The Freeline axle range is very broad to guarantee the best possible performance of the chassis in relation to the features of track and driver. The axles are classified according to their rigidity. In the list below, the range of the most widespread Freeline axles is listed from the softest to the hardest:

1. model S of module 335
2. model B of module 362
3. model D with 2-mm and 2.5-mm spacers, respectively of module 407 and 494
4. model F of module 452
5. model M of module 543
6. model K of module 769

The Birel chassis are supplied by the manufacturer with 1040-mm axles model F for the 100 range, and 1040-mm axles model M for the 125 models. This equipment is a good starting point as it ensures the proper combination between insertion, smooth flowing, support and traction.
Let’s know examine the other options in detail.
The axle B belongs to the family of soft axles: it ensures more traction, smooth flowing in bends and a more effective braking compared to the range of harder axles.
On the other hand, soft axles penalise drivers when entering curves and bends quite a bit due to the “softness”.
It is used with a 100-mm rear hub and a 139.8-cm track.
Models S and D are also part of the same family: these are also soft axles to be used following the same principles as model B. The range of “soft” axles is better suited for performing tyres with a hard frame.
These last two models have given excellent results in the U.S. Championships races.
Moving on to harder axles compared to model F , we find the M model: in 90% of the cases it is used in the 125cc , since the engine has a greater power and the chassis is strained by a heavier load.
This axle is recommended if there are problems with inserting the forecarriage.
It has to be used with 75-mm and 100-mm hubs and with a 139-cm track.
The K is even harder: it can naturally be allocated to non-rubberised urban tracks which are very slippery. It ensures excellent directional stability to the forecarriage.
With this axle, the set-up of the rear axle has to include a 138.5-cm track and 75-mm or 100-mm hubs.
The axle behaves in a markedly different fashion depending on the different axle families: if we want to achieve a compromise, we have to alter the length of the axle itself.
In fact, if type and track are the same, a longer axle bends less than a short one. This happens because the combination hub-axle becomes more rigid due to a greater interpenetration between the two. To give a practical example, if I need a bit more traction with a 1040-mm F axle, I can stick to the same model (F) by simply using a 1000 mm axle.

AXLE BROCHURE TO BE DOWNLOADED