Maelochs

Sort of hesitant to get in here again, but .... apparently a cup-and-a-half of coffee isn't enough to wake up my brain so here we are ......

The aero bike is Likely but not certainly going to be more stiff .... which could but won't necessarily transmit more vibration and shock to the rider.

The endurance bike is likely but not necessarily going to be more compliant.

Neither frame is necessarily going to be more "comfortable" for this specific rider.

There is a long list of "all other things being equal" considerations here .... tire width and pressure being paramount.

Also it has to be assumed that on either bike the rider will find a set-up which is comfortable. "Long and low" is not inherently more uncomfortable and every person is different. "More upright" is obviously not necessarily more comfortable.

The only real answer here would be to buy both bikes, and test the rider's Cd at different points on his regular rides ..... does he start out aero then get tired and sit up more, does he sit up while climbing (lower speed, lower aero loss) and get enough rest that way, does each route have such a ratio of climbing to flats (or sitting up to getting low) that the aero benefit (as he rides it, not each bike's inherent drag) tilts in favor of the more aero position? Is his normal riding position such that whatever aero gain the frame offers is mostly negated by his own dragging body?

We all understand that in a wind tunnel, bikes are measured in either steady-state or occasionally (particularly when wheel-testing) with some yaw, but not (that I have ever heard) with a variety of riders on a variety of varying terrain at a variety of fatigue levels .... in other words, no manufacturer is testing its bikes to suit this guy's specific riding routes and characteristics.

I think the physics shows that In General a slight drag reduction offers more benefit over more of most rides than a slight weight reduction .... but whether this specific rider will notice that gain or even experience it, depends on this rider, his routes, his rides ......

Will he actually gain that two-watt advantage which a hypothetical slightly slicker bike gains over a slightly lighter bike .... yes, hypothetically. Will this hypothetical edge make him happier with his new aero bike? Will he enjoy riding more knowing he has the hypothetical possibility of going .01 percent faster on average with his new aero frame?

Well, now we have left the realm of science.

But isn't he really asking, Not the pure engineering question, but at root, "Which bike will make me happier?" When he says "best for me" does he really want the bike which is mathematically best over the exact rides he will take on said bike? No, because no one has that information anyway. What he wants is to Believe that his bike gives him more of an edge than some other bike he might have bought.

Being admittedly unscientific, I would wager that if someone could convince him that one of his options was "better," he would really enjoy riding it, and if someone else could convince him that the other bike was "better," he would enjoy riding that bike just as much.

If he really wanted the numerically,, mathematically, experimentally-verified "best bike" he would need to either build a portable wind tunnel and test at varying points along his ride for a year or so, or would need to ride for a year in a full sensor suit and then try to replicate each ride in a laboratory, to see who much power, how much heat, water intake, pedal revs, incline, wind speed, atmospheric conditions, traffic (in case it factored in) plus any effects of drafting on a group ride (which could negate any loss of the light bike if it even was less aero ...) ... and how much his output changed over the length of his ride, over the course of a week, over a month ..... And then if the next year he pulled a hamstring and took a month off, all his data would be invalid. And this would have to be done every couple of years to remain accurate ......

What he really wants, as i see it, is the assurance that "all other things being equal" (which is a state which never exists) that one type of frame would be "superior" by whatever measure, to another. He wants to be convinced. He wants to be "sold," by "experts" but in fact science only deals in either very narrow specifics (the observed results of a single experiment (however often repeated) and calculations based thereupon, or ... gross generalities, as in "Based on the results of our experiment we think this theory is supported" but of course it is only really supported in the precise conditions which obtained during the experiment. The rest is extrapolation and imagination ......

So, to the OP----get the aero bike. It will give you a slight advantage in every situation. You will be faster, you will be happier.

Funny thing about life is that you cannot approach it scientifically. You cannot have a series of "experiment" lives and a "control" life. There is no way to know if after buying on bike or the other, he would be more or less happy with the other. He cannot live the two lives side by side to compare.

Therefore .... buy the Aeroad, and ride it with the confidence born of knowing that you are doing less work for more result with every pedal stroke compared to the other bikes. Buy it and never look back.