Guypie

Slapped a coat of primer on this and took it up to the top of Pirongia on sunday for a couple of laps. What a machine! it's better than I expected.

I was worried about the pedal kickback but it really isn't noticeable when decending. On the flow trails it pops really well and soaks up the larger chunky stuff and the big hits very well. Pirongia is pretty smooth so its hard to tell but I think its weakness will be high frequency chattery braking bumps and that kinda stuff. The other issue that might be able to be resolved by adjusting the shock damping settings/air chamber volume is it is lacking a bit of mid stroke support. Probably due to the linear nature of the single pivot so there's no ramp up at the end, though the bottom out is super smooth due to the position sensitive damping. It also pedals up pretty well, but it was hard work mostly due to the seat post being too short to get full leg extension. Though it does weigh in around 17kg so not super light, though it is certainly in the ballpark for a DH bike.

On the whole, super stoked with how it rides.

Will take it for a few more preliminary runs before giving it a proper paint job as there is a good chance I will figure out I need to change something in the mean time. It also needs a few parts swapped out as there are a few issues, not to mention I robbed 2 other bikes to scrounge enough parts to put it together.

More tig brazed cable guides

I drew up a little design for the shock mount on the down tube and got it sent away to a waterjet place. This is something that I would do again in future, but only if I had drawn them up right at the start of the project because the lead times on small jobs at industrial place is a bit painful. So I sat around for a few weeks waiting for my bits to come back and when the eventually did I finally got to see what the end product might be...

(drumroll please)

I finished welding the shock mount today, gave the front triangle a coat of primer and spun up a few spacers for the shock mounting today. I want to put one more brace in the rear triangle and then off to the bike shop to use their head tube reamer and assemble it for a shakedown ride.

First thing I did once I got to this stage was to attach the front to the rear, mostly just to see how it looked. 

Looking good to me

Pivot detail

Next I made a little jig to attach the disc brake tab to the rear triangle

Good bit of practice on the mill

And it did the job, doesn't seem to rub and looks straight

This time I bought cable guides ahead of time because the ones on bike #1 took an eternity to make. I tig brazed them on and was pretty happy with how they worked out. Got into a bit of a routine after the first couple of guides.

Added a little brace there for the reinforcement below the disc tab

The rear triangle felt like it took forever to come together, mostly because each node point needed to be designed and fabricated and usually took a fair few hours. Especially because I stuff things up on a fairly regular basis.

I started with the shock pivot points, there's 2 holes so you can go between 200mm travel and 190mm. This is futureproofing in case I decide I want to go to 27.5" wheels, it will rub the seat tube at full compression on 200mm setting otherwise.

Some wiggly dog leg things for the chainstays

Added some roundy things to the holes for attaching tubes and to preload the swingarm bearings

The tubing for the Chainstays is 22mm and the dropouts are designed for 19mm max, so I pie sliced the end and welded it back together to get it to fit nicely

Then started putting it all together

I like this picture cause it looks like cthulu or a sea beast or something

Lots of notes on the jig so I don't smack the cranks on the chainstay like last time hahaha

And that's a mostly complete swingarm!

Well I let the cat out of the bag a little bit in the show us your shed thread so its time to share round 2. Bike number 1 is still working magnificently, but it is lacking something. A rigid bike is great fun, but boy does it beat you up on a rough trail. So I decided to start building bike number 2 with some suspension travel. I figured I would go right to the other extreme of mountain biking and make a 200mm travel DH bike. There's a couple of reasons for this number 1 - I have never had a downhill bike they seem like fun and looks sweet. Number 2 - I figured I would make a single pivot bike (for simplicity reasons) and wasn't sure if the suspension kinematics would be any good. So just make it have lots of travel to compensate for any flaws and don't worry too much about pedaling efficiency.

I started out by figuring out what I wanted the geometry to be, its mostly very standard DH bike stuff. 63*hta, 450mm chainstays etc. I cant remember what the reach was but it was as long as I could go and still be comfortable. I bought a copy of linkage x3 (mtb suspension design program) and chose the pivot locations and all that kind of jazz, then when and drew a 1:1 scale drawing on paper. That has been super useful and I think I will be doing that for all builds in future.

I had to mess around with the brightness/contrast to get it to show up in a photo but that gets you a rough idea. Next I copied that onto my "jig" that I used last time. It's a piece of MDF with 3d printed standoffs if you didn't follow my previous build. I had to print some bigger standoffs because this has a 44mm headtube vs the 34mm one on the previous frame.

I did the cutty cutty thing with the holesaws and got to this stage:

The seat tube is a recycled down tube from the old marin that donated its head tube and bottom bracket to bike number 1, hence the dent. it also has bottle bosses on the other side near the bottom haha. I cut the pivot hole at the same time as coping the bottom bracket but in future I would do that after welding the main triangle.

I also added some bracing to the head tube and seat tube

It was very difficult getting into the corners with the tig, lots of regrinding tungstens etc.

After that I had to decide how I was going to make a nice bearing pocket welded into the frame. I decided the best way would involve a vertical mill and a boring bar. I happened to have a mill but no power for it or boring bar so I ordered some lovely aliexpress goodies and waited for them to turn up...

that nflixn 9100 looks an awful lot like my ecogoo 9100...

I am going to get 3 phase in my shed at some point, but the variable speed on the mill is worth its weight in gold. Even in terms of dialing in a cutting speed you can just turn the dial until the cut feels/sounds about right. Mine has a belt drive head with a backgear for slow speed so a speed change without the VFD would involve stopping the cut and changing belt position unless you are out by a factor of 5x or howevermuch the backgear does. I also dont really want to use the backgear until I have done a bit more investigation, not sure if it has an oil bath or not and the head has been weeping a little bit of oil so need to address that.

I put the vice off my shaper on it the other day, its actually too big for it and I had to rotate the base to the 45 degree mark so the bolt holes would be on the table. I am just loving this machine though, its so nice to use. I was drilling some holes the other day and the difference between the mill and a drill press is like the difference between a drill press and a hand drill. So smooth and nothing moves, I bet the drill bit life would be significantly improved judging by how smooth the cut is.

It is also slowly getting cleaner, I have a couple of bits of scotch brite and after each job I clean off the chips and scotch brite the rust stains in the t slots etc.

As it stands now:

It's done!

I found myself rooting for this particular colour on the poll and figured that was a strong indicator it was the right colour. Anodised purple accents for maximum 90's mtb style points. Will probably get some purple valve caps just to finish it off. On my computer the images look a bit more blue than the bike does in real life, probably because auto white balance on the camera or something.

Side sharn, my first mountain bike was a 1995 marin rocky ridge. It was a chrome plated ali frame and when I got it second hand it had a purple anodised so it feels a bit like a throwback to that. I still have the frame hanging in one of my sheds, it has cracks in the headtube. Probably becuase of all the horrendous abuse I gave it.

The bars are some aliexpress mx/pitbike bars that may or may not stay, they are way too flexy without the cross brace and the fasteners/holes for the cross brace are a bit sloppy so you can feel a bit of a clunk in the bars when you pull/push on them that is reminiscent of a loose headset. I could probably turn up some little bushings but I'm undecided.

The paint is PPG deltron DG and it is by far the nicest paint to apply that I have ever used. So easy to tell when you have the right amount applied and not a single sag or run on the bike. Theres a couple of less than perfect spots but nothing anyone will notice. I put on some braap wrap to keep it tidy, would recommend so far in terms of application, went on really easily. Currently has the old tyre tube on the chain stay jobbie for protection from chain slap, will probably get some vhs tape when it comes back in stock.

Now all I need to do is go get it dirty!

I was thinking about how this bike might compare to @yoeddynz's bike and managed to find this sales catalogue for the 1990 fat chance range:

https://www.mtb-kataloge.de/Bikekataloge/PDF/Fat_Chance/1990.pdf

It lists a 71 degree head tube angle, 1.5" fork offset. If anyone is interested in trail measurements theres a very nice calculator here:

http://yojimg.net/bike/web_tools/trailcalc.php

the yo eddy works out to 79mm of trail. That must make for a very lively ride! It also lists the fork weight as 1lb 12oz, which in non retard units is 793 grams. My fork weighs 1200g~ish so there must be something to the whole butting thing, very impressive! Though mine easily clears a 29" wheel and has clearance for a 4" tyre so theres probably a bit of weight there too.

Anyways, after my inaugural ride and celebration beersies @hampie came home from work and I was still fizzing to ride my bike more. So we popped into town with some lights to ride around Hamilton gardens and for a little jaunt down the river trails. We started out at the south end and rode up to the cemetery and went for a little hill bomb down the grass into the gardens carpark.

So me being the speedy speedster I was out in front and @hampie was following me down the hill, it was twilight at this point. So coming up to the carpark there are bollards around so I pick a gap just as I get in torch range I notice a chain between the bollards...

uh oh, no time to even bunnyhop, just gotta plow on through!

I stayed on the bike, but the chainring did not fare so well! The chain between the bollards must have been poorly attached because it came detached on one end clearing the way for @hampie to sail through uneventfully, phew!

So in order to limp back home we found a convenient non-marring anvil (top of a wooden bollard) and large conical orange mallet (roadcone) and bashed the chainring around until it was somewhat rideable and limped back to the car. No damage to the frame, not even a scratch in the paint! Many lols were had at the time.

Anyway, next day I changed the chainring as I had a 32 tooth one in my parts bin and after a bit of fettling we went out for another ride. This time we started from Kaniwhaniwha and did a road/gravel loop 40km which encompassed the old road to raglan (old mountain road) through Waitetuna and back to kaniwhaniwha. We are slowly upping our mileage because early next year we are planing on doing the Kopiko Aotearoa which is 1100km from cape Egmont lighthouse to East cape lighthouse and we want to average 100km per day. 

Some highlights from the loop:

This is a tank trap that was put in during world war 2 as this was at the time the only road through from the west coast to Hamilton and they thought that the Japanese army might invade from that direction.

And this is the top of the hill on Waitetuna valley road. I spent the entire climb up whistling little wing to myself and zoning out. You can see the wind farm on the hill behind which is the same one visible from Te Uku on the way to Raglan.

So I chucked the bike on the roof of the trusty ol' honda (with matching primer!) and took off to the local mtb trails

(for yarns about the crappy honda click below)

I figured I would start on something pretty chill to get the feel for things so I went on Apprentice, a nice grade 2 that gently winds down the mountain. The first thing I notice is that the brakes are terrible, underpowered and needing bedding in so I had to adjust my braking distances to suit. But after I got used to that and started flowing I found that the bike handles fantastically! it loves to dart into the corner but doesn't feel skittish. I think this is a product of a long wheelbase for a rigid bike (1195mm) giving it stability but the 65mm offset fork reducing the mechanical trail. As a point of reference I figured out that my full suspension 29er trail bike has just under 100mm of mechanical trail, but the Pi bike has about 89mm. It feels a little odd in a carpark test but on trail it just works.

I did have some misgivings about the long chain stays, wondering if they were going to be an issue/make the ride boring. Turns out its not a problem, they do make it harder to wheelie and I can't manual it (I can manual my full sus bike but haven't really managed it on other bikes for some reason. I think a bit more practice is needed). But when you get it up on a wheelie, it wants to stay there and I think it would be the same with manuals. On trail I think it it probably not so much of a is it better or worse having long/short stays but a personal preference. It isn't what makes the ride thats for sure, it just feels like you have a bit less leverage over the rear wheel if you are chucking the rear end into a slippery berm.

After taking it down Apprentice for a shakedown run I climbed back up and took a brave pill and went down the jump trail to see if I was going to have a catastrophic failure of the fork. The bike jumps nicely, I didn't clear as many jumps as I usually do as I wanted to be conservative with my speed in the event of a breakage, but casing a jump is usually harder on the landing than clearing so you could say it was a torture test. Some of the rutted out sections were fairly horrific on the rigid, but all in all it was awesome, and I am not writing this from a hospital be with a severe concussion.

In terms of climbing, it climbs as well as the next bike, the 2.8" tyres are nice on the bumpy track up Pirongia. I would probably go a degree or 2 steeper on the seat tube angle next time around, because then I could get away with a slightly longer reach/front centre with the same distance from saddle to handlebars.

Anyways After this I went home for a beersie in the sun.

I am absolutely stoked on how well this bike rides. I made some odd design choices cause I don't see the point in making something that could just be bought off the shelf and I am really glad to see that they all came together to make a great ride.

Oh, and I measured the wheelbase again after the ride, it was the same. Woo, no bent forks!