Karting chassis question from my lad....

[silverback mike]

Hi folks....
why are kart chassis are made from Chrome Molybdenum Steel and not an Aluminium Alloy, besides regulations. Is there any reason why this couldn't be done?
Thanks
Mike

[HustleRussell]

silverback mike said:

Hi folks....
why are kart chassis are made from Chrome Molybdenum Steel and not an Aluminium Alloy, besides regulations. Is there any reason why this couldn't be done?
Thanks
Mike

I know very little about karting but a limited amount about engineering materials and chassis fabrication from passing interest...

Steel, first of all, has a higher tensile strength to weight ratio.

Chro-moly steel has a relatively low content of alloying carbon which means that while it has a higher tensile strength and greater hardness than carbon steel, it is also exhibits greater elasticity and a greater resistance to work hardening- that is, it will withstand repeated deformation within its yield strength limits while reliably returning to its original shape and without hardening and cracking with repeated cycles.

On the downside it is rather tricky to weld.

But it can be readily brazed- and as it happens, brazing is the preferred method of joining steel tubes for bicycle and kart frames and space frame car chassis. This is because brazing is a lower temperature process- it does not require the tubing material to be heated into a moulten state or cause localised hardening of the material as welding does.

Wrapping up, in the context of a kart frame, Chro-moly steel has the required springiness to enable a level of flexibility in a kart frame which, apart from the pneumatic tyres, if the only form of suspension a kart has. It also has the toughness to flex in this way repeatedly thousands of times without losing its ‘spring’ or failing by cracking.

A welded frame, be it Carbon Steel or Aluminium, will fatigue at the welded joints in the HAZ- Heat Affected Zone.

Also, Aluminium in particular has a very undesirable tendency to work harden when repeatedly elastically deformed which means that you’d need more aluminium to provide the same durability as the steel frame and the aluminium frame would then be too stiff and inflexible to provide any kind of ‘suspension’ effect.

[silverback mike]

Much obliged to you - great post