Bike 001 - Spank My Brass Demo
- 27.5+ wheels and tires
- Velocity Dually rims
- Shimano XT hubs, Boost spacing
- Maxxis High Roller II tires: 3.0" front, 2.8" rear
- DT Swiss Competition spokes
- Fox Factory Float 34, 140mm, 27.5+ fork
- Shimano XT components throughout
- 1x11 drivetrain, 32Tx11-46
- 30T front ring for loaded bike packing
- Fox Factory Transfer, 150mm
- Shimano Pro saddle, seat post clamp, stem, bars, and grips
- Cane Creek 40 headset
- Various materials
- Paragon Machine Works head tube
- Paragon Machine Works bottom bracket
- Columbus Zona top tube
- Columbus Zona down tube
- Columbus Zona seat tube
- True Temper Versus chain stays
- True Temper Versus seat stays
- Paragon Machine Works rocker dropouts
- Paragon Machine Works braze-ons
- Spectrum Paint and Powder Works finish
- Head tube angle: 67.0° @ 20% sag
- Seat tube angle: 72.5° @ 20% sag
- Frame weight: 4lbs-11oz
- Bike weight: 29lbs-0ozs
This is the first Pornstar frame built (hence the 001) and my 27th frame in total since I started building in 2011. The goal of this frame was to showcase what Pornstar is all about: sexy, fun, fillet-brazed mountain bikes that can handle their business. It is also and upgrade to the trail capabilities of my current bike (a 100mm travel fat bike I built a couple years ago, see below) while still sticking with a hard tail frame. This was achieved by:
- using a longer travel 140mm fork,
- slackening the head tube by 1.0° to 67.0°,
- lengthening the top tube to 615mm from my normal 595mm while shortening the stem from 70mm to 50mm (certainly a standard modern geometry upgrade), and
- running 27.5+ wheels/tires
The good news is that I really like this bike frame! I know I'm intrinsically biased as the builder, but I do aim to be as critical of my work as possible. It's obviously much lighter than my fat bike in all respects and much easier to handle. Flick-able even. The bike handles great both up and down hill.
Uphill, I'm was honestly initially surprised it performs as well as it does; I was a little worried the 140mm fork would raise the front end too much and I'd just be wheelie-ing uphill the whole time. But it climbs wonderfully both in the saddle and out. And downhill, its 140mm fork, slacker head tube, longer top tube, and shorter stem make it much easier to handle in the steep sections. It also goes faster, but feels slower and more controlled, which was the goal after all.
We'll see how it avails itself over the coming weeks. I've got about 600 miles of unsupported bike packing to do on the Colorado Trail in July that'll put it to the full uphill test for sure. We'll get to know each other very well.
As a final note, Spectrum Paint and Powder Works did a killer job on the finish. It came out awesome with the black base, pink, panel and Kashima Coat-matched star logo in the panel. Plus the head tube badge looks pretty sick, too!
Challenges (Bad Stuff?)
Whether I like it or not, I learn something new on each frame I build. This is a good thing in the long run, but it can also be frustrating, as the consequences of learning are usually lost time and materials.
For this frame, my learning curve was largely a result of switching tubing manufacturers from True Temper to Columbus. As you likely know, True Temper made its last shipment of tubes in 2017 and is now no longer manufacturing bike frame tubing. I still have a few True Temper tube sets laying around, but wanted to try out Columbus' mountain bike tube offerings because it seemed likely that I'd likely be using Columbus tubes often in the future.
In general, my main issue with Columbus tubes is their relatively thin walls. This is great for weight savings. I've used Columbus tubes to make a few road bike frames and have really enjoyed working with those tubes. However, for mountain bike frames, I'm more interested in making a bomb-proof frame, even at the risk of being a bit heavier. So I'd rather have a 1.6mm wall thickness on a head tube or seat tube compared to a 1.1mm or 0.9mm thickness (i.e. True Temper vs. Columbus dimensions, respectively). In the future, I'm going to use Vari-Wall tubing instead of Columbus because everyone seems to be raving about it and it has very similar dimensions to True Temper's.
My first spot of trouble came with the head tube. I was initially committed to going full Columbus on this bike and so I ordered up their 46mm head tube to use with the 1.5" tapered fork I had ready for the build. Columbus' 46mm head tube has a 1.1mm wall which is similar to their other head tube offerings (i.e. 36mm head tube for 1-1/8" steerers). For 1.5" tapered steerers, I have always used Paragon Machine Works' 1-7/8" OD head tube with the larger relief at top and bottom. These work great and have a ~3.25mm wall thickness at the headset cup areas. And (spoiler alert) I ended up using a Paragon on this frame, too.
For the sake of comparison, the straight head tube I used to build with for 1-1/8" steerer MTBs is the True Temper MHT; this has a 37.0mm outside diameter with a 1.6mm wall. I figured the extra diameter of the 46mm head tube compared to a 37mm head tube would make up for the 1.1mm to 1.6mm wall thickness difference in the tubes, respectively. Even with a little heat distortion, I thought I'd still be left with a minimum wall thickness of 0.8mm after reaming the ID from ~43.8mm to ~43.96mm.
Although I wasn't positive, I thought that would probably be enough wall thickness. But my uncertainty led to do a test braze and ream on the head tube just to be sure. After actually seeing the post-reaming wall thickness, I became worried that it wouldn't be enough, so I reverted to the Paragon head tube that I typically use for 1.5" tapered steerers. I am also going to say that I won't be using Columbus' 46mm head tube again. (Now what am I going to do with all these 46mm hole saws I bought?)
Similar to the head tube, the seat tube is a smaller diameter, external-butted seat tube compared to True Temper's VERSUSSTMAG seat tube I have been using for dropper post bikes. The True Temper has an outside diameter of 34.9 and a wall thickness of 1.6mm at the top to accommodate a 31.6mm dropper. The Columbus ZON113550001 seat tube, meanwhile has a 32.7mm outside diameter for most of the tube and a 33.5mm external butt for the top 80mm. Wall thickness is 0.5mm in the center of the tube and 0.9mm at the external butt.
I am much less concerned about this tube than the head tube, however, I certainly do give it some thought for longevity. The seat tube on this bike is a very short run between the bottom bracket shell and top tube, so the 0.5mm wall thickness is not too concerning. Plus, it's pretty filled up with the solid body of the dropper post. The only potential issue here would be if during the reaming, the heat-distorted seat tube (i.e. not perfectly straight or round) interfered with the reamer and some of that 0.5mm wall was cut away. Based on how the reaming went, I don't believe this happened.
What I'm more concerned about is the thickness of the wall at the top of the seat tube. Because of uneven heat distortion, the wall thickness along the back side is only about 0.7mm. This isn't terrible, especially since it is supported, again, by a very solid seat post with a lot of seat post inside the seat tube. This reinforcement should aid the thin wall, but I am curious to see if there is any spiral fracturing over time. I've heard this is an issue from other builders and have always either used thick walled seat tubes or have brazed on a false lug for support to avoid it. We'll see what happens. I'd be bummed to have to scrap this frame if an issue arose with the seat tube.
The third issue I encountered was inadequate dimensioning on a Columbus drawing for their bent down tube. Read more about that here. Initially I was going to use a bent down tube with the wider Fox Float 34 for 27.5+, but I ended up going with a straight tube after having some issues with the bent down tube on another frame I was building. I very much like the straight tube better both aesthetically and functionally compared to the bent one.
So, in summary, I don't really think Columbus tubes are great for building the bomb-proof mountain bikes l like to build. In the short term, I'm going to switch to Vari-Wall and in the long term, I'm going to see how this frame holds up over the coming seasons. Hopefully I get to eat my words and this Columbus seat tube will be just fine.
I had a few other little challenges that I did not anticipate. The first one was having to grind down a bit of the bottom bracket shell mount on my alignment table to accommodate the slightly more outbound (~1-2mm) run of the chain stay for the Boost rear spacing on this frame. This is the first Boost frame I've done. When I put the front triangle on the alignment table and cranked down the handle, I discovered that the edge of the bottom bracket shell mount was interfering with the chain stay. The solution was simply to grind down the edge of the mount with an angle grinder to allow for the requisite clearance.
This next challenge was one that I had come across before, but had forgotten about. (Hopefully this blog helps me remember some of these past issues). Paragon's post mount rocker dropout interferes a little with the tapered edge of the chain stay on the non-drive side of the bike. This interference does not allow the rocker to travel through its full range of motion (i.e. the last 20-30%). This isn't a problem on this bike, but would be on a single speed. I used rockers on this bike so I can run a wider tire (like a 3.0" compared to the current 2.8") on the rear if I want to by moving the dropout back just a bit. The best solution for this is using Paragon sliders instead of rockers.
The last challenge I had wasn't much of an issue, but just a concern. It also arose from using the rocker dropouts with the low-rider brake mount compared to sliding dropouts with the standard brake mount. This frame has a pretty short seat tube length and, subsequently, a pretty low angle between the chain stay and seat stay. When I went to test fir the seat stay, I became concerned that there may be a bit of interference between the seat stay and the brake caliper. Just to be sure there was clearance, I put a little dimple in the seat stay. Again, the dimple works fine, but in the future, I'd just use a sliding dropout instead of the rocker.
In case you were curious, the reason I used a rocker was that the brake hose routing is cleaner when running along the chain stay instead of the seat stay. Basically, you don't need to jump the hose over the space between the seat stay and the chain stay. This is an aesthetic touch I wanted to include, but it turned out the functional cost was higher than it was worth, so I'd just as well, again, use a slider instead of a rocker in the future.