Articles – Seven Cycles

Chainstay Material: Off The Charts

Seven takes multiple design approaches to drivetrain engineering. Here are a few examples.

There is chainstay stiffness and drivetrain stiffness. Both are useful to understand and to consider separately.

Chainstays account for about 50% of a drivetrain’s stiffness. The rest of the stiffness comes from a combination of:

Dropouts & axle interface: Seven’s are machined titanium and the stiffest by about 3x compared to any others we’ve tested — titanium or carbon.
Disc brake mount: Seven’s is bolted to the dropout rather than being welded to a thin tube or a molded carbon shape.
Bottom bracket shell: Seven’s is machined from the thickest material available.
Down tube & seat tube: We use a number of tube sizes and walls to tailor drivetrain stiffness.

See Figure 1 for more details.

Next, we turn these parts into a frame. Riders choose either of our framebuilding methods:

Seven Simple-Custom^TM program, where we offer three tubesets that are both size-specific and usage-specific.
Seven’s full custom program, where we individually design the tubeset from the ground up.

Simple-Custom

We offer three levels of frame stiffness. See figure 1 for an example of the differences and overall range of stiffness.

RocketShip^TM tubeset is super stiff. Typically about 25% stiffer than our Benchmark drivetrain. As much as 70% stiffer for our largest frames. This is a specialty tubeset that is not ideal for every rider.
Benchmark tubeset is the sweet spot; it’s balanced and optimized for most riders. For example, all of our world champions have ridden our Benchmark tubesets.
SuppleState^TM tubeset is super smooth and plush. This is a specialty tubeset for specific types of riding.

Specificity

Each tubeset is size-specific and function-specific.

Size-specific: We typically offer 12 frame sizes for each Simple-Custom design. Each of these 12 has a distinct and different tubeset from the other 11 sizes.

Use-specific: We have over 30 Simple-Custom frame designs (gravel, allroads, mountain, bikepacking, etc.). Each of these models has a distinct tubeset we optimize for the use. For example, an allroads benefits from a different tubeset than a gravel bike.

20-Plus Titanium Tube Sizes

We start each design with a choice of more than 20 raw tubes or starter stock. From there, we butt, machine, manipulate, modify, and bend each tube to optimize it for its mission. See Figure 2 for an image of 23 distinct tube profiles.

Full Custom

Concerning drivetrains, in our full custom program, we can make drivetrains over 250% stiffer than our popular Benchmark. While that kind of stiffness is not beneficial to most riders, it provides a good illustration of how extreme our full custom program can get.

Figure 3 shows how stiff the chainstay material can get, 155% stiffer than our Benchmark. Once we add in all the drivetrain elements (dropouts, bottom bracket, etc.), we can nearly double that stiffness.

Figure 1: Overall drivetrain stiffness of Seven’s Simple-Custom tubesets.

Figure 2: An example of 23 distinct starter stock sizes of titanium that Seven uses daily.

Figure 3: Raw stiffness of Seven’s titanium tubing range. Compared to the industry’s most popular 3/4″ titanium chainstays.

Gravel Bikes in 1988

Words: Rob Vandermark, Seveneer

The other day, a few of us were discussing the state of gravel bikes and when we first rode what we’d consider a gravel bike. What is a gravel bike, after all, other than a rig you ride on dirt roads and trails? That could be anything. We used to ride our road bikes on trails all the time and still do once in a while. Even Buster Keaton rode a Penny Farthing on singletrack back in 1926 for the film The General.

So, the term “gravel” doesn’t mean much. The definition Seven starts with is “a drop bar bike with at least 38 mm knobby tires and lower gearing than a road bike.” Everything else is open to interpretation.

The conversation reminded me of my late ’80s project bike, the Singularity; a drop-bar mountain race bike I designed and built at Merlin Metalworks. This is the only image I can find. It’s an old photocopy of a black-and-white photo from Mountain Bike Action magazine.

Today, this design is called a “monster cross” bike.

Zapata Espinoza, editor of Mountain Bike Action, printed a couple of pages about some of the prototypes and project bikes we had at the Merlin factory. Maybe we’ll share more of those at some point. As far as I can decipher, the photo is from the June 1991 issue of MBA.

I had two missions for this bike project:

Build a titanium bike stiffer than a Fat City Wicked. At that time, I loved the ride of steel frames. Merlins were super plush, but back then, as a 20-ish-year-old problem child, I didn’t particularly like the Merlin ride. Gwyn Jones (one of three Merlin founders) gave me his blessing to build a super stiff Merlin.
Build a singularity bike. At least, that’s what I called it. The plan was to have one bike that I’d race road, mountain, and downhill on. That’s a whole other story for another time.

I accomplished both missions with the Singularity. It was way too stiff (particularly because it was the days before front suspension), but I found it race-worthy in the woods and in criteriums. This bike started me on the path of size-specific tubesets and the realization that tubing specification really matters quite a lot.

The bike was a prototype on a number of fronts, not just because of the drop bars. Here are the elements I remember that were unique or firsts back in the late ’80s:

1.5″ down tube and top tube: This made the front end stiffer than the standard Merlins by about 60%. At the time, Merlins had 1.25″ front triangles. Interestingly, the Fat City Wicked of that time had front-end stiffness similar to that of the original Merlins. My Merlin Singularity’s front end was about 40% stiffer than a Wicked.
1.5″ seat tube: This was wild at the time. Steel frames typically had 1.125″ seat tubes, and a few aluminum bikes had “massive” 1.25″ seat tubes. Because I wanted a super-stiff drivetrain, I thought I needed the seat tube to be ridiculously oversized.
A custom-modified front derailleur: The 1.5″ seat tube meant that a standard derailleur clamp wouldn’t fit. Even today, there’s no 1.5″ front derailleur with a 38.1 mm clamp. I machined some parts and rivet-nutted the derailleur directly to the frame. Then, I had to modify the derailleur to get more inboard swing to the cage. It worked well, but I could see the tube warp during shifting under load.
Custom seat post sleeve: The seat tube, being so much larger than a standard diameter, required a special seat tube insert. I machined it from titanium and welded it in a series of overlapping sleeves that looked a bit like Swiss cheese with speed holes everywhere.
Hot swap bar system: I had a quick connect hot swap setup for the bars. I could remove the entire bar and stem assembly as one unit and switch between drops and flat bars. I’m sure someone had done this before, but it was the first time I’d seen it.
5 cm stem: The stem was progressive even by today’s standards. In the photo, and in my memory, it looks like about a 5 cm stem. It was an old quill stem from a Columbia(?) cruiser. Chipped chrome plating and rusting in places. It had a socket head thru-bolt to hold the wedge in place and a socket bolt for the bar, too. I went with this stem because, with the hot swap system, the stem’s short reach worked better with the drop bars hood grip reach compared to the mountain bar grip reach. I had been building titanium stems by this point, but I was in a hurry, so I went with what I had in my parts box.
Shoulder strap pad: In those days, mountain bike courses were a bit different than today. There was almost always some hike-a-bike. I used to love those sections. The shoulder strap made shouldering comfortable and a lot easier to run with. I had the strap rivet-nutted to the frame.
Double wheel system: 26 x 2.25″ mountain bike wheels and 26″ x 26 mm road race wheels.
- I wasn’t aware of anyone doing this back then. While Specialized offered a 26″ x 26 mm road tire, I hadn’t seen anyone use it for a mountain and road bike in one.
- I was able to use 700c Mavic road rims cut down and rerolled to 26″ size. Keith Bontrager was making them at the time. Super light and super narrow. Can’t have everything. I loved them. The rim width had to be identical for both wheels so that the cantilever brakes would work properly. That meant very narrow mountain bike rims.

I designed, machined, and welded this frame.

Mountain bike performance results: I think I raced and trained offroad on the drop bar setup for about a year and a half. Once I had the bike in the drop bar configuration, I rarely swapped it to the mountain bar setup. I loved drops.

Road bike performance results: I raced many a local training criterium on this bike.

The bike’s weak point was the drop bar brakes. The lever arms for drop bars were different from mountain bike levers, so it was difficult to get enough braking power from the cantilever setup. Also, the brake levers themselves were too small for my hands and, therefore, difficult to hang onto during rocky descents. Otherwise, it was a good setup that got me through many rides.

I don’t recall what happened to the Singularity frameset. I was never much of a keeper. Of the hundred-plus prototypes and project bikes I’ve built over the years, I kept only one.

Hat tip to John Tomac, one of my cycling heroes. He used to race drop-bar mountain bikes back in 1990. I think I might have first seen him race that way in 1989, but I can’t remember. The internet says 1990.

Photo caption explained: Zap had this weird thing where he’d add a second last letter to our first names. Don’t ask me why. Zap stayed at Merlin for a few days. When not riding and talking shop, a group of us watched some bad movies, as he mentions in the photo’s caption. I don’t recall what we watched, but I’d wager there was a Godzilla movie on the docket and probably something starring Burt Reynolds. I recall that Zap was not impressed with the humor. I forgave him because he was, and is, an incredible documenter of the times. No one did more for mountain biking in the early days than Zap and Mountain Bike Action. Here’s to Zap for documenting so much over the past 35-plus years in Mountain Bike Action, Road Bike Action, and other media.

+++

Time tracking: Frame build date circa mid-1988. I estimate that date range in part because Zap visited Merlin in the winter of 1989-1990. (I remember riding with him in the freezing cold. Fine riding weather for us Bostonians, but not great for a guy living in LA.) The bike was pretty beat by the time he took this photo. I must have had about a season of riding on it already.

Frame Welding: Still Beads Run Deep

The Seven weld bead may be the most misunderstood aspect of our work. It looks so simple, uniform, and beautiful (or so many people tell us).

Getting to this serene point began 35 years ago when Tim Delaney, Seven’s Lead Technical Welder & Teacher, developed the titanium welding techniques that most builders use today.

We’ve refined and improved our welding techniques countless times over the years. We’ve run countless in-house fatigue tests to enhance our weld durability and to ensure we thoroughly test any improvement concepts.

The weld bead beauty you can see is good; it is a sign of care and quality. The underlying engineering and testing you never see are what make Sevens tougher and truer than any other.

These images of Stef welding show a few examples of the intricate techniques we employ. During her nearly 30 years in the industry, Stef has welded more than 10,000 titanium frames, more than any other human. Regardless, Stef’s work is all about quality, not quantity.

As part of our Special Projects Team, Stef is responsible for welding Seven’s one-off SOURCE Endurance Race Gravel project bike, shown here. Seven’s special projects are frame designs that go beyond Seven’s already extreme customization. In this case, as relates to welding, the SOURCE project has tube interface geometry and tube wall manipulation we’re combining in new ways; it requires nuanced, self-aware welding skills. Stef is the perfect person for the SOURCE project.

Here, Stef uses a shielding technique to ensure zero oxygen contamination of the titanium weld. The inside of the frame is purged of oxygen, the backside of the weldment is protected from contamination by a shielding device, and the oversized torch cup protects the weld itself. These time-consuming techniques, along with a many others, are critical to providing the strongest, most durable weld possible.

Stef, like all of our welders, focuses on one frame at a time. She will only work on the next project once she’s completed this frame. This singular focus helps build better bikes. There are no distractions and no conflicting information. We want our builders to focus on each frame as if it’s for a family member.

Our welders use special titanium alloy welding wire that is more supple than the adjacent tube. This weld bead ductility provides increased strength and toughness. Additionally, we use three types of titanium weld wire, each optimized for specific methods of welding.

Stef checks each frame on our granite surface plate, confirming frame alignment. She’ll repeat this check multiple times during the welding process to verify what she already knows: There is no straighter frame. Stef knows this because she follows welding techniques Seven developed over the past 35 years. We call this technique induction alignment; our use of welding techniques to achieve proper tolerances rather than solely relying on cold setting the frame after welding. Induction alignment makes the welds stronger and the frame straighter.

We use a multi-pass weld technique. We don’t use pulse welders or other process simplification methods. There are no shortcuts to building the most durable frames available.

Frame Tacking: Hidden Precision

Most of Seven’s framebuilding efforts are invisible. That’s okay. We know what we did.

Tube specification accuracy, material cleanliness, as-machined frame alignment, joint fit-up, etc. These types of hidden precisions throughout our tack welding process are fundamental to building a strong straight frame. Equally important, these obscured cornerstones provide the beginnings of Seven’s legendary ride.

Stef understands these nuances better than most. She is part of our Special Projects Team. With nearly 30 years of frame welding experience, she is one of Seven’s Master Welders. Here Stef works through the tack welding procedure for our SOURCE Endurance Race Gravel project bike.

Stef tack welds the seat tube and bottom bracket assembly, the first phase of frame tacking. A tack is a small weld that holds the tubes together. These steps allow her to remove the assembly from the frame jig and weld the frame without fixture hindrance.

Stef checks the accuracy and alignment of this seat tube assembly. The bottom bracket is the foundation of the frame. If, after welding, the seat tube is not perfectly aligned to the bottom bracket, the frame will not be straight and will not ride true. Working precisely now and at every step makes perfect finished frame alignment possible.

Stef welds the internal guides and ports. Some internal housing routing welds are done before tacking and some after. It’s complicated.

Stef modifies each of her welding helmets and shields, making them as light as possible. This subtle mod allows her to work faster and with higher precision. Make no mistake: Stef’s weld quality is second to none. Regardless, even after 30 years, she constantly refines her craft.

Stef tacks the down tube in place. The coped tube fits its mating tube within a few thousandths of an inch — about the thickness of a human hair. This invisible accuracy helps us build straighter frames that roll faster and live longer.

Stef tack welds the top tube and seat tube. The titanium weld area is cleaned and prepared in a four-step process. This is yet another unseen tedious procedure that set the stage for the strongest, most durable welds possible.

Handcrafted: One Frame At A Time

Skip is part of our Special Projects Team. He is Seven’s most Master Framebuilder, with more than 30 years of custom machining experience. Here he completes a one-off project code named SOURCE Endurance Race Gravel. The SOURCE integrates a number of details and advanced features in a new combination we’ve not yet offered publicly. Details to follow. And available soon for all.