Fat bikes

[Undies]

Been asked to build a fat 26er for a client
Never built one before so was hoping I could get some advice on geo considerations and tube selection (client is keen on stainless fillet)

Thanks

[fortyfour]

Geo depends on whether client intends to use it year round (so trail usage) or mostly on snow. If mostly on snow, you want that head angle slack to get the front tire out in front of you and "push" the big bubble of air in front of you - I've been learning that this helps to stabilize things a bit so you're not fighting those big tires as much when they start to wander. Lowering the bottom bracket will also help to quicken steering a bit but also lower the riders center of gravity to help "ground" the bike. Not to mention that stepping off for a dab it's a shorter trip. If a mix of trail and snow, then you have to consider what the balance of both worlds would be: not too steep but not too slack. More float = more better on snow. 135 front / 170 rear offers up a lot of options presently but I do know that 190 is also coming up too to offer a bit more choices for bigger fatter tires for more float. Rim choice also plays a role in tire clearance - wider means the sidewalls stand more vertically so you'll need to consider that, vs narrower, the tire profile / sidewalls begin to pinch. Personally, I've had good luck with 4.8 out front and 3.8 out back on Rolling Daryl's. Next one most likely for myself will have more room for a bud/lou combo on the same wheelset and spacing.

1x10 / 1x11 setups seem to be best esp. for fat bikes to keep weight down, simplify the whole setup, and eliminate one of the clearance issues. I know on a ride today I'm running a 12/36 cassette with a Wolftooth 30t ring up front and it was a blessing in fresh powder / crust. I'm thinking now a 28t up front would be perfect with that cassette.

Tube selection it's up to you to match ride quality with usage. Build with lots of room internally for water/muck to drain.

Good luck.

[Undies]

We don't get much (any) snow down here in New Zealand so this will be a winter mud ride (we do get lots of rain)
Thanks

[fortyfour]

We don't get much (any) snow down here in New Zealand so this will be a winter mud ride (we do get lots of rain)
Thanks

Did not look at your location actually, but the above still stands for other applications (snow). With that in mind, I'd most likely build it more like a mountain bike then. 70* HT angle, 73* ST angle, 12-12.25" bb height and depending on what you can do with tooling/tubes, short stays (16.5" is what this ones dialed in at and was built a bit more to hit the best of both snow and trails.)

[chumlypogward]

I have nearly finished my fatbike, have been riding it the last few days, but it still needs brazons and paint. There are a few things i came up against, mostly with the drivetrain - as above I had to go for 1x10 to clear the Surly fat larry's, that is with a 170mm rear spacing. The geometry worked out extremely well, it is a joy to ride. There are a few things I will do differently next time, but overall it is a fantastic machine so far.

I have the design in Solidworks, I am happy to send through a layout for reference. I am in NZ too, so if you want to chat about it sometime, let me know...

[fortyfour]

There are a few things I will do differently next time

This especially holds true as you first start building fat bikes. It really becomes a game of millimeters, and you will not get it right the first time. The debate of "just how far can I push this" comes into play immensely. I know the handful I have made, I've learned a lot especially around the bottom bracket area. Not to mention just how much you can learn from physically riding them in all conditions. It boils down to getting the bends and such "just so" to reap the maximum amount of clearance out of everything. I can see where 190mm spacing comes into play after working with 170mm rear spacing and riding out there on the trail, in snow and muck how much tire pressure and the size of the tire come into play. Everything really vibes off of one another.

Bigger tires / wider rims for more float but that creates clearance issues. Lengthening the chainstays helps this, but then you've got a bike that handles like a big boat. Get rid of the front derailleur and you create more options, lower the tooth count of the chainring up front on a 1x setup, you simplify the drivetrain and physically move the location of the clearance needs forward, so you can add more clearance, shorten the stays and get the performance back into the equation. Less is more but more is better depending on what part of these bikes you're looking at...

[randonneur]

Kris, I really appreciate how open you've been in sharing your knowledge in this thread (and many others too). I'm not planning on building a fatbike anytime soon, but if I was, at least I'd know where to start!

[Simonhi]

If I ever "needed" a Fat Bike, Kris would be my "go to" builder.

Looking back through his builds you can see how each time he improves something with every new frame and you can note just how much he pushes the design envelope on what is still a genre of framebuidling that is it it's infancy and finding it's set standards. A very generous guy.

44 Bikes is nailing it right now.

[bencooper]

I like the fist measure - my fat tyre clearance gauge was a little more sophisticated but not much:

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Fat bikes are definitely a thing where you can't just draw it up in BikeCAD and assume it'll work, it needs mocking up and testing with the actual parts used to make sure there's clearance.