Power on the downhills

While I can put out solid power on the downhills, the question is: is it worth it?

Yesterday I went on a short 15 mile ride where I tried to hold FTP, which for me is right around 320 watts. I averaged 313 watts for the 36 minute ride, and was probably pushing 280 watts on the downhills. In that case, my goal was to hammer the whole ride, but on a regular training ride I may not have pushed so hard on the downhills.

Now, in a race I'd probably conserve that energy. The extra 1-2 mph you may get may not be worth the extra 80-100 watts you need to put out. I can spin pretty easily at 200 watts on a slight downhill at 28 mph - to get to 300 watts I may not gain a ton more speed, but I'd be taxing my body a lot more. Is that tiny bit of speed worth the effort?

The difference in feel may also be due to gearing. Pushing a big gear downhill is harder on your legs than spinning in a smaller gear climbing. Even if I'm doing a quick climb with a cadence of 95 and putting out 400 watts it doesn't seem as sternuous as 300 watts on a downhill.

I think it depends on the grade of the downhill.  If it's steep enough to hold speed without pedaling, then pedal over the top of the hill, get up to speed and then coast.  If not pedaling takes away 1-2mph, I would keep the crank spinning. 

I'm always surprised in races when I see people stop pedaling as soon as they crest a hill.  I'm fine with giving the legs a rest, but wait until you get up to speed first!

Agree with your discussion above.  It's harder to push watts on the downhill simply because of the lack of resistance.

I also think that if you watch the form of someone climbing vs descending, you'll see noticeable differences.  When we climb, our shoulders tend to rock, and we use more overall body movement to generate power.  When descending, we tend to be in more of a "tuck" and only use leg movement to generate power. 

Yep it's harder.  Well, maybe not physically harder but it certainly takes me much more mental focus to maintain watts.  So if it's isn't really harder, it does feel harder to me. 

If I'm in my hardest gear spinning 95 rpm @250 W that isn't any different physiologically than spinning 95 rpm at 250 W in my easiest gear (save the ~25 mph difference)....right?  I can't answer that but logically, they should be the same.

It's because of the crank inertial load. When you're climbing you're typically using a gear ratio that produces low crank inertial load, while when you're descending you're typically using a gear ratio that produces high crank inertial load. Many (most?) riders have difficulty modulating their power when the CIL is high so they have to concentrate more to keep power steady (and high). Conversely, when CIL is low many (most?) riders have immediate feedback that helps them to modulate their power and keep it steady (and high).

[Edit:] CIL varies with the fourth power of gear ratio. So, if you're climbing a hill in a 39/26 = 1.5 gear ratio that's low CIL while if you're descending in a 52/13 = 4.0 that's high CIL.

That makes a lot of sense.

I've heard (no hard evidence to back it up, but a reliable source) that about a 3% drift is better (3% harder up, 3% easier down).  Obviously, that depends on a lot of factors and is probably tricky to do well, so aiming for even power is most likely the best option for most of us.  Even trying your best to maintain even power you might end up with 3% swings too.

Interesting comment re CIL.  Thanks.

I'm new to this PM thing and, while I understand the idea behind maintaining equal power on the uphill vs downhill, I find it doesn't impact VI that much to have quite different power levels uphill vs down.  Notable differences still give a VI of ~1.03 on a hilly course. Subjectively, it 'feels' like it's not worth the effort to try to level things out more than this on a hilly course.  But that might just be because I'm not (yet) used to maintaining power downhill.

In any case, having a PM is certainly providing unexpected insights into my riding.  Whether it impacts performance remains to be seen.

This was going to be my follow-up question.  As Michael has previously pointed out, basic physics indicates that power up should exceed power down.  Any ideas on how much?  On a flat course with no wind, it seems that a VI of 1.000 would be optimal.  What about on a hilly course?  At what point is trying to lower VI counterproductive?  (I'm guessing quite close to 1.00.)

ETA:  Quick BOE calculation -

Using 3% and equal up/down times: (0.5*1.03^4 + 0.5*0.97^4)^0.25 = 1.0013

Using 3% and 3:1 ratio in up/down times: (0.75*1.03^4 + 0.25*0.97^4)^0.25 = 1.016

Not so sure on that one. It's presumably going to depend on a number of factors.

From the perspective of time gained per watt/calorie expended, there's more to be gained from investing in uphills. I plugged some figures into bikecalculator.com, to check on the gains to be had by going from 300w to 330w on the flat, a 5% climb, or a 5% descent. (Drops vs. aerobars doesn't seem to change the numbers much.)

5% climb: 21s/mile gain, ~4-5s/minute

flat road: 5s/mile gain, ~2s/minute

5% descent: 1-1.5s/mile gain, ~1s/minute

So that looks like more bang for your buck when you spend your watts on the uphills.

Of course, the downside of uneven expenditure is that you don't want to spend too much time relying on time-limited energy systems. In technical terms, that's burning matches. I'm not sure how to build that into the cost/benefit calculation, but I would guess that the downside of uneven wattage increases in shorter events, where you're more likely to be spending time at higher FTP percentages. Conversely, that downside is mitigated by the ability to rapidly recover from higher intensity periods. So it might be possible to train the ability to make better use of variation in wattage.

There must be power geeks out there who have figured this out in detail.

Very helpful.  Thank you.

A 3% swing is nothing for a hilly course.  Variability index can top 1.1 or much higher for very hilly courses in order to ride your fastest.

You need test these things out in training and racing and find the range that works for you.

To give you a personal example, I just rode a 12 mile very slightly rolling tri course. I set my power range from 150-450 watts and did a good job holding it. My variability index was 1.01 for this ride.  So for all practical purposes I held nearly steady power. At an average power of 340, I went 190 watts below this at times, and 90 watts above it at others. I also coasted at 0 watts for 30 seconds of the 26 minutes.

Again, 3% is nothing. Think 30% as a starting point.  You want to be able to vary your power as much as possible without those higher numbers having a huge effect on your ability to run or continue riding. Most can do ok going into Zone 5 (106-120% of threshold), it is getting deeply anaerobic that will come back to bite you, especially the longer the race. 

I don't want to disagree with Fred again, cuz he's right.  Long course racers need to be careful. 

HIM and IM racers should probably limit themselves to threshold power on uphills and be very wary of any bursts over this level. Coasting on the downhills is a good strategy. Anaerobic stuff will hurt long course athletes, whereas for a sprint you can utilize much larger power swings.

There is some science to all this of course, but there is also an art, and it comes from riding your bike a lot and being aware of how your body responds.

x2

Yes, stopping the effort at the top violates rule #1 of pacing:

The slower you are going the harder you are pedaling within your pre-determined range.

There is no rule #2.

So coming over the top you should be pedaling at the top of your pre-determined range and gradually ease off as you pick up speed. If you have an ultimate descending speed for this particular hill of 30 mph, get there fast! and then recover at the bottom of the hill. Don't coast up to 30 mph slowly and then start pedaling. Minimize the duration of the slower periods by pedaling hard to get through them.

Yup.

Robert is probably more tuned in to this than me, but I have seen the results of some modeling software where you essentially input a course and your threshold power and it spits out exactly how hard to ride when, where and for how long. Neat stuff indeed.

On the other hand, I think an intricate knowledge of the course and your abilities can get a person pretty close to those results. I know that riding a course by feel and experience and laying down a power file like Picasso laid down paint is an art form all to itself.  Looking down the road and seeing a hill and knowing what is around the next bend and then nailing the numbers is a stupendously gratifying experience. I really think it is a skill that will improve with every ride, to the degree you allow your awareness of such things to expand.

Awareness always begins as a point. That point is where you are with it right now. Simply notice things as you ride, your success as well as your failures. Withhold judgement as long as possible. Allow your awareness of pacing to become an expanding sphere.  Eventually that sphere will encompass any course you ride on.

Ok, it's getting thick now. Gonna take the rest of the afternoon off...

Thanks for the discussion, everyone.  Very helpful indeed.  The big takeaway is 'pay attention', which is always a good lesson to bear in mind.

Motivated by some comments here, I did some reading through old threads on the wattage group and learned a lot as well.  One quite interesting article I found is this one by Simmons:

http://www.clochette.co.uk/TTF/Articles/POI+Discussion~v.Word97.doc

(link is not to the wattage forum but you can find it there too). Probably old hat to the experts, and maybe they want to share an opinion about it, but as someone new to training with power, I found it very interesting.