Elevated chainstay fatbike

F23-snow-frontElevated chainstay bikes usually just plain ugly. But they’re practical for a few reasons.  They prevent chainsuck and allow for shorter chainstays for a given tire size than on a traditional double-diamond frame without any dimpling/crimping of the tubing.  They are  less stiff laterally at the bottom bracket but especially on a fatbike running 5psi..I am not sure I give a damn.  They also may fail at the seat tube if not built properly but there are many still around from the late 80’s that show their potential longevity.

Built up!
With skis and Jandd Trunk pack, fits wider skis than these or Nordic skis.
Holds the skis tightly so they don’t hit me in the back of the head.
Brooks Range Mountaineering ski straps bolted to the rack braze-on.

This is my 4th fatbike build. I’m still riding the first one but it got a nice facelift (black frame below).  The latest frame is a much nicer version of my 2nd fatbike that also had elevated chainstays.  Generally that was a “prototype” frame created to test some stuff for a friend (along with testing my framebuilding abilities at the time).  That frame fit Big Fat Larry’s on Clown Shoe rims and had the same basic geometry as the Surly Moonlander (brown bike below).

Number 9, 1st fatbike.
Number 11, 2nd fatbike
Number 21, 3rd fatbike
Number 21, 3rd fatbike

The newest frame’s design was inspired by the many old MTB elevated chainstay bikes, but also because for fatbikes it makes even more sense. Especially with 4.8″ tires on 100mm rims, there is very little room between the chainring and the chainstay when you give the precious little room for tire clearance.  Shorten the chainstays a bunch and it gets even harder.  The Surly Moonlander is offset in the driveside direction by 28mm to accommodate the need for a better chainline and increased tire and chainring clearance.  E-stays has been done before on fatbikes (i.e., 3D Racing, Minneapolis Bike Company’s “Murphy”) so it’s nothing new. Nnothing ever is with bikes these days.

This fatbike’s geometry was inspired by a conversation with Mike Curiak who likes his fatbikes to have similar geometry to his “all-mountain” MTB rigs – short chainstays and slack head tubes.  This usually translates into long front centers and a bike that’s not great at slow speeds or climbing hills (wheel flop from lots of trail). I’m paraphrasing and expanding on what he said, but Mike argues that the traditional geometry model doesn’t fit the fatbike world with its low pressure fat tires, especially while on variable and soft ground.  Having a slower steering rate (from the slack head tube angle) and a long front center makes it more stable even at slow speeds especially when there’s soft snow for the front wheel to plow through.  You don’t swerve as much while trying to hold your line as you do with steeper headtube angled frames. The short chainstays provide increased traction and float better with the riders weight more on top of the rear axle.  In addition to the slack head tube angle, having a greater % of your weight over the rear wheel also helps reduce the slow speed twitchy steering from any slight movement of the bars and that stops the wheel to from diving one way or the other because of reduced traction while riding on snow.  I’ll see how these theories play out when I get to riding the new bike but I trust Mike when speaking on fatbikes since he’s been riding them longer than most and with many more geometries than others.  My previous fatbikes have had much different geometry with 69.5, 70, & 70.5 degree head tube angles, and regular chainstay length for fatties (447 for the black one, 467 for the Moonlander e-stay, 450 for the newer orange one).  I’m pretty “sold” on the slack head tube theory but not yet with the short chainstay part. Mainly because I think of it in terms of a ski – longer skis float better in snow than shorter skis.  So a longer wheelbase bike should (in my mind) offer better floatation and more stability — a Cadillac versus a Jeep.  I’ll update with any thoughts of course later once I get to riding it more.F23-snow-Side

This frame has a 68 degree head tube angle, 72 effective seat tube angle, 24.5″ top tube, 715mm front center, and a 45″ wheelbase (sorry for not sticking with the same units).  You’ll likely notice the head tube, it’s a rather long 170mm since I like having my bars level with my saddle using as few headset spacers as I can. The fork is also mine with a 450 axle to crown and 50mm of offset giving the bike 100mm of trail (93 of mech. trail). Even though it looks like more, it’s got 6cm of BB drop for a BB height of just over 12.6″ using the Bud/Lou tire combo (without accounting for the sag from low tire pressure).  For parts, it’s built up with a XT clutch rear derailleur, a 26t ring on 170mm crankarm Surly O.D cranks, and a 10-spd XT 11×36 cogset.  If a SRAM X9 would fit without the crankarms hitting the chainstays I’d have chosen that for more gearing options using Wolf Tooth rings. The front wheel is a Clown Shoe with a Fatback 135 hub and the rear wheel has a 190mm Borealis hub. I made the stem – 90mm with 8 degree rise and it’s clamped to a Watson Ti “Revelation” bar.

For those interested in some fabrication details, i used a 38 x 1/0.7/1 True Temper Supertherm for the downtube with the longer butt on the bottom bracket side.  That way, it stiffens up the less-supported BB and also let me weld the e-stays to the thicker wall of the tube.  I supported the e-stays at the bent seat tube (31.8 x 0.035″) with a piece of streamline 4130 (1.18 x 0.5″, 0.035 wall). This should provide superior stiffness and strength than a plate but that’s just my take on it.  The 3/4″ x 0.035 4130 chainstays were s-bent by me and mitered like seatstays to attach to the downtube (definitely had to spend some time on that one). The hooded Paragon dropouts were key in allowing a higher placement of the chainstays on the hood but getting the derailleur hanger at the right angle according to Shimano’s specs. I made a wishbone seatstay to get the huge tire clearance as my current tube bending mandrel isn’t tight enough in radius to get that much bend so soon before the seat tube (I have a 9.375″ mandrel and think you’d need at most a 7″ if not a 5″).  I routed the two cables (rear brake and derailleur) through the top tube and externally from there to the rear dropouts.

The color is a bronze powdercoat to match the root beer colored Clown Shoe rims. It has little silver specks but without sun they don’t sparkle.  The rear rack will hold my skis and a Jandd trunk pack while I hunt for turns. Just need some snow!

about 1cm clearance on all sides.
Plenty of room for Lou with 16.9″ (430mm) chainstays!
Nice new 190 hub and sweet finish on the Surly rim

12 thoughts on “Elevated chainstay fatbike

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  1. Oh, I can do ugly. Are you seriously challenging me? We should probably get Garro in on it too, he and I have had a “worst frame picture” contest going for a while. I think I won by posing a frame in front of the diaper pail.

    I have always wanted to take a Paragon head tube and drill some big speed holes in it… maybe this is my chance. There are a bunch of hideous dropouts that Nova sells that would be good… make the seatstays larger diameter than the chainstays (A LOT LARGER!)…downward curving toptube…huge long bi-lam lugs with holes drilled in them? Oh, and I *like* headset spacers… so I’m going to do a 100mm head tube and 100mm of spacers.

    I think mixing joinery styles would be good too. Big huge fillet for the toptube/headtube, then minimalist TIG for the downtube?

    See? Just off the top of my head I totally kicked your ass. Now go ride your pretty little fatbike.

    1. Oh man…that’s freaking awesome. I can already picture it, please do it! I’ll be happy to lose if you build yourself a fatty to ride in Park City and piss off the nordik’ers. We could have a category at the next NAHBS even. Bikes nobody can buy not because they’re too expensive but because they’re hideous!
      But did you SEE my 2nd fatbike? The other brown one? It’s even uglier and it actually has some of the “features” you mention in your comment… Seastays larger diameter than the chainstays, check! The BB cluster is a veritable clusterf*&k of tubes:

  2. We would need some kind of secret society – you bring your ugly bike with a “UB” somewhere on it so others will know. Then we can have a vote on the ironic/intentional winner and the non-ironic unintentional one. I have a feeling the overall would go to an unintentional entry, but who knows?

    Might be fun to have an unsafe-bike contest too. We’ll put on full body armor and takes turns riding them off a curb. Whichever bike shatters in the most satisfying manner wins. Bonus points if the bike also won a “real” award at the show. If your frame breaks on the first pedal stroke, or when someone sits on the saddle, even more bonus points.

    1. I think people will know just by lookin at it, no need for a “UB” badge! The unintentional entries would be hilarious since we could ‘brand’ them as UB and totally offend the creator.
      Man, this is starting to sound a bit like Sadoff’s bike show award categories:
      I laugh out loud every time I read that post.
      The drywall bilam is by far the unsafest thing I’ve ever heard of! I’d love to have the category for the most “environmental” bike where if you left it outside for more than a month it’d biodegrade completely. Only by constant care would it live (literally) longer.

  3. I am thinking glued-together drywall covered with a thin layer of carbon fiber for appearance (bi-lam!) might be a good material for the unsafe bike contest. Think of the dust cloud when it disintegrates! And as long as you kept the carbon super thin, I don’t think you’d cut yourself on the shards or anything, either. You could go down in a cloud of drywall dust and get up with practically nothing left of the frame!

  4. Full disclosure on this build and some words of caution for people attempting this type of bike – watch the chainline and S-bend chainstay interference. Specifically, i put too much bend in the 2nd bend so it is too close to the cassette. So much so that my chain rubs on the inside of the chainstay while in the lower cassette cogs. I’ll try messing with the crank’s chainline with the BB spacers but..nothing much else I can do about it now. Crimp the stays, shorten the chainline, and deal with it till the next try. Experimental build, didn’t have the 190 axle and wheels on hand, should have waited! Live and learn.

  5. So, how does it ride in soft snow – does the short chainstays and slack angles make for good soft snow handling? A super interesting bike!

    1. Jay,
      I do like it better than more normal geometry in soft snow. Positioning your weight over the back more has a big benefit for pedaling and maintaining momentum through soft snow. Downhills you have to use more body english to weight the front tire more so you don’t wash out, but I think that may be able to be helped with a shorter top tube/front center.

      Short chainstays give better traction while pedaling and better soft conditions stability, and mixed with the high trail/slack HTA which unweights the front axle and gives the wheel the freedom NOT to dig in and take you in the wrong direction on a narrow trail (the soft unpacked sides). You still get wheel flop because of the high trail and your weight towards the back, but there’s no ‘consequences’ to it, if that makes sense. Your front wheel can kinda wander a little and plow through the snow and not take you off your desired course.

      I think i’m realizing fatbikes are like all other bikes, you can’t have just one if you ride in different conditions. I would not take my XC bike to Whistler, so for what I envision the mid-west to be like (or places that are always groomed) I’d have a more ‘regular’/steeper longer geometry fatbike to cruise the miles away.

      I’ll have more thoughts on this as the winter goes on since I’m making v2 of the latest E-stay fatbike, and it rides a ton different than my 1st e-stay fatty. I had a whole blog post of my thoughts last year but decided to get more time on them…and then winter never really came to my area 🙁

      1. That makes sense, thanks for taking the time to reply. In my personal experience, high trail/slack HTA definitely makes for a nice snow bike (or at least all the steeper HTA ones I have tried don’t ride well in snow), and now I am wondering if a shorter chainstay would improve things even more. Do you have any plans to make frames like this for customers?

      2. I’ll definitely make short and slack fatbike frames for anyone! In fact I have two in the works right now. But they won’t look like this e-stay one. I’m drawing up v2 of the e-stay one this week since it’s starting to snow finally…and hope to build it up on one of the upcoming weekends

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