brawlo

brawlo

Divebrian

I'm a realist...just hanging with them is my goal. I'm sure there will be people there that participated in mass start events at Masters Nats last month and are training for mass start at Worlds in October. This is my first official mass start race in a long time and previously when I did them, I hadn't learned to be selfish and was always up front pushing the pace. I have now learned and understand the philosophy of being selfish, but don't know if I'll have the self control to implement it. I have no illusion of coming out for my first race and getting my gearing and tactics spot on.....if I get either of those two right, I'll consider it a success. I'm going more for the fitness aspect.....

carleton

Comfort. It all starts with comfort.

Comfort on the bike. Comfort on the particular track. Comfort with your bike handling. Comfort of your legs and lungs. All of that will come with time-on-task.

Once you are comfortable, your mind will stop worrying about those things and be free to strategize.

Also, many people focus on "trying to win". I like to think from the other perspective, "trying not to lose". If you note the few things that cause one to lose and address those, at the end of the race, you'll find yourself in a position to win...or be beaten. There is nothing wrong with being beaten by a better competitor. We always get down on ourselves for losing based on something we had control over.

Regarding GPS data:

It's booty for track data analysis. Zero data is better than GPS data for track efforts. Seriously. GPS data can simply be misleading. Misleadingly high values or misleadingly low values. RPE (Rated Perceived Exertion) could be a better metric than bad data.

What happens is that the speed is calculated based on your GPS location changes between satellite pings. So, if the satellite thinks your location changed 50 meters in 5 seconds, then that's 10 m/s (22 mph). The problem is...satellites are not accurate. Not as accurate as a magnet on your wheel tripping a speed sensor.

For example, if you look at maps of files from track efforts that used GPS, you'll see the rider teleporting across the track. That's because the signal dropped somehow. So, the head unit does a "best guess" and assumes that you rode a straight line from the back straight to the home straight (across the infield) instead of riding through turns 3 and 4. I thinks you made that trip slowly.

Anecdote: I used to have a Garmin 500. When my SRM was off for service, I used the Garmin to track speed and cadence during a day's workout. I was sitting in the infield between efforts with the bike leaning on the bench. The start/stop beep kept sounding off. Basically, the head unit thought the bike was moving a few mph as it stood still leaning against the bench. I looked at the screen and indeed it showed a speed value.

GPS is totally fine for long rides. But, if you are analyzing track efforts, you want to see as close to exact numbers as possible. You don't want to do a flying 200 and see a max speed of 20mph...or 60mph.

A $20 wired Cateye would seriously provide more value. Just remember to note your top speeds and reset between efforts. You can rest assured that that number is very accurate.

gl98115

I have an ANT+ speed sensor (magnet on wheel, not accelerometer based) on my track bike which takes care of any GPS issues.

colnago62

Clythio

One guy did the same at Master Worlds 2017 at Carson Velo... but it didn't end well... ;-) It was not a case of "the right gear", but the "wrong suplement", lets say.

brawlo

When you go out and play those games, probably best not to go out and put a big target on your back

carleton

bitingduck

The satellites are extremely accurate, it's how your Garmin decides to calculate your velocity that isn't. A GPS unit has to track the frequencies from all the satellites it's locked on very accurately, and those frequencies are known and very stable. They can use the doppler shift (which they get for free from having to track the frequencies) to get velocity to cm/s or better. GPS's for cycling don't do that because the typical user wants to know the average speed over some relatively long distance that took some relatively long time.

brawlo

bitingduck

You don't need an atomic clock to do it - the velocity measurement is just a doppler shift measurement, and it's one that every GPS (including cheap ones) has to do in order to lock on the satellite signals. Consumer-priced GPS units could do it if people wanted it - there are ~20 year old publications of people doing ~cm/s accuracy with cheap consumer grade GPS units. A magnet and a frequency counter are a lot cheaper, but given the large numbers of expensive GPS units I see on bikes, it wouldn't be unreasonable to expect it from GPS units. I really just wanted to address the suggestion that GPS speed is intrinsically inaccurate (that Carleton implied) - even consumer grade GPS *can* give very accurate speed, they just aren't sold with that feature for cyclists.

carleton

Thanks for the correction and education, bitingduck and brawlo!

Is battery power one reason why the devices aren't configured to record more accurately? Internal memory?

Divebrian

Thanks to those that responded, turned out that 52/14 or 51/14 were the correct gears for me this weekend, it was a combined field of 18, all Master men and Open women.....did the 1st race on a 52/14, felt good, had plenty of power but wondered if I was over geared, dropped down to a 50/14 for the next race and had to stay in a higher rpm range than I prefer, did the 3rd and 4th races on a 51/14 and at times, it left me wishing I had the 52/14. I'm more of a diesel engine than a high revving 4 cylinder.....


And a special thanks to topflightpro for taking the time to personally show me around the velodrome on Sunday and proving that 50/14 was too small of a gear.

tobukog

Hey, were you the guy with the cart? If so, I think you did great in getting back into mass start racing. I'm always amazed that gearing is such a strange thing -- the difference between a 51 and a 52 14 is about 2%, or perhaps~ 2rpm. That's 2 extra rotations spread out over a whole minute. Yet it can be the difference between feeling comfortable and feeling bogged down or spun out.

Divebrian

Yep, that's me...we're you one of the 40 yr olds that always seemed to have energy for one lap more than me?

tobukog

I was the Asian guy with his mess spread out next to your cart who was coughing and dry heaving into the grass after every race. I didn't race Saturday -- I had promised my team mate that we'd go up to Tennessee instead. It was a LONG weekend.

bitingduck

I suspect it's lack of user demand.

topflightpro

I'm surprised to read GPS has such accurate technology. I was reading an article about autonomous cars and one of the technology challenges was the lack of accuracy of GPS systems - they were good to pinpoint vehicle locations within a few feet, which isn't accurate enough to prevent crashes.

brawlo

brawlo

bitingduck

You don't need accurate position to get accurate velocity. A police radar doesn't know where you are at all, but when used along line of sight can give accurate velocity with no position information via the doppler effect. All you need is the frequency shift from each satellite and the direction to each satellite, and you can tolerate relatively large position errors because the satellites are far away so the angular error is very small. In order to even get the signal from each satellite any GPS receiver has phase locked loops (PLLs) that it has to adjust in frequency to match the doppler shifted signal from each of the satellites. That frequency deviation gives you the velocity along the line to each satellite. The GPS receiver knows where each satellite is in the sky, so a little bit of vector arithmetic gives you the instantaneous velocity. Many consumer GPS units do already use a variation of this to measure velocity, where they use the phase shift from measurement to measurement to extract velocity (somewhat less accurate, but better than differencing successive positions), but it can also be done in a similar cost single-frequency GPS using the doppler shift that the PLL is tracking. It's more useful to self-driving car makers than for cyclists.

brawlo

krispenhartung

I wasn't sure where to put this, or if it would even be useful to anyone besides myself, but here it is. I can send anyone the source spreadsheet as well.
I created a custom spreadsheet gearing chart, which shows the range of gearing options incrementally from low to high vs. plotted in a matrix with cogs and chain rings on the x and y axes. This made it easier for me to develop a gear changing strategy, also allowing me to filter on a particular cog or chain ring size if I was attempting to stay with one cog, for instance. You can see the Velodrome Shop’s gearing chart here for reference and comparison. I used 54 as the largest chain ring and 13 as the smallest cog. I could easily go higher or lower by adding new rows.
K-

carleton

On a related note, if you are an iPhone user, I've created a free app where you input your inventory of chainrings and cogs (for road or track bikes) and your target gearing, it will output how to make that gear using what you have on hand.

I call it a "Reverse Gear Calculator":


I also provide a standard gear calculator:


All outputs are gear-inches, gear-meters, or ratio (chainring/cog).

FREE:
https://itunes.apple.com/us/app/trac...or/id925659197

I made this because I was tired of using gear charts