raria

So I've done this controlled experiment for the last 2 weeks and found I can ride my CAAD at 20.5 mph and the Fuji at 17.1 mph averaged over 7 rides each.

Variables Controlled For:
a) Same Flat 15 mile Route (In/Out MUP with No Traffic Lights or Stops)
b) Time of Day (I alternated the days for each bike)
c) Shoes (SPD and same shoe)
d) Same Tires (both using 25mm)

Here are the key differences beteen the bikes. Which ones do you think are the main reason(s) for the speed difference?

a) BB and Cranks- (CAAD is PF 2 piece. Fuji is 3 piece ST).
b) Geometry (CAAD Stack/Reach 563/393, Fuji 588/383)
c) Frame material and/or stiffness (CAAD is Alu, Fuji Steel)
d) Weight (CAAD is 18 pounds, Fuji 26 pounds)
e) Wheelset (CAAD is sealed bearing 1600g, Fuji is touring wheels with loose balls and 2200g)
f) Something else?

ColonelSanders

Whilst I can see the width of your tyres are the same, are the tyre compounds the same?


Also I imagine you are more aero on your CAAD, than on your Fuji.

raria

Yes, same compound.

Yes, due to a lower stack and longer reach I'm more aero.

colnago62

HTupolev

Insignificant, unless one of them is broken or if the dimensions of the cranks (particularly q-factor or crank length) are creating a fit issue.

Gearing could make a difference, but considering that the route is flat, probably not.

Stack and reach mostly matter insofar as they affect your fit. If you've got both bikes fit exactly the same, then it's not particularly important.

But if you ride the CAAD more aero than the Fuji, this could make a HUGE difference.

Insignificant from a pure power transfer standpoint.

It might matter if your body and legs prefer how one frame or the other pedals and rides, but this is hard to predict.

That's a pretty big difference, but if the course is actually flat and you're riding it steady, it shouldn't make much of a dent.

Unless one of the wheelsets has bearings that are absolutely trashed, the bearing difference will be insignificant. And again, if the course is truly flat and you're riding it steady, the weight difference shouldn't be significant (although it will definitely contribute to the bikes feeling different to ride).

If a road bike fits and provides the postures you want for the riding you're doing, has gearing appropriate for you and the riding you're doing, has fast tires, and is generally functioning well, that's pretty much the low-hanging fruit. Diminishing returns start setting in hard as you go beyond that.

It's normal for even sporty touring builds to end up a bit slower than racing builds for a multitude of reasons, but 3mph is an astronomical difference. Since you claim your tire setup is the same, and since the gearing is probably not creating issues for you on a flat ride, my biggest suspicion would be fit discrepancies. If you're less aero on the Fuji, and especially if you don't have a posture on it that's comfortable for powerful pedaling, that could explain a sizable chunk of the performance gap.

Yeah, this too. Some folks ride harder on bikes they feel zippier on. Although, if the conditions aren't highly variable, and you're riding your guts out every time, 3mph should still be quite a ways below the noise floor after 7 runs.

smashndash

Hm. I'd say take the wheels off the old Fuji and turn the axle by hand. If you feel any roughness or tightness beyond a quality combination lock, the cones may be too tight or the bearings may be shot (very common).

My second guess is that you're putting in more effort. When you're leaned over, you're not just more aero (which would help a lot with speed, don't get me wrong) - more of your weight is over the pedals. This forces you to push harder on the pedals to keep the weight off your arms. It becomes more comfortable to go fast than go slow. The combination of these two effects could easily account for a 3mph difference on the flats.

EDIT: guy above me said the same thing. Ugh

raria

I did this ride at 8am every day and my mind set was go flat out. By the end of it i was dead!

ColonelSanders

An interesting experiment that you could try out if your wheels are interchangeable, is to swap wheels between the bikes and see if that makes any difference.

gregf83 

Position and effort.

raria

They are both 130mm rear spacing, but the CAAD is 11 speed and the Fuji 8 speed so I'd need to add a spae to the 11 speed wheelset. Too much work!

I figured it was that and/or frame/crankset stiffness (i.e. power transfer)

rms13

Yes. Fast bike makes you ride faster

HTupolev

Frame/crank power transfer losses are so small that there have basically never been published measurements of them. Whatever they are, they're not on the right order of magnitude to be a significant portion of the 3mph difference you're dealing with.

chip1

Aside from the actual frame geometry, any stem spacer differences?

rubiksoval

No power = a massive uncontrolled variable.

WhyFi

Yup.

Sy Reene

A flat route could mean you're spinning in the same gear over much of the course. On the CAAD, which gear is this? Putting the Fuji in the same gear and attempting the same cadence as on the CAAD, what happens?

RChung

Usually, yes, but if you can find a time with zero wind and you have a way to record second-by-second speed (will a Strava phone app do that? I use a head unit that lets me do this so I don't know if a phone app does) you can do zero power coast downs on a flat road (or a hill, but a flat road works, too). If you start at different initial speeds and the tires/tubes are the same, you can isolate both the rolling and aero resistance. Two runs (one at low speed, one at high) for each bike. We're not talking a long ride, nor a long steep hill; I've done this over a two-block long road that had a 5m drop from beginning to end. Each run took 30 seconds or so.

69chevy

RChung

When you coast you know your power is zero.

PepeM

What color are the bikes? That's a huge unaccounted for variable right there.

datlas 

Maybe 3 MPH difference in tailwind?

Honestly, assuming you are pushing the same power/watts and your position is the same (frontal area/aerodynamics), the difference should be modest.

raria

Surprisingly no one is saying its the frameset, material, crankset things we spend most of the time discussing on this forum.

So I think I can see several major explanations coming out:

1) Its not the bike its my power output.
Unfortunately I don't have a power meter so this is an uncontrolled variable. But I did 7 rides each of the bikes over two weeks (alternating bikes) and I went flat out (only 15 miles) always after a high carb breakfast. I can genuinely say that I tried to put out maximum power each time

2) Aero and pedaling position.
The CAAD is definitely more Aero and I'm definitely longer and lower on it. Not sure how the geo differences cause different pedaling efficiencies.

hsuehhwa

What's the power?

Are the CAAD 12 faster than the Fuji with the same power output?

We're all just speculating without a power meter.

seau grateau

Rider's body on the bike is the greatest source of aerodynamic drag, so changing the riding position makes a big difference.

DrIsotope

I bet you throw some clip-on aerobars on the Fuji and it will suddenly be faster than the CAAD. Aerodynamic drag is 90% of what's limiting you. When I'm moving at 20mph, aerobars require about 20 less watts than being in the drops. The difference in required output between hoods and drops is comparatively insignificant. Elbows in, head down = faster.