Hi,
probably this post will not be of too much value for the whole community, so I hope that Josh & Co. might contribute anyway to this special topic:
I will participate in the Paralympic handcycle race on the Brands Hatch F1 race course near London where I want to crown my career with a Paralympic TT medal.
Now it comes to the question which is the best ZIPP wheelset to support my goal. The race course is a 7.5k lap with 120m hd per lap, for the TT 2 laps in clockwise direction will have to be done.
I expect a riding time of 25:00 min. which corresponds to an avg. speed of 36 kph.
Following factors should be taken into account:
- A handcycle has its drive wheel in the front and two free-standing wheels in the back, rear wheels are not covered by tubes
Because of the low gravity center point and the front wheel alongside stabilized by the legs, crosswinds are not a big issue regarding steering, allowing a disk to be used as front wheel. - Speed distribution is different from racebikes as uphill a handcycle is far slower than a racebike, whereas downhill it’s slightly faster due to aerodynamic recumbent position (expected speed on this race course at 10% uphill 15kph, 10% downhill 70kph). Consequently a larger percentage of riding time happens uphill.
- Due to recumbent, more aerodynamic rider position, wheels contribute at a considerably higher percentage to the aerodynamic shape of the entire system (bike-rider)
- All wheels except Sub-9 and Super-9 are available as rear wheels, and all wheels, also Sub-9 and Super-9, are available as front wheel for handcycles
- Average wind speed in September (when the TT takes place) is 17k/h, SW direction. The race course mainly takes course in WE and EW direction, therefore a fairly high yaw angle can be expected.
The challenge here is probably the trade off between aerodynamics and weight.
To roughly quantify weight differences I tried the following computing example:
estimated guess: 30% = 450s of race time performed on sections where weight matters (more precise formula is welcome)
Weight difference between 2 front 808s and 1 rear 808 vs. 2 handcycle disks and 1 Sub-9 = 878g
Weight of the entire system bike-rider = 74kg
Percentage of weight gain = 1.19%
Speed gain = 0.019x450s = 5.34s
Speed loss on downhill sections??
ZIPP’s aero flyer tells me that an 808 looses only 3 seconds vs. a 900 at 40k which might lead to round about 1.5s at 25 min., but this applies probably at a higher speed and for wheels ‘drafting’ behind the seat tube.
Thanks a lot in advance for your thoughts and answers,
Elmar
http://www.handbike-power-endurance.de