The "Saigon Swerve" & 3 Millimeters of Misalignment

The notorious "Saigon Swerve" is an everyday driving hazard in Vietnam. Note the left side 'Kill Zone' where the car and motorbike blindspots overlap.

My adopted home of Vietnam is well-known for it's steady economic growth, its resilient people and amazing food and coffee culture. It's also known for careless, dangerous drivers and chaotic, overcrowded traffic. After years of living and cycling in Vietnam, the odds finally caught up with me. An impatient motorbiker executing the treacherous “Saigon Swerve”, slammed into the front of my bike and sent me flying into the air.

Miraculously, I dusted off basically unharmed. My bike took the majority of the impact. I rode away with a smashed left brake lever/shifter, a scuffed-up fork and a nasty dent in my rim. Compared to the carnage I've witnessed daily on Vietnamese roadways, I was lucky to make it home alive!

A mechanical damage assessment is straightforward. Structural damage, defects and alignment problems are much harder to diagnose and resolve.

As I pedaled homeward, I felt my bike drifting toward the right side of the road. When I gained speed descending the narrow shoulder of the Phú Mỹ Bridge, the rightward pull increased. It felt like I was fighting a crosswind and steering against a flat tire to keep from veering into the concrete barriers! Although my bike looked OK, there was something seriously wrong.

At home, I performed a closer inspection. My fork blades were bent 3 millimeters offset towards the right (drive-side) of my bike. The bent fork caused my bike to track sideways. Riding with a misaligned fork or frame is like having an unseen set of hands steadily applying steering force to your handlebars and pushing you off-track. It's both disorienting and hazardous.

At slow speeds, riders will compensate for frame and fork misalignment with tiny, frequent steering corrections. Skilled riders will dynamically shift and redistribute their weight over the wheels to keep a misaligned bike steady. But new, inexperienced riders will often struggle to pedal in a straight line and navigate uneven terrain and obstacles. Since alignment problems are nearly impossible to detect visually (without proper gauges and tools), troubleshooting alignment-related handling issues can remain a mystery.

Alignment checks require proper gauges and tools. https://www.parktool.com/en-us/blog/repair-help/frame-alignment

Thankfully, I could fix my bent steel fork. Steel retains its strength after successive rounds of bending, whereas aluminum and carbon fiber will fracture when pushed to their yield limits. After an hour of repeated measurements and slow bending, a test ride confirmed that the re-alignment procedure was successful in restoring predictable handling.

The damage to my fork demonstrated how even a relatively small deviation in alignment can ruin the "feel" of a bike ride. There are endless subjective and vague standards cited in bike reviews. Frame geometry, tire pressure, aerodynamics, spoke tension, the routing of cables and wires, suspension tune, weight distribution & center of gravity...on and on.

Yet none of these factors have an irreparable impact greater than asymmetry of the frame and fork. Misalignment at or exceeding 3mm introduces serious risks for instability and can cause the dreaded "death wobbles" at higher intensity riding and speeds:

The "death wobble" is the most terror-inducing riding experience not involving incoming traffic. https://www.youtube.com/watch?v=VfngbsIUSj8&ab_channel=dbozak

A bad experience or crash linked to poor bike handling and speed wobbles are terrifying and can turn away both new and veteran cyclists. Its common to hear riders exchange recommendations like squeezing the top-tube with their knees to dampen moments of high-speed instability. While marginally effective (and comical) it doesn't address the root cause of stability issues. Nor will these techniques help riders on bikes with low stand-over drop frames common on E-bikes. These negative riding experiences can result in botched retail test rides and lost sales. With D2C brands, it can cause unsatisfied customer returns. For D2Cs, processing and shipping warranty returns might fully eclipse the original units' sales margins! Guaranteeing exceptional riding experiences should be the highest priority for brands fighting for customer loyalty & profitability.

The growing popularity of E-bikes and Pedalelecs is edging up average riding speeds and bringing less experienced riders into more challenging conditions. Of particular concern is lightweight E-bike stability at higher speeds. This is of utmost concern on fast & twisting descents where precise, high-speed cornering is safety critical. As electric drive motor torques increase, so do the torsional forces that flex frames and magnify handling problems. Misalignment presents real safety and bottom-line costs when unhappy or injured customers seek compensation and pursue litigation after a mishap. 

The unfortunate truth is that a surprisingly high number of shiny, new bikes at all price-points will consistently fail a 3 millimeter centerline frame & fork alignment check! Spending $3,000 rather than $800 isn't a guarantee against purchasing a bike with a misaligned frame & fork:

Wheel flex and tire rub against chainstays can become a serious problem on misaligned frames. Tire abrasion can destroy carbon laminates in high-stress areas.

"Alignment errors shouldn't be ignored...these are red-flags and early warnings of more serious engineering & manufacturing defects..."

Frame alignment problems on new bikes should prompt closer inspection of welds and bonding points for early signs of stress or failure. https://www.pinkbike.com/forum/listcomments/?threadid=221630&pagenum=6

Misalignment = Manufacturing Red Flags

The most critical focus for bike brands should be overall risk-reduction for serious failures, reworks and recalls. Alignment errors are red-flags and early warnings of more serious engineering & manufacturing defects. These can be symptoms of improper material handling, cutting, welding or layup during production.

Improperly cut and mitered tube sections can result in permanently misaligned frames.

Discoveries of alignment problems and other frame defects should trigger detailed audits and root-cause investigations to resolve problems. Resolving frame defects prevents systemic failures, safety concerns and brand-threatening losses & recalls!

Producing straight and stable bikes is an achievable goal for every brand. With skilled and experienced leadership, improved frame alignment doesn't require an ongoing price negotiation with vendors. It can be an engineering requirement for doing business and permanent source of brand value and profitability.

Aligning on Quality

Both human and automated manufacturing processes require active QC management. It's wishful thinking that 3D design, optical scanning and other advanced tools for prototyping has solved frame manufacturing alignment problems. Powerful tools for design visualization don't regulate or control the variables of mass-production. Likewise, automation isn't a magic wand. Poorly managed systems will reproduce streams of fabrication errors- especially if QC staff & process are dismissed or treated as optional redundancies.

While vendors and OEM manufacturers may maintain some internal standards for frames and forks, every client should understand that they are responsible for defining GO/NO GO requirements. No surprise that vendors will work to reduce costs and use time-saving optimizations wherever possible. If brands want to create exceptional riding experiences and prevent serious production problems, they must set clear internal quality standards, share detailed requirements with vendors and stay actively engaged with manufacturing.

Strong Frames of Bozeman, MT USA demonstrates the frame table alignment check process. https://www.strongframes.com/design-and-fabrication/tour-the-building-process/

So what can designers, engineers and manufacturers do to improve frame and fork alignment? Here are some examples of problems and solutions at different stages of the bike development and manufacturing lifecycle:

Design: Centerlines and reference datum must be marked on all design documents. Review and approve all 3D and 2D drawings in prototyping and production for critical alignment tolerances. This must also include design and engineering review both internal and externally designed/sourced frame & fork components. Remember to include allowable variation within overall brand quality standards.

Sourcing: Confirm that vendor and “factory tolerances” and production process controls meet your product requirements and expectations. Remember that some facilities will default to weaker internal standards that may break your design and quality requirements. Client call-outs and corrections must be shared and agreed prior to finalizing purchase orders.

Quality Engineering: Invest in proper Quality Management expertise. Purchase and use reliable gauges and tools to perform detailed prototype & sample review to inspect for alignment errors. Note sample errors, report them back to OEM/factories. Require new sample production until the vendor can meet all requirements. Make sure that pre-production samples are made use factory tooling. Set sample size quantity to scale appropriately based on your overall production plan or purchase orders (POs).

Proper use of basic gauges and tools can be the most cost-effective and efficient method of frame & fork inspection. Setting a consistent sample evaluation process is key. https://forum.customframeforum.com/t/frame-verification-and-alignment-surface/560/3

Production Planning: Use production tracking tools like QR codes, Microdots, RFID, Barcode scans to set step-by-step production tracking for product traceability and recall prevention.

Manufacturing and Mass-Production: Review factory production plans and process controls to ensure that appropriate checks are performed to identify and remove defective items. QC scrap rates should be tracked and shared between vendors & clients. Review scrap rates at least quarterly and make sure that continuous improvement plans are working towards eliminating frame and fork defects.

The mass-production alignment checks used by some OEM factories may not be adequate to automatically meet all brand and client QC standards. Most mass-produced steel and alloy frames are checked and "aligned" using hammers and mallets!

If want help to improve quality outcomes or want to set new management systems for productions, True.Quality Engineering can help start the process. True.Quality Engineering will on-board new or current vendors with quality improvements. We perform factory audits to ensure vendor & OEM quality management systems are working at peak efficiency. We can resolve specific problems and offer total quality management solutions. Contact us for a free consultation to discuss your needs. Reach us directly to with your specific needs. Info@truequalityengineering.com

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