Product Design: Chainstays

June 5, 2012

in Bike Design, Engineering

Chainstay design at Seven Cycles is an ever evolving process.  There is never any endpoint; once a stay is “designed” it changes as bicycle components and accessories evolve.

Update  |  October 24, 2012  |  Worked some on Seven Cycles’ chainstay spreadsheet dummy today.  To prove the new decision-tree methodology for choosing, and designing, the optimal chainstay for any component configuration.

Here’s an example of what goes into designing a chainstay:  Chainstay designs for mountain bikes.  I’m certain we’ve got 10 times more designs than we had two three years ago.  We’ve got way too many options happening.  It’s what Seven Cycles does as a custom framebuilder.  Here is some of the craziness that affect chainstay design.  Of course all of these aspects interact so in combination if feels almost infinite in complexity:

  • Wheel diameter:  29er, 700c, 650b, 650c, 26″, 24″
  • Tire width:  Anywhere from 20c up to 2.5″ tire – and everything in between.  We’ve even built a couple snow bikes but I don’t think we’ll be doing that again.
  • Tire profile: slick, file tread, knobby, how knobby?  Of course, one company’s 38c measures 38c, another company may measure 35c or 42c.  No ture standard, in my view.
  • Drivetrain type:  Belt or chain?
  • Number of chainrings:  three, two, one, blast off.
  • Gear inches:  What size front rings?  A few teeth difference alters the shape and clearance of the stays.
  • Chain-line:  road vs. mountain vs. belt drive vs. triple vs. my patience
  • Gear mech:  Single, internal, or classic.  Additional detail issues with single and internal because of the belt or chain tension method.
  • Chainstay length:  Most people want the shortest setup possible.  Actually, about an inch shorter than possible.  Not necessarily for the right reasons.
  • Other frame geometry elements:  Primarily seat tube angle and bottom bracket drop.
  • Bike handling:  Chain stay length affects weight distribution over the wheels.
  • Bottom bracket type:  68 mm threaded, eccentric, BB30, etc.
  • Brake system:  Disc, drum, or other?
  • Drivetrain rigidity:  This is tubeset choice:  Tube diameter affects design, clearances, and possibilities.
  • Accessories:  Fenders, chain guard, foot size, cleat set up, and more.

A quick sketch for a 29er belt drive stay. All production drawings are in SolidWorks.

Project work in reverse:

October 24  |  Worked some on Seven Cycles’ chainstay spreadsheet dummy today.  To prove the new decision-tree methodology for choosing, and designing, the optimal chainstay for any component configuration.

October 22  |  Made some progress on the chainstay decision tree program.  Looking forward to beta testing this next week.  Maybe this week.  I’m going to pass this off to Neil to clean up once I’ve got the proof of concept completed.

October 19  |  Working on a new chainstay design system for Seven Cycles.  With Neil D. and Dan V.  Basically we’re developing a faster way to codify all the variables that we factor to provide the ideal chainstay type for any given bike.  It’s basically a big decision tree; we’re looking at a way to take the hundreds of variables and determine the ideal stay – out of hundered – within about 30-seconds.

September 11  |  Chainstays – again.  Working on next generation belt drive system for 29ers.  Gates belts have:

  • Two chain-line options – actually more than that
  • Two different belt systems – center track and classic
  • A bunch of ring sizes

All told I think there are about 35 combinations that affect chainstay length.  This may seem a bit odd because most companies that work with belt drives offer a complete bike:  one belt, one ring size, one tire size, etc. so it’s fairly easy to design the bike – really that’s designing the bike model.  With Seven every bike seems to get a different combination based on rider size, needs, interests, style, terrain, etc.

September 4  |  Stef A. is working on some SolidWorks training so we can expedite, organize, and track our endless design updates.  We’re already seeing good results on the reorg but we have a ways to go.  Stef is taking the lead.

August 28  |  Stef’s working on a stay design.  Design number 3,000 or so.  This is a 50mm slick tire belt driver 29er with a too short chainstay.  It’s a bit trickier than it should be.  Bike shipping on Thursday.  I feel like our system for stay design is getting faster and more formal.  Years ago it was this way; entropy ensues.  With Stef’s and Neil’s help we’re wrangling entropy for a moment.

August 23  |  Today we’re messing around with chainstay designs for mountain bikes.  I’m certain we’ve got 10 times more designs than we had two three years ago.  We’ve got way too many options happening.  It’s what Seven Cycles does as a custom framebuilder.  See the above bulleted list for details.

August 20  |  Working on Seven Cycles chainstay designs.  The design is somewhat infinite because every bike is custom.  Within that infinity we have roughly 50 design parameters or templates account for about 99% of our bikes.  I’m working on two design aspects right now:

  • An updated version of Seven’s 1″ chainstays – these are the stiffest titanium chainstays on the planet.  Not suitable for most riders, these stays are definitely for a small number of specialty bikes.  And, I’m working on a couple ways to incorporate thsese stays on more bikes – making the 1″ stays more versatile, more adaptable, and more appropriate for a wider range of riders and bike designs.
  • Fatigue testing program that relates to titanium as a material.  I’m hoping the testing program goes well becuase we’ve got some ideas I’d like to implement.  More variety.  More specialized applications.  But many of these ideas require pushing the technical parameters of the material a bit farther – hence the testing to determine where are the boundaries.

June 20  |  Seven Cycles has been designing frames with 1″ chain stays for a while.  We’ve been working on broadening the frame design options with our 1″ stays.  Today we iterated our road racing design.  These stays are more than 2x stiffer than our most common 7/8″ stays.  These are definitely not right for everyone.  But, on some applications they make a big difference.  We’ll be introducing a few more variants throughout the rest of the season.

June 5, 2012  |  A few months ago Seven Cycles introduced out 1″ chain stay design.  It’s a specialty design that’s appropriate for about 1% of riders.  But, that’s what we do, we design for every type or rider and riding situation.  Matt O. reminded me about it yesterday.

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