bore shifts below 50ms, including clutch operations.

The MDCT was not only faster, it was smoother, and faster all over the RPM range. 

Those that complain about the MDCT being rough at low speeds have spent too much time in actual planetary gear'ed automatic transmissions such as the ZF 8 speed. 

The MDCT has its share of leaking issues - but otherwise, the mechanicals are solid. 

We gave up on the SMG.

Must enthusiasts moved on from the SMG transmissions when the MDCT was released, there was no way to hide its limited effectiveness.

V10 enthusiasts have since been chasing the MDCT dreams of the M5 CSL prototype.

E46 M3 SMG2 owners have been waiting for the pumps to pop to do the 6spd conversion.

All they have to do is essentially removing the SMG wizardry around the casing and voila - you have a Getrag 420G waiting to be rowed. 

The SMG3 isn't an SMG2 

Unfortunately for V10 owners, the Germans are Germans - they overengineered the SMG3 chasing milliseconds in a narrow range. 

Das Ssss Mmm Gee iz da tupz of de line!
- [insert German sounding engineer name here]

The SMG3's shift pattern is optimized for shift speeds as it pushes actuators instead of rowing a stick. 

The consequence: the shift patterns are not made for humans.

[...] but a GS6-53BZ is a GS6-53BZ.

The USDM 6spd E60 M5s ended up skyrocketing in prices for reasons that deserve to be exposed. 

There's really nothing that special about the OEM 6spd, and the conversions are better. 

You can convert an E60 M5 SMG3 using an E9x M3 transmission and the S65 2009+ flywheel and clutch pairing. 

It boasts an oil cooler too - unlike the original E60 M5 that easily overheated, causing BMW M to disallow owners from turning off DSC.

The guys at InnovAuto have converted various M5 SMG3s to 6spd using the E9x M3 transmission. It's cost effective, and fast. 

 

The V10 is about speed. 

The 6spd takes away from the M5 V10 experience in a crucial aspect to the experience: top speed. 

To this day, the M5 V10 with its Vmax limiter removed remains at the top of the M food chain with the highest top speed ever recorded. 

The M5 V10 could break the infamous supercar performance threshold: it can reach an aerodynamically-limited top speed of 205.7 mph. 

The 6spd transmission is geared at 2.93 whereas the SMG boasts a 7th gear and final drive of 3.62. If you want to play catch up to an SMG, you need to put in a 3.85 or 4.10. It cuts down on your top speed drastically. 

Whether you stick to stock or go shorter gears, the 6spd is a performance sacrifice: acceleration or top speed, you choose. 

Truth be told, I like the E60 M5 for its awkwardness and hilariousness. 

It should have never existed - but It did. 

It had quirks. It had shortcomings - but it had soul. 

It's an experience matched by none - ever.

The SMG is at the core of the experience. 

Technology moved on. Most of us did too.

As Johnny Tran famously said: "Too soon, junior".

Up next, I discuss my driving impressions with the YFCM carbon driveshaft. 

The fix is in.