Mr Zee

Stolen at gun-point from a friend of mine on 19th June. On Mains road in Kenilworth, Cape Town. Unfortunately no record of Frame# Bike is stock standard, as per specs: https://www.giant-bicycles.com/za/trance-3-ge-2018 Only upgrades: Black and silver Gobi saddle, XT shifter and Yari Fork- Serial# 04T80411695

I presume the sort of heat you refer to is way beyond that which is generated by MTB discs? Perhaps with motorcycles the sort of forces and temperatures involved make this tensile 'advantage' more relevant? This still implies that the motorcycle engineers have stipulated their disc orientation through some extensive r&d and it surprises me that the MTB industry have ignored this- I suppose at the speeds and forces involved with MTBs, it does not really matter and it is thus some sort of fashion statement...

I appreciate that, but the principle remains the same- why have the two industries opted for different configurations?

This has been puzzling me for a while, as I have owned several motorcycles and the arms of the disc rotors on them sweep backwards, rather than forwards, as indicated clearly on all bicycle disc rotors with angled or swept arms (see the two images attached). A mechanically minded motorcycle friend explained that most metal is stronger under extension, rather than compression. The motorcycle disc rotor arms in the photo are thus under extension (caliper grabs rotor and it pulls on hub via rotor arms, which are trailing, thus being stretched- good and strong...) In the case of the bicycle, the rotor arms are under compression (caliper grabs rotor and it slows hub with leading arms which push back against hub- not as strong...) This may be purely academic, as there certainly haven't been any instances of disc failure that I have heard reported, but it interests me that two industries using discs are so adamant about the direction in which the rotor arms HAVE to point and, yet they have them opposite way around. Is there something about bicycle disc technology that is different? Can anyone shed some light on this for me??