Have just recently started using my Powertap outdoors and am surprised how much power i need to sustain a reasonable pace. While I have not done serious formal tests, i have done some estimates based on recent rides on flat terrain:
200 watts = 34kmh on tri bike,
250 watts = 36kmh (23mph) on tri bike, 34kmh (22mph) on roadie
I am 189cm (6ft 2in), weight 75kg (165lbs). Have about a 10cm drop on the TT bike (saddle to elbow pads) and also a 10cm drop on the roadie (saddle to handlebar). The tests were done with a standard helmet and a hed jet 60 front, training wheel with PT on the back.
Do those numbers sound about right? …Or does it mean that my aerodynamics could be way improved?
On the tri bike, i intentionally put the bars up a bit higher since i wanted them to be comfortable for an Ironman event… How can i best optimize aerodynamics and comfort? Trial and error?
How can i best optimize aerodynamics and comfort? Trial and error?
The optimization should be for speed over the entirety of the race. That’s going to entail aerodynamics, power, and comfort that will let you run afterward. I don’t know of any way other than trial and error to do that. However, good coaches and consultants can help you cut down on the number of iterations.
A 50watt increase from 34 to 36kph seems a little high. From your numbers you would be over 300watts for 25mph which seems high, particularly since you were using aero equipment. I get over 25mph on a hilly course with 300watts with an aero helment, hed stinger front, and water inflated power tap rear, around 26mph on a flat course. I’m 190 pounds and 5’ 11". Ain-Alan Juhanson road in the 4:20’s at Kona from what I remember a little over 300 watts and he is over 200pounds. I would say you have some room for improvement.
A 50watt increase from 34 to 36kph seems a little high. From your numbers you would be over 300watts for 25mph which seems high, particularly since you were using aero equipment. I get over 25mph on a hilly course with 300watts with an aero helment, hed stinger front, and** water inflated power tap rear**, around 26mph on a flat course. I’m 190 pounds and 5’ 11". Ain-Alan Juhanson road in the 4:20’s at Kona from what I remember a little over 300 watts and he is over 200pounds. I would say you have some room for improvement.
You should be way faster on the TT bike than the road bike. We do a TT series here on a 14 mile course with an aero and non-aero class. The TT records are about 30.40 and about 34.00 (former BMC pro).
I can’t compare with a flat course, but I rode 32km/h with 180W Avg at Kraichgau HIM, and that course has ca. 3600 ft of climbing, spread over lots of short sharp climbs.
In IMCH in 2009, I rode ca. 32.5km/h with 175W Avg, that course has also about 3600ft of climbing.
A friend of mine in 2007 rode 4:49 in the Frankfurt IM with 220W Avg (and ran a 2:58 Marathon, but that’s another story), and he’s about your height and weight (maybe 1 or 2 kg’s lighter) - that’s about 37km/h
hth
Richard
PS What makes a MASSIVE difference is road surface. In Germany, they are very good. When I ride at home in the UK, I feel like I’m standing still for the same effort.
PPS Forgot to say, I’m 73-74kg, 1.76m
The replies are confirming my suspicion – my speed, given power, is modest. I don’t think this is due to Crr as the roads that I have been riding on are reasonable; I think it is more a question of CDA.
It seems like the starting point to optimize CDA is to lower the handlebars / elbow pads and secondarily to bring the pads nearer. Is 10cm drop between elbow pads and saddle average or on the low side? My (old) Cervelo P1 had more, but I was not able to ride in aero position for a long time due to comfort…
Richard Albert – do you know how your friend has setup his bike, given that he is more or less my size?
Yup that’s right water. I wanted to find out the effects of riding heavier wheels and a local bike mechanic suggested inflating my wheels with water, it worked great and rode wonderfully. Goes through moderate side winds practically unchallenged, its easy to mash in watts, practically effortless to ride straight enough to stay within a white line, and everyone thinks I’m a nut for it.
A 50watt increase from 34 to 36kph seems a little high. From your numbers you would be over 300watts for 25mph which seems high, particularly since you were using aero equipment.
The power required to generate a given amount of velocity is proportional to its cube. So if everything else is constant, if I’m doing the math right, you’d get a constant ratio of cubed velocity to power. In your data, that ratio gets about 5% worse, suggesting that if the lower power numbers are correct, you should be going more like 36.5kph at the higher numbers - which strikes me as not a huge difference, given measurement error (the cube effect means small changes have large effects).
Note that you can back into your implied CdA and then figure out how much room for (practical) improvement there is.
For someone of your height, I would say 10cm of drop is below average. Based on Slowman’s formula, if you are trim and fit and riding a good position, someone with 78cm saddle height riding at 79* seat tube angle should be between 14.5 and 17.5cm. Increase the saddle height or ride steeper, and the range for drop will increase.