MTM wrote:
jeffp wrote:
i have run back to back different tires over the same first 4 miles of a TT. results obtained in tunnel correlated pretty freaking well in the field. I flatted and had to restart. used different tire second run.(tested both in tunnel)
But I don't believe you test at 15 degrees in the tunnel? ;)
There seems to be two questions in this thread. One is whether we actually experience the yaw angles that marketing departments are happy to tell us about, the other is whether wind tunnel results apply to the "real world". The latter is genuinely believed (and proven) to be true (with small caveats like the ones rruff is mentioning). The first is a little more open for debate, but the general concensus is that yaw angles outside ~10 degrees are usually only seen if you are either riding decently slow (<35 kph) and/or on specific courses/days (high wind, open fields or coast lines, riding perpendicular to the wind direction).
Note for Damon: The last point is why we would still like drag vs. yaw graphs and not just a "dumbed down" weighted average drag so you have no idea about in which conditions specific products excel and vice versa ;)
If we assume an equal probability that wind can come from any direction, then I obtain the following graph which represents the % of wind angles for which yaw is greater than 10 degrees.
Code is here: Feel free to implement and check the math.
clear all;
V = [5 7.5 10 12.5 15 17.5 20 22.5 25 27.5 30 32.5 35 37.5 40 42.5 45 47.5 50 52.5 55 57.5 60];
w = [0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25 27.5 30 32.5 35 37.5 40];
for j = 1:length(w)
for k = 1:length(V)
count = 0;
for i = 1:360
wan(i) = i*pi/180;
VR(i,j,k) = V(k)*sqrt(1+2*(w(j)/V(k))*cos(wan(i))+(w(j)/V(k))*(w(j)/V(k)));
A(i,j,k) = (w(j)/V(k))*sin(wan(i))/(1+(w(j)/V(k))*cos(wan(i)));
psi(i) = 180*atan(A(i,j,k))/pi;
if psi(i)>10 || psi(i)<-10
count = count +1;
end
end
P(j,k) = 100*count/360;
end
end
surf(V,w,P);
hold on;
xlabel('Ground Speed [kph]');
ylabel('Wind [kph]');
zlabel('% Above 10 Deg Yaw');
Chris Morton, PhD
Associate Professor, Mechanical Engineering
co-Founder and inventor of AeroLab Tech
For updates see Instagram