Fun with Power #s

[benb]

I'm starting to have enough power #s to see some interesting stuff in my riding.

E.x a few weeks ago I did 12 minute threshold intervals. I did the first 7 minutes on an easy dirt trail to avoid car traffic, interruptions, etc.. there is a gentle uphill on this trail. It's mostly non technical, but just dangerous enough I would not feel safe doing this effort level downhill without switching to my MTB (which does not have a PM). If I do the uphill, I can take a right turn at the end and finish the interval without any intersections to worry about. This is also very close to where I live & work so t's very convenient.

Anyway, 2 weeks ago:
#1 Average 248 watts, time 7:32
#2 Average 268 watts, time 7:12 (turned out I tied the KOM)


Today (slice of 15 minute intervals):
Average 258 watts, time 8:16
Average 266 watts, time 8:03

Same bike and setup.. what was the difference? It was raining today. My first effort I could feel my tires getting bogged down and it probably made my power output yo-yo. Second effort I made big efforts to find the dry spots to avoid bogging down. My perception was that I was going much faster the 2nd time up, but it wasn't much at all. Very interesting to see how much of a difference the wet sand makes.

Here is the other one, a favorite local hill. This one is interesting due to bike setup. I did this same hill last week during a threshold interval when I was not feeling good, and again today when I was feeling good. Wind is not really a factor most of the time on this hill as it's pretty heavily wooded.

Last week:
Avg. Power 237w, time 3:59

Today:
Avg. Power 300w, time 4:09

Difference there is the bike... shocking unless my two power meters are reading really different, and I doubt they would explain it. The time last week was on my Domane with 28c tires, today was my Space Horse with 38c tires and fenders.. about a 10lb difference in the two bikes. Interestingly I've done a 3:52 on the Space horse with the wheels and tires from the Domane, but I don't have a power reading for that day, that was more of an all out effort though I think, not part of a 15 minute interval. 60 watt difference seems huge, and I was feeling really terrible last week.

[rnhood]

Seems almost meaningless since you are not using any standard test protocols. Do a 2X20 or other accepted FTP test to find out your threshold, and then derive your zones. If you are concerned about accuracy then check other rider readings after a good Saturday group ride of about 60 or 70 miles. If your weights are close then the readings should be close.

[wasfast]

You didn't mention which PM you're using but Quarq's should have the zero offset set before each ride. They will vary with temperature also.

[carpediemracing]

Your numbers, relative to each other, seem to be in line with one another. Your long dirt hill numbers are lower the first time, higher the second (so warm up more for the first?), and about the same wattage (time is not as relevant, although you do note the difference wet sand made).

The two different bikes thing is more interesting, but, again, your notes on the two efforts seem to make sense.

Power numbers do vary from powermeter to powermeter - at 270w, for example, a 2% margin of error is over 5 watts, so you could be as far as 10w off from one effort to another (+2% on the higher, -2% on the lower). This means that a 10w difference may not actually be a 10w difference, it could be close to 0 watts. Other powermeters may vary as much as 5%, making your margin of error for 270w +/- 13.5w. That means that comparing two different readings you could be off as much as 27w.

I find that it's useful to have an idea of my FTP but also an idea of what I can do for, say, 30s, 60s, 5m, 10m, for a given FTP. I don't train or even race using power but I do review power data after races and the more extreme training rides.

Because I hate intervals and calculating FTP sort of requires doing some kind of interval I rarely measure my FTP. However, when I do, I have all sorts of data from around that time. At some level I can say, okay, I'm seeing such-and-such numbers, which are similar to the ones I saw when my FTP was 208w, so I'm realistically on the lower end of my FTP scale. Or, oh, now I see stuff that I saw when I was 218w, so I'm realistically as fit as I get. Etc.

I think as you get a feel for what you can do you'll start to see a "reasonable" range of numbers and a "more extreme" range of numbers (high and low). You may be able to spot a trend before you feel it, like "oh, my power seems low for such and such effort but my HR was high... I wonder if I'm getting sick".

[benb]

They are both stages... I do the zero offset fairly often but not every day. Stages don't need to be zero offset for temperature changes. My #s seem to come out pretty darn similar most days on the two different bikes, I'm sure the two PMs have variance from each other but it doesn't appear to be horrible.

rnhood these were not tests, I've done the standard test 2X this year, last time was about a month ago. This is just 4 data points from Strava segments when I was doing intervals in the exact same places and my power was supposed to be in the same range. All of these 6 data points I should have been riding about the same average power, and all of these 6 data points have no stoplights, stop signs, intersections, etc.. that screw with data.

I have been doing way more intervals since I got the power meters, I am finding I like doing them a lot, particularly on weekdays when I would otherwise just be riding unstructured around the same areas over and over again and it's easy to get bored since you can't go ride somewhere new and interesting. Carpediem I do find my first interval is usually lower.

[wallymann]

even on an MTB the slightest favorable/unfavorable breeze can have meaningful effect on power.

[kramnnim]

Something seems wrong with the 60w/10 second comparison.

[Ti Designs]

I'm really trying to wrap my head around the use of a power meter, but I'm struggling with it. As the coach who's worked in the bike shop for 30 years and doesn't see the need for a power meter on most bikes, I've been given a number of them (probably just to shut me up or get me on board - clearly that failed...)

I do use two power meters, neither of them are mounted on bikes. One is my trainer, which is magnetic and pretty close to linear across most of the range I'm interested in, so rear wheel speed = power. I don't really care about how many watts I'm producing, just the gains I can make or how quickly it's falling off as I get older. Knowing the number would be depressing. The other is on my isolation test bike which replaces the inertia of a moving wheel with a stack of weights. At any given time I know the mass and displacement, so I can calculate torque, which is the component of power I care about on that device.

I get testing in controlled settings. I don't get the endless discussions about wattage or training with power meters, given that there are different power meters, non-controlled conditions, and the response to a certain type of training varies wildly from one person to the next. It's like accurately measuring a block of jello. Worse, it's like accurately measuring jello and then comparing your numbers with your friend's numbers.

The real problem with numbers is that they suck your intelligence out your eye sockets. Anything on a glowing screen does that to most people, but your own numbers have a special draw that can't be resisted. It's so easy to lose track of the big picture and focus on your numbers. I had a math teacher who would always have us graph an equation first, what he called "getting a first look at this thing". He didn't care if the graph was accurate, he wanted a feel for what it looked like, so when we did get answers we could compare them to the graph to see if it made sense. That's what's missing when living by the numbers.

I'm far more interested in baked goods than I am in watts.

[ergott]

Originally Posted by Ti Designs

I'm really trying to wrap my head around the use of a power meter, but I'm struggling with it.

I really reaped the benefits the last time I went up Bear Mtn. (last Saturday). I was able to confidently crush my PR by keeping within a range of power I knew I could hold for the duration. It helped me push a little harder when the road flattened and I also knew to back off a bit when I was pushing too hard. I really put myself out there and left nothing more in the tank. That kind of pacing is priceless for me. I wouldn't have put in as hard of an effort worrying I would blow up.

The PM also helped me both pace myself for the rest of the ride (112 miles) and also help pace my buddies home with me. I kept the pace smooth on the front (4 riders) as they tucked in behind me on 9W. Didn't drop anyone and there were no conversations either so I know the pace was right in the zone. Easier to keep the average speed up with more power on the flats/downhills where they can benefit from the draft and easier over the rollers with no power spikes.

[leftyfreak]

Originally Posted by Ti Designs

I'm far more interested in baked goods than I am in watts.

Yes, but how many watts does it take to bake a salted caramel cupcake or a double chocolate muffin or a cider donut?

benb, I should let you know that Ti Designs is actually much nicer in person than he appears to be on the internet. Don't let the persona discourage you from joining us on a ride at some point. And yes, we can find baked goods, if that is desired, which does tend to make everything better.

A question for you, benb. What routes did you use for your two tests, the dirt trail and the favorite hill? I'm curious.

[ripvanrando]

I have two Powertap hubs. One is 3% high and the other is 1% low for a 4% variance.

Some bikes are faster.

I very recently joined Strava and did a couple segments on my randonneuring bike. I rode hard. My time was well below average. I got my racing bike out the next morning and wore lycra instead of wool. KOM on two segments and top ten on a couple more. I certainly did not get stronger overnight.

I use the power meter to titrate my output on long ride. At 225watts or lower, my lactate levels are low (below 2 mmol), my fat burning percentage is high, and I'm not producing a lot of difficult to recycle byproducts that contribute/cause fatigue. Without the meter it is very easy for me to put too much power out on long gradual hills. I think of it like a governor.

[nooneline]

The extent to which power readings are correlated with speed is affected by a ton of other variables - your bike, your body conditions, the temperature and air pressure and moisture level. That's why power is useful for training when speed isn't - because speed is an output affected by many things (some of which you can control, some of which you cannot), but power is your input. It's totally normal to see higher power numbers result in lower speeds sometimes.

[benb]

Haha.. lots of others have already explained the benefits of the PM so I don't have to say anything.

It's been really useful for me pacing myself on long rides, up climbs, and normalizing efforts between 2 bikes that are pretty different in terms of speed potential.

I know Ti Designs is a nice person, I've met him a few times.. I used to go on some of the Harvard team rides that went by Belmont Wheelworks like 12 years ago. I went and looked at his Jewelry once too.

[ripvanrando]

Originally Posted by Ti Designs

I'm really trying to wrap my head around the use of a power meter, but I'm struggling with it.

Maybe you just aren't a numbers guy? Some like RPE and focus on breathing and feel. I like to ride without any electronics sometimes but not when the ride is for training. Just me.

I do not care about another rider's numbers.

I don't care whether my power meter is different than yours.

I only care that my meter is repeatable.

With the tiniest amount of analysis of power data, riding with a power meter can help maximize performance whether the objective is a 24 hour race or a 8-10 minute breakaway effort during a RR. This ain't rocket science.

How power data is used in training is a separate can of worms.

If a rider's training plans call for an endurance ride, how does a coach know whether they are riding at the correct intensity unless it is by looking at the power data?

I wonder if any professional cyclists race or train without a PM?

[Ti Designs]

Originally Posted by ergott

I really reaped the benefits the last time I went up Bear Mtn. (last Saturday). I was able to confidently crush my PR by keeping within a range of power I knew I could hold for the duration. It helped me push a little harder when the road flattened and I also knew to back off a bit when I was pushing too hard. I really put myself out there and left nothing more in the tank. That kind of pacing is priceless for me. I wouldn't have put in as hard of an effort worrying I would blow up.

The two riders I've coached who have turned pro use their power meters the same way. Heart rate or even how you feel is a trailing indicator, by the time you get the warning it's too late. Both of them also had problems in racing adjusting to the tactics of others...

From the time I was racing as a junior I've practiced time trialing. It's a matter of learning your body well enough to set a pace in the first two minutes that can be sustained for almost an hour (we did 40K's back then). Now I have the climbers I coach doing the dreaded 4x8's. It's four 8 minute segments in increasing gears. There's two speeds: Sustain is just getting the body weight on the pedals and letting gravity and position dictate cadence. Up tempo is what I call throwing the body weight at the pedals, trying to get the upper body to reverse direction by the time the pedal crosses 3:00. Sustain lowers the HR, up tempo raises it beyond a sustainable limit. The first time it's all sustain - kinda boaring. The second time two 30 second up tempo segments are added to each 8 minute part - the idea of a binary system where one's too easy, the other is too hard takes hold. After that every 4x8 is an experiment. In theory, 60% up tempo is the best you can hope for, but over time people learn to close the gap between the two. The end result is someone who can hold a power output without using a power meter. The up side of this is that good days or bad days are taken into account. You FTP doesn't factor in that 8000 feet of climbing you did the day before... When it comes to reacting to tactics, knowing how to play the over/under game is a huge advantage over the preset rev limiter.