AFS, the essence of the Optimal Balance

Understanding cycle geometry is as simple as counting to four…because the frame can be broken down into four distinct areas, each with its specific role.

  1. Top tube rear (section A)
  2. Top tube front (section B)
  3. Chainstays/rear triangle length (section C)
  4. Front center (section D)

As the chart illustrates, the dimensions of each section evolve incrementally and evenly so as to preserve well-balanced proportions in all sizes, XXS to XL. This ensures all framesets have ideal ergonomics and flawless handling, regardless of size.

Top Tube Rear and Top Tube Front (section A and B)

This seldom-considered idea is at the heart of AFS: rather than considering top tube length overall, AFS divides it into front and rear sections. The dividing point is found directly above the crankset spindle.

Each section has a distinct function and when modified, entails different effects:

Top tube rear (section A)

This section is important in that it determines saddle setback. Setback is to a degree a matter of rider preference, but above all, is set according to the cyclist’s physical dimensions, notably femur length. Practically speaking, given two individuals of same height, if one has a longer femur, that individual will need to increase saddle setback. This setback, one of the most critical parameters in bike fitting, is largely determined by the seat tube angle. Argon 18 chooses its seat tube angles so as to allow enough leeway for a sufficient range of adjustment.

“Saddle setback is to a degree a matter of rider preference, but above all, is set according to the cyclist’s physical dimensions, notably femur length”.

Taking the Gallium Pro for example, the next table lists top tube rear measurements for the six frame sizes offered. As this illustrates, the seat tube angles and top rear measurements are incrementally increased together as the frame gets bigger. This makes sense; after all, an individual 1.80m tall will have a longer femur than one only 1.68m tall. This kind of detail, which may not seem very important at first glance, requires use of a different mold for every frame size.

AFS means incurring extra expense and trouble in the manufacturing process for the sake of better ergonomics on the bike.

Argon 18 Sizing Seat Tube Angle Rear Top Gallium Pro (cm)
XXS 75,5 11,5
XS 74,5 12,7
S 74 14,3
M 73,5 15,6
L 73 16,8
XL 72,5 17,8

Top tube front (section B)

The forward section of the top tube plays a different role entirely. It determines the effective length of the bike, thus it also determines rider comfort to a large degree. This length increases gradually with frame size, according to the rider’s physical dimensions. This balanced lengthening offers more flexibility in positioning.

Argon 18 Sizing Total Length (cm) Top Front Gallium Pro (cm)
XXS 50 38
XS 52 39,3
S 54 39,7
M 55,5 39,9
L 57 40,2
XL 58,5 41,7

Chain stays / rear triangle length (section C)

In the design process, determining chainstay length is a simple operation. Two factors are involved:

  • How quick-handling we want the bike to be.
    The underlying principle: the shorter the chainstays, the quicker-handling the bike, bearing in mind that if the stays are too short, the bike may well turn out to be too quick for its intended purpose. Some makers build excessively short rear ends, making their bikes twitchy at slow speed, and increasing unstable at higher speeds. We at Argon 18 believe bikes are made to be ridden to the rider’s full potential and requires reasonably long chainstays. This is why our bikes are always stable, even above 55 kph.
  • The mechanical requirements and standards for correct functioning of components, notably Shimano’s
    . Shimano mandates a chainstay length of at least 405mm for proper derailleur functioning and accurate shifting. This is why the Gallium Pro’s chainstays measure: 406mm in sizes XXS, XS and S, growing to 408mm in size M and finally, 410m in sizes L and XL.

Front center (section D)

Consistent and even graduation of front center dimensions determines much of a bike’s handling and steering characteristics. As with the rear triangle, an disproportionately short frame will have an unpredictable, twitchy ride that tends to stray from the intended line. Conversely, too long a front triangle reduces manoeuverability.

This area of the geometry is the most revealing of a bike’s overall balance of proportions because, along with headtube angle and fork rake, top tube front length is what primarily sets the front center dimensions.

We make sure both our top tube front and front center lengths are optimized.

Argon 18 Sizing Head Tube Angle
XXS 71
XS 72
S 72,7
M 72,7
L 72,7
XL 73

Fork rake, all sizes: 43mm

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