Dually Travel Analysis

In developing the new Ahrens Austin dual-suspension design, I set out to achieve a few broad goals for the suspension system.

GOALS:

1. Minimum rear wheel travel ~5.5" [140mm]
2. Shortish chainstay length for good handling and climbing ~16.9" [429mm]
3. Neutral BB height that's just tall enough to avoid cranks/pedals hitting the ground under full load ~13.5" [343mm]
   
4. Rear axle path traveling upwards/rearwards for optimal traction
5. Leverage ratio ~3:1 or less to minimize shock overloading
   

In analyzing and refining the design, it became apparent very quickly that achieving these goals would not be easy! But with some diligence and great 3D modeling software, pivot placement was continually tweaked until all of the original goals were met. Below is a graph which details only the swingarm motion (from zero to full-travel). It does not take into account front fork motion at this time.

FINDINGS:

1. The rear axle path moves in an upward/rearward fashion without any abrupt direction changes. Smooth travel upwards, smooth travel downwards with progressive damping in both directions - simple and effective.

2. As rear wheel travel increases, so does BB height and crankarm/pedal clearance. This trait is unique in that most frame designs exhibit the opposite; more travel typically yields lower BB height and less crankarm/pedal clearance. And since the front fork will ultimately be part of the overall system, the BB height should hover near 13.5" which has been my sweet spot for many years.

3. The leverage ratio on the rear shock is 2.97:1 which is acceptable for this frame style. The frame will accept shock lengths of 7.875" x 2.0" stroke and my plan is to offer both Fox RP23 or DHX 5.0 options depending on the application.

4. Chainstay length is fixed at 16.9" and with a concentric rear axle pivot, no chain growth can occur which means pedaling efficiency should be excellent. This setup also minimizes 'brake jack' to some extent although the ideal solution is a fully-floating setup which hasn't been designed yet!

5. Overall travel tops out almost 6" (151mm) which is a nice bonus since it's more than originally planned.

In summary, the main objectives listed above have all been met and in some cases exceeded. When I envision riding this bike, I want the suspension to do it's job in a clean, quiet and effective manner. This design will inspire confidence with its stout construction, lateral rigidity and frame geometry that's proven to handle well in a variety of terrains.

Where is the NC Dually?

This is an email I get about once a week....when are you building the 'NC Dually' prototype and 'when can I order one?' Well, that time is almost here. And we're not sure of the name yet...but we are sure that it will have AHRENS AUSTIN on the down tube. The AHRENS part is obvious but the AUSTIN is my business partner Brandt's middle name. Without Brandt, this bike project would have died off for sure and since he'll be fabricating these frames in-house, his name is on the bike too! Through continual brainstorming and countless hours of design time, our team effort will yield a unique trail bike that incorporates many of the ride characteristics my bikes are known for.

As I mentioned above, I've partnered with people that share my passion for design, manufacturing, metal working and process control. We've setup a new shop in Livermore, CA to streamline operations while keeping all frame building tasks under one roof including heat treating. Our new venture is called DEVISE SOLUTIONS and since I'm a partner in the new company, I have a vested interest in its success. This new company will ultimately handle day-to-day operations of Ahrens Bicycles by acting as a primary distribution channel for the brand. Over the last two years, the company has seen explosive growth and this strategy should enable the brand to grow more cohesively moving forward. And hopefully the economic situation will deliver a new influx of cyclists! We've invested in very accurate Anvil machinery for tube coping/mitering with a dedicated Cincinatti horizontal mill that's central to this operation and truly vintage. There's also a new Miller Dynasty 350 TIG welding machine on the floor, huge granite surface plates and also a programmable Despatch heat treating oven. I even scored a 36" wide HP Design Jet plotter last week for free which is a great tool for printing out 1:1 scaled drawings.

So back to the NC Dually project This bike will be hand-built at the new shop using a process that emphasizes quality every step of the way. We are working closely with our network of high-end machine shops to produce the CNC parts required for the new dually....and there are almost two dozen parts that need to get made! Needless to say there is still a bunch of work ahead of us but in the end it's all worth it. I dream about carving down coastal singletrack on a this highly-engineered, handmade machine that's been optimized for performance. The first frames I ever designed were duallies and I'm VERY EXCITED to get back to my roots with this project.

Here is a brief overview:

• Constructed with 7005 aluminum alloy
  
• Compatible with both 26" and 650B (27.5") wheel sizes
• 150mm rear wheel travel achieved through modified four-bar linkage
• Rear axle path moves in an upward/rearward direction
  
• Zero chain/chainstay growth is achieved through 'Semi-URT' design
• Low BB height also achieved through 'SEMI-URT' design (as rear wheel moves through its travel, the BB height increases for additional crankarm-to-ground clearance)
  
• Concentric rear-axle pivot minimizes brake jack
  
• Designed around Fox 15QR front fork in 140-150mm travel range
  
• Compatible with Fox RP23 and Fox DHX 5.0 rear shocks (7.875" overall length and 2.25" stroke)
• ISCG-05 mount comes standard
  
• Shimano Direct-Mount front derailleur (uses ISCG-05 mount)
• Front derailleur follows swingarm path for superior front shifting
  
• Shimano Press-Fit Bottom Bracket shell > 92mm width
• Shimano Press-Fit bearings used within Main Pivot housing
• Rock Shox MAXLE 12mm bolt-thru rear axle system for superior stiffness
  
• 135mm rear hub spacing
• Rear 'international standard' disc mount
• Hand-formed rectagnular chainstays maximize heel clearance
  
• Front triangle has low standover height and low center of gravity
  
• Widest bearing spacing possible at every pivot point; ENDURO MAX bearings used throughout
• Interrupted seat tube enables rocker arm to pass through for shock acuation
  
• Swingarm components easily serviceable
• Replaceable rear derailleur hanger

DRIVE-SIDE VIEW:

CHAINSTAY SUB-ASSEMBLY OVERVIEW:

Enjoy and if you've read this far, thank you!

Beer Logo Generator

My wife found this 'beer logo generator' on the web....click here to try it out for yourself!

Sliding Dropouts

Recently displayed at the Rocky Mountain Bicycle Show, this Chris Kopp townie prototype features Sliding Dropouts from Ahrens Bicycles....click here for more info.