For good or for bad I'm obsessed with numbers related to my riding. Before the ride I plot out my expected time on a control by control basis. It gives me something to shoot for and I'm usually within 20 minutes on a 300K or 400K. I know my average speeds, I know how different terrain, time of day, distance, etc affect my speed. I only have personal data out to 400K though.
My question is what kinds of reduction in speed have others seen or measured in multiple day events. Measurements of my own long rides suggests (very roughly) 0.3 mph fall-off in speed for each 100K. So for a 1200K started at around 14 mph I'd finish at around 10.5 mph. That sounds reasonable. I know there are many many variables that make a linear extrapolation of speed unlikely to hold up over a four day event but I'm just looking for general trends.
So what are your experiences with your own speeds over multiple day events?
On a multiple day event, you've also got to factor sleep into your calculation. On a 1200K, I'll usually ride the first 400K, at least, all in one go. But it is in the remaining 800 km where I get my 5-8 hours of sleep.
Here are my average speeds on the Rocky Mountain 1200 ... the first 1200K I did. These average speeds include all breaks of course.
03-03-10, 03:14 PM
I have GPS tracking info on 107 rides of a century or more, including BMB and nearly all of PBP, plus four SR series. The tracking info is broken down into (typically) five mile intervals, over which I know speed, moving time, stoppage time, ascending and descending. And I know what time it is, so I know if it's dark out. Plus from weather records I know the temperature through the day. My forecasting model for moving speed is:
MovSpeed=f(Intercept,Bike & gear weight, ascent rate (feet per mile), descent rate, dist into ride, miles of riding in previous 30 days, drafting, nighttime, sickness, tandem, and extreme temperature).
Running this model only for rides that were brevets or permanents, I get an adjusted R-squared of 57%, i.e. the model explains 57% of the variability in moving speed. All variables have significant T statistics. Parameter values are as follows:
Bike & gear weight= -0.074
Ascent rate= -0.053
Descent rate= -0.010
Distance = -0.00657
So the interpretation is: average speed would be 21.2 mph with a zero-weight bike, on flat terrain, at the start of the ride (dist=0), being generally fit from commuting but not having done any centuries in the prior month, riding solo in the daytime, healthy, and in temperate conditions (i.e. temperatures between 32F and 90F).
For every ten pounds of extra bike weight, I get slowed down 0.74 mph. I typically have 40 pounds of gear so that makes a base initial speed of 18mph on the flat ...
A 1000 foot climb over 5 miles would be an ascent rate of 200 feet per mile and would slow me down by 10.6 mph (200*-.053). So if my base speed is 18 then I'm down to 6-1/2mph, which sounds about right for an extended 4 percent grade.
Descending apparently slows me down, too ... I'm guessing that this is because if you're in terrain with ascents then you also have descents, thereby violating the maintained assumption of independent explanatory variables, so the descent variable is picking up some of the variability from the ascent variable.
For every hundred miles into the ride, I slow down by .657 miles per hour. So if my load-adjusted base speed is 18mph at the start, then by 750 miles into a grand randonee, then I have slowed down by 4.93 mph to 13mph. Sounds about right.
If I rode an extra 100 miles within the prior 30 days then I am somewhat fitter, and that makes me faster by .0626 mph on this ride.
Drafting makes me 0.621mph faster. Nighttime makes me 0.465mph slower. Being sick makes me 0.281mph slower. Riding the tandem makes me 0.674mph faster (about the same as drafting). Really cold or hot makes me 0.631mph slower.
Your mileage may vary.
PS, In case you're wondering how I know about drafting ... it's a sufficiently rare occurence that I'm drafting anyone for any length of time, so for those times when I have been drafting during an interval, then I can add that to the info for the given leg.
03-07-10, 09:37 AM
I guess some one using a Power Tap could try and track how they are working for several days at a time. But for my own experience, I would have to say there simply is no way to measure performance this finely.
For the most part, like the weather, you will find an ebb and flow to your power range. These sorts of statistics are charted by the "pro" coaches all the time and they would tell you there's no good way to account for why certain riders will reach certain "zones" after multiple days of racing....... (all though they surely would like to know the why and how of it)
03-09-10, 06:57 PM
Count me in the camp of "there are way too many independent variables and not enough opportunities for data collection to draw meaningful conclusions about performance degradation over time." The execption would likely be RAAM and guys spending 20+ hours on the bike for multiple days. There's a bunch of great data on the RAAM website and you could go play with that to see how speed changes over time.
But for randonneurs and the rest of us slow folks.... I think you'll find results are all over the map. On one 1200K I had no change in speed over time. But then I spent almost 24 hours at the overnight controls (that was a seriously fun 1200K!). On the same route 4 years earler, I was 20 hours faster in my finish time but my splits were 50% on Day 3 of what they had been on Day 1. I was very tired and I was injured.
But then I'm about as unscientific about this stuff as they come. Power Tap? Heck, I don't even use a cycle computer any more!