Why am I faster on my tri bike?

more aero/stiff.  i think you just answered your own question.  i'm usually 2-3 mph faster on my TT bike over my road bike for routes i ride often. 

It's all aerodynamics.

OP take a look through this article, the amount of power required to ride at the same speed (25mph) on a RB (drops) vs TB is significant.

http://www.bikeradar.com/road/gear/article/how-aero-is-aero-19273/

Unlikely.  Most people actually find they create somewhat less power in an aggressive TT position.  But they are still faster.  Again, it's all aerodynamics.

So this is the premise that Rotor Q-rings/Osymetric rings are suppose to be helpful, or is that another subject all together!

Originally posted by gsmacleod

Originally posted by mike761 From what I've heard most people produce a little less power on a TT bike than on their road bike. However it is my understanding that your body position on the 2 should be very similar just rotated about the crank to put you in a more aerodynamic position. If this is true shouldn't you be producing the same power on either bike, but moving faster on a tri bike because of aerodynamics? If you are not producing as much power on the Tri bike does this then me you are not set up properly?

If you consider this image: This is for riding at a normal (72ish) STA and you can see that the hip extensors are involved basically from 12 o'clock to about 3:30 while the knee extensors are from about 2:30 to 5:00 and the ankle plantar flexors are from 4:00-6:00. If you ride steep you are going to change when the various recruitments happen and for most, even if perfectly setup, your power will be decreased. It is quite likely that the engagement of the hip extensors will be delayed (say until 12:30) so you delaying the power phase and while you may be able to continue the power phase a little beyond 6:00 due to the rotation, the ankle plantar flexors are much weaker than the hip extensors so the added push at the end (even if you are able to do it) is not likely going to makeup for what is lost at the beginning. Shane

I'll go with scientist Shane's explanation. 

My comment was mostly observational.  I do know people who say they can achieve the same power in road and TT position.  But I think the big difference is that as you go more agressive, you close your hip angle further.  I assume that helps account for the different engagement patterns that Shane is taking about.  You certainly don't want to close up this angle so much that you lose a lot of power and negate any aerodynamic savings.  But, becuase aerodynamics are so critical, you can afford to lose some power and still be faster.  Of course, a seperate issue is if you are comfortable enough in riding that way to get off and run well.  That can depend how long you have to saty in the position (eg, a sprint vs. IM).

The difference in stiffness of bike frames has no measurable difference in power transfer to the road.  If your TT bike is too teeth-jarring for you, let a few psi of air out of your tires.

I'll not nit pick either, except that I will.  

Power that is transfered to the frame (through flex) is mostly returned to the pedals (minus a VERY small amount of heat loss).  The amount of loss is so small that I suspect you would not be able to measure it with most power meters and can safely ignore when trying to figure out what might be making you 3mph (or even 0.1mph) faster.

Agree.  IMO, the only people that need to worry about stiffness are road race sprinters and track riders.  The stiffness only matters for a few seconds while putting out max effort...and even at that, may only save them 0.2 seconds.  But to them, that's an eternity. 

If during a triathlon, you're putting down so much power that you're actually giving away speed due to stiffness...you probably need to be more concerned about your run to follow.

I was able to dig this up through the wayback machine.  Towards the bottom, there is an experiment you can do for yourself.

http://web.archive.org/web/20090323002006/http://bikethink.com/Frameflex.htm