Metro: I think I may have misunderstood (read too fast) your post. I thought you were asking if it made a difference if you started at 110 km/hr or 90 km/hr, and were thinking of starting at a variety of different speeds to do coastdown testing, and I remembered that co_driver had pointed out the viscous component of the equation that can change the results slightly. However if you look at the last post from the link above, he found his viscous drag component was about 1 Newton per Meter/second, and he was using a 90' Firefly. Sorry for the confusion, but you may be able to use a similar rule of thumb when doing your testing and obtain even more accurate results. Good luck!
Quote:
Originally Posted by co_driver
As one is bound to find (from all of the discussions in this forum), there are no simple solutions. But there are rules of thumb.
In a spreadsheet that I have developed (its a beast!), I do include the viscous component - and guestimated it to be ~1 for a 2-wheel drive vehicle (where F(viscous) = cV*v (v in [m/s]). It could be ignored, but will have an influence on the standard pair of coast-down tests (high speed and low speed). Hint: (greater than) 3-speed coast down tests will show this minor factor (did this in uni many years ago w/ driveshaft torque measurement and data logger).
This is notably small when compared to the other two inputs:
eg. '90 Firefly:
@ 25 m/s:
F(friction) = 81.3N (cF = 0.010, m = 830kg)
F(viscous) = 25.0N
F(aero) = 236.3N (cD = 0.36, A = 1.75m^2)
[Disclaimer: YMMV, above numbers may or may not simulate real life, ...]
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