Even at 10% slope the Crr is still 99.5% of Crr on flat ground.
I would do separate testing of Crr and CdA improvements since neither is very likely to be constant across speed anyway.
And at 10% the contribution of rolling resistance is probably very low.
Even at 10% slope the Crr is still 99.5% of Crr on flat ground.
I computed the cosine factor here. So 0.999 etc., so it looks right. Thank you so much for confirming.
But although it tracks the same initially, it does cause a discrepancy eventually in my VE (See profiles in the graph below - formula = standard, formula2 = formula with cosine factor.)
Scratch my head… maybe there is an error in my code I didn’t see.
profile(runs)
discrepancy: cos(-0.0372) = 0.9993 (-0.0386)
discrepancy: cos(-0.0609) = 0.9981 (-0.0632)
discrepancy: cos(-0.0557) = 0.9984 (-0.0588)
discrepancy: cos(-0.0648) = 0.9979 (-0.0689)
discrepancy: cos(-0.1003) = 0.9950 (-0.1062)
discrepancy: cos(-0.0937) = 0.9956 (-0.1013)
discrepancy: cos(-0.0762) = 0.9971 (-0.0855)
discrepancy: cos(-0.0587) = 0.9983 (-0.0696)
discrepancy: cos(-0.0583) = 0.9983 (-0.0706)
discrepancy: cos(-0.0533) = 0.9986 (-0.0670)
discrepancy: cos(-0.0163) = 0.9999 (-0.0305)
discrepancy: cos(0.0073) = 1.0000 (-0.0066)
discrepancy: cos(0.0193) = 0.9998 (0.0059)
discrepancy: cos(0.0167) = 0.9999 (0.0038)
discrepancy: cos(0.0356) = 0.9994 (0.0235)
discrepancy: cos(0.0502) = 0.9987 (0.0392)
discrepancy: cos(0.0577) = 0.9983 (0.0478)
discrepancy: cos(0.0270) = 0.9996 (0.0176)
I found today that Charles Henry conducted tests back in 2015 on a tarmac velodrome in Switzerland. His graph confirms the Crr1 and Crr2 where Cr1 is a constant and Cr2 a tiny speed dependent factor for bicycle tires.
I too think that independence of Crr from speed and load is an approximation, however it may often be justified.
Tests on my “big” drum test rig usually show increasing Crr with increasing speed and / or load or normal Force respectively.
Tests on my “big” drum test rig usually show increasing Crr with increasing speed and / or load or normal Force respectively.
Thanks for sharing! What tire is that? Is there an appropriate conversion factor from the Crr on your drum to smooth tarmac? Maybe just wishful thinking.
Thanks for sharing! What tire is that? Is there an appropriate conversion factor from the Crr on your drum to smooth tarmac? Maybe just wishful thinking.
I have to check, but I think it was a Conti Supersonic 622-23 with latex tube at 8 bar on a Citec 8008 ultra.
An appropriate conversion factor? I don‘t know how smooth a smooth tarmac is in the US. I think here a good rolling smooth tarmac is not that much worse than my drum. I guess the conversion factor is definitely smaller than 1.5.
I added the windmeter for testing. It is mounted rigidly but a distance above the vehicle, just like with Solar car testing.
Here is the Speed vs. AirSpeed on an almost calm night. Looks quite good to me.
I wrote code to Merge the recorded windspeed data on my iPhone with the Garmin .tcx file.
I added the windmeter for testing. It is mounted rigidly but a distance above the vehicle, just like with Solar car testing.
Here is the Speed vs. AirSpeed on an almost calm night. Looks quite good to me.
I wrote code to Merge the recorded windspeed data on my iPhone with the Garmin .tcx file.
Is that on an “out and back” or loop ?
I added the windmeter for testing. It is mounted rigidly but a distance above the vehicle, just like with Solar car testing.
Here is the Speed vs. AirSpeed on an almost calm night. Looks quite good to me.
I wrote code to Merge the recorded windspeed data on my iPhone with the Garmin .tcx file.
Is that on an “out and back” or loop ?
Out and back on the same road with a cul-de-sac for a non-braking turnaround.
After midnight, no traffic.
I use the lap button to start and stop the recording at the same location.
There is braking required to go around a rotary at the end before returning to the start, but that section is excluded by software.
I added the windmeter for testing. It is mounted rigidly but a distance above the vehicle, just like with Solar car testing.
Here is the Speed vs. AirSpeed on an almost calm night. Looks quite good to me.
I wrote code to Merge the recorded windspeed data on my iPhone with the Garmin .tcx file.
Is that on an “out and back” or loop ?
Out and back on the same road with a cul-de-sac for a non-braking turnaround.
After midnight, no traffic.
I use the lap button to start and stop the recording at the same location.
There is braking required to go around a rotary at the end before returning to the start, but that section is excluded by software.
So it looks like the air speed needs a small factor applied to it (maybe an offset, but probably a multiplier)
The difference between airSpeed and speed is basically wind
In theory the wind on the out = -1 * wind on the back
So if the yellow line comes up a bit, you will have a tailwind on the out and a headwind on the back
If I am reading your chart properly
So it looks like the air speed needs a small factor applied to it (maybe an offset, but probably a multiplier)
The difference between airSpeed and speed is basically wind
In theory the wind on the out = -1 * wind on the back
So if the yellow line comes up a bit, you will have a tailwind on the out and a headwind on the back
So how to determine a value for the multiplier? Perhaps when the end points match up (same elevation)? Would that be reasonable?
Thanks!
So it looks like the air speed needs a small factor applied to it (maybe an offset, but probably a multiplier)
The difference between airSpeed and speed is basically wind
In theory the wind on the out = -1 * wind on the back
So if the yellow line comes up a bit, you will have a tailwind on the out and a headwind on the back
So how to determine a value for the multiplier? Perhaps when the end points match up (same elevation)? Would that be reasonable?
Thanks!
Different aero sensors/apps have a protocol to determine this. The level of “sophistication” from app to app varies.
I noticed you are posting in the Cda/Crr app so if using that I am pretty sure they have one.
The windmeter manufacturer uses a linear ax+b formula to convert from impeller rpm to m/s wind speed. So I read impeller rpm and just use the values of the constants a and b that they provide.
Doing k(ax+b) where k is a fudge/calibration factor doesn’t seem so easy to do. There is always a bit of wind outside. Seems it’d have to be done indoors (no wind), ride at a selection of fixed speeds down some long corridor. Then one might as forget k and just use the new empirically determined a’ and b’ values.
The windmeter manufacturer uses a linear ax+b formula to convert from impeller rpm to m/s wind speed. So I read impeller rpm and just use the values of the constants a and b that they provide.
Doing k(ax+b) where k is a fudge/calibration factor doesn’t seem so easy to do. There is always a bit of wind outside. Seems it’d have to be done indoors (no wind), ride at a selection of fixed speeds down some long corridor. Then one might as forget k and just use the new empirically determined a’ and b’ values.
Yes, the rpm to speed formula is published by the manufacturer. I have one and have tested it a few times. Good for what it costs, but not stellar. But Let’s say for a minute that number is right.
The issue is, the airSpeed measured at the windMeter is not the airSpeed if, for example, you placed the windmeter a few feet out in front. There is a correction that must be applied to the wind speed.
If there is 0 wind, and I put the meter 10feet out in front of me, and I go 36km/h I will probably see 36km/h. If I put the meter 1m in front of my torso, I will probably see 33km/h, however 36km/h is the number I want to be using in my calcs.
Windmeter calibration is not trivial. Very coarse calibration is easy, very precise calibration is not.
The issue is, the airSpeed measured at the windMeter is not the airSpeed if, for example, you placed the windmeter a few feet out in front. There is a correction that must be applied to the wind speed.
If there is 0 wind, and I put the meter 10feet out in front of me, and I go 36km/h I will probably see 36km/h. If I put the meter 1m in front of my torso, I will probably see 33km/h, however 36km/h is the number I want to be using in my calcs.
Windmeter calibration is not trivial. Very coarse calibration is easy, very precise calibration is not.
In my case, the windmeter is mounted on an extension stick. I’m not sure it’s completely in free air, but the windspeed there should be close to that of free air.
In the eco challenge machine, they mounted it even closer to the body. The book doesn’t mention a correction factor.
you might want to do a little experimenting
.
you might want to do a little experimenting
Yes, good to see if it’s right.
I’m trying to think of a building that has enough room or a sheltered-enough parking garage,
Unfortunately, no underground parking garage at work.
There is a low pressure “bubble” above a train. So, if high pressure means a lower reading and low pressure means a higher reading for the windmeter, it could be overestimating the “true” airspeed (green). I raised the windmeter up but maybe it’s better to raise it even higher.
Hi, Robert I am having some trouble with Golden Cheetah. Hoping you could help or point me in the right direction. I am using a Garmin Edge 130. I turn off the GPS on the unit, I am using a magnet speed sensor. I feel like my route is good no brakes consistent lines. I do not get any elevation data, am I using the wrong head unit? Should I leave GPS on?
Hi, Robert I am having some trouble with Golden Cheetah. Hoping you could help or point me in the right direction. I am using a Garmin Edge 130. I turn off the GPS on the unit, I am using a magnet speed sensor. I feel like my route is good no brakes consistent lines. I do not get any elevation data, am I using the wrong head unit? Should I leave GPS on?
A 130 should have a barometer for altitude. However, maybe it needs GPS to initialize, really not sure.
I would do this. Turn on GPS. Put a speed field on the display, lift the wheel and spin it. If speed registers you know speed is being picked up by the speed sensor and you should be good.
Also, verify there is no altitude in the “performance chart” not in the Aerolab chart