What sort of speed improvement can I expect going from a $1000 hybrid bike (Merida Crossway Striker) to a $2000 road bike (Cannondale CAAD 10 - 105), all other things being equal?
Presently I can commute to work (9km) in 17-18 minutes. It's mostly flat on a dedicated cycle path.
I am hoping to shave maybe 30 seconds off my time. Is this a reasonable expectation?
Other answer is good - I got pulled away before I could finish this post
I have nice day bike and a rainy day bike and they have less difference than those two bikes and pick up more than 30 seconds on the about the same commute even rainy bike on a nice day
Factors:
You were getting petty good time on the hybrid. SPD shoes will also help. Adapt your riding technique to the road bike.
The 23mm tires on the road bike are more efficient but less rubber contact and susceptible to pinch flats. For commute I would go up to 25 and even 28 if the frame will take it. My rainy day bike has bigger tires and is more comfortable and more stable. I even ride the rainy bike on nice days when I want to relax.
I'm not sure that anyone is going to be able to give you a definitive answer... especially since you are asking if your commute will improve by 30 seconds when the commute time you give has a range of 60 seconds. But 30 seconds out of 17.5 minutes is about a 2-3% improvement, which seems reasonable...
The more interesting question would be "what can this speed up be attributed to?" There are 3 factors I can think of: rolling resistance, weight, and wind resistance.
Rolling Resistance: How much friction is produced by the wheels? Moving to skinnier tires, and inflating them correctly, will reduce your rolling resistance dramatically (not always a great thing when it comes to stopping time / cornering). The Merida Crossway Striker looks like it has fairly skinny tires, so this won't be as noticeable as moving from say a mountain bike.
Weight: I include this because it is one of the properties often touted by expensive bikes. But mass is only a factor when you are trying to change velocity. So, especially on a flat course with few stops (and thus little acceleration), reducing the weight of the bicycle will have little effect. Not to mention that the rider's mass dominates the total weight... and it is much cheaper to shave off ounces on the rider than the bike!
Wind resistance: this is likely the biggest factor, especially since wind resistance increases exponentially with respect to speed. The smaller profile of an expensive bike will play a small role... but like weight factor is again dominated by the rider. However, the rider's position when "in the drops" is far more aerodynamic, so switching away from straight handle bars will likely have a noticeable effect at high speeds. That is assuming that you are not wearing parachute pants.
Surely there are other factors, such as the damping effect of the Striker's shocks, or maybe the efficiency of the components in transferring power from pedals to the wheels, but I think rolling and wind resistance are going to be the only noticeable factors.
