Time Trial by power

robkit

ok now i'm a convert... variable power it is!

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I am my favorite rider.

flanman

There was a time trial in colorado last weekend. 6 Mile out/ 6 mile back with a screaming tailwind out/ headwind back. It was a crosswind, so I'm not sure of the portion parallel to the course. Out was nearly -1% gradient, back +1%. The time splits were typically in the ratio of about 1.5:1 between back and out.


Intuitively, it would make sense to push it with the tailwind and conserve slightly with the headwind. I ran some simulations with the kreuzotter.de calculator and they all indicated that it was slightly advantageous to push it with the headwind. This is with power -5% out and +3% back (to make average power constant). A greater power variation will have greater results.
However, depending on the wind, the difference isn't huge. About a 2 s advantage for 5mph wind and about 10s for a 15 mph wind. I don't trust the calculations that much as they predict a speed that's much too high on the outward leg (can't spin that fast).

A power variation of +/- 10% is probably too big, unless you've got great recovery powers.

I've read one paper by Swain and was not impressed.

In short, you're probably better off just trying to concentrate on breathing well and dipping your head slightly against the headwind than worrying about power variations. Pushing it on hills is definitely the way to go though.

rmur17

geez this ain't rocket science guys: when you start to slow down: push harder ...

seriously.

Now on our trad. local course here we have a long false flat ~10k @1.6% going out , then a cloverleaf turnround with grades +/- 8-9% and the fast -1.6% leg home (total ~21k).

Ignoring the prevailing winds, it's definitely faster to ride this course with higher power going out vs. coming home. The turnround is best ridden with pretty variable power and normally even standing up for a portion.

Running the course thru the NP pacing algorithm suggests the overall best times (in calm conditions) will be done with IIRC around 20% power delta outbound vs. return. Practically speaking I find the limiter on that course is how much I can average for 15-20min going out around 40-42-43 kph going out vs. the 55-60kph return leg.

just ran some numbers and the model suggests the following outleg/retleg power ratios vs. outleg headwind:

Calm ........ 1.17
+1 m/s ..... 1.22
+3 m/s ..... 1.31
+5 m/s ..... 1.43

-1 m/s ...... 1.13
-3 m/s ...... 1.06
-5 m/s ...... 0.99


anyhow it's just an example where the overall duration may be 26-30 min but a big limiter is 15-20MP. It definitely doesn't teach one good pacing and it's not a route I like for TT training either. but for racing, it is what it is ...

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rmur

koger

Thank you for those very great links!

wattsup?

I would love some pacing analysis on this in the spirit of this thread.

Here's a file from Stage 1 of last year's San Dimas Stage Race, which is the infamous 3.8 mile uphill GMR TT. It starts with a brief, flatter section then goes into a fairly constant 5.5 to 6.0% grade with plenty of switchbacks.

At the time and by RPE, I thought I rode the course great. But in looking at the file, I made the classic error of going out too hard and gradually weakening as I progressed. My plan was to go steady and punch it hard from the 1k mark to the finish.

All the stats in the file were accurate at the time. My numbers have improved since last year. I'd therefore like to see an improvement in my time commensurate with the work I've done. The TT is in 2 weeks.

327 watts for 17:30 at 75kg netted me 33rd place in the Cat IVs. The winning time was 14:29 for our group. The 'mortal' IVs were coming in around 16:00.

Here is a link to the Power File and a Gradient Map of the course of which we ride the first 3.8 miles.

What would you do differently were you me on this course? If any other info would be helpful, I'll be happy to provide.

Thanks for reading,

wattsup?

swampy1970

I can't open the powerfile but the course is not that long, not all that steep and if the road surface is pretty good I'd treat it like any shortish time trial with one caveat - start reasonably conservatively. The five or so seconds you may gain in the first 1/2 mile will be more offset with the time that you lose in the last 1/2 mile if you light it up too soon. Just get a really, really good warmup and get to the start with a couple of minutes to spare.

If you have a similar hill in your area, I'd do some testing climbing mostly seated Vs mostly standing and at the very least sitting/spinning and sitting/using a slightly larger gear that allows 70 to 75rpm.

As it's a hill climb, if you have the time and inclination, remove everything absolutely not required for riding your bike up hill. There are no prizes for fancy bar tape, unused 53t chainrings, front mechs, excess brake and gear cables, bottle cages and bolts... If you're really fussy you can argue that shorter chainring bolts for a single ring weighs *cough* significantly less than the double ring bolts. It always made me wonder why people would spend thousands on a bike to save a pound and then do hill climbs with pound and a half of unused equipment.

Same with clothing too - unless it's brass monkey cold. Glasses, mitts, undershirt and maybe even socks can all sit in the pile of "uneeded" stuff - the clothing is an easy one pound saving.

wattsup?

Thanks for the great info. Last year, I used RPE and HR for pacing. I'd like to try to use AP this year, as well as a lower cadence as I have seen the best results in my climbing numbers coming in at a lower cadence, around 80RPM. Just need to remember to do the right things in the excitement the day of.

wattsup?