Abe’s 29 plus or minus

Abe and I met about 5 years ago at the local bike shop where i was displaying my bikepacking rig as Isaac was giving a talk on the art of bikepacking.  I remember Abe talking about wanting a custom bike some day and that if he were to pull the trigger it would be for a gearbox build for its practicality in touring – very little maintenance and virtually bombproof.  Fast forward 5 years and that’s not at all what we made.  Since then he has been riding a Salsa Woodsmoke that has treated him well but like all carbon frames there is a little bit of trepidation when he is out on a long bike tour in such places as Baja California.  For example how the head tube has no metal inserts for the integrated bearings to sit upon which may be ok but not confidence inspiring. How if the frame breaks your tour is done. With steel you can bend or get it repaired almost anywhere in the world.  Yes that does happen and it’s a real thing!  He knew he was going way up in frame weight but he wanted something that rode like the Woodsmoke but in steel. He wanted the super short chainstays and as big a front triangle for storage, lots of bosses for a bolt on bag and bottle attachments, as well as the well-loved but rarely used portage handle. He chose Paragon Rocker dropouts for wheelbase/chainstay/tire size adjustability; a tapered head tube mostly for that integrated look with the fork crown; water bottle bosses on the lower seatstays that would house a tall thermos and avoid the legs on a small puffy-stuff rack that would carry maybe 5lbs of stuff (in lieu of a saddle bag that sways up high and isn’t great with a dropper post). The rack has high/low mounts so it can be as close to the tire size he chooses whether it’s 29×2.3 or 29×2.8, though likely never over a 2.6 he says. The rest was up to me on how to connect the dots.  I built the bike with different geometry than the Woodsmoke but with the fit he has come to love on his old bike. It’s slacker and longer – more Forward Geometry – and more fun and confidence inspiring.

I asked a friend involved in the Trek Stache+ design for advice. I had been shown an early metal prototype of that frame so that’s what i was going off with where this build was going. He said that they kept “throwing material at it” (the frame) to make it strong and stiff enough since an elevated driveside chainstay introduces potential for lots of new stress risers in places double-triangle frames don’t have (like the middle of the seat tube), and introduces lateral flex of the rear triangle and rear wheel from the dropout being cantilevered out there – especially with low-mount dropouts like the Rockers.  As far as I know, Doug Bradbury made the first known MTB of this design way back in the 90’s sometime as a Manitou (see below photo). The benefit is pretty obvious: you get rid of the pinch point of the tire/chainrings/chainstay so you can run shorter chainstays with a bigger chainring/s. Back then i think it was more about getting rid of chain-suck (we were using 3x’s) and chainslap while not going full elevated chainstay which was found to be flexier and weaker. This was a middle ground of adding more frame strength, less flex and similar same ride characteristics of a double-triangle frame. I’m not sure why it didn’t catch on until decades later…

Manitou asymetric e-stay
Photo swiped from @secondspin Instagram
IMG_7371
Tapered head tube for IS41/52 headset, internal stainless housing for dropper post, and a big gussett since Abe is gonna jump and rail on this bike and it doesn’t only look cool it’s practical.
Abe2
With the Rocker dropouts you get about 18mm of swing for chainstay length adjustment, to add tire clearance or make the bike a singlespeed, or just have different chainstay length based on route or ride characteristics. The cutout is for heel clearance since with super short 410mm chainstays and a Boost rear end with low-mount dropouts it gets tight. 
Abe-outside-DS
I wanted as much bracing as possible without adding too much weight. It was difficult to fit the chainstay braces and not interfere with the tire, heel, and mostly the chainring and chain itself.  Lots of moving parts to visualize in 3 dimensions and mocking it up as i built the frame was the only way i could accomplish it. Yes, that’s time consuming!
Abe-outside-NDS
You can see where the internal dropper housing comes out and goes back into the seat tube. I used to make this happen on the driveside but with all that is going on over there with the gussets and chainring i swapped sides.  I added that little ovalized tube between the lower downtube and seat tube to resist seat tube twist, another suggestion from a friend. It wasn’t something I had thought of but another reason to continue the driveside chainstay to the downtube with a brace connecting the chainstay to the seat tube if I ever build an asym-e-stay like this again.
Abe-portage
The portage handle has an internal cable routing port so the housing doesn’t have to go around the handle and get in the way of tire clearance, and just keeps it tidy. The Salsa rack-lock collar is a cool way to attach small racks without adding more holes to the frame.
Abe-prebuilt-2
Before paint i built up with parts off my bike, didn’t take more than 10 minutes since i didn’t have any internal cables to deal with and the size is similar to my own bike. I loved the ride characteristics! Super fun geometry and felt like no other 29er i’ve ridden or built.
abe-rack-test
Puffy-stuff rack. In reality this is pretty beefy but still under 400g. Being a full custom rack it only fits on THIS frame and has a high/low position for getting it as low to the tire as possible without buzzing the rack contents/straps.
Gusseted-seattube-rear
Gussets got ya covered…and a ton of welding.  I kept throwing more material at this just to be sure it doesn’t crack here. Being a bent downtube mitering these gussets were a total PITA.
IMG_7596
This is the weak point of the frame so i made sure to gusset it to keep it strong and stiff laterally – as much as this design allows. The gussets are cut from 4130 that is 0.058″ wall thickness.  Next time I make a frame like this I will probably choose to continue the driveside chainstay to the downtube so the bend doesn’t have to be so severe to meet the seat tube, and there would be less need for the gussets on the seat tube. But then the downtube would need a sleeve or to use straight gauge or a really long butt at the BB end.

2 thoughts on “Abe’s 29 plus or minus

Add yours

  1. Beautiful! Aesthetically, and functionally! This is the right direction for bikepacking evolution! Very pleasing to read this build up! Y’all are some bike wizards!

Leave a Reply to Mike Cancel reply

Powered by WordPress.com.

Up ↑

%d bloggers like this: