Dilemma...upgrade current bike, or get new one??? (Page 2)

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2012-06-12 12:19 PM
in reply to: #4257675

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Subject: RE: Dilemma...upgrade current bike, or get new one???
chris948 - 2012-06-12 1:31 PM

You're the one who's calling everything incorrect, by all means show me any test that discusses anything aero at 15mph.


I've pointed you to a few and given you equations for looking at it yourself.

I myself don't know how to calculate CdA for a given bike, mostly because it's dependent on velocity unless you want to get into more math than I can actually do.


CdA is not velocity dependant; I even gave you a couple of CdA values to investigate.

I recognize that mass is in your equation, obviously.  My point is you can't say "weight is irrelevent" it isn't.  I'm not talking about microacceleration.  I'm talking about how in the real world people are constantly fluctuating speed and just like a flywheel when you force a human's engine to work harder, it has a negative affect on the rider.


Weight is almost entirely irrelevent in a tri or TT situation and there are lots of data to prove this; I've given you places to start in your search and also an equation to play with to see what impact weight has on power.

It's nice that people can throw around simple math that says you gain maybe .02 seconds by losing a lb in an hour and yet "aero x is worth 20 seconds in a 40km TT" completely disregarding that everything is relative in aerodynamics.


Such as? What am I missing that is relative in aerodynamics?

Enough with the road bikes are good for hilly courses, the OP has a TT up a hill listed in his races.


And for an uphill, point to point TT, then it might be worthwhile to consider a road bike over a tribike; if the grade was somewhere >5% then for a typical AGer, a very light bike would make more sense than a very aero bike.

I've attached a spreadsheet; it is for an actual TT course and you can play with the variables to your heart's content to see how things change as you manipulate weight and/or CdA.

ETA - couldn't attach; here's the link:

http://www.whitemountainwheels.com/Speed_Power_v2.xls

Shane

Edited by gsmacleod 2012-06-12 12:22 PM

2012-06-12 1:25 PM
in reply to: #4257783

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Subject: RE: Dilemma...upgrade current bike, or get new one???

gsmacleod - 2012-06-12 12:19 PM CdA is not velocity dependant; I even gave you a couple of CdA values to investigate.

Thanks, every equation i've seen made me think it was, and then I looked at wiki for Cd and still thought it was.

At any rate, obviously it's dumb to be constantly arguing on the internet. sorry. 

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