An example of the difference between a TT bike and a Road bike (Time Trial comparison)

So there are always those on the forums who are asking "What kind of time difference between a tt and road bike" "Is a TT bike worth it" etc... ya know.

Well we have plenty of literature... John Cobb says this, Slowman said that, Cancellara does this... ya know. But what about an Age Grouper? Is all that junk worth it? Well hold on to your Cham pads, cause here comes possibly the most unscientific, n=1 "study" ever.

Every Wednesday, the local Cycling club has an 8mile Time Trial. So what do I do, I ride one week on my Tri bike, and one on my road bike... so here goes, the results of both, but first, some information on the bikes / me.

Road Bike Ride info:
2009 Scott CR1 Team
3t Ergonova bars
175mm crank
7 1/2 cm of drop from tip of saddle to top of bars.
Shimano Carbon shoes (no booties)
Rudy Project Sterling helmet
1 Bottle on Downtube
Zipp 404 front (Pro3Race 23mm tire w/100psi)
DTswiss RR465 wheel w/PT (4000S 23mm tire w/100psi)

Tri Bike ride info:
2009 Planet X Stealth
Vision Base Bar / levers
Cobb Wrist relief extensions
170mm crank
16cm Drop from Saddle tip to Forearm Pads.
LAS Chronosomething helmet (the bonktown aero lid)
Shimano Carbon shoes with Aero Booties on
Specialized Virtue Fairing Bottle
Zipp 404 front (Pro3Race 23mm tire w/100psi)
DTswiss RR465 wheel w/PT (4000S 23mm tire w/100psi)

Me:
5'10"
148-152 lbs depending on the day.
LG triathlon suit (onesie)
shaved legs

Course: East TN style of hilly (rollers for you mountain men, and mountains for you Floridians)

Ok, on to the results.

8 Mile TT

CR1-
Total Elapsed Time - 22:35
Distance - 7.98 mi
Avg. Cadence: 89
Avg. Watts: 233
Max. Watts: 769
NP: 246
Avg. Speed: 21.25mph

Stealth-
Total Elapsed Time - 20:26
Distance - 7.98 mi (same course)
Avg. Cadence: 84
Avg. Watts: 233 (strange, but yes, it's the same)
Max. Watts: 592
NP: 244
Avg. Speed: 23.14mph


So, 2 minutes and 9 seconds is the difference.

With my H3 Front wheel / Renn 575 disc I put down a 19:48 time, however, no PT so no data on that.
So, for me at least, a TT bike makes a pretty significant difference at the same Avg. Watts.

There you go... the least scientific test ever.