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Changing weight post-ride?
Posted: Sun Apr 13, 2008 9:57 pm
by sl@enposte.net
I had a great day to do some aero testing yesterday. Only problem was the scale I took didn't work. So I had to guestimate weight and ended up under by a little over a two kg (about 3lbs, 183 used, should have been 188lbs.)
I did two sets of coast downs and 4 mile rides for two different wheelsets. The numbers look reasonable. But presumably are off slightly due to weight being under by about 2-3%.
Is it possible to fix in ibike2 application?
For the record:
P2C - Aeolus 6.5 - Veloflex Record - 120PSI Cda 0.200 Crr 0.004
P2C - Aeolus 5.0 - Bontrager XXX LIte - 120PSI Cda 0.195 Crr 0.006
The Cda numbers look a little iffy. The 6.5's are a deeper (65mm) profile than the 5.0s(50mm). The Crr numbers look a bit better. The Veloflex Record Tubular is supposed to be very good for Crr.
Thanks.
Re: Changing weight post-ride?
Posted: Tue Apr 15, 2008 9:45 am
by Hyde
I don't know if it's good to do your coast downs with an inaccurate weight but I change my weight daily on my main bike depending on what I'm carrying in my pack. My assumption, & I could be wrong, is that you would want to do your coast downs with everything correct.
Sounds like you have a nice ride, BTW.
Re: Changing weight post-ride?
Posted: Thu Apr 17, 2008 2:53 pm
by travispape
sl@enposte.net wrote:I had a great day to do some aero testing yesterday. Only problem was the scale I took didn't work. So I had to guestimate weight and ended up under by a little over a two kg (about 3lbs, 183 used, should have been 188lbs.)
I did two sets of coast downs and 4 mile rides for two different wheelsets. The numbers look reasonable. But presumably are off slightly due to weight being under by about 2-3%.
Is it possible to fix in ibike2 application?
For the record:
P2C - Aeolus 6.5 - Veloflex Record - 120PSI Cda 0.200 Crr 0.004
P2C - Aeolus 5.0 - Bontrager XXX LIte - 120PSI Cda 0.195 Crr 0.006
The Cda numbers look a little iffy. The 6.5's are a deeper (65mm) profile than the 5.0s(50mm). The Crr numbers look a bit better. The Veloflex Record Tubular is supposed to be very good for Crr.
Thanks.
You can change your coast-down weight after-the-fact. Go to "profiles->edit profiles...->advanced profiles settings..."
Re: Changing weight post-ride?
Posted: Thu Apr 17, 2008 11:44 pm
by sl@enposte.net
Yes, but that doesn't redo the calculations for the coast-down etc...
Is there anyway to fix that? Or does it matter all that much?
Re: Changing weight post-ride?
Posted: Fri Apr 18, 2008 1:46 am
by travispape
sl@enposte.net wrote:Yes, but that doesn't redo the calculations for the coast-down etc...
Is there anyway to fix that? Or does it matter all that much?
The error in the weight setting in the iBike did not invalidate your coastdown results--the fric and aero numbers would have been the same if you had the correct weight setting in the iBike's setup page at the time. However, the weight does make a difference in the reported Crr that is calculated from the coastdown results. Yes, for the small weight error you are talking about, it is only a small change in the Crr that you will get. Also, you do not have to worry about the weight error for the 4 mile ride.
Note, however, that the weight setting in the iBike does make a difference for the power measurements during a normal ride. Again, for the small 3 lb error it is only a small difference, but you can correct it using the "iBike Settings..." button in the "Detailed" tab.
Travis