Chassis Geometry

A program called Linkage X3, published by BikeChecker.com has been very useful in this investigation.  The software is intended for bicycles where it's easy to make measurements directly from a photograph (photogrammetry) because all the pivot points are visible.  

But it works for motorcycles too – if you are willing to do a lot of precise measuring.  Because all the Dragonfly's suspension pivots are visible, it makes the job much easier. 

Other Measurements

Shock Length  Ohlins says 210mm, which is what I measured.  This is the center-to-center distance for the shock's eyelets.

Shock Stroke  Ohlins says 55mm.  Metal to metal contact occurs at 49.9mm of travel on the Dragonfly shock.  And yet, there is not a stroke spacer installed to limit the travel (see page 7 of the TTX22m.2 Owner's Manual to see what I'm talking about).  I measured 33.5mm of stroke prior to encountering the bottom-out bumper.  The  bottom-out bumper is 25mm tall.

Swingarm Center-To-Center  I measured 530mm.  Again, the position of the rear axle affects this.  530mm is pretty much in the middle.  There is a +/- 10mm range of adjustment in the swingarm slot.

Rear Wheel Radius  I measured 347mm .  Linkage X3 does not accept axle height or tire circumference directly.  The software  makes it much easier by allowing you to enter the size of your bicycle tire.  However, there are no motorcycle tires listed, so I got a value directly from Geri at BikeChecker.com for the proper bicycle tire to specify: 26 x 2.26.

Front Wheel Radius I measured 337mm.  The bicycle tire to specify is 26 x 2.66.

Sprung Mass  Mecatecno states 43.1 kg calling this the Suspended Mass in their “Launce Edition” specifications. 

Unsprung Mass  Mecatecno states 16.9 kg  calling this the Ground Mass in their “Launce Edition” specifications.   Note that 43.1 + 16.9 gets us to the original claimed weight of 60 kg.  The actual bike is slightly heavier.  In the model, this value is intended to include the weight of the fully-dressed rider.    

Rear wheel travel  174mm claimed (this checks out with linkage X3 and physical measurements).

Front wheel travel  170mm claimed (I have only been able to measure 158.5mm).

Swingarm Leverage Ratio

Linkage X3's calculation agrees quite well with physical measurements made for me last year.  Mike ran the swingarm from 32mm through 170mm of travel.  The data was pretty noisy, but the average leverage ratio was 3.5.

A falling leverage ratio produces rising rate forces at the wheel.  That is, the wheel experiences more and more of the spring's force because the swingarm's leverage is decreasing. 

The wheel's lever arm is longest when the swingarm is horizontal.  Above or below horizontal, it gets shorter (but not by much).

The side of the swingarm says “Linkless Progressive Damping”.   Although true, I would not brag about it.  The leverage ratio is nearly constant, starting at 3.6 and ending at 3.35 (a factor of 1.075 different).  This curve would look really flat if the X-axis scaling started at zero rather than 2.95.

The graphs below were produced with the standard 605 lbf/inch spring given 1mm of preload.  Effects of the bottom-out bumper are not considered in the model.