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TKART magazine Under Review | S55, the “all 30” chassis by TBKART
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18 April 2021
CIK-FIA 2014 - 2021

The approval of the TBKART has been extended until 31/12/2021. In fact, the S55 is in the list of chassis to which the approval has been extended until 31/12/2021 by FIA Karting to try to overcome the production and commercial problems of the manufacturers given the health emergency due to COVID-19.


The chassis is suitable for both use with single-speed and geared motors. In this article we address it in a single-speed version.


A chassis can usually be made up of 30 and 32 mm tubes or a mix. In this case, the tubes all have a hollow circular section of 30 mm with a thickness of 2 mm.


TBKart uses a hand method of welding for the construction of the S55 chassis.


The accessories of the S55 chassis are made of magnesium, a material that is much lighter and at the same time has excellent rigidity and good mechanical characteristics.

The fundamental characteristic of the TBKART S55 model is that of being made up of tubes all with a diameter of 30 mm, unlike the other model of the Italian manufacturer, the S197, which is instead "entirely 32". The S55 is available both in a single-speed version (the one this article covers) and in a gear version. The latter stands out for the obvious accessory kit specific to this type of kart (braking system also on the front axle, gear lever and clutch), but also for the different axle bearing supports.

With the S55, TBKART wanted to create a chassis that in a single-speed version goes well with the grip conditions that most practicing kart drivers from all over the world encounter, therefore tracks that are not extremely rubberised and the use of tyres with a basically hard compound. In order to further meet the needs of the drivers of the various classes, TBKART then differentiated its production, developing a particular body design with geometries dedicated to the Junior classes, which need - given the lower power involved - greater smoothness. On the contrary, for the Senior classes, always working on small production details of the body, it instead favoured grip when braking and smoothness when exiting bends. The reduction of unnecessary welds has allowed a general lightening of the chassis and a stiffening of the body: having fewer welds for the attachment of accessory elements means stressing less side stringers and crossbars, or the main tubes of the body.
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Considering this, the rear bar attachments were eliminated so as to leave the properties of the tubes unaltered in a sensitive area such as that close to the engine, which is very stressed by vibrations and consequently more exposed to breakage. The same logic underlies the decision to eliminate the previous attachment for the support of the exhaust, replaced by a special aluminium support that is screwed to the left plate support. A long refinement work in relation to which TBKART is very proud is that carried out on the quality control of the entire production chain of the raw material the body is made of: 25CrMo4 steel alloy tube. Although so-called chromium molybdenum steel is a material imposed by the regulations in FIA homologated kart chassis, its chemical composition allows - even if only by slightly modifying the percentage of one of the elements (Carbon, Silicon, Manganese, Phosphorus, Sulphur, Chromium or Molybdenum) – the attainment of completely different mechanical characteristics. Finding the right "blend" is the first step in a manufacturer's research and development. The second step is to stabilise and make constant, in terms of quality, the steel supplies from suppliers. It is a long and laborious process, which however in the last 10 years has made it possible to completely change, for the better, the standards that TBKART offered in the years 2010, 2011 and 2012. The current type of steel used, with a low carbon content, is distinguished by its mechanical (tensile strength, yield strength, toughness) and technological (easily weldable) properties.
The latest version of the S55 body has been optimised from a welding point of view. The [1] C's are now welded in a different way. On the other hand, some non-structural elements were eliminated at the rear, such as the exhaust support now screwed to the [2] left plate support and the [3] attachments for the rear torsion bar.
The attachment of the silencer support is made of aluminium and is fitted to the plate support using two self-locking nuts. In this way there are fewer welds that heat and stress the chassis.
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The 30 mm circular tubes of the S55 chassis are hand welded using continuous wire by TBKART technicians. It takes about 1 hour and a half to weld a body.
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