What makes a $3000 frame so much better than a $300 frame? Is there really that much of a difference? Does the frame really matter?

Besides the frame being lighter, so is the rider by $2,700! Never try to solve a significant problem by adjusting only one knob. Lowering both frame and rider weights is the better way to go.

It depends.

Stiffness (power transfer), aero, weight, compliance, aesthetic, etc.

What's the best frame for no more than $900?

"Best" is very subjective and implies only one. Good might be a better word.

What kind of riding? Road? Mountain? Cross?

Are you talking about just the frame or a complete bike? If just the frame, what groupo of components are going to go on it?

Things to think about before even 'good' can be answered.

Road bike and just the frame...I was thinking Shimano 105 for the group

I think your best bet is a very lightly used or close out new high end carbon frame from a high volume company like Giant, Specialized, Cannondale, Trek... I often look on ebay to see what they have in Giant TCR Advanced or TCR Advanced SL frames. Maybe not $900, but there are usually good discounts. You may get a Cannondale Caad 10 frame for this price , too. Another source is Bike Island which has a bunch of frames in all materials at good prices.

Performance what a few frames, some even with forks, in your price range.

https://www.performancebike.com/bikes..._400001_400314

Colorado Cyclist has a few frames at a little over your price including a LiteSpeed and Eddy Merckx. Well the Eddy Merckx is more than a little over your price range.

Are you going to do the work yourself? If not you'll have to add a lot more money. Don't forget wheels!

Unless you have a spare set of wheels and a lot of the other parts, it's often cheaper, quicker, and less frustrating to buy a complete bike.

So it would be cheaper to buy a complete buy and upgrade a few parts?

Yes.

The free one you get when you buy your group from some place like bikedirects.com or maybe even Performance.

Shimano's OEM discounts are _enormous_. You can get a generic bike and wheelset including a Shimano group (perhaps with brake and crank substitutions) for about what you'd spend on just the group from someplace inexpensive overseas (US retail markups on bike parts are rediculous even on-line) like the UK (ribble, shiny bikes, etc.)

Unless you want something odd (sporty geometry, low bottom bracket not cyclo-cross height, longer chainstays for pannier clearance, frame couplers), want Campagnolo (where your $1200 Chorus group built into a bike will carry a $4000 price tag), or have a shed full of spare parts (It's amazing what can accumulate over 10 or 15 years - as a one bike sort of guy I'd still need only a set of brakes and stem + bars to finish a frame set) you'll be better off financially with a complete bike.

if you want a 105 bike performance has some 105 complete bikes for $1000 and you don't have to uprade anything, just ride.

Cash is barely more common than dinosaurs and dodo birds. Money is mostly electronic these days, it doesn't weigh anything.

My friend Mary is looking for a lighter-weight bike. She's about 30 years old, and about 100 pounds. She eats 1,500 calories a day and runs (not walks) to work and back. I'll pass your advice on to her.

There's no evidence that differences in stiffness between modern road bikes makes a noticeable difference in power transfer.

Is this for real?

The frame is the most important part of the bike. Then wheels and last is components.

If a frame is all you want, a CAAD 10 frame is not far off of that $900 number. I have not looked for a while, but it was not too far off of that. Cannondale builds a bike over three grand on that frame.

That's your test....what is the best bike a manufacturer builds off that frame?

I'm spoofing the move "Secretariat" where the jockey says he looks a lot taller to women when he is standing on his wallet.

The difference between a $300 frame and a $3000 will be very significant.

You're looking at ~3-4 lbs of frame weight, and cheap Steel or Aluminum vs Carbon-Fiber and Titanium. The $3k frame will absorb bumps better, sprint better, handle better.

For reference, I had a friend try my Infinito ($3k bike) compared to his <$1k Motobecane. His comment was "I need to get one of these." We were doing an long up-hill section, so it wasn't shifting or anything just the raw difference in frame.

My thoughts exactly... why put any effort into answering someone who has done zero research and decided to start an extremely broad thread with vague thoughtless posts?

Yes. Yes.

You don't need to spend more than $1k to get a really nice bike that will take you anywhere for a long time to come. An extra $2k doesn't translate into anything tangible to the vast majority of riders.