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....bikes are not just fast. They have to be fast and sweet.

Ha ha, working on that.

I wasn't thinking of the rider so much as the perception. Like when a reviewer says a certain bike feels fast or sluggish or uninspired or something. From the replies it sounds about what I figured. I suppose lighter rims would feel fast because they accelerate easier, a racing position would feel faster because it's a racing position, a stiffer frame might feel fast because of less wasted energy while pedaling...

When half of us have to explain to the other half what OP meant, it's time for a nap.

Speed of bike is proportional to size of the big ring, all else being equal.

I think the main things that make a bike fast, are good fit, so that the rider is comfortable, and a geometry that puts the rider in an aerodynamic, powerful riding position. Another important factor is bicycle maintenance, it is hard to be fast if your bike is breaking down, or your chain keeps falling off, or you have excess friction somewhere. Tires matter a lot as well. Aerodynamics of the bike and bike weight also contribute some but I'm guessing not quite as much as the first things I mentioned. As for the details of all the above and what work's best, well I don't know about all that.

I just went from a Synapse aluminum to a carbon Madone. I have faster times on the same roads with the madone. I did not change in a week. I am faster on that madone and therefore I would say it's a faster bike.

We have a winner! That's definitely a fast bike -- especially with the backwards fork providing a massive amount (150mm or more) of trail for extra high-speed stability

A bike that feels stiff and quick (including short chain stays plus all the other characteristics already described) make you ride harder. That alone makes it faster.

Then if you have aero wheels and an aero frame, you have to ride quicker to keep from getting embarrassed.

Finally when you spend money, it's important to justify the expense to yourself. So you ride harder and more often.

Any bike powered by e.g. Cavendish is typically a fast bike.

Is it a coincidence that my fast bike is the one I had 30 years ago when I was thirty years younger and fifty pounds lighter?

A fast bike is a tri bike. Faster at a given power output.

My 30lb Le Tour.....gets 3 gallons a mile and all speed baby!

You been tracking the wind on your rides?

Over-inflated tires

A bike going downhill with a tailwind.

Pretty much the same weather and it is over a couple of rides on the same area

Fast and slow are relative terms. It is a combination of things that makes people refer to one bike as their "fast bike". It may have to do with the weight and material of the bike, as well as specific features of some of the components, such as having slick tires. With the same engine, one will not go much faster than the other, but it might not feel that way

I dusted off my 'fast' bike last night. In addition to the Schwinn, I also have a LeMond Poprad which hasn't been ridden in about 5 years. Both bikes have essentially the same tires, 700x28 vs 27x1.25 but, in addition to being a couple pounds lighter, the steering on the Poprad is a bit quicker and it doesn't have fenders so I suppose it does 'feel' a bit faster.

Look who the cat drug in.

And to answer the question, it's one that can be dialed up to 400 watts.

Hey, my kid is finally old enough where he is entertaining himself. That gives mom and me a little bit of free time to get back into our old hobbies

Fast is a relative term but grabs attention.

Fast compared to what?

A fast bike is the one that finishes first i guess...

How about your position? Is it identical? I went from a 15 year old AL bike to a 2013 Madone. I thought for sure I was suddenly faster. My first few rides were actually faster because of my extra excitement on the new bike. Over time, I realized the bike really added nothing to my speed. If I wheel out the old bike and hit the same road today, it'd be nearly identical. That said, the new bike has a smoother ride, so I can ride harder for longer. In that sense, it is a faster bike perhaps, but that is probably 90% switching from 23mm gatorksins to 25mm gp4000s.

Edit: let's not forget that all of this can be quantified with a power meter. Same position, same wind, same watts, yet more speed? Faster bike.

I think this is the best analogy I have heard on this topic. Spot on.

Not having a power meter - I guess I will never really know but it sure feels faster to me.

And the camera can make the difference