Seven Design Philosophy – Understanding Chainstays
Seven Cycles offers a variety of chainstay styles, each with their own unique features and benefits. Our most popular designs include our Inline stays and Chopped stays.
The popular perception is that chainstay length is one of the most important factors in bike design because stay length affects bike handling, acceleration, climbing ability, and descending stability. While it’s true that chainstay length has an important impact on all those aspects of a bike’s character, stay length is only one factor in more than 200 design parameters that go into developing an ideal bike.
Anytime we put too much emphasis on one design element at the sacrifice of others, the result is a sub-optimal riding experience.
With more than 30,000 custom bikes designed and built, we think we bring unique experience to each new bike project. We help riders navigate, prioritize, and balance their bike’s performance elements, like choosing the appropriate chainstay design, length, and stiffness. We consider how the bike will be used, today and tomorrow, the type of riding you’ll do, where you’ll ride it, your body kinematics, component choices, and many other factors.
Seven’s chainstay design philosophy seeks to optimize these competing factors:
- Chainstay length: We optimize for the kind of riding you will be doing, rider size, center of gravity, the local terrain, and much more.
- Component choices and constraints: Tire size, wheel size, rim width, chain ring spec, brake type, and axle system all play a critical role in determining the proper length of the chainstay.
- Drivetrain stiffness: We normally equate stiffness to performance and acceleration, often balanced against the bike's overall weight.
- Weight saving: For some riders, grams are important. A shorter stay is lighter, but Seven also offers lots of other ways to save weight, without limiting performance or durability.
- Price, investment, and value: Some Seven stay designs require an upcharge due to their complex geometry and material cost.
- Bike aesthetics: Seven's many chainstay options can have an impact on the aesthetics of the bike. While this is entirely subjective, it is important to many riders.
Regardless of these important and sometimes conflicting considerations, most people want the shortest chainstays possible. Why?
The most common request Seven receives regarding chainstay design is to make the stays as short as possible. We know why riders make this request. We also know, from building more than 30,000 custom bikes, that shorter is not always better. In fact, shorter is often worse.
First, some of the benefits of short chainstays:
- Quicker handling: The shorter the bike’s wheelbase, the more agile it will feel. On the trail, a shorter rear-end will help get the rider around tight singletrack turns more easily, and the bike is more responsive to "body English," which adds to that feeling of agility.
- Better traction: The shorter the stays the closer the rear wheel's contact patch will be to your center of gravity. This increases traction when you need it most – when climbing and in conditions with poor traction – snow, mud, sand, and loose gravel.
- Stiffer drivetrain: A stiffer drivetrain provides improved acceleration and, to some extent, improved climbing, too. All things equal, a shorter chainstay is stiffer, but just barely. On average, one centimeter of titanium chainstay length reduction equates to about a 1% increase in drivetrain stiffness. for our engineering friends out there who will check our math, while the chainstay tubing itself is, all things equal, about 2.5% stiffer in isolation, the drivetrain system including dropouts, bottom bracket shell, down tube, seat tube, and crankset, not to mention other components, all overshadow the chainstay tubing's benefits that are minimal to begin with.
- Lighter: A shorter chainstay is lighter, just barely. On average, one centimeter of titanium chainstay length equates to about 14 grams or 0.5 ounces. Meaningful to some.
Most of these features sound great, right? Some subset of these benefits are characteristics that most riders want. So, why not always design a bike with the shortest chainstays possible?
Now, some of the potential downsides with short chainstays:
- Squirrelly handling: The generally positive trait of ‘agility’ quickly becomes ‘squirreliness’ when the rest of the bike’s geometry is not well balanced. Handling that’s too quick is at best exhausting and at worst dangerous.
- Front wheel instability: This is caused by the rider's center of gravity being too far back over the rear wheel. Sometimes the front wheel lifts off the ground while climbing. It becomes irritating and sometimes quite difficult to keep your center of gravity balanced between the wheels when the front wheel is continually trying to lift.
- Component compatibility:
- Tire clearance limitations. Seven can optimize chainstay design for any specific tire type. We use all of our experience, plus some help from 3D modeling software, to arrive at these very customized designs. But, it&rquo;s helpful to remember that if we are asked to optimize for a specific tire, you may be locked into a sub-optimal future. We’ll design to the spec a customer requests, but we always recommend future proofing the bike when we can – without hindering the bike’s performance today. An issue can arise that after one year of use, the rider may want to try a different tire, or may find enjoyment in a new type of riding that benefits from using a different tire, or may find one of the endless stream of new tires looks appealing. Seven’s default design philosophy is to optimize for your ideal while simultaneously future proofing your ride with a maximum tire fit – unless you don’t want us to. We find it very common that riders tell us they end up using their Seven’s for a much broader use of riding because they like their Seven so much.
- Chainring size limitations. We can’t tell you how many times we&rsqu;ve design a bike for a specific chainring in order to minimize stay length to find two years later the rider wants to make a gearing change. Just like tire choices we think about future proofing gearing choices, too.
- Manufacturers’ standards: Drivetrain manufacturers specify minimum chainstay lengths for proper shifting performance. Seven can make chainstays shorter than most of these minimums, but we don't recommend it because this decreases shifting performance, increases wear, and can cause significant problems with some parts kits.
- Disc brake rotor clearance: In some situations the rotor can become the limiting factor for shortening the chainstays. Seven has some clever ways of mitigating this, but it can be a challenge.
- Heel clearance: This is an uncommon issue, but it is important to some. A shorter stay exacerbates heel clearance issues. Because every Seven is custom, there are ways we can mitigate this even with short stays, but modern disc brake systems limit heel clearance possibilities more than ever.
- Accessory considerations: It is important to consider any accessories the rider might uses when optimizing chainstay length. Panniers, racks, and fenders are a few popular examples.
- Curved seat tube: As a feature, a curved seat tube isn’t good or bad, but if the rider is focused on the shortest of the short chainstays, we usually need to pair them with a curved seat tube. The primary considerations for this feature are aesthetics and cost. We charge a bit more for the curved seat tube, and some people prefer the look of a straight seat tube.
Providing the benefits of short chainstays without limitations
There are a number of ways to design a bike that handles predictably and with agility, climbs like a mountain goat, and provides traction like fat tire bike. Chainstay length is merely one factor in a sea of many.
How can Seven provide the benefits of a short chainstay while eliminating the downsides?
Some of the tools in our design toolbox include:
- Quick handling and better traction can be achieved through:
- Tubeset engineering plays a much more significant role in handling performance than chainstay length.
- Frame and fork geometry play vastly important roles, too. Specifically, the front end geometry of the bike has a greater influence on handling than stay length.
- Center of gravity, between the wheels. Coincidentally, when you want to improve rear wheel traction, that typically means putting less weight on the front end. This can improve or decay the bike's agility. The rider’s center of gravity has a complex relationship with tire contact patches and bike handling.
- A higher center of gravity makes for a faster handling bike, all else equal. A small change here can have a big impact on handling.
- Drivetrain stiffness is all about tubeset engineering, not chainstay length. For example, Seven's 1" chainstay design provides better than a 50% stiffness increase as compared to the roughly 1% stiffness gained from short stays. The tubeset we choose for you determines frame stiffness. Frame geometry is barely relevant to chainstay stiffness.
- Weight savings is all about tubeset engineering, most importantly tubing profile and butting. While shortening chainstays can save an ounce or so, total tubeset profile optimization can save many ounces. A good example of this is Seven XX upgrade, which saves an average of 8 ounces on the frame and has no negative impact on drivetrain stiffness.