Hans Christoph Timm
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As I recently wanted to change the rear spring rate on my FS tandem, I
have become interested in the distribution of the team weight onto front
and rear wheels. Suspension specialists will calculate your needed spring
rate for a single if given rider weight, suspension travel and mechanical
advantage of the suspension design. But how to deal with a tandem?
To solve the problem I designed an Excel spreadsheet which would calculate the weight distribution depending on the two rider weights and a few data points about the frame geometry. It is then easy to calculate which weight of a rider on a single bike would put the same amount of weight on the rear wheel.
Here are two examples for a typical male/female and male/male team (assuming I got my geometry right) which show that while single bikes tend to place 40% of the rider's weight onto the front wheel, tandems tend to stress the front wheel much more:
80kg/60kg (176lbs/132lbs) -> 47% front/53% rear
-> front equivalent to 160kg (352lbs) rider on
single
rear equivalent to 125kg (275lbs)
rider on single
80kg/80kg (176lbs/176lbs) -> 45% front/55% rear
-> front equivalent to 175kg (385lbs) rider on
single
rear equivalent to 150kg (330lbs)
rider on single
You should be able to download the spreadsheet from http://tandem-fahren.de/Mitglieder/Christoph_Timm/weight_distribution.xls
Playing around with the spreadsheet reveals that the assumed height of the respective centers of gravity does not affect the result. Only its fore-aft-placement does. Note that my assumptions about the actual placement of a rider's center of gravity may be wrong (it may be a bit further back), but as I assumed the same location for riders on tandems and single bikes (I have my bikes set up to allow me the exact same position), my conclusion is still valid!