"These build journal entries are part of a Special Series on the development of the S85 SMG3 carbon forged steel lightweight flywheel by TTV Racing.
This entry covers my first impression and long term review over 9 months and 15,000KM with the flywheel and carbon driveshaft combination. I discern the benefits between both and set the expectations right.
But first, it's science bro!"
The burden of proof.
Testing and reviewing the flywheel has been the most thorough as of yet for any products on EuroConnex for a few reasons.
I've had a great experience with the DCT lightweight flywheel in my M3 V8, documenting my process here.
It isn't a perfect modification: there is some idle chatter, although definitely not as bad as other flywheels I've heard. The drivability is second to none, and the benefits are massive.
I was anxious to try the lightweight flywheel concept with the V10 for 2 reasons: it's a luxury daily driver first, and the SMG doing SMG things.
My tolerance thresholds with added noises would be lower, and I anticipated the transmission would struggle with the flywheel.
The testing conditions.
I had the flywheel installed in September while the V10 was down for a radiator fan. My M5 V10 has since traveled over 15,000 kilometers and experienced +25 down to -35C in mostly humid, rainy, and snowy conditions.
No matter the weather, it got driven. It's been my daily driver.
In December, I had piled up about 4,000 kilometers of the 15,000km total planned until Spring.
I made this video.
I made this statement.
The difference is immense - I could not go back to stock. The low to mid range inertia & response differences are massive.
Some comments highlighted the myths.
It has since been viewed over 310,000 times and amassed a lot of comments, questions and dubious feedback.
This one gave me a good chuckle. The equivalent throttle inputs over the equivalent time length will produce a faster engine pick up speed with a lighter flywheel, more so in neutral.
This one is a hallmark of the fundamental misunderstandings about how flywheels operate.
We had captain know-it-all jump on to defend the guy above and explain how it wouldn't work on daily drivers.
If we're being intellectually honest, he was sort of half way there but was fumbling the ball by the middle and dropped it at the end.
It's science bro!
This table compares the OEM flywheel versus TTV's lightweight forged steel variant. The only input data changed is the flywheel mass: 32 lbs versus 18.7 lbs.
Source / HP Wizards
The physics of lightweight flywheels indicate the lightweight flywheel has most impact in gears 1 through 3.
It's where rotational inertia measured by the flywheel's mass is highest along with its rate of decrease as you run through the first 3 gears.
Those gains could be measured on a dyno. While it does not increase crank horsepower, it will make more power at the wheels.
You will unfortunately hardly see this on a dyno, as the 6th gear is used for its 1:1 ratio to most accurately measure engine power and torque.
Long term driving impressions.
I will further answer the common myths expressed above using my own experiences, and I'll dive into my nitty gritty details on the specifics of this flywheel on this application.
It fixes the S85's biggest weaknesses
The TTV flywheel drastically improves the engine pick up speed in gears 1 to 3 and in the low RPM range.
You zip to the 5,000 RPM + power zone in a flash, even in part throttle application. It's similar to driving a high torque turbo application on part throttle - you can feel there's something powerful waiting to be unleashed.
The lighter flywheel creates the impression you're gliding on the road.
[...] and puts to use the E60's sublime chassis.
The E60's wheelbase, relatively larger rear tire and purposeful multi link rear suspension create massive grip. In stock form, losing grip in 1st gear without a Euro launch is nearly impossible.
The flywheel makes use of BMW M's chassis prowesses and catapults you into the power zone without losing grip. 285 is plenty for this chassis, even on dubs.
It makes the SMG smoother, and faster.
The flywheel and carbon driveshaft make for much faster SMG operations at full tilt and high RPMs.
To prove it, I aligned my draggy times showing my Stage 3 V10 with headers, flywheel and carbon driveshaft on the left, an my Stage 1 V10 with air intakes on the right.
Both were on Winter tires, driven in S6. Similar slopes, colder temperatures for the Stage 1 run.
The blue and orange lines are what matter to us.
The flattening of the blue curve shows the shift. The 3rd to 4th gear shift is right in the middle of both graphs.
The left graph shows how much more time is lost with the stock drivetrain. On the right, the SMG fitted with this combination is nearly DCT'esque fast at WOT and redline.
The orange line shows the acceleration G forces. Both suffer the same drop in G forces, but at much different rates
On the right, the upgraded drivetrain is nearly a straight line down and up. On the left, the stock unit is heavier and slower to loose and gain G forces. That's rotational inertia in full display.
If you apply these parameters to the 2nd to 3rd gear shift early in the graph, it gets even faster. It's difficult to explain how absolutely brutal this shift is on a stock drivetrain.
Another concern I had was the SMG's smoothness in cold temperature environments upon start ups. I expected it as fluids are heavier and engine revs higher to warm up the cats.
I faced these issues with the M3 V8. I run Mike @ BPM's custom cold start. It's an exaggerated sequence because race car that makes the DCT flywheel extremely grabby. I always wait it out.
It gets cold up here, ever more when you factor humidity. The BMW ambiant temperature sensors do not
This time around, I planned ahead. I chatted with Salman at Infinity and we opted for cold start delete.
It eliminated all the issues I experienced with the M3 V8. The cold start delete made the SMG smooth as butter in -40C drive off conditions.
Raised Idle Speed Testing.
Another concern I've had with the DME's ability to compensate for the lighter flywheel coming to a stop or in faster 1-N-R-N-1 operations that could reflect stalling speed with a manual transmissions. This may also happen when you hesitate on throttle applications and the DME dumps or pulls the clutch.
I didn't experience these issues on the stock idle speed, but we still decided to test it with a 950 RPM idle speed. Stock is roughly 700.
The raised idle speed improved the SMG in start off conditions and made the friction point smoother. It also sounds pretty nice I must say.
My biggest surprise: no noise.
That's it, zero.
The E60's luxurious nature, the SMG keeping the throwout bearing pulled and the loud VANOS idle noises make the flywheel indiscernible, in any conditions.
You can see this in action in the video below.
Discerning the benefits from the carbon driveshaft.
I extensively documented the carbon driveshaft benefits on the S85 and SMG3 pairing here.
In short, the carbon driveshaft is not about rotational inertia, it's all about making the drivetrain tighter - thus smoother, and faster.
With science on our mind, we now know the flywheel is all about rotational inertia and engine pick up speeds.
The pairing complements each other and slightly overlap in the SMG smoothness across the range & speed of shifts.
If I could only budget for 1 of the 2?
If you should only get one for budget purposes, I would fit the carbon driveshaft first. The SMG3 needs more help than the S85.
The installation is easier, and the benefits are impactful across the entire RPM range, in any gear - including reverse.
In closing thoughts, I'm doubling down: the carbon driveshaft and flywheel combination is a must have.
There are no downsides.
There are only budget limitations and priorities when it comes to owning a V10 M car.
You can source the flywheel year long here.