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Automotive Components

Defontaine’s excellence renowned for the design of flywheels and ring gears

Defontaine designs and manufactures flywheels and starter ring gears using high-performance industrial equipment. Our production lines are automated and our distribution platforms are designed to ensure secure delivery and supply. This production tool, combined with skilled staff, guarantees high-quality production of starter ring gears and flywheels.

Our expertise allows us to provide for the complete supply of parts ready to be mounted on car engines as first-tier subcontractor for many of our customers.

Millions of starter rings and flywheels are produced in our factories every year to equip new vehicles. Our expertise is recognised by manufacturers and equipment suppliers throughout Europe.

Guaranteeing costs and deadlines through lean manufacturing

We implement a detailed monitoring process for each project we undertake with our customers. Our customers call on our expertise in the design and production engineering of precise parts based on specifications. We implement a transparent and comprehensive project planning to ensure full visibility for our customers of every step of the production process.

We rely on our internal lean manufacturing process to promote the visual aspects and simplicity of each process. We design accessible, easy to use tools for our production sites, based on a time-saving process.

Our organisation is renowned for its excellence and uses various methods, such as VSM, Takt Time and Kanban. As a result, we are constantly eliminating all non-value-added transport, overproduction, defective parts and oversized stocks.

anneau d'inertie pour moteur automobile du groupe defontaine

Starter ring gear expert

At Defontaine, we use special processes for each part designed in our workshops, for the production of parts such as starter ring gears.

We define the material specifications and heat treatments adapted to the intended use of our products based on starting torque and engine speeds, for the design and manufacture of starter ring gears. These materials are manufactured by approved and certified steel mills.

The gears undergo hardening and induction tempering processes to obtain the required hardness values for the selected steels. We monitor the process in order to control all the significant parameters of the machine related to the quality of the hardened area (depth of hardening, hardness, etc.), ensuring a quality level complying with the highest automotive standards.

The starter ring gear transmits the torque from the starter to the engine crankshaft. The stress levels on the gear are calculated and verified based on calculations developed by Defontaine.

Do you need flywheels and ring gears for your engines?

Our range of flywheels and ring gears

Defontaine is a partner of the most prestigious car manufacturers and the main Tier 1 equipment manufacturers.
The starter ring gear transmits the starter torque to the engine crankshaft. From design based on functional specifications to production based on drawings supplied by our customers, our starter ring gears are unanimously recognised for their durability and quality. We adapt to your hardness and dimensional requirements thanks to our flexible production unit based in Tunisia at the gateway to Europe. We guarantee the best costs and delivery times on the market.Millions of cars are started every day throughout the world thanks to Defontaine starter ring gears.
The flywheel is sized based on the following non-exhaustive data:
  • Gearbox casing
  • Crankshaft nose dimensions
  • Clutch geometry
  • Maximum engine speed
  • Data on acyclism
  • Clutch friction force
  • Tightening torque for crankshaft mounting bolts
  • Operating temperatures
Defontaine Flywheel
Based on this data, we carry out the CAD studies to meet dimensional and inertia requirements, and perform finite element calculations to pre-validate the design and determine the material before manufacturing the prototypes. Depending on the calculated constraints, it is possible to use the following materials:
  • Lamellar cast iron (200 to 300 Mpa)
  • Vermicular cast iron (300 to 500 Mpa)
  • Spheroidal cast iron (400 to 700 Mpa)
  • Steel (above 700 Mpa)
Inertia rings are components of the dual-mass flywheels, and are dimensionally designed based on the following non-exhaustive data:
  • Flywheel housing
  • Inertia
  • Maximum engine speed
  •  etc.
Our forging and machining production facilities allow us to produce the most complex geometries for this type of ring, optimising the material used to produce these parts. Depending on the calculated stress levels, the following materials can be used for the flywheel of the inertia rings or peripherals:
  • C10 C15 or S355 steel
  • C35 to C45 steel
inetia rings defontaine
Defontaine enables manufacturers to obtain the required information on engine speed or wheel speed using timing rings. These products are partly manufactured using the same process as a starter ring gear, and fit perfectly into Defontaine’s production lines.All types of steel, from C15 to C45 as well as S355, can be manufactured to comply with customer requirements, with a wide range of dimensions from 100 mm to 350 mm.
timing rings defontaine
To respond to the growth of the electric vehicle market, the Defontaine Group assists major clients in the design of new products for hybrid and electric vehicles. Many products are currently being developed to meet the challenges of reducing the level of greenhouse gases in the automotive industry:
  • Ring gear with optimised and helical gear quality
  • Planetary gear ring with internal helical gear
  • Parking brake wheel
  • Pawl ring
Defontaine is continually adapting its processes and production resources to support the production engineering of these new products.
E-mobility Components defontaine

Why choose Defontaine flywheels and ring gears?

The design of flywheels, starter rings and inertia rings is validated on our test benches for your safety and the safety of your customers:

  • Burst test
  • Torquetest bench
  • Starter ring gear unfitting test
  •  etc.

and in an anechoic chamber to characterise the noise level in operation.

At Defontaine, we control all the stages of our production through the supply chain. We carry out audits to qualify and take responsibility for the qualification of materials from our suppliers. Our factory in Tunisia, the gateway to Europe, and our logistics platforms positioned close to our customers, allow us to offer optimised costs and control of lead times.

Our expertise provides for the outstanding quality of the materials used for your engines, with a short supply cycle.

Sectors concerned

Associated services

Study & design



Spares & Services


Defontaine is a specialist in flywheels and starter ring gears for internal combustion engines, and focuses on the development of components for e-mobility, providing advice and guidance in finding the most suitable solution for your application. We are at your side to develop and industrialise high-performance products.

Our key processes

Roulé-soudé par étincelageFlash-butt welding
Usinage et rectification de précisionPrecision machining and grinding
Trempe sous pressePress quenching
Traitement thermique par inductionInduction heat treatment
Procédés spéciauxSpecial processes

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