Looking for the best iphone app toÂ…

[FrankDay]

Looking for the best iphone app to…

get speed data to allow one to assess aerodynamic drag using the chung coast down technique. Anyone done this?

 

[pedaling squares]

I doubt it, Frank. Even computer geeks have their limits.

 

[FrankDay]

I doubt it, Frank. Even computer geeks have their limits.

Huh? All one needs is accurate speed data in small (1 second) intervals while coasting down a hill to gather this data. I am sure there are several apps that do this but it is hard to tell by reading how they are promoted as I am sure this is way beyond the average users need.

 

[Martin318is]

I know of a few iPhone apps for cycling but they are more around gps based riding etc.

Most of the solutions I can think of quickly all involve one device or another (such as a Garmin or Polar unit) that downloads to a PC... Otherwise, I'd need to develope and build you something.

are you asking for a device that can take those numbers and then at the end of the run give you the calculated value in real time? Where would you mount it? Would you be taking speed from a wireless sensor?

 

[Boeing]

coachlergie is inventing it and will test run with durainrider

 

[FrankDay]

are you asking for a device that can take those numbers and then at the end of the run give you the calculated value in real time? Where would you mount it? Would you be taking speed from a wireless sensor?

No, all I am looking for is an app that can give me the raw data (speed vs time, perhaps altitude so you can double check the signal) so at some later time that I can get this data into my computer and then put into a spreadsheet and do the calculations.

 

[Moose McKnuckles]

No, all I am looking for is an app that can give me the raw data (speed vs time, perhaps altitude so you can double check the signal) so at some later time that I can get this data into my computer and then put into a spreadsheet and do the calculations.

What precise variables do you need? Speed, altitude, what else?

There is no app that can give you wind velocity. At least not one that I know.

 

[FrankDay]

What precise variables do you need? Speed, altitude, what else?

There is no app that can give you wind velocity. At least not one that I know.

The formula requires that one do coasting (zero power) repeats on a hill with variable slope with different starting velocities when there is light or zero wind. (the different starting velocities are necessary to separate rolling resistance and wind resistance). Looking at and comparing the speed variation on the two (or more) trials allows one to determine both wind and rolling resistance with great accuracy.

Here is a link to a discussion of how to do this and what one needs from the horses mouth.

 

[BroDeal]

get speed data to allow one to assess aerodynamic drag using the chung coast down technique. Anyone done this?

I thought you did not trust any of that newfangled technology. Using an iPhone to asses drag is dangerously close to using--dare I say it?--a power meter.

I suggest you ask a few people for their anecdotes about drag. No matter how outlandish their claims, believe them wholly and completely. Then spend years on the interwebs asserting the numbers as gospel truth.

 

[DirtyWorks]

No, all I am looking for is an app that can give me the raw data (speed vs time, perhaps altitude so you can double check the signal) so at some later time that I can get this data into my computer and then put into a spreadsheet and do the calculations.

Runkeeper looks like the right idea. http://kelsocartography.com/blog/?p=584 Geolocation with an iPhone isn't very accurate, so I don't know if there's enough resolution to get you good data. But, it looks like Runkeeper gives you the opportunity to at least set the sample rate. Note well, a high sample rate will suck the battery empty. Fast!

The measuring will not be easy. But, who know what may come out of it. Go for it!

 

[Martin318is]

No, all I am looking for is an app that can give me the raw data (speed vs time, perhaps altitude so you can double check the signal) so at some later time that I can get this data into my computer and then put into a spreadsheet and do the calculations.

If thats all you need then a powertap will give you exact values in 1 sec increments and can be downloaded to PC as a file that can be opened straight into a spreadsheet.

Also, as I mentioned above, there are several non-power bike computers that will allow the values to be directly downloaded, including high end Polar HRMs and Garmin Edge 500, ettc.

 

[42x16ss]

Statistics (and, I suspect, power data analysis) is for losers and people trying to justify their jobs.

This sounds like a bit of an about face Frank

I'll agree with Martin318 here and say that a Garmin 500 will do everything you need (including gradient and altitude) with the added bonus of being able to mount it where you can view and access the basic data immediately.

 

[Notso Swift]

this is actually the exact method of the iBike isn't it

 

[DirtyWorks]

If thats all you need then a powertap will give you exact values in 1 sec increments and can be downloaded to PC as a file that can be opened straight into a spreadsheet.

Also, as I mentioned above, there are several non-power bike computers that will allow the values to be directly downloaded, including high end Polar HRMs and Garmin Edge 500, ettc.

What is the GPS precision in all of those devices? It becomes an issue when you are trying to compare results where the differences are less than or equal to the precision of the device. It's why the iPhone isn't a great device for the job. It might generate something useful, but the validity of the data is suspect.

 

[Fatclimber]

What is the GPS precision in all of those devices? It becomes an issue when you are trying to compare results where the differences are less than or equal to the precision of the device. It's why the iPhone isn't a great device for the job. It might generate something useful, but the validity of the data is suspect.

Speaking of the Garmin 500, you can have speed info gathered by gps or other ant+ sensor. I'm with you that the magnet on the wheel sensor would be more accurate than gps (if that's what you're getting at).

 

[FrankDay]

This sounds like a bit of an about face Frank

I'll agree with Martin318 here and say that a Garmin 500 will do everything you need (including gradient and altitude) with the added bonus of being able to mount it where you can view and access the basic data immediately.

I know I can spend hundreds and get the data. The question was about Iphone apps (that cost anywhere from free to $24.99) that might do the same thing. So far, the GPS on the Iphone seems to be particularly reliable such that it might be "good enough" if all one wants to know is "is this better than that" and not what the actual drag number per se is. I mean, do you really care what the actual drag number is? Isn't all we are really interested in finding out is whether a is better than or worse than b?

And, holders exist for mount the Iphone on a bike where you "can view and access the basic data immediately.

 

[ramjambunath]

Considering you're calculating drag resistance, won't you also need the Reynold's number of the fluid. There'll certainly be an error percentage if an assumed number is taken, especially at altitude.

 

[ramjambunath]

Considering you're calculating drag resistance, won't you also need the Reynold's number of the fluid. There'll certainly be an error percentage if an assumed number is taken, especially at altitude, not to mention atmospheric conditions at the time of the test.

 

[FrankDay]

Considering you're calculating drag resistance, won't you also need the Reynold's number of the fluid. There'll certainly be an error percentage if an assumed number is taken, especially at altitude, not to mention atmospheric conditions at the time of the test.

One would need that if one were calculating actual drag numbers but one doesn't if one is looking at relative drag numbers for trials done under the same conditions.

 

[Martin318is]

What is the GPS precision in all of those devices? It becomes an issue when you are trying to compare results where the differences are less than or equal to the precision of the device. It's why the iPhone isn't a great device for the job. It might generate something useful, but the validity of the data is suspect.

Don't use the GPS feature for this type of testing - use the speed sensor.
Powertap - its in the hub
Garmin and Polar - either a fork or chainstay senor.

 

[Martin318is]

I know I can spend hundreds and get the data. The question was about Iphone apps (that cost anywhere from free to $24.99) that might do the same thing. So far, the GPS on the Iphone seems to be particularly reliable such that it might be "good enough" if all one wants to know is "is this better than that" and not what the actual drag number per se is. I mean, do you really care what the actual drag number is? Isn't all we are really interested in finding out is whether a is better than or worse than b?

And, holders exist for mount the Iphone on a bike where you "can view and access the basic data immediately.

Not even in your wildest dreams is the iPhone GPS good enough for this. You might get enough data to confirm that rolling normally is faster than riding with your brakes on but that is about it. If you look at the actual GPS data that is recorded (rather than the line shown on the screen) you will find that it will show you wobbling all over the road like a drunk.

There is no way that I would bother doing this type of test if that is all I had. May as well just use a stopwatch and time yourself through two gates during the roll to see which position/equipment is faster.

If you are married to the iPhone idea, get an ant+ speed sensor and a dongle for your phone to pick up the signal.

 

[FrankDay]

Not even in your wildest dreams is the iPhone GPS good enough for this. You might get enough data to confirm that rolling normally is faster than riding with your brakes on but that is about it. If you look at the actual GPS data that is recorded (rather than the line shown on the screen) you will find that it will show you wobbling all over the road like a drunk.

There is no way that I would bother doing this type of test if that is all I had. May as well just use a stopwatch and time yourself through two gates during the roll to see which position/equipment is faster.

If you are married to the iPhone idea, get an ant+ speed sensor and a dongle for your phone to pick up the signal.

I am not married to any idea. No one is more willing to try new things than I am. I simply was wondering if there was an Iphone app that might do the job.

 

[Martin318is]

sorry, last comment sounded harsher than i meant. didnt proof read.

the iPhone idea itself sounds pretty good because you could create a simple app to do the calcs for you, store them and potentially give you comparisons and recommendations (if you chose to add THAT much intelligence into the app).

The bit where it would need improvement is in the data capture. I am not opposed to the iPhone for that either, however I really do think that to do this in a reasonable fashion you should use measured speed rather than GPS speed. For that, there are a number of options out there as add-ons for the phone. Like this:

http://www.wahoofitness.com/Products/Wahoo-Fitness-Wahoo-Bike-Pack-for-iPhone.asp

 

[DirtyWorks]

sorry, last comment sounded harsher than i meant. didnt proof read.

the iPhone idea itself sounds pretty good because you could create a simple app to do the calcs for you, store them and potentially give you comparisons and recommendations (if you chose to add THAT much intelligence into the app).

The bit where it would need improvement is in the data capture. I am not opposed to the iPhone for that either, however I really do think that to do this in a reasonable fashion you should use measured speed rather than GPS speed. For that, there are a number of options out there as add-ons for the phone. Like this:

http://www.wahoofitness.com/Products/Wahoo-Fitness-Wahoo-Bike-Pack-for-iPhone.asp

You should definitely use a wheel sensor. For meaningful results you need to know if the the speed sensor returns results in sub-meter precision. If the device is using a single magnet, I don't know that it will be enough. If the wheel magnet is a ring, the sensor will have plenty of data capture opportunities. And then confirm the sample rate with the software developer.

I can't picture a slope test where the resolution on the GPS sensor in an iPhone will give you meaningful results. GPS is worth using along with the speed sensor to see what the results are like.