Sports scientists have compared combined hand and leg cranking with legs alone and some of this work suggests there is a performance benefit although it is not conclusive (e.g. see Wilson, Bicycling Science, MIT Press, P.83.)
But the Swithcblade arm power system is probably more efficient than arm cranking. Using it all the time can be tiring but used properly, it offers a clear improvement, whatever your fitness level. Intermittent use is best on flatter terrain; for accelerating, for a quick burst of power over a rise, or to help you hold onto a higher gear. For steep hills, it feels quite similar to climbing out of the saddle on an upright bike. It reduces lactic acid and fatigue in the legs and generally keeps you fresher.
I’ve developed a new system for the front suspension mount; it helps the seat to become more reclined and it improves the function of the Row-Power system. Its taken a long time to work out and but now its done I hope to be properly back on the road in a few days. Here’s a rough and ready picture of a mock up.
It looks rough but it proved the idea.
Not a terrific performance from me; not even the fasted Street Class machine at this meeting. No time to prepare the bike properly either, which largely is to blame for two crashes on the day.
The Switchblade ‘Speed’ position has seat and bottom bracket heights typical of a lowracer, like the Challenge Fujin to my right in this picture. (The yellow bodywork is another bike, in the background. ) This particular Fujin rider is much quicker than me though.
A day of racing at the BHPC International Festival (http://bhpc.org.uk) although a puncture, gear problems (and perhaps a lack of rider energy) led to an early exit. Lots of very useful comments about the bike though. Unlike at Hog Hill, I seemed to get no benefit from the row-power system on the Fowlmead track. The row-power advantage when climbing is more obvious but, on the flat, and going hard (above the lactate threshold), it may not be useful. More investigation required.But there will be an update soon on handlebar reconfiguration; I think the position and action can be optimised further.
Although the Switchblade is not intended to be a racing machine, the act of riding at speed with lots of other recumbents, of all shapes and sizes, as well as just putting in high physical effort sheds light on the way the bike behaves. Its been very useful and I need to do more.
I managed to get to the Hog Hill meeting of the British Human Power Club yesterday (http://www.bhpc.org.uk/rules-and-classes.aspx). I went to a couple of meetings in 2009 but basically went back to the drawing board for four years. Hog Hill appealed (even though it’s a 400 mile round trip) since I thought the Switchblade would show its advantage best on the Hill. Unfortunately, it wasn’t included in the race circuit, which was therefore substantially flat. But it was worth the trip (http://www.bhpc.org.uk/Data/Sites/1/archive/events/events13/hoghill-13.html) so am very pleased with the bike’s performance. Basically, the Switchblade was the fastest unfaired bike in both rounds, giving me a first and a second place. (Winning a race is very exciting.) It has to be the bike, rather than the rider: having just come back from holiday, I’ve only ridden it once in the last three weeks. Although I was giving all I had.
Despite last-minute tribulations, the bike didn’t break down when it mattered. Well done bike.
It’s at a point where everything works quite well on the new frame but road testing always throws up a few minor issues. These usually are reliability problems; little bits failing too early, neglected routine maintenance that is easy to overlook when the focus is on wider issues. But things are running well now and I’m hoping a 200km event is possible within a couple of weeks.
There is also the option of BHPC circuit races and Hog Hill this Sunday is what I’m working towards. It’s a hilly circuit so generally a lot more demanding for recumbents, but not the Switchblade, I hope. The BHPC are very accommodating; one can just turn up, pay a small entry fee and race.
Here’s a summary of the improvements incorporated into the new frame design:
- Use of carbon and aluminium hybrid construction – some new fabrication experiments have got me closer to developing a consistent production method and has improved the reliability of my carbon fabrications but I think I need some good advice from experienced composite specialists for the next version.
- Frame weight has been reduced by about 2kg and it’s probably easy to lose the same again and so get close to mainstream low racers with a bit more detail design. All-up weight is about 38 lbs or 17 kg. (But, even with the current weight penalty, climbing is still much improved over other recumbents.)
- Much more responsive and compliant ride – less energy wasted and less harshness. In the absence of quantitive measures, my perceptions of the feel or ride of the new frame, compared with the old, are the best indicator I have of how well the frame responds to shock loading which is the primary way in which a frame will waste energy.
- Improvements in geometry – a lower bottom bracket was needed and the seat angle is shallower at 17 degrees. This means the Switchblade ‘Speed’ ride position is the same as a European low racer. The lower bottom bracket, in the ‘Climb’ position may benefit hill climbing too although there is a bit more foot-wheel interference.
- A means of locking the two frame members behind the seat in the ‘Speed’ position – the main aim of this was to improve efficiency of the ‘Row-power’ propulsion system in this ride position. This seems a worthwhile improvement and was the most difficult development to realise over the last few months.
No photos yet and it’s not finished but the new frame is running well. To be frank, its only 70% what I intended and is still too heavy. (But many recumbent riders will try to tell you weight isn’t necessarily the key issue.) What the new frame seems to demonstrate is that rigidity or stiffness are at least as important as weight. I think this is about energy conservation; what might be called bumping losses or hysteresis.
While it would always be nice to have quantitive measurements of performance related stuff, it’s never as easy as it sounds and, although there is a risk of bias, my objective evaluation of the new frame is that it feels completely different to the old one; substantially less energy wasted on rough roads.
There may also be an interplay between the importance of a compliant or rigid frame and wheel size. The Switchblade has 20″ wheels which probably gives it fairly high rolling resistance, compared to say, a 700c-wheeled bike. Perhaps a less energy-wasting frame is more important with small wheels than it is with large ones.
The new frame feels better, not just in terms of the way it rolls but also in terms of the effort required to hold speed. My Garmin Edge is only slightly better at estimating how far I’ve ridden (i.e. up to 15% error) than I am by having a blind guess so, once again, I’ve got no hard quantitive data on performance but, on flat terrain (i.e the Cheshire plain) I think its 1 to 2 mph quicker. This bodes well for some good event times, when I’ve sorted out a couple of technical hitches.
Producing a frame from carbon is getting closer: the use of carbon over aluminium tube is a reasonably efficient structural combination – offering improvements in specific strength mid-way between the two materials, whilst improving the relatively low fracture toughness of carbon used on its own. This approach allows some easier manufacturing options too. More on this later.
The current prototype is too heavy but this is not seen as an intrinsic design issue: the Switchblade has about the same level of complexity as a full suspension touring recumbent so, with judicious use of carbon and some detail refinements, a target weight of around 30 lbs is anticipated for the next prototype.
The format of the current prototype is based on a ‘compact, low-racer’, with 20 inch wheels front and back. Different wheel sizes are being investigated and this is one of the variables the new design will consider.
For the moment, front wheel drive is a preferred option, accepting that on steep hills in the wet, it can fail to keep traction. A rear wheel drive Switchblade is a future option but our current focus is on weight reduction and optimising wheel size, not the drive train.