"This entry is part of a Special Series on my S65 lightweight flywheel experiments.

In this entry, I examine the old, and the new: I compare the original DCT lightweight flywheel design to the latest 2 piece design revision."
- Matt

The backstory. 

Back in 2020, I had discovered discussions surrounding the use of a lightened flywheel on the DCT. They were inconclusive. 

Some owners were trying to get information from a French Motorsport team running the a unique lightened flywheel design - I speak French! 

I researched and understood it was made by TTV Racing, a fairly unknown brand to most except a few European motorsport outfits. I started chatting with Ben at TTV Racing to better understand who they and why & how they do what they do. 

TTV Industrial has been a manufacturing group in the precision engineering and machining industry for over 30 years located in the East of England. 

A core group of enthusiasts in the family run business launched TTV Racing.They design and manufacture automotive parts for high end original equipment & motorsport, club racer to world championship.

"The first flywheel we made lapped Nürburg for 12 months before we sold any."
Ben @ TTV

The original design.

I received one of the first units in the Spring of 2021. It shipped via DHL and got here within a matter of days. It was properly packaged.

The original design was plain - there was no surface area destined for clutch contact. It was a strange thing to look at having had experiences with manual transmission flywheels.

The design incorporated the required crank sensor tabs, its one larger gap, and the starter gear teeth. It also has one larger crankshaft bolt hole for starter alignment. TTV has 2x in-house high speed balancers to achieve proper balancing to OE specs. The balancing is done using machined holes across the circumference of the flywheel.

Most importantly, it was light: the original design of DCT lightweight flywheel weighted 5.8 kg (12.78 lbs).

A new coating [...] led to a new design.

In late 2021, TTV started offering the first version of the flywheel with a new nitride coating. It is used a titanium, hard ceramic material applied as a vapor over metal alloy components. It hardens and protects surfaces from heat, scratches and overall wear.

Below are few of the original plain designs with the nitride coating. You can see the non homogenous aesthetics of the coating over the surface of the flywheel. 

The only area that benefits from the properties of nitride coatings is the hub and spline. It's where the overwhelming majority of heat is transferred between the crankshaft, flywheel and input shaft of the transmission. 

"Our flywheel spline is harder than a standard BMW spline and the same length so our product is superior to a standard flywheel spline without the nitride treatment.

We nitride the flywheels because a customer of ours has a forced induction cars. We thought it would be best to continue with it as a standard practice until we change the design so that only the drive hub is nitrided.

Having 1 flywheel nitrided is nearly the same price as doing 10 so makes sense to have them all done together to keep costs down for the customer."
Ben @ TTV 

The new 2 piece design. 

The nitride coating is excessively expensive. TTV's concerns were about cost and technical requirements. To achieve their cost targets and market viability, TTV used a 2 piece design they previously developed in OE contracts with Super Sport car manufacturers. They cannot mention names due to NDAs.

I was able to review the latest design in-hands and experience it for myself as a local member had it fitted to his S65.

The 2 piece design divides the flywheel at its core: the hub and its spline can be moved and removed entirely without the bolts sandwiching it to the crank. It feels alien at first - but it works. 

The latest DCT design retains the titanium nitride coating on the spline. The hub and flywheel were further machined for weight optimization. The flywheel features varying diameter speed holes by the circumference - approximately 500 grams are shaved with this new design.

In addition to removing weight, they help in balancing the flywheel. No matter the design improvements, the flywheels are dynamically balanced and smaller holes are machined to precise specifications. 

"Balancing holes are added until the flywheel is perfectly in balance, the amount of balancing holes will vary on each flywheel. The flywheel is safe past 9k."
Ben @ TTV

New hardware. 

The initial design was machined to take N55/S55 bolts. The latest design comes with bolts supplied by TTV and specifically graded for use on the S65. They retain the original BMW torquing procedures. 

The MT 6spd version remains unchanged!

The same design remains. It is machined to fit with the 09+ OEM clutch. The nitride coating wasn't deemed necessary on the MT. 

Up next: we get the original version fitted to my S65. 

I cover the mission critical steps to completing this installation correctly.