Profile advice

[Todj]

I have two profiles that I have set up and calibrated etc on my iPro.

Profile 1 is for my road bike (hoods position), and Profile 2 is my TT bike (aero bars, skinsuit, pointy hat etc etc).

Looking at the numerics of these profiles I'm pleased to see that the TT profile has a Cda of 0.270 compared with 0.369 on the road bike.

However, the TT bike shows Friction as 13.656, whereas the road bike is 7.489.

Screen images are attached.

Does this 13.656 look correct? The bike itself is on 23mm Vittoria Corsa CX tubs at 125psi, 50mm deep Zipp front rim, and Corima rear disk. Both wheels run very smoothly and esaily, and there's no brake binding. Hence I'd expect Friction to be low??

Thanks in advance.

[travispape]

The fric number factors in the riding tilt also, so they are fine. The number to look at is Crr. You have the same rolling resistance of 0.055 for both bikes, which is probably good. Don't try to compare fric numbers.

Travis

[Todj]

Thanks Travis. Much appreciated.

Is a Crr of 0.0055 a bit high for some fairly decent tarmac (or 'pavement' in US)?

[travispape]

We've found that 0.0055 is good for a typical blend or roads. Chip seal would be worse. And if you've got a silky tarmac to ride on, it would be lower.

Remember you always have the option of measuring the Crr by doing a set of coast-downs together with a calibration ride. After you do them, connect the iBike to the computer and choose "Profile -> Download Coast Downs & Calibration Ride..." If you have an important TT and you want to get it just right, do you coast-downs somewhere on the course or roads with the same surface.

[Todj]

Remember you always have the option of measuring the Crr by doing a set of coast-downs together with a calibration ride. After you do them, connect the iBike to the computer and choose "Profile -> Download Coast Downs & Calibration Ride..." If you have an important TT and you want to get it just right, do you coast-downs somewhere on the course or roads with the same surface.

Great stuff. Thanks.