Since joining the sport of triathlon a few years back I have struggled with climbing on tri bikes with steep seat angles. As a the ‘techie’ partner in a new triathlon shop with a history of amateur road and track racing I remember wondering back on 2003 after my first ride on a P2K what could be done to remedy this problem. Having spent a lot of time on a track bike I liked the power of steep angles and there were no restrictive UCI rules to prevent them – so why not? When my partner and I opened a triathlon shop last fall we quickly realized that this was also a key issue for many of our customers who simply dismissed steep seat angles claiming that they do not climb well. Having done some informal testing of my own that seemed to confirm this sentiment I have found it difficult to argue the point. Perhaps this explains why only a handful of tri-bike suppliers even offer geometry that can be truly classified as ‘steep’; most are still under 78 deg.
I had heard about Dan Empfield’s expertise through Cervelo and decided to look into the matter. I read a few of his tech articles and was not surprised to discover that the idea of a sliding seat had been tried 15 years ago. My curiosity was piqued. When I posted an enquiry about it on this forum Dan responded and explained that sliding seats are heavy but more importantly unnecessary if the proper TT climbing technique is used. He referred me to a thread from an experienced cyclist who had rediscovered the TT climbing technique which I affectionately refer to as “aero-spinning”. By using the aero-spinning technique this cyclist explained that he was able to limit his climbing power loss on his tri bike to 5 -10 watts below his road bike on an 8% grade. Problem solved. This was impressive since I had measured a loss of 20 to 30 watts in my testing albeit I was testing with my hands on the pursuits – not “aero-spinning”.
Aero-spinning is a somewhat counter-intuitive technique that calls for the rider to climb in the aero position while ‘spinning’ (I believe there is some general agreement that ‘spinning’ requires a cadence above 85 rpm). I say it is counter-intuitive because the point is not about reducing air drag but rather optimizing power output. The aero position however is the preferred position for climbing when a steep seat angle such as 81 deg is used because it ensures the rider is in this optimum power position.
Personally, I have unwittingly done a lot of my own aero-spinning and found it to be quite effective on softer and shorter grades up to about 3 or 4 percent. I fully understand the role of leg velocity in the power equation but when a hill is steep and/or my speed drops below 15 kph (10 mph) the urge/need to sit up and climb with a slower cadence in an upright position is almost overwhelming, of course sitting up on a bike with a steep seat angle is equivalent to shutting down the engines. So before asking Dan further questions on the subject I decided to do a little more testing.
So “what’s behind the urge/need to sit up” on a steep hill? I suspect Dan might advise that too much road biking experience and/or a lack of willingness to commit to a triathlon climbing style when the going gets tough. Another possible answer is that something changes or some new variable appears on steep slopes that compels the change in position.
With these two possibilities in mind I charged up my SRM and headed out for our 120 km Saturday morning hilly club ride. On the slopes of the mountains around Vancouver 8% grades are common. We have an abundant mixture of short and steep (15%) as well as very long (1 hr) climbs (8% to 10%) to the ski resorts above the city. I knew I was onto something after the first climb – a short 1 km dash. I used the aero-spin technique and maintained a cadence of 85 with my smallest gear of 39 inches (39 front, 27 back, 700C wheel) from bottom to top. This translates to a speed of 15.48 kph (9.6 mph). My SRM read 400 watts and my quads were a little toasty at the top. After the ride I employed a little elementary physics and calculated that at my Clydesdale class body weight (197 lb) plus bike, bottles, etc (23 lb) the slope of the hill was about 9.5%. I excluded mechanical and air drag as they are relatively small values compared to the power required to overcome gravity on a steep hill. I ran the numbers for lighter riders on the same slope. A 140 lb rider on the same 23 lb bike only needs to put out 296 watts: less is more as they say. I also computed output required on different slopes and created a little spreadsheet to graph the results. The only variable that remained constant was speed using the 39 inch gear and 85 rpm cadence. The limiting factor with aero-spinning became obvious quite quickly – Power. Even pros who can pedal an entire 180 km Ironman above 300 watts would start pushing the aero-spin envelope in a race with a lot of steep climbs. For example, a heavier pro that weighs 160 lb would need to generate 315 watts on a 9% grade to push a 39 inch gear at 85 rpm; this is roughly equivalent to holding 40 kph on the flat. My sense is that when the power output required to spin the smallest gear can no longer be sustained, a rider’s body will instinctively tend to compensate and recruit different muscles by changing positions, perhaps sitting up or standing on the pedals and dropping his cadence.
It’s a short stretch to conclude that every cyclist has a maximum sustainable power output which depends on many factors such as slope, elevation, body weight, strength, leg speed, muscular endurance, fatigue, hydration and so forth. In my experience most age groupers doing a hilly Ironman such as IM Canada cannot sustain the power required to spin a 39 inch gear at 85 rpm on the second major climb that comes toward the end of the race; the elites certainly do have the power and for them aero-spinning is effective. For the age-groupers lower gears and 650 wheels may or may not be enough for some to lower the power requirement sufficiently to support aero-spinning. In my view until someone engineers a proper seat shifter/slider to allow upright climbing at lower cadences using a road bike with a clip-on on hilly courses is the only other option.
Seeing as how my FTP is sitting at ~285W right now, I’m not going to be doing stuff at 300W for very long. In any case, like I said above, the limiter on how steep of a climb I’m comfortable “spinning up” seems to be more a function of gearing than anything else, and not by the power I’m putting out.