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Discussion Starter · #1 ·
I took delivery of a Transonic 2.3 a few months ago, and have been enjoying it. I was curious as to how it compared to my other road bikes - a Trek 5200 and a Specialized SWorks Tricross (running road tires).

I timed myself on this segment (Tunnel Road) - Tunnel Time Test - Bethlehem Township, NJ - a straight 1.3 mile descent at a steady grade of 4.6% and an elevation drop of 377 feet. A fairly remote road with no traffic, smooth surface, and well sheltered from any wind.

I tried to be as consistent as consistent as possible, starting from a dead stop, hitting it pretty hard to get up to full speed in about 15 seconds and coasting the rest of the way, sitting upright with hands on the hoods, elbows locked. Calm wind and dry road on each test run. I was running Mavic Open Pros on the Trek and SWorks, with 23mm front / 25mm rear Gatorskins. Same setrup on each bike with respect to saddle bag & water bottles. The Transonic was stock 2.3 spec'd.

The finishing order was as you might expect:
Transonic - 2:35
Trek 5200 - 2:41
SWorks Tricross - 2:43

I was doing at least 30 mph at the finish, so at that speed each second is about 44 feet. I can't say how much of the difference can be attributed to the frame versus the wheels, but it's the total package that counts anyway.
 

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It's a cool idea. But, unfortunately, from what you've described there are at least two variables that you've not accounted for that can be significant players outside of frame and wheels. The first is your initial momentum developed during pedaling. The second is the tires and inflation pressure used, which I didn't see that you mentioned.

Bicycle Quarterly has been doing comparative rolldown tests on the same bike for about a decade. They've done that to understand the role that inflation pressure plays in rolling resistance. I suspect they've about perfected the technique. As I understand it their test starts on the side of the hill pointed down, no pedaling, all gravity to get things going.

Second issue - tires and pressure: if you want to compare the "total package" then you need to include tires and pressure as well.

Final point - single point tests don't really say anything about how reliable your stated times are. You need to repeat those tests several times (days), on different days, in random order of bike beng tested, to eliminate any biasing due to conditions.

At this point, for the above stated reasons, you can't really say one is faster than the other in any reliable way.
 

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Any cars that passed you would have messed up your results. I don't doubt the Fuji is more aero. But if you really want solid data, you need a power meter and need to do the Chung field test. That is a field test that even pros do. Would give you CdA and show you the difference. But it is fairly specific and strict. Any passing cars disrupts the airflow and invalidates the data.

Also, "doing at least 30 mph" leaves a lot of variance. 30.1 mph or could even be 35 mph. You really need to be more standard in testing and need to repeat the results many times over.
 

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Discussion Starter · #4 ·
As best as I can recall, no cars passed me on any of my runs. I only cited that I was "doing at least 30 mph" at the finish to approximate how the time difference translates to distance. In response to ibericb, I routinely inflate my tires to 110 psig before every ride, so you can eliminate that variable. And I did specify what tires I used. As for the reliability of my stated times, I don't use a cycling computer of any kind. I simply use a wrist watch with a second hand, start the run when the second hand hits 12, and then quickly look at it when I cross the finish. It's a very reliable watch ($8 from WalMart), so my numbers are dead-on balls accurate (it's an industry term).
 

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As best as I can recall, no cars passed me on any of my runs. I only cited that I was "doing at least 30 mph" at the finish to approximate how the time difference translates to distance. In response to ibericb, I routinely inflate my tires to 110 psig before every ride, so you can eliminate that variable. And I did specify what tires I used. As for the reliability of my stated times, I don't use a cycling computer of any kind. I simply use a wrist watch with a second hand, start the run when the second hand hits 12, and then quickly look at it when I cross the finish. It's a very reliable watch ($8 from WalMart), so my numbers are dead-on balls accurate (it's an industry term).
Your timing method is fine, so long as you have marked start and stop that are exactly the same in each case. A watch is a perfectly good timing device. A bike computer wouldn't change anything. But you initial momentum could radically alter the results.

Same tires, same width rims? If not, then the "tires" aren't the same.

As I noted, you still have to account for the initial momentum variance. The easier way to do this is start on a downhill, and don't pedal at all - just simple rollout.

A far as concluding the basis for being faster, it could be a result of being more aero on one bike vs. the others, which can be related to design, set-up and fit, e.g., you can go faster on a road racing bike than on an more upright mountain bike.

BTW - the Fuji should be well faster rom a Cd viewpoint, and if fit were optimized for aero that would only make it even better. The point is, you comparison doesn't establish how much in any relaible or meanningful way.
 

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Discussion Starter · #6 ·
ibericb - while I appreciate your attempts to invalidate my test, I stand by my methodology and results. Like any experiment, it has to be repeatable, but I have no desire to make multiple runs in the name of quality control. The results are good enough for me to conclude that one bike is faster than the other. Which I pretty much already knew, I mean did I really expect my cyclocross bike to be faster than the aero road bike? I was just trying to quantify the difference. But thanks for playing today's episode of "let's criticize the OP"
 

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ibericb - while I appreciate your attempts to invalidate my test, I stand by my methodology and results. Like any experiment, it has to be repeatable, but I have no desire to make multiple runs in the name of quality control. The results are good enough for me to conclude that one bike is faster than the other. Which I pretty much already knew, I mean did I really expect my cyclocross bike to be faster than the aero road bike? I was just trying to quantify the difference. But thanks for playing today's episode of "let's criticize the OP"
Let's be clear - you haven't established the degree to which any bike tested is faster than another. The results are consistent with what would be expected based on the designs of the bikes (no surprise or revealing insight). But your tests offer nothing to quantify the differences in any statistically valid or reliable way.

As you stated,

I was just trying to quantify the difference
You haven't done that.
 

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Discussion Starter · #8 ·
Let's be clear - you haven't established the degree to which any bike tested is faster than another..
Of course I did. Read my original post again. The Transonic was 6 seconds faster than the Trek and 8 seconds faster than the SWorks. Since my methodology was valid and consistent, there no need to make multiple runs. All of the variables that could affect the results have been taken into account. There's no need to make multiple runs to establish "statistical validity". I mean, seriously, if you wanted to compare the weights of 2 objects, using the same scale, how many times would you weight them? Once is good enough. Well, good enough for me at least.
 

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Discussion Starter · #11 ·
Great minds think alike. Bikerumor's results were right in line with mine - about 5%. I wish they had disclosed what the other bikes were.
 
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