Pros and Cons of Iron vs. Stainless-Steel Motorcycle Brake Discs

On a conversation about Supermoto brakes, someone asked, which brake disc material is better for Supermoto racing? Iron or Stainless-steel? The conversation continued with some riders who preferred iron and others who preferred stainless-steel. Based on my experience dealing with brakes and racers since 2010 and having discussed the issue with GOLDfren Brakes engineers, my immediate answer was stainless-steel. But personal preference is one thing, in the end hard facts are what matter. So I decided to further investigate to objectively evaluate the most relevant characteristics of these two metals applied to motorcycle racing.

Cast Iron had been the metal of choice without question until the 1980s until the birth of sintered brake pads which was triggered by the government ban on asbestos, a mineral contained in most organic brake pads.   Since then stainless-steel gained the preferred status in most racing categories due to its superior compatibility with sintered brake pads as well as other factors listed below. It is important to note here the exception of MotoGP, they use carbon brake discs which deliver a far superior performance and weight reduction but it only works well when the system reaches high temperatures.

Let's take a look at the more relevant characteristics comparing Iron vs. Stainless-Steel brake discs:

 

Iron Stainless-steel
It is heavier It is lighter
It is quite brittle and more prone to crack It is stronger less likely to crack
It has low impact resistance It is more resistant to impact
It wears more quickly It doesn't wear as fast
Ventilation holes are not recommended to avoid cracks Ventilation holes are possible which allows excess water or debris to be dispersed
It can produce higher friction coefficients especially with organic and kevlar brake pads usually containing asbestos.  It is not compatible with most sintered pads It produces the best friction coefficient when used with sintered brake pads.  It can be used with any type of brake pad.
It is prone to oxidation especially in humid environments It is oxidation resistant
It is cheaper It is more expensive

 

In my opinion, stainless-steel remains the winner, but the decision of using iron or stainless-steel will greatly depend on the careful evaluation of the before mentioned factors, personal preference.

If you have tested certain combinations of brake discs with different types of brake pads and want to share your results please, we would love to hear from you.

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