Looking for ideas/help on my position. This is a video I had taken on a trainer ride last week. This is a Supra-Threshold effort so I am moving around a bit to hit the interval number but that’s probably a realistic view of how I’ll be on a climb or into a headwind. My CdA (calculated using speed and power via Golden Cheetah) is in the .26-.28 range at best. I can’t figure out why it’s so bad.
Stats and info:
2020 Giant Trinity TT
6’1 180lbs
Power2Max NG crank power meter (calibrated)
GP5000 25” tubeless tires
At race pace efforts (280-300W) I’m only getting 23-24mph. This is both during outdoor testing shorter efforts really focusing on position, as well as longer workout efforts (usually 5x20 min back and forth on a long road I have near me)
Any help or things to try? My bars are at 25°. Did a testing session awhile ago where I tested 10-30° in 5° increments, 25 and 30 were the fastest, then 10. 15 and 20 were slowest.
Assuming your knees are tracking close to the top tube, I think your position is good.
You didn’t mention how long you’ve been doing this. If it’s a fairly new thing, I think you should ditch the oval chainring, and maybe come back to that after you’ve got a few years behind you. It might also be giving you inaccurate power meter readings.
This will be my 3rd year. Could the oval ring be causing aerodynamic drag? I’m not struggling to get the power out, the issue is the lack of speed that comes along with it
“I’ve talked to P2M about this issue some time ago and I’m using Q-Rings for 2 years together with a Type S without any problem.
Regarding accuracy P2M told me, that the irregular (uneven) chain-speed (e.g. the speed of one single tooth on a single revolution) compared to a even cadence while using an oval chain ring will lead to a constant calculation offset of your power.
Therefor in reality my Type S, compared to a Powertap Hub, shows constantly 7% higher values while on standard Q-Rings. For QXL-Rings this would be even higher, but still the same over the whole range of power, cadence, and so on…”
"Sampling rate doesn’t have anything to do with accuracy when it comes to oval rings. They are sampling TORQUE at 50hz (which they claim is fast – but SRM and rotor are sampling at something like 200hz), with no mention of how fast they are samplying cadence/rotational speed. The only way to make a crank-based power meter accurate with oval rings is to calculate power at that same rate (i.e. take every torque reading x distance x 1/50th of a second) and average out those readings every second. an average of torque x distance/time readings around the rotation will give accurate readings.
The problem is now that all the readings are averaged, then multiplied by the distance traveled in 1 second. This uses an average speed that isn’t representative of the varied speeds occurring across each pedal rotation when using an oval ring."
I have a small loop, I had the bars at 10°, rode the loop 4 times clockwise, ended the activity, then 4 laps counter clockwise, ended the session. Then I ran them through Golden Cheetah with the air density etc, if they were the same to 3 decimal places I accepted the test and did the next 5° increment. I kept rolling resistance the same for all the inputs. I’ve read on the forum that RR isn’t the same between runs but other than checking the tire pressure between runs, I’m not sure how I could measure that.
power2max power meters are claimed accurate with oval rings by the manufacturer. Specifically, power2max says the cadence interval on their power meters is not discrete per crank revolution. Rather, the accelerometer data is sampled continuously, just like power data. In other words, they don’t make the assumption that pedaling velocity is constant and therefore, are not impacted by the use of oval rings
It’s very possible you are right though anyway. The excerpt you sent was about a different power meter mfg’d by P2M, but the power readings could be higher than reality. I have a road bike (regular circle chainrings) with the same make and model power meter, I can try and test both against my trainer in a very unscientific method of comparing them.
Looking from the side, I don’t see any obvious reason why your position couldn’t be fast. I guess it comes down to how narrow your shoulders are and how well you can tuck your head (and still be able to look ahead) while actually riding outdoors at your race efforts. From my experience, quite small changes in stack, reach, and tilt of your cockpit can make a big difference even if not obvious from a video, especially from side. It might take quite a lot of tweaking and testing. I would first play around with adding ~1-2 cm to stack and/or reach; maybe even move your saddle ever so slightly back and/or lower a couple of mm (this helped me). Try to have as narrow shoulders and low head while still being able to look ahead (without tremendous effort), and also film your position from front.
I wouldn’t get hung up on “power meter reading discrepancies” - I’m suggesting you move back to a round chainring for physiologic reasons.
What really counts is how fast you are, and unless we are all missing a gross deficiency because of no frontal view, it’s probably (as others are suggesting) going to be some fine tuning of your current position.
Without getting caught up in saddle setback and seat height, the first thing I want to do is add reach. You look a bit squished up to me ? More reach, drop head into that gap.
Sorry I rode outside over the weekend and I don’t have a film crew to get footage out there. Here is the front video. Again, this is during a threshold session so there’s a little pain in my face.