watts/kg and predicting race speed
I've got the full Vineman coming up, and wondering about what my increased FTP and reduced weight is going to mean on race day. This is only my second year with power, so I have no experience .
Assume my ftp last year was 200. At 75% IF, my goal watts 150 for the vineman 70.3. May weight of 165 last year would give me a watts/kg on race day of 2.0. Lets say my ftp were 220, and goal watts 165, and I lose enough weight so my watts/kg at goal watts is now 2.5. Does that mean I will vcover the same coruse 25% faster?
Since I'm doing the ful instead of the half this year, could I then apply a factor that recognizes my reduced goal watts (.7 IF instead of .75) and predict at time for the full?
Lastly, I was new to power last year, so my vi was 1.17. Probably means that I've wasted at least 10% of my power. If I could ride with a vi of 1.05 or so, does that mean I get 10% faster?
It's probably not that simple, but some of you will know. Thanks
Comments
Also, the faster you go the more air resistance/drag you have to overcome and the more watts you need to make smaller gains. In other words, to go from 15mph to 20mph may only take an additional 50 watts, but to go from 20mph to 25mph will likely take closer to 100 additional watts. Diminishing returns kicks in and it takes a huge improvement to get to 30mph, etc.
All that said ... a change of .5 w/kg will make a noticable difference and there are calculators out on the web that will help you sort this out. It will depend on your weight, position, course, etc so it is hard to us someone else as an example. Also, the lowever VI will definitely help to allow you to use the watts you have available.
The reduced body weight will likely help even more on the run then the bike. Some people say about 2" per mile per lbs lost faster, but I find that to be a little aggressive for me personally.
Hi Bob — while I am no WSM and a newbie to boot, I would like to add to Matt's point abount weight loss and running speed. I have read a few times that reducing weight (assuming it is fat rather than running muscles) has a proportionate impact on your VDot. The calculation that I've seen is you take your old Vdot (at your old weight) and multiply it by your old weight, and then divide that number by your new weight — that is a prediction of your new VDot at your lower weight.
That said, I have lost over 15 lbs this year and the suggested calulation give more speed improvement that I have been able to achive so far. However, I have improved my running a lot since early january.
just my two cents.
Bike Split was 2:39, NP= 215, My weight was 163
Bob - More thoughts for your stew. This is what I'm telling myself now when I start to day dream about times for IM CDA, June 26:
First, its a *little* early to start worrying about/predicting your time for this race. Better to focus on just getting the workouts done on a daily basis, and getting the most out of your training and body comp work.
Second, there are SO many variables that trying to predict race times based on a simple watts/kg formula will probably just be frustrating. There are hills, wind, temperature, turns, ability to hold an ideal aero position, quality of taper, effect of "drafting" in a large crowd of racers spaced 5-10 meters apart, etc, etc.
Finally, I've found the best way to predict race day splits is to look to your second Race Rehearsal 3 weeks out from the IM. That takes the best shot at your then current fitness and transposes it to what you can do over 112 miles followed by a quality one hour run. If you can hit your pace targets for that one hour run, then you can probably go 5-10 min faster on race day on the bike, as you will be rested on race day and you're not rested for the RR.
I suggest leaving predictions for time on race day to a point in time much closer to the race. It'll just make you anxious to try and do it now, because you won't like what you predict based on your current training, and your current training is not really geared to giving you the type of information you need to predict well.
Get as fit as you can and as lean as you can, execute like a ninja on race day, and your time will take care of itself.
@Al - I'm sure you're right - better wait until closer to the race to worry about it. I'm not sure my RR will tell me much about my time on race day - hard to duplicate the course even though I do live in NCAL. It's just sort of fun to ponder.
@David - my weight will be about the same as yours, but np will be quite a bit less - if I lose the weight and increase my np by 15% over last year - I guess I'll be in between what I did last year and your time.
@Matt - I've seen the running prediction formulas, but never one for cycling. I really need to work on my vi - I was new to power training last year, and never really got the hang of it - especially on hills - but more power and additional practice should make me a lot better by the end of July.
Here's a link - http://www.analyticcycling.com/ForcesPower_Page.html .
There are three main forces that want to stop you from moving - wind resistance (a function of your cross section and the square of your speed), rolling resistance, and gravity (depending on the grade and your weight). How much they want you to stop depends on how fast you go. The gist of this all is that there is a cube of velocity term in this equation which means going twice as fast takes closer to 8 times as much power rather than twice as much. Going just 10% faster can take as much as 33% more power. There are some linear terms that make it not quite so bad but in general, one should be pretty happy if a 10% increase in power gives a 3% increase in speed on the level. When climbing, that 10% increase in power will give much closer to a 10% increase in speed if you're going slow enough that the gravity aspect is more important than wind resistance.
The weight loss is important in a straightforward way when climbing. On the level, the impact is not so much the loss of weight but the fact that you are smaller which means less cross section for the wind to push (back). Measuring your effective frontal area tends to be complicated but if losing weight reduces it, you'll go faster at the same power.
I completely agree with Al that RR is a far better predictor for actual race performance and even that prediction can't account for all the conditions of a given race day...
Regardless, you can probably guess within about 30 minutes based on a SWAG. After that, it doesn't matter. What matters is what P sez, focus on being able to do the work to ride at that intensity for the expected duration and run off it. If you can, you've maximized your potential for the day.
I find the predictor stuff more fun for the "how much faster/stronger do I need to get between now and next year to have a shot at XX:YY time goal?" other than the "as fast as you can possibly get" response!