Minion

Before 2000, the civilian GPS signal was intentionally degraded to 100m. This was turned off in that year and, given the prevalence of GPS use by airlines etc., I'd say it's highly unlikely it will ever be turned on again. I may have been a bit incorrect in my previous statement. 3m is a best-case measurement where the GPS can see lots of satellites and can also receive additional signals from WAAS base stations (only in US). The 3m accuracy means that 50% of all reading will fall within a 3m radius circle. About 95% within 6m radius and 98.7% within 7.5m radius. http://www.kowoma.de/en/gps/accuracy.htm

I think, for navigation devices, it's still around 3m. You can get survey GPSs with millimetre-level accuracy, but they need to be standing still for a while to reach that level.

Here are two comprehensive articles comparing GPS device accuracy: http://www.dcrainmaker.com/2011/06/2011-sport-device-gps-accuracy-in-depth.html http://www.dcrainmaker.com/2011/06/2011-sport-device-gps-accuracy-in-depth_09.html The accuracy varies with the type of course and terrain you're travelling on. The GPS will be generally be less accurate than a calibrated wheel-based sensor.

Buycycle.co.za, though it may take a while before they get stock. I've found that a lot of the SRAM/Zipp stuff that comes through the local agents is very well priced compared to CRC etc.

It also directly affects the rolling resistance.

Methinks American need to toughen up a bit. Far too much brick-shitting at the slightest thing.

Probably up Hendrik Potgieter, parallel to the N1.

I think I head 2:35 being mentioned for the men.

Does anyone know if it will be possible to collect numbers on the day? The race office appear not to want to answer their phone or reply to my email.

I think it would depend a lot on the course. With 400m of ascent in 12km it looks quite hilly. Playing with some numbers on Analytic Cycling shows a 1-2min gain over 12km is not unreasonable for an inclined course. You'd need some idea of the course profiles for both tests to really judge it (1-2s/kg sounds more feasible on a flatter course).

I did this again with my Ride 4 Sight data. There was an almost 100% difference between actual and calculated power. Not unexpected considering the shielding effect of a bunch.

I doubt the worn chain will have a measurable effect on power loss, compared to a new chain if you're replacing it when you're supposed to.

I did a comparison of the Sporttracks GPS2PowerTrack plugin and actual power data. It comes out fairly well. Average power was between -9% and 3% of the measured value, while normalised power ranged from -9% to 17%. The power distribution plots were also generally OK, though some bands showed major differences.

I'm not disputing that it happens. I'm just wondering whether the cause is due to CO2 pH or whether it's due to the cooling effect from a bomb. The test I proposed would allow you to check whether cooling causes the balling by removing the influence of CO2. Have a quick look at the canister specs here: http://www.genuinein...-cartridge.html If you do a quick PV = nRT calc it gives an internal pressure of about 42MPa for a 21cc canister containing 16g of ideal gas CO2 at 21°C. This is almost 10x the vapour pressure of CO2 at that temperature. There must be liquid in the canister.

I'm not so sure this is the case. The canister gets very cold because the CO2 is converting from liquid to gas in a small volume. The overall temperature in tyre would drop, but I don't think it would be by more than 10°C or so. There might be some localised freezing by the valve but, unless it sets off a chain reaction, I think it would only cause a few balls to form. Edit: It should also be fairly easy to test. Fill a spare tube with sealant, chuck it in the freezer overnight, install it in the tyre and pump it up with a floor pump (in case pressure has an effect). Spin it around, let it get to room temperature. Take it out and cut it open to look for balls.

Completely wrong. Air is around 78% N2 and only around 0.04% CO2.

Very good point. Here's the spacer in question:

It usually happens when the distance from the dropout to the first cassette sprocket is slightly different. You could probably get around it by putting a shim between the hub body and the cassette or between the hub body and the axle on one of the wheels. Alternatively, you just need to keep track of how many turns of the barrel adjuster are required to adjust for each wheel.

An accurate estimate would first require you to have good estimates of your weight on the day, coefficient of rolling resistance (Crr), coefficient of drag (Cd) and drag area (A). Weight is easy to measure and shouldn't vary by more than 3-4% during the ride (and that much only if you drop something or become dehydrated). You could make your estimate more accurate by modelling a linear (or some other relation) decrease in weight from start to finish value. It is possible to get a good estimate of Crr and CdA using a power meter (and also without a power meter under some conditions) with the Virtual Elevation method. The Crr value would change with pressure so you would need to make sure you pump your tyres to the same value every time. It would also vary with road surface conditions. As a thumb-suck, I reckon it could vary as much as 5% during a ride. The variation would be unpredictable and you wouldn't easily be able to account for it. The CdA value would vary with position on the bike and equipment and kit used. It will also vary with wind direction to some extent. If you could measure wind direction, you'd still be left with the problem of cheaply measuring CdA variation with wind direction). You could eliminate variation due to equipment by riding the same bike and wearing the same kit for each ride. You could measure CdA for each position, but you'd still have the problem of monitoring which position you're in as you ride. I think CdA values could vary by 10% or more. You would then need to have accurate values for speed, elevation change and wind conditions around your bike. Speed can be accurately and consistently measured using a GPS-calibrated wheel sensor. Elevation change could also be fairly accurately measured using a barometric altimeter (a pure GPS altimeter would add extra innacuracy). Wind conditions (particularly direction) around your bike are the biggest source of variance. A differential pressure sensor would give a rough estimate of wind speed, but not direction. You can get weather station data for your ride that will give global wind speed and direction, but will not account for local effects such as environment shielding or local turbulence. There is currently some development being done on a commercial bike wind sensor (that may even work with ANT+) - Google 'Chung-on-stick'/Aerolab. Measuring values eliminating as many sources of variation as possible, I think it might be possible to get accuracy of around +-20% for post-ride analysis and perhaps better for rides done in one position on a calm day. The Strava website estimates power based on speed and weight and there is a plugin for Sporttracks that also estimates power using more parameters. I haven't compared either estimate to actual power values (it's on my to-do list). Real-time power measurement would be a more difficult problem: The iBike Aero 'power meter' measures front wind speed, speed and gradient in real time and is reported to give average values for rides over 20min that are within 15% of conventional power meters. For shorter durations, it's accuracy is, apparently, worse. I feel that these power estimates are OK for rough comparisons and comparing long-term training effect, but they're not much better than using a HR monitor for this purpose and they aren't currently practical for measuring and controlling short intervals which is where the PM is most useful.

? I've bought huge amounts of stuff from them. There are certain product lines that they don't ship to SA though e.g. Lemond. Set your destination to SA on their site and everything it shows can be shipped here.

Claimed life is about 400hrs of riding, but I found mine didn't last much more than 250hrs. There's a special tool to take off the end cap, but you could probably also use a large shifting spanner to do it. Once the cap's off it's easy to replace the batteries and they're fairly easy to find.

The most important thing for tracking improvement is consistency. Absolute accuracy is not too important in this case. Find a nice 20min TT course and ride it as hard as you can every month or so. Try to do it at the same time and with similar weather conditions each time. Your average speed will give an indication of improvement (faster = improved). You could upload your Garmin data to Strava.com to get a very rough estimate of power. You could get a more consistent indication if you do the test on an IDT. Once it warms up, the speed-power curve is fairly consistent. Once again, faster = improved. There's a Sporttracks plugin that will allow you to estimate power from IDT speed data. Last time I looked at it, it was pretty consistent for steady-state riding.

Both the Garmin and Look pedals embed the strain sensors in the pedal spindle and have a detachable electronics pod. I suspect it would be very hard to catastrophically damage the pedal spindle in a 'normal' crash. The electronics pod also looks fairly shielded. If it does get damaged, Garmin, at least, says it will be possible to get a relatively cheap replacement. DC Rainmaker has some in-depth articles on both and it looks like he'll be reviewing the Look meter in the next few weeks. http://www.dcrainmaker.com/2011/09/everything-you-ever-wanted-to-know.html http://www.dcrainmaker.com/2011/09/everything-you-ever-wanted-to-know_19.html SRAM claims the new Red Quarq will do L/R balance, but it'll be interesting to see how accurate the turns out to be. We'll probably have to wait for it to be released and for someone to do side-by-side rides with a pedal-based meter before we find out.

The article implies he's a public figure, well-known in connection to cycling. The Modimolle monster was unknown before his offence, so his hobbies/profession didn't have much relevance. There're plenty of articles that have, in the past, referred to well-known rugby/soccer/cricket players. Without their prowess in those sports, they wouldn't be public figures and we probably wouldn't even have heard about the stories.

Why not? I do it all the time. The only real downside is that it's about 45-60min of riding before you actually get to the Cradle, limiting the number of loops you can do there.