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I got a Fat Bike...could use some advice maybe?

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I got a Fat Bike...could use some advice maybe?

Old 01-03-24, 07:41 PM
  #1  
Clark W. Griswold
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I got a Fat Bike...could use some advice maybe?

So long story short the owner at my shop passed and he had a Soma Sandworm with Rohloff that he had stopped riding a while back and now I have it. It was converted to an e-moped and I am converting it back. I have some new tires (Orgin8 Super Cells 26x4.0) but need new cranks. I think I want an FSA crank because I can get a belt ring for it easily from Gates so I can keep the belt drive on it. I am I guess curious how deep I should go on it or just get it functional and comfortable for me? We rarely see enough snow but I do have normal single track near my house.

It is a Sandworm with Rohloff hub, belt drive, Magura MT5 brakes, Bluto Fork 26" tires on probably Surly rims with a Hope Fatsno front hub. Bars are super narrow so I am probably going to widen them up but unsure if I want to go adventure style and stick with some faves in Surly Moloko or VO Crazy Bars or should I do a more traditional flat or riser bar with less sweep back? I am usually not one to be so unsure but I have never owned a fat bike and haven't really ridden one much beyond some test rides and this one for a second in the shop to make sure it was functional enough and the old tires inflated. I don't have pictures yet but it is a pretty blue Sandworm that was built decently enough that it had Rohloff and a Hope hub and good brakes)

I guess I am just excited.
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Old 01-04-24, 08:34 AM
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I didn't even know that Soma had made a fattie.

By modern standards - that is limited to 26x4.0 tires, which are pretty narrow, the rear is spaced at 170mm QR instead of the modern 197 TA. But none of that really matters, as you've got wheels you want to run, and a Rohloff is nice. And if you want to go wider on the front (I highly recommend) that Bluto fork should clear up to 4.8"

Those tires don't look like they're really made for anything but ebike or for people riding fat for style on pavement. If you haven't bought the Origin 8 tires yet, get some 26x4.0 Schwalbe Jumbo Jim tires. I love those for riding both in the summer on trails and in deep snow.

As far as cranks, the bottom bracket is BSA thread, 100mm wide shell. If you really want to do FSA, their fatbike crankset is the "comet"
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Old 01-04-24, 09:19 PM
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Clark W. Griswold
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Currently have the Origin8 tires but haven't installed them and just have them for back up. I got them for real real cheap so it was a wash. Plus a 4.0 tire is pretty wide for me but I know more modern fatties can get wider and that is neat but for a bike I didn't need to put together and came close enough to something I would do anyway minus the conversion and I also didn't have to pay money just time it was pretty good.

I was going through the parts bin and realized I had some 130 BCD cranks old Shimano 600 post Arabesque pre Tricolor and they look a treat and with them polished would be super neat and the belt ring is 130 BCD so I might try this VP 100x164mm square taper bottom bracket and see what is possible. I don't know if long enough but I realize my initial measurements where with a motor and were not the most accurate due to that and I can probably make it work-ish with that much narrower BB. I am going to bring in the cranks and measure it all and see if could potentially work but if not the BB is cheap and will at least get me going till I decide on the FSA.

Thanks for the help. I think Jumbo Jims might be in the future but it looks like I still have a little life on the current tires so my service manager and I decided run those till they start cracking in a year and then replace. They have a little tread on them and hold air just fine and I don't even know how much I will ride the thing but it just fell into my lap and would be fun regardless.
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Old 01-06-24, 05:31 AM
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On Fatbikes, the tires have an outsized influence on the ride. Way, way more than any other kind of bike.
Not telling you to buy the JJ's now, but I've seen someone go from hating his fatbike to riding it exclusively after swapping the tires. Some of them are that bad.

See if your wheels let you run Jumbo Jims tubeless when you move over, that's an additional way to mitigate the drawbacks of a fatty. Tubes are heavy, and the rolling resistance with them is significant.
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Old 01-06-24, 09:22 AM
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I can't help much, but that sounds like a REALLY cool bike with the Rohlof/belt setup. Pics would be great!
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Old 01-06-24, 07:48 PM
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Clark W. Griswold
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Originally Posted by schnee
On Fatbikes, the tires have an outsized influence on the ride. Way, way more than any other kind of bike.
Not telling you to buy the JJ's now, but I've seen someone go from hating his fatbike to riding it exclusively after swapping the tires. Some of them are that bad.

See if your wheels let you run Jumbo Jims tubeless when you move over, that's an additional way to mitigate the drawbacks of a fatty. Tubes are heavy, and the rolling resistance with them is significant.
I can run tubeless no problem but I know I will not be running this bike often so tubeless doesn't make sense for me and a little weight of tubes doesn't bother even if I know they can be a pound which is significant. If I lived in an area with a lot of snow or lived more near a beach or a flat area I would probably want to ride it more but the bike kind of fell in my lap and couldn't say no but I know myself and my riding. I would have built this thing differently had I truly needed a fat bike but in this case I don't really need it and just want it but don't want to deal with tubeless sealant until I know I will be riding often.

I do hear you though and understand what you are saying 100% but I have to be realistic with the number of bikes I currently have an some I don't ride as often and need to sell or replace them.

Originally Posted by cegerer
I can't help much, but that sounds like a REALLY cool bike with the Rohlof/belt setup. Pics would be great!
Thanks it is pretty neat, I will have to get photos once it is finished. Right now I am still figuring out cranks and the square taper set up truly won't work without going to some odd custom builder and having them make something but I think the FSA stuff will work well so I am holding on for that. I also had a leak at my brake master cylinder so I had to replace that which sucks but is what it is.

My boss sometimes did some whacky goofy stuff but also some really good builds. His last mountain bike was one I probably would have ridden had I gotten the chance at that one but then again I helped spec a lot of the parts.
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Old 01-08-24, 02:19 PM
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1. There are square taper BB's out there that are wide enough. Lots of entry level bikes come with them.
My fattie uses RaceFace Turbine, which are another terrific option.
2. The change to tubeless is significantly more difference than you'll see in a road or MTB tire. It's not just the weight, it's a huge amount of energy loss from all that surface area.

3. I ride my fattie on trails in summer as well. I have no other MTB.
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Old 01-08-24, 07:08 PM
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Clark W. Griswold
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Originally Posted by Viich
1. There are square taper BB's out there that are wide enough. Lots of entry level bikes come with them.
My fattie uses RaceFace Turbine, which are another terrific option.
2. The change to tubeless is significantly more difference than you'll see in a road or MTB tire. It's not just the weight, it's a huge amount of energy loss from all that surface area.

3. I ride my fattie on trails in summer as well. I have no other MTB.
There are square taper bbs that have the correct B.B. width but the spindles all show too short I need probably a 190-200mm spindle according to my and my service managers measurements. I had been looking and finally said done. Luckily FSA will work and I found a place that can get me the correct belt rings so all is good on that front. Though if you know of a square taper BB that is for a 100mm shell but has a long enough spindle I might consider it. Race Face looks good as well though but need belt ring compatibility and don't want to mess around with spiders if I can avoid it.

You are seriously making me consider going tubeless now if only I could have a tire butler who could keep everything inflated for the times I don't ride it, I have a lot of bikes that get more minimal usage and honestly I don't want to throw sealant in and have it leak...
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