Hi epicyclo,
Definitely a trials motorbike look going on there.
I would recommend the use of an extra long mudflap on the front wheel to intercept all the water and grit before it sprays the chainset and bottom bracket. We have tried Sturmey Archer hub-brakes in the past and found that if water got in it got trapped and then oozed out as a black liquid for ages. We now use Shimano Roller-Brakes that are more powerful, better cooled than the Sturmeys and when packed full of waterproof grease, are completely waterproof
At Cleland we believe in zero maintenance and big mud clearances despite our use of mudguards. Below is a picture of a modern Cleland test machine. Despite being a full suspension machine everything is protected. The chain runs through tubes, the mudguards move with the suspension and are mounted above the fork bridge and an seatstay bridge so that the tyre/frame clearances are not reduced. It has additional grease ports so that parts can be re-greased without disassembly. With over two years of mud-riding I have done no maintenance apart from the occasional chain lube and squirt of grease, and no parts have needed replacing or repairing.
I hope to use this know how to build a Fat-Bike with similar levels of protection. The On One Fat-Bike with its extra steep geometry and highe bottom bracket is a serious contender. Though the extra wide rear axle would could limit the drive chain possibilities.
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