Wednesday, December 29, 2010

30% increase in power since Sep 2010

Well, in just 12 weeks of training, I've increased power over the same interval distance/session by 30%, which is a bucketload. OK so there wasn't that much there to start with, but improvement is improvement.

This increase in power over shorter distances has also translated into some PB times over 20km, 28:51 notably, which is an all time PR.

Tuesday, December 14, 2010

Zipp releases Firecrest rim shape

Well the folks at Zipp are at it again. A new rim shape, dubbed Firecrest, has been developed and looks like being rolled out across the Zipp lineup.

The shape is less toroidal, and more boxlike, with a much fatter rim profile than before. I suspect this is to allow the use of 23C tires which can also help lower the rolling resistance of the wheel.

There's only one problem... no data. Can't find a single test result (either within Zipp) or externally that has any kind of data. Instead we just have more Zipp marketing speak:

From their webpage explaining the new shape:

"The performance benefits are substantial. With Firecrest, the latest 404 Tubular (58mm rim depth) matches the aero performance of the pre-Firecrest 808 (81mm depth). And the new 808 Tubular is faster than any competitor’s 90mm rim."

A bit better: from a press release:

"At a 10-degree wind angle, the performance improvements from Firecrest are substantial: 9 seconds over 40km for the 404 Tubular, and 15 seconds for the 808 Tubular that is now faster than any 90mm rim and even some disc wheels. At higher wind angles, the benefits are even more dramatic."

But this kind of data is still really annoying, it doesn't give you any idea of how the rim shape actually performs in different conditions ...

Edit: Zipp have since released some data on their website which shows the 404 Firecrest shape performing in comparison with other wheels.



This data shows the Firecrest shape on a 404 outstripping a 2010 808 by a reasonable amount.



Enter YouTube: Finally some real data from a presentation at Interbike ... I'm not even sure how I found this now, but it appears to be the only source of real data available for the Firecrest shape on the web currently (edit: until the above graphic surfaced on the Zipp website).

This presentation is by Josh Portner, the Zipp Technical Director, and (obviously) the dude behind Ask Josh on the Zipp website, and actually explains why and how they have been able to reduce drag and make the wheel more stable in cross winds.



I'm wondering if Zipp had some cross pollination from some CFD work that was published recently ... in that study, the side forces of the wheels were measured and plotted as side axial forces acting on the wheel (they also collaborated with Zipp to check the CFD results against tunnel data). (Paper available as 3.2Mb PDF)


It does make a lot of sense ... if you can design a wheel where the side axial force pushes right on the centre of the wheel, it actually doesn't exert any turning force at all on the wheel, and so behaves so much more nicely in cross wind, rather than having to wrangle it like some carbon fibre cowboy.

Here's a screenshot from the video showing the reduction in drag in a crosswind, both on the front, and on the trailing edge of the wheel as well:



Mind you, this is comparing the Firecrest shape to a traditional V design, so you'd expect to see quite a bit of difference. It's clear how the more rounded back of the rim, once it is the leading edge of the trailing side of the wheel becomes closer to a traditional NACA foil shape with a thinner trailing edge, and therefore has less drag.

There is an interesting side story here, one which Zipp has conveniently avoided by clever use of comparisons... they've compared a FC 404 to 2010 808, and a FC 404 to 2010 404 and a FC808 to a 2010 808, but why not FC 404 to FC 808? The answer appears in the following graphic:



This graph shows a mixture of data from HED and Zipp and plots the FC 404 v the FC 808 directly against each other - what is clear is that the better wheel is probably the FC 404! Why? Because the wheels have almost identical drag down to 10 deg Yaw, and the FC 808 only manages a slight drag decrease to 15 deg yaw, and then the drag on the FC 808 rises significantly after 15 yaw because the wheel is stalling and starting to cause massive turbulence at that point. So the (pretty much) age old rule of deeper=better may not necessarily hold in Firecrest country, the FC 404 should perform almost the same as the 808, and once it gets windy, it performs significantly better than the FC 808. It will also probably cost a lot less than a FC 808 as well.

I'd still like a please explain from Zipp (or HED) as to why their data for the H3 (top line) goes nowhere near the H3 data from Hed (bottom line). What does this tell me? It tells me that there are a myriad of ways to get data from the tunnel, and it is easy to pick or inadvertantly make data that may show you in a more positive light than your competitors (for example, put a nice fat tire on a skinny rim and see how poorly it performs). It also says that perhaps the only true way of telling "faster is faster" is field testing it yourself to see what works for you, relying on marketing speak may well be a sub optimal method for buying speed.

Wednesday, December 1, 2010

Pedal selection and aero characteristics



It isn't very often that companies post raw wind tunnel data, but kudos to Speedplay for coming up with the goods... not only have they tested their product at one of the better tunnels, they've released the raw tunnel data that clearly shows their product outperforming competitors. While there may be some sources of error that could allow the data to show their product in a more positive light than the competitors (for example testing on a different day, with different atmospheric conditions and then not adjusting for air density), we're pretty sure that this is not the case.

The results shown indicate the following CdA's:

Speedplay4 0.237 = 11.35 m/s = 40.86 kmh (25.5mph) = 58:44 40 km (25 mi)
Speedplay3 0.242 = 11.27 m/s = 40.57 kmh (25.2mph) = 59:09 40 km (25 mi)
Shimano 0.243 = 11.26 m/s = 40.54 kmh (25.2mph) = 59:12 40 km (25 mi)
Look 0.243 = same as Shimano

That's 28 seconds faster over 40 km, and a pretty surprising result for the 4 hole cleat and 4 seconds for the 3 hole cleat. Also it isn't 33 seconds faster over 40km as claimed by Speedplay ... but that depends on the input parameters you use to do the calculations (in the above case 0.004 Crr, 85kg, 0 slope, 250w, 1.226 air density), but it is in the ball park.

With the bottom of the line speedplay retailing for around $150, this is quite good return on investment at $18 per second (4 hole), and not so good $37.50 per second for 3 hole.

Now I'm a bit intrigued as to why there is such a difference between the 3 and 4 hole mount systems... I suspect it has a lot to do with the way that the 4 hole system requires less bits to mount and therefore makes a lower profile underside to the shoe. As the following graphics (copyright Speedplay) show, there is probably at least an additional mm, perhaps more of material under the show with a 3 hole system. Which means, of course, that you may need to look at some new shoes as well to get that time difference.




vs.






You can read more about the Speedplay testing:33 seconds saved

Thursday, September 9, 2010

Back on the wagon

After a long layoff (having squashed 6 competitive seasons into 3 calendar years) - needed a long break to recharge and recover... that done, its been a hard road for the last month getting back in the pool and on the bike and out running.

Blood test shows Vit D level of 19 ng/ml, which is less than half of the minimum optimal range recommended by numerous health bodies... (32-50 lower end of optimal range, 65-70 upper end of optimal range). Melbourne winters are hard on the sun absorbtion factor, and the one just past was worse than the last few years as we finally got some relatively normal rainfall...

However, onward and upward.

Sunday, January 31, 2010

Next wind tunnel session 6 Mar; Pacing Optimisation

Yee ha - back to the tunnel - 6 Mar. Like a drug that thing.

Hot Gatorade race in Melburn today... 37 deg C and with a run time approaching my cycle time I still somehow managed 10th in my age group.

Also been working on a pacing optimisation calculator. Alex Simmons has a ripper one in Excel, but it's pretty slow (well Excel is pretty slow at the best of times) - it takes 20-30 min to optimise a course with 100 segments. The idea is that if the course is hilly (or there is a stinking headwind like today) you can actually be faster by applying more power on the uphill/headwind sections, and less on the downhill/tailwind sections, while still keeping the normalised power at the same level as if you rode the course at the same even power.

Executing such a pacing strategy is pretty simple if the course is hilly - add % grade to the screen of a Garmin 705 alongside power and ride X power for Y gradient.

So I figured I'd have a crack at the same problem, but using a different technique: genetic algorithms. A genetic algorithm is a way of finding solutions to maths problems, but without doing every possible calculation required with brute force. You come up with a way of encoding the problem as a gene (you set the power for each course segment), then determine how well the gene solves the problem (arrive at the end of the course with a specified Normalised Power and fastest time).

By creating a population of genomes, you can then calculate how good each gene is at the problem, and rank the results. Then comes the fun bit, you take the best genes, divide them into Mums and Dads and then start creating children by swapping some of the gene segments of the Mum and the Dad into the babies. You also get to mutate the gene pool randomly to keep things interesting.

Preliminary tests are that I can calculate a population of 1000 genomes on a 6 segment course and do a full generation every half second or so(each 1000 genomes calculate how good they are at the problem, have babies and die off, then a few might get mutated); so in a minute could calculate 120,000 attempts at solving the problem. Because the genes adapt to the problem, picking the better solutions each generation, this might be a lot faster than using Excel... time will tell.

I'm planning on factoring in bearing, wind bearing and wind speed as well as the course (elevation, CdA, Crr) etc. You'll be able to vary things per segment if you need to (like a really rough section of course, or an exposed windy section). If the thing is fast enough, you should be able to run it on the website from your mobile browser on the way to the race site. Under a minute good, longer than that not so flash. And it should be easy to use - upload a TCX/GPX file from a Garmin or exported from WKO and there's the course - tweak the input parameters and solve away!

3 weeks till Nationals - CTL 70.

Monday, January 11, 2010

Oops

Raced yesterday after 1 week of full training (instead of just swimming); accidentally won my age group after fastest swim/ride and very slow run. 4th overall fastest ride. All the work in the pool and in aero is paying off. Gotta figure out this running caper... somehow.

Monday, January 4, 2010

Whoa! Cool nerd tool under development

Finally had some time to sit down and fritz around with some new(ish) Microsoft technology that I've been meaning to catch up on for a while (Visual Studio 2008, Microsoft MVC and some other stuff).

And it's good - in fact great. Really streamlines web based development and makes things much faster to develop.

Anyway I won't bore everyone with the tedious technical details, here's a screenshot of the first part of the application:

View of the new power calculator

A brand spanky new power calculator that does, amongst other things, calculate one of Crr/CdA/Slope/Speed/Power from given information, draw a graph of power v speed for current CdA/Crr, and generate split times for a variety of length rides from 20k to Ironman®.

Kind of like analytic cycling, but roided up for the 'teens (we are 2010 now after all). Plus I fixed the stuff that annoyed me over there (sorry Tom Compton) like not having CdA as a single measure, and having to calculate metres/sec all the time from kmh (divide by 3.6). Also now that I programmed in a proper air density calculator, it should be a lot more accurate than guessing at air density values all the time.

Anyway there is a bit more to do on this, but should have something publically available before I have to go back to work towards the end of Jan.

I'm thinking conversion of imperial units for altitude (ft -> metres), temperature (deg F -> deg C), and pressure (inHG -> kPA), plus an override for pressure for people who actually have their own portable weather station (Andy Coggan: Google Wattage for one ;-)), rather than the sea level reported pressure.

CTL up to 50. Big week, including riding with some A graders. Ouch.

Friday, January 1, 2010

Will a Simkins Aero brake be worth it?

Recently saw Matt Simkins new aero brake design - kinda like the old Hooker TT brakes (which incidentally go for a very pretty penny on eBay). The big question is: Are they worth it?



According to Matts real world aero calcs (performed by Tom Anhalt, Google Wattage member), the Simkins brake had a CdA of 0.2125 vs the Cervelo brake mech of 0.2152, or a difference of 0.0027.

That's gotta be a pretty small difference... heading on over to analyticcycling.com:

250w, CdA 0.2152 = 11.62 m/s or 41.83 kmh (25.98 mph)

250w, CdA 0.2124 = 11.66 m/s or 41.97 kmh (26.07 mph)

So a difference of 0.04 m/s... thats 4 cm (about an inch and a half) further per second.

Over 40 km, that's 57:22 compared with 57:11, a scant 11 seconds saved for $335 USD or $30/sec.

Worth it? Might be if the race was a biggie, and the winning margin is less than that! Probably not if 10 seconds can be gained reasonably easily by some other means, like practicing a transition between swim and bike. For TT's only, there would be more merit as the podium is frequently exchanged on the basis of a few seconds here and there.

As an aside I actually sanity checked what a front brake assembly was worth in CdA terms; Cervelo front brake mech on and off the bike the CdA difference was 0.004 - roughly double the difference between the Simkins brake and the Cervelo brake. So the test results do seem to be reasonable.

You can check out Matt's site: www.simkinsdesigns.com