Custom Fat Bike - Paint, Prep and Build

Since the last post I brazed the fillets on the seatstays, attached the cable stops/guides, and brought the frame over to Hiawatha Cyclery to get the head tube and bottom bracket shell faced and reamed/chased.  A big thanks again to Jim and Mark for all the help and service!

Looking back, I should have painted the frame before the facing and chasing... oh well, lesson learned. After taping off the headset cups and bottom bracket threads, I gave the frame a few coats of dark gray primer over a period of a couple days.  And that's how I'm going to leave it; I just want something to keep it from rusting, and I like the matte, dark gray color.

I also skipped the framesaver, I was just too excited to build and ride this thing!  If it holds together long enough to rust out, I'll be a happy camper.  Once the paint was dry, I attached the head badge with some strong double-sided tape from 3M, and the frame was complete!  In the end, I think my first frame turned out well... thanks to a fair amount of luck.

Now it was time to build it up, which proceeded without any major, unfixable issues.  The chainstays ended up a bit offset near the bottom bracket, but two 1.8mm spacers on the drive side centered the cranks nicely.  This also gave me some extra chain/tire clearance.  I had been concerned about the crank arms being too close to the chainstays, but I ended up with sufficient clearance.

The disc tabs on the Enabler fork weren't aligned correctly to work with the Avid BB5 caliper/front adapter, but a couple washers fixed that issue.

Unfortunately, I didn't research front derailleurs before building the frame.  I brazed a cable stop to the back of the seat tube assuming the front derailleur would be like all my others; bare cable running to the derailleur from a stop on the frame.  The Shimano direct mount derailleur I ended up using has a built-in cable stop... I should have added a cable guide instead of a cable stop.  A few minutes with a small hack saw removed the narrow end of the stop, a little black paint, and now the stop is simply a slotted, cylindrical cable guide.  It should work just fine.

My lack of research regarding front derailleurs also became apparent when mounting it to the frame.  I'm pretty sure I'm running it higher than it is supposed to be; it is hard to tell since the crank has 2 rings and bash guard, and I'm used to setting the derailleur height based on a third (outer) ring.  It shifts alright so that's good enough for me.  The issue is clearance between the top of the chainstay and the bottom of the front derailleur's chain guide.

The main discrepancy between the plans and the final product has to do with the geometry.  Once built up I measured the angles and they came out slacker than planned (which is better than coming out steeper, in my opinion).  The planned 71 degree HT and ST angles both ended up at 69.5 degrees.  In the end I think it was a blessing in disguise, and likely caused by messing up the angle between the chainstays and the seat tube.  My hunch is that if I measure the BB drop, it'll be more than originally planned.  The quality control dept. got a little lazy near the end of the frame building process...

So far I've gotten out on 2 rides; both had a fair amount of pavement, but one included a lot of doubletrack with sand, and the other had some tight singletrack.  I hope to get in another singletrack ride soon; I'll wait until then to write up a full ride report.  At this point, it is comfortable, handles predictably, tracks straight through sand without any squirming, and has a ton of traction in the turns on singletrack.  More on the ride soon.  For now, here's a photo of the bike in its natural habitat (MN River Valley) and a full spec list...

Full Spec
(I tried to keep the budget low; many of the parts are from the parts bin, or taken off the Poor Man's Pug):

Frame:  4130 Steel with double-butted main tubes, Surly Instigator dropouts, Paragon Machine Works 100mm bottom bracket shell, fillet brazed (mostly unfiled)
Fork:  Salsa Enabler
Handlebars:  Titec H-Bars (front extensions cut short)
Grips:  Ergon GP1
Stem:  Salsa SUL, 120mm x 15 degrees (dimensions are an estimate, but it's a normal sized stem!)
Headset:  Cane Creek Forty (with only one 10mm spacer between the headset and stem!)
Brake Levers:  Shimano Deore
Brakes:  Avid BB5 (front), BB7 (rear)
Shifters:  Suntour XC Pro 7 speed thumbshifters
Front Derailleur:  Shimano XT with Problem Solvers direct mount adapter
Cranks:  Race Face Prodigy DH - Bash/32T/22T - ISIS
Bottom Bracket:  FSA Platinum DH 100mm - ISIS
Pedals:  Sun Ringle Zu-Zu with Beard foot straps
Rear Derailleur:  Shimano Tiagra (short cage)
Cassette:  5 cogs from a SRAM 8-speed cassette (15T, 17T, 19T, 21T, 23T), plus spacers
Chain:  SRAM PC 870
Front Hub:  DMR Single Speed Freewheel (rear) hub, 135mm
Rear Hub:  Salsa Mukluk 3, 170mm
Rims:  Surly Rolling Darryl (front), Marge Lite (rear) with Surly rim strips
Tires:  Surly Big Fat Larry (wire bead, 120tpi)
Tubes:  Surly 26 x 4.0 (the old, heavy ones)
Seatpost:  Ritchey Comp 27.2mm w/ generic QR seatpost clamp
Saddle:  Specialized BG

Woohoo!  It's done!

Surly Krampus

A couple weekends ago I got a chance to ride Surly's newest bike; the Krampus.  It's a fat-tired 29er they are calling 29+.  The bike is built around the Knard tire (29 x 3.0), mounted to 50mm wide 29er rims called the Rabbit Hole.

Even though the frame was too small for me (it was a large), this bike was a lot of fun to ride.  I only rode about 3.5 miles on it, but it was enough to get a decent feel for the bike.  I then rode the same trail on my fat front Fargo.  It was a good opportunity to compare the new Surly to my current, familiar off-road ride.

The Krampus was noticeably faster than my Fargo (the Surly is lighter, which helped).  The Krampus rolled along really well... the front wheel was on par with my fat front when it came to comfort and traction.  The Surly's rear wheel was noticeably smoother and gripped loose sections of trail better than my standard 29er rear wheel.  I don't have very many off-road miles on a regular 29er, so it took a bit of time to get used to the large diameter front wheel.  I ended up really liking the feel of the tall, wide wheel up front.  At first it felt like the front wheel was way out in front of me, but after a few turns it just added to the "ride over anything" feel of the bike.  

I'm glad my custom fat bike will fit the Knard/Rabbit Hole set-up... I'm sure I'll eventually build a pair of these wheels for it.  I liked the ride so much, I think my next frame building project will be a 29+ frame in my size to replace the fat front Fargo.  I always thought I'd build a 36er at some point, but I think 29+ might be a more useful, realistic wheel size.

Two posts this week... scroll down for an update on the custom fat bike project.

Custom Fat Bike - Seatstays

It's been a busy week/weekend so this post is coming a little later than usual.  As I had hoped, I got a chance to build the seatstay yoke, braze it to the frame, and attach the seatstays.  I also brazed in the rear disc brace.  Below are some pics...

The brace between the dropout and the chainstay on the brake side was kind of a pain; for the simple reason that it was hard to hold in pace for brazing.  Using a small clamp ended up doing the job well enough.

The bottom bracket attachment on the jig was just wide enough to hold the seatstay yoke.  Once the yoke was brazed to the frame I was able to cut, miter and braze the seatstays.

As of right now, the seatstays are only tinned in place (an initial brazing pass where I focus on getting the brass to penetrate the joint and form a small internal fillet).  This week I'm planning to build the seatstay fillets and attach the cable stops/guides.  Then a trip to the local bike shop for facing and chasing of the HT/BB and it'll be ready for framesaver, paint, and parts!

Custom Fat Bike - Chainstays Pt.2

Lately I've been forgetting to bring my camera with me when I go do my brazing, so unfortunately I don't have many pics for this post.  Over the last week I got chainstays brazed to the yoke, and the yoke  brazed to the front triangle.  I also built the fillet around the bottom bracket shell.  As soon as it was done soaking I checked the BB shell with the bottom bracket and it still fit...  another possible warped tube avoided!

It's too bad I forgot my camera because the level of jerry-rigging involved to get the chainstay/yoke assembly in place for brazing was quite impressive, if I do say so myself.  The angle of the chainstays is one of the most important pieces to the geometry since it impacts the bottom bracket height and both the seat tube angle and head tube angle.  Once again the jig didn't look all that professional, but it did the trick.

My final project for the week was the dropouts.  I'm using Surly Instigator dropouts due to the fact that they are easy to get, inexpensive, and have the rear disc brake mount integrated into the dropout.

And here is the current state of the project...

I figure by the end of next week I should have the rear triangle complete.  Then another week or so to do all the little things (brake and derailleur cable stops/guides, clean it all up, framesaver, prime and paint, head tube badge).  I'm guessing the bike will be ridden within a day of the paint drying...

Elm Creek Revisited

A rare mid-week post this week...

We're finally getting some mild summer weather in MN, and last weekend I figured I was due for a trip to Elm Creek (the last time I rode there was summer of 2011).  I've had some fun rides at Elm Creek in the past, but they weren't entirely worth the long drive up to the NW 'burbs.  Previous rides at Elm Creek have either been on really hot/humid days, or I was riding with off-roadies.  Not ideal riding experiences in my book.  I don't do well with heat and humidity, and Elm Creek has a lot of open, unshaded trail.  And I certainly don't adhere to the racer mentality of attacking the trail.  I like to go fast, but not constantly... I like to enjoy the trail at more of an "unracer" pace.  I also like to stop and take photos, and ride the technical features.

Last weekend's ride was a completely different story from my previous Elm Creek rides... low humidity, highs in the upper 70s, cruising at my own pace, riding the features, and stopping to take photos.

The trail crew at Elm Creek has been busy since I last rode the trail.  One particular feature I liked was a spur trail that sent you down the banks of a little gully...

A bunch of new elevated features have been added too...

The 2 photos below are of a downhill log ride, with a pretty good slope to it... a really cool idea and nicely done.  It is good to see the trail crew taking advantage of Three Rivers' progressive technical feature guidelines.

Log Ride Entrance

Log Ride Exit

Elm Creek is a REALLY fun trail.  I had a total blast.  The fact that it is so new is a big part of that... the tread is just so smooth and fast.  A couple sandy corners in the prairie sections, but that's it.  The technical features and overall layout are also a big part of it's appeal.

The one exception regarding my fondness for this trail is the number of tight trees to squeeze through... the trail frequently cuts between trees that are spaced slightly wider than a handlebar's width apart.  Narrow bars might be advantageous at Elm Creek (I prefer my bars fairly wide).  In slower sections they're kind of fun, but not so much when they pop up at the end of a fast section.  Being unfamiliar with the trail plays a role in that though...

One reason I think I enjoyed the ride so much last weekend is that I'm finally getting my mind out of "trail maintenance" mode while I'm riding.  Even though it's been several years since I've been involved with trailwork, I still find myself frequently thinking about the trail condition, maintenance issues and possible fixes whenever I'm riding a trail.  It's taken a while but my focus is finally returning to riding the trail, instead of analyzing it.  Part of it is the fact that I wasn't riding at Murphy, where I did most of my trailwork, but I also think the trailworker mindset is finally wearing off.

Murphy will always hold a special place my heart, but Elm Creek might just be my new favorite metro trail!  Nice work Three Rivers and the Elm Creek trail crew; thanks for building a fantastic trail.  Weather permitting, I hope to get up to this awesome trail more often this year.

Custom Fat Bike - Chainstays Pt.1

I got started on the chainstays this week; undoubtedly the trickiest part of a fat bike frame.  I went with a chainstay yoke to provide clearance between the frame, cranks and tires.  The long chainstays give me some extra wiggle room, but the yoke really saves the day and allows me to use the stock bend on the chainstays.

I'm hoping the yoke will be stiff enough to prevent any flex issues; the actual yoke is 1/4" thick 4130 so it should be good.  I'm also hoping the brazing work is sufficiently strong... getting that thick piece of steel up to temperature was tough.

One of the advantages of this frame design is that it will fit Surly's new 29+ wheels (and still have loads of clearance).  I don't have specific plans to buy a second pair of wheels for this bike, but it's kind of tempting since I'll have a bike that'll fit these new tall, fat wheels.  Maybe someday.  If you haven't seen the new fat 29er wheels from Surly, they consist of 50mm wide rims and 3" tires.  Click here for some more info.

After the yoke was brazed, I was able to cut and fit the chainstays.  The jig looks a bit jerry-rigged at this point but it should do the trick.

I also laid down some fillets on the front triangle this week.  Once again the head tube suffered some distortion.  I'm cautiously optimistic that it isn't too severe.  It's good to know that I will never be heating the head tube again.  Part of me thinks I should get it reamed and faced so that if it is junk, I don't put the effort into attaching the rear triangle to it.  I did some quick filing of the fillets, but I don't think I'm going to put a bunch of time into them.  At least not at this point.  That might change once the frame is all one piece... it'll all depend on how nice it actually turns out.

I plan to have the yoke and chainstays brazed and attached to the front triangle this weekend.  Once the yoke and bottom bracket shell are brazed, I can finish the last fillet of the front triangle (a.k.a. my final opportunity to warp the BB shell).  The frame should be coming together fairly quickly now... my fingers are crossed that it'll come out OK.