The calibration ride (GenIII units)

coachboyd · Post by **coachboyd** » Fri Feb 20, 2009 9:55 am

OK, this has come up a few times and I figured I would make a little post about the calibration ride.

When you do the calibration ride, two numbers are stored into your iBike, wind scaling and riding tilt. As long as you don't change bikes or the position of your iBike (going from handlebar to stem), you should only ever have to do ONE calibration ride. The values get stored into memory.

When you do coastdowns, you get an aero and a friction number. These are the two forces that slow you down when you are coasting. Combining these values with the stored wind scaling and riding tilt numbers will give you a cda and a crr. This means that if you are trying to get a new profile you ONLY have to do the coastdowns. You can use your previous stored values for wind scaling and riding tilt and you will have a new profile. Make sure you have a good tilt and wind offset calibration before doing any coastdowns.

Riding tilt is not as important as it used to be, the important number to make sure you have right is crr (rolling resistance). Real world numbers for crr are .004 for smooth roads, .005 for typical asphalt roads, and .006 for heavy chip seal roads. Most people have a riding tilt of -.3 to -1.0

What you can do for your crr number is to set that number in your profile based on your typical road conditions. You can guesstimate a riding tilt number and change the friction values to get crr correct. If your riding tilt is not correct, the Gen III will correct the tilt line within 5 minutes of starting your ride and your watts will be correct. But most people don't start off the first 5 minutes of a ride too concerned about their wattage and it won't be off by very much because the tilt would only be off a couple tenths of a degree.

When you do your calibration ride, try to do it on a calm day. Wind scaling is basically taking average wind speed vs. wheel speed on the way out compared to the way back and giving both a zero average. If you have a fairly gusty day you can have inconsistent wind data on the return trip and this will throw off your wind scaling number. Since you only have to do the calibration ride ONCE, it's best to make sure you have a good day to calibrate.

rruff · Post by **rruff** » Mon Feb 23, 2009 11:45 am

coachboyd wrote:What you can do for your crr number is to set that number in your profile based on your typical road conditions. You can guesstimate a riding tilt number and change the friction values to get crr correct.

The only issue with this is that Aero and Fric are extracted from a total "drag"... so if you change your Fric value manually, then Aero needs to change in the opposite direction... some unknown amount.

Extracting accurate Aero and Fric values via the CDs is actually a difficult task. That is why you need to do a *lot* of CDs and take an average. Fric is the smallest factor so has the most chance of error. I think it would be nice to have the option of selecting a Crr (and Fric) and having the software use this to calculate the best fit for Aero.

The Crr numbers you mentioned (.004-.006) sound about right if you have some of the best racing tires and latex tubes. From all the field tests I've seen from people using other PMs, .004 is about the lower limit on real roads. With "normal" tires and tubes .0055-.0075 is probably more realistic.

The 4mi ride works pretty well to get the wind scaling, but if your wind offset is off a little, or the wind changes a little during the ride, this will effect the accuracy. If someone is interested in checking this value, I suggest doing a series of out-back trips over a shorter course (this eliminates the possible issue of wind variations) and checking the "analyze wind' in iBike3. The net wind should be zero or very close to it.

lorduintah · Post by **lorduintah** » Mon Feb 23, 2009 12:00 pm

Most of my normal rides - that those not used for calibration - are not symmetrical. Consequently, I do expect on average to find that I do have an average wind speed to be non-zero. This has been the case (usually < 3 mph) and wind offset = 0.

I have found it to be critical on calibration rides to have only a minimal breeze along with the symmetry of the out/back. The next question is what would be a reasonable average speed to do this ride? It has been suggested that you do not need a gut-buster, but I would think that a granny ride is also not a good choice.

The last item I have found to be interesting and a great way to mess all of this up is to make an adjustment to the altitude during the ride. This gets interpreted as a change in slope and really mucks things up.

The altitude at the same position on earth will have an apparent change - if the air pressure has changed - and this has also been mentioned, along with a more subtle temperature effect. So I typically set the altitude at a known spot as well as double checking the wind offset before any ride and especially before a CD set or a cal ride. Alternatively, you might ignore the altitude - maybe not a good idea if you live in the Rockies or some place having some terrain to it.

Tom

jvandyk · Post by **jvandyk** » Mon Feb 23, 2009 3:59 pm

Quick question regarding the new Gen III units. I upgraded from the Gen II to III and was wondering do I have to re-do the coast down and 4mile calibration rides with the new Gen III or can I simply upload the original data/profile from the Gen II to the Gen III computer? This would obviously save time. As a note I have NOT changed anything on the bike I calibrated the Gen II unit on.

Thanks and please direct me to an apporiate link if this has already been addressed.

Jack

rruff · Post by **rruff** » Mon Feb 23, 2009 4:37 pm

jvandyk wrote:I upgraded from the Gen II to III and was wondering do I have to re-do the coast down and 4mile calibration rides with the new Gen III or can I simply upload the original data/profile from the Gen II to the Gen III computer?

You certainly need to redo the calibration. The unit itself must be calibrated.

rruff · Post by **rruff** » Mon Feb 23, 2009 4:41 pm

lorduintah wrote:I have found it to be critical on calibration rides to have only a minimal breeze along with the symmetry of the out/back. The next question is what would be a reasonable average speed to do this ride? It has been suggested that you do not need a gut-buster, but I would think that a granny ride is also not a good choice.

IMO you'd like to replicate your "normal" riding speeds. One thing you need to be sure of is that you don't go slower than a tailwind. If possible, if there is wind, it is also good to ride on the same part of the road in the out-back ride.

coachboyd · Post by **coachboyd** » Mon Feb 23, 2009 5:39 pm

jvandyk wrote:Quick question regarding the new Gen III units. I upgraded from the Gen II to III and was wondering do I have to re-do the coast down and 4mile calibration rides with the new Gen III or can I simply upload the original data/profile from the Gen II to the Gen III computer? This would obviously save time. As a note I have NOT changed anything on the bike I calibrated the Gen II unit on.

Thanks and please direct me to an apporiate link if this has already been addressed.

Jack

If you are confident in your cda and crr for your profile, then you can just transfer that profile to your new Gen III. Go out and do a cal ride (no coastdowns) and you will get new aero and friction values (based on the new riding tilt and wind scaling). You will now have your new profile.

coachboyd · Post by **coachboyd** » Mon Feb 23, 2009 5:42 pm

rruff wrote:
lorduintah wrote:I have found it to be critical on calibration rides to have only a minimal breeze along with the symmetry of the out/back. The next question is what would be a reasonable average speed to do this ride? It has been suggested that you do not need a gut-buster, but I would think that a granny ride is also not a good choice.
IMO you'd like to replicate your "normal" riding speeds. One thing you need to be sure of is that you don't go slower than a tailwind. If possible, if there is wind, it is also good to ride on the same part of the road in the out-back ride.

Yeah, I usually just go out and ride it. I don't worry about trying to keep any sort of speed but I'm not just putting around either. If you are doing a profile based on DFPM data it's good to incorporate one slight uphill and downhill. This will match the watts with the speed slow (for better crr) and with the speed fast (for better cda)

rruff · Post by **rruff** » Tue Feb 24, 2009 2:05 am

coachboyd wrote:If you are confident in your cda and crr for your profile, then you can just transfer that profile to your new Gen III. Go out and do a cal ride (no coastdowns) and you will get new aero and friction values (based on the new riding tilt and wind scaling). You will now have your new profile.

The Aero value will vary with each unit... so will the software compute a new Aero value based on the CdA you have stored? That's interesting if it works...

coachboyd · Post by **coachboyd** » Tue Feb 24, 2009 10:37 am

Yep, I main goal is to have a correct cda. So if cda is known, and you change the wind scaling number by doing a cal ride, it will change the aero number with respect to the new wind scaling number to reach the known cda number.

Aero * Wind Scaling = cda

For example, say you transferred a profile with Aero = .360, Wind scaling = .9, and cda = .400
If you go out and do a cal ride with your new Gen 3 and find out this unit has a wind scaling of .8
The new values for your profile will be Aero = .288, Wind scaling = .8, and cda still = .400

xptxc · Post by **xptxc** » Fri Mar 06, 2009 3:46 pm

So,

Does this mean that on a daily usage, I can forget setting tilt and just concern with wind offset? and Ibike III will automaticley adjust after 5 minutes?

Regards,

Velocomp · Post by **Velocomp** » Fri Mar 06, 2009 5:23 pm

Yes, that is exactly correct!

coachboyd · Post by **coachboyd** » Fri Mar 06, 2009 6:28 pm

I still check my tilt about once per week on a known spot on my garage. If it's off a bit and you're like me where the first five minutes of your ride are just to warm up the legs, then you are good to go. If you leave the house and immediately start going hard, then you might want to check the tilt once or twice a week

tyhaar · Post by **tyhaar** » Sun Mar 08, 2009 9:48 pm

I decided to use my Gen III unit today on my fix gear. I had been using the my old Gen II unit and getting what I thought were good/accurate numbers for fix gear riding.

Today the Gen III was way to high for my 3.25 hr. fix gear ride at 308 watts average. I'd be cooked if I really could hold that for 3 hrs. let alone on a fix gear. My threshold is only 296 watts for 30 minutes (NP=301) testing last weekend on my road bike profile.

I did the orginal coast downs and 4 milers with the Gen II so I was using that profile. I did check and input new tilt (was off) on my sweet spot in kitchen/weight/offset was good, and altitude in the Gen III for my fix gear profile loaded.

I take it since I did not do a 4 mile ride for the Gen III it was messed up in calculations?

I did do the coast downs/4 miler ride originally with my flip-flop hub in place with the Gen II.

To get this more accurate for the Gen III and would have to do 4 mile rides for all profiles?

Velocomp · Post by **Velocomp** » Sun Mar 08, 2009 10:31 pm

You really should do a new set of calibrations for the Gen III. Riding tilt and wind scaling are critical factors that might shift when moving to the Gen III.

coachboyd · Post by **coachboyd** » Sun Mar 08, 2009 10:52 pm

Do you have the ride file from today? I can check out a couple things.

If you have your set cda and crr for your fixed gear then you should JUST need to do the out and back ride. This will give you a new wind scaling number which is really the most important number in the whole iBike. It's what gives you a cda from an aero value, and it's what makes the wind speed correct.

tyhaar · Post by **tyhaar** » Sun Mar 08, 2009 11:03 pm

coachboyd wrote:Do you have the ride file from today? I can check out a couple things.

If you have your set cda and crr for your fixed gear then you should JUST need to do the out and back ride. This will give you a new wind scaling number which is really the most important number in the whole iBike. It's what gives you a cda from an aero value, and it's what makes the wind speed correct.

Yeah thats what I was figuring that I should have done a out and back with the Gen III with this profile. I did with my road bike but not my other two profiles. Here's the orginal file from the ride today... Thanks.

iBike_03_08_2009_1445_56_Miles-ORGINAL.csv: Fix Gear Workout 3/8/09; (2.49 MiB) Downloaded 299 times

coachboyd · Post by **coachboyd** » Sun Mar 08, 2009 11:20 pm

OK, basically what I did was change the wind scaling so that you had a 0mph average ground wind speed for the entire ride. This gave you a wind scaling of 1.114, and I kept the cda the same by changing the aero number. The watts and wind look pretty good. I'll be interested to see what you wind scaling actually is when you do the cal ride.

Your new profile (temporary fix), is also embedded in this ride file. Make sure you extract that profile.

tyhaar · Post by **tyhaar** » Sun Mar 08, 2009 11:35 pm

coachboyd wrote:OK, basically what I did was change the wind scaling so that you had a 0mph average ground wind speed for the entire ride. This gave you a wind scaling of 1.114, and I kept the cda the same by changing the aero number. The watts and wind look pretty good. I'll be interested to see what you wind scaling actually is when you do the cal ride.

Your new profile (temporary fix), is also embedded in this ride file. Make sure you extract that profile.

Thanks for the temp. fix. I'll do another fixie ride next weekend and definitely do a cal. ride and post. Hopefully it will be mild wind. I go to a wooded subdivision and cuts the wind down with the tall pine tree's.

stevevarnum · Post by **stevevarnum** » Mon Mar 09, 2009 7:20 pm

Well, it is obvious the CD's and Cal ride are very important...problem is getting a day to do one. I am in Houston (downtown area) for a few weeks (maybe as many as 6-8 weeks) and it has been windy every with lots of gusting wind. (As an aside, in my home area -- Georgetown, TX just north of Austin, we are advocating for more bike paths...here in Houston, they just need a road without patches that are 2" high or potholes that are even deeper. I have never seen roads as bad as these are...I use to hate chipseal...but I'd take chipseal over this mess any day. I see guys dressed in regular bike clothes riding sidewalks -- never saw that anywhere!)...Sorry I just had to vent!!

Anyway, since it is virtually impossible to get a "calm" day, which would be better (1) use the estimatng procedures for iBike3 or (2) just ride with the wind (and gusts)?

Thanks...

Velocomp · Post by **Velocomp** » Mon Mar 09, 2009 9:13 pm

I would use the EST CDA for now, but do a cal ride now, even if it's gusty winds. That will help determine your riding tilt and Wind Scaling factors.

You can do coast downs later on when the wind calms somewhat.

racerfern · Post by **racerfern** » Mon Mar 09, 2009 9:35 pm

I live in a windy area and finally solved my dilemma by doing my CDs before the sun was up and it kicked up the wind.

Even if you can just get a couple of CDs it would be better than estimating. The ideal road would be a bowl shaped road (CoachBoyd's suggestion). Something you can build up speed going down, then coast down up the other side. That makes them easy to do and they take very little time. The next ideal choice is a road with an incline. It doesn't have to be a killer hill, even a 1-2% grade is good.

Then do the calride. Ideally light winds but not so critical since you will be riding the same road in both directions. Try your best to avoid a road with cars since they will give you a negative wind effect in both directions.

Velocomp responded as I was typing and of course they're far more experienced but you get the picture between the two posts.

MultiRider · Post by **MultiRider** » Tue Mar 10, 2009 7:00 pm

Coach Boyd suggested to me that doing all coast downs in the same direction is optimal. I was doing mine back-and-forth in a bowl and got significant variation in the results. Probably due to wind.

Also, Coach Boyd also told me not do CDs up a steep hill as that will change how you weight the bike front-to-back. Flatter is better so you sit more naturally. Applies to the out-and-back as well. I was doing my out-and-back on a very hilly road because that was all that is near me. Coach Boyd looked at my o-and-b file and said the road was too hilly, need to drive somewhere to find a flatter road because I would be leaning forward on the ups and back on the downs and they would not necessarily average out due to speed/time on each (slower/longer on uphills and faster/quicker on downhills).

I think it would be a great idea to have a sticky thread with best practices for coast-downs and out-and-backs like the one called "Hows and whys of wind offset". Probably should be included in the user guide, too.

coachboyd · Post by **coachboyd** » Tue Mar 10, 2009 11:11 pm

I am actually thinking about writing the "very simple guide to getting the iBike up and running".

But for coastdowns, I have found that a coastdown that lasts about 20-30 seconds gives the best results. I usually do mine on a bowl shaped road. The uphill isn't very steep, about 3-4% at the max, but this helps me slow down so that I'm not coasting for a minute introducing all sorts of variables into the coastdown equation.

Russ · Post by **Russ** » Thu Mar 12, 2009 8:53 pm

Coachboyd,

You said to tyhaar:
"OK, basically what I did was change the wind scaling so that you had a 0mph average ground wind speed for the entire ride. This gave you a wind scaling of 1.114"

How did you calculate the 1.114 from the available data?

btw Just loaded the 3.08, can't wait to try it out !

Thanks,
Russ

coachboyd · Post by **coachboyd** » Fri Mar 13, 2009 1:42 am

I looked at Tyharr's specific ride file. I made a couple assumptions and looked at the data to come to the conclusion. If you have some questions I can take a look at your file.

It works best if you do a solo ride that starts and finishes at the same point.

Russ · Post by **Russ** » Fri Mar 13, 2009 7:19 pm

Coach Boyd,
Well, I live here on East Coast with vagaries of wind and all. I have been attempting to hone a dummied up profile from my prior gen2, and an early gen3 profile from a prior mount (same approximate location but new external battery mount).
I am one who's gen3 improved greatly with 3.06, though not quite home free. I see what appear to be jumps in my wind offset (like near 0 and then in 1-2 range and maybe back to near 0 by itself). If that is actually a problem, I am not yet convinced.
My latest few attempts to get an accurate wind cal figure have been multiple runs up and back on a straight stretch about 1/2 kilo long. The wind has never been truly steady during these runs and I get some traffic, usually below the neighborhood 25mph limit.
I noticed in your 'processed' csv for tyhaar, with the 1.114 windcal, that the win power tool showed 0's in both offset and ground wind fields.
I had achieved this for two of my 'multiple runs' mentioned above with two slightly different windcal values by iterating through an experimental profile in which I placed different wind cal values and bracketed in on the best value for each. Then I took the middle value from those two runs and did another 'multiple run' ride on the straight stretch to test the new profile. I was not able to get a great result from that either and did notice, at the end of those runs, a 1-2 range of wind offset values.
I was hoping you had a method that could directly calculate the wind cal value from the wind tool screen values (before and after speeds, offsets, etc).
Lets see if I can paste the three files in here ... never tried this before.....

Well that doesn't work, I know someone described how to do it but can't remember the process.
How does one paste the files? ( perhaps, if what I am doing is the only way, I will keep tinkering for awhile instead of taking your time - still waiting for optimum conditions to do a hopefully good cal ride with this setup).

Thanks,
Russ

coachboyd · Post by **coachboyd** » Fri Mar 13, 2009 7:31 pm

Hey Russ,

If you want you can send those three files to me directly at boyd (at) totalcyclist dot com. I will take a look at them and tell you what I see. You might want to send the files in separate emails ifthey are each over 2MB.

Russ · Post by **Russ** » Sat Mar 14, 2009 2:10 pm

Coach Boyd,

I sent two by email, forgot to expressly mention that I had tweeked the second ones profile for crr and cda, using a more reasonable crr as a starting point. I think I did it correctly, so please take a look at that too.

Notice that I named those _raw because they were the unprocessed copies saved first.
My third (earlier) ride that I mentioned above, I neglected to save _raw so I hope the two will do.

This is a rainy weekend, no rush for the help

.

Thanks again,
Russ

AeroPod, PowerPod and Newton

The calibration ride (GenIII units)

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