Power meter on a fixed gear

@jrenaut 125059 wrote:

My Garmin came with a power meter.

Did it come with a power meter or a cadence sensor? Because those are two very different things.

@jrenaut 125059 wrote:

but then I was thinking, can’t you calculate power from speed when you’re riding fixed?

In a very specific and tighly controlled environment, yes. You need to account for Crr, CdA, Grade, and Wind Speed and they all need to be constant. So unless you are on a track, or rollers in your basement it is not feasible.

I assure you that 8mph up 15th and 8mph down 15th street require vastly different amounts of power output even on a fixie.

You would want a Power Meter on a fixed gear bike for the same reason you want it on any other bike. 1) you are serious about training and power is the most useful metric. 2) to brag about your FTP

@jrenaut 125094 wrote:

Ok, this all makes sense. I really need a power meter. The cadence sensor might be nice too, but the main reason for me to get a power meter is to have more squiggly graphs vs time on Strava.

FTFY

Having a cadence sensor on a FG is slightly pointless if you have a speed sensor too. But it will let you verify your crazy spinning/stupid mashing, and you could calculate your gear inches from your data. Also, if you’re a skid stopper you could see that too I guess!

I have used a Stages power meter on four of my bikes, it’s handy. I verified that towing a trailer with kids on a folding bike uphill needs more power. But mostly because yeah it is the most useful metric if you’re trying to quantify your actual output. Wish it was easier to have one on every bike (n+1 problems…)

@vvill 125199 wrote:

I’m interested to try a power meter on the FG (I have run it once or twice on my converted hybrid when it was FG), mostly because I’m curious if a FG ride will result in lower power at the same speed. Of course, even just spinning the cranks you use up calories, but I did notice it was quite easy to spin on flats/downhill showing 0W.

Well, this is about as good a comparison as I can probably ever do. Same length of the same section of road (123>Chain Bridge>Great Falls), yesterday on the R3 and today on the Cinelli. Speed, and HR are practically the same, but average power on the R3 was 15W higher with slightly lower average cadence. I attribute that to a bit more wind yesterday, small difference in power meters (Vectors on the R3, Stages on the Cinelli), higher drivetrain efficiency with the Cinelli, and I think the R3 may be a pound or so heavier than the Cinelli. It’s also a bit wonky since there are differences in the timing I hit the various lights along the route. Also interesting is that total kJ for each ride were basically identical.

That said, it does seem that a fixed gear running a large-ish gear (48×16) is more efficient (less power to maintain the same speed) than a geared bike, but there are still a lot of variables…

[IMG]https://farm1.staticflickr.com/575/21385375903_8a7528570c_h.jpg”[/IMG]

@MattAune 125680 wrote:

Just to be a pain, I will mention that I routinely see greater than a 15w variance between my stages and Quarq/Powertap on the same bike on the same ride. Then throw in wind, Crr, CdA differences and it is really hard to make any conclusions.

One day maybe I will do a few back to back runs on the same bike and same power meter switching between fixed and singlespeed because it is a pretty interesting question.

Don’t forget drive train inefficiency! You’ll have the least power lost at the pedals, then crank, then finally by the time you’re measuring at the hub you’ve could definitely have lost a few watts. Remember that article testing different chain lubes to see what the biggest watts saver was?