cholly

Just picked up an old (1989/90) Schwinn 754 for very cheap.... needed some tweaks and updating, but a good ride. Compared to my 2021 Giant Contend AR, it's almost night and day smoother with much less vibration, with equal size tires and psi (25c/90ish). Both bikes are aluminum, Schwinn with a steel fork, Giant with carbon. Schwinn is several pounds heavier, but not looking to keep weight down, just a better ride.

With all the marvels of modern carbon, engineering, light and aero, etc. (so we're 'told')-- am I missing something? The Giant feels and sounds like a rattle trap compared to the Schwinn.

slow rollin

What you are missing is design goal of the bike designer. Some bikes were known to be stiff out of either aluminum or steel. Same can be said with aluminum. Carbon is no different. I have heard of people replacing 1in steel forks with carbon to get a stiffer, more precise fork.
Then, later on I hear of companies designing seatposts out of carbon to be flexible.
The reality is both can be true. A stock aluminum or steel fork from the 80s/90's could be more flexible then a nice carbon one. When I sit my big bum on a bike with lots of carbon seatpost at 27.2 bumps are damped. Isn't the same with most aluminum, and this can be attributed to wall thickness or tube design.

I have realized that the only way to tell is to ride the bike. I suspect many carbon bikes are harsh for racing, and use 32+mm tires to compensate. Obviously this is not all carbon bikes, but it's a great solution.

Man I kinda want one of those weird schwinn aluminum bikes. The quill seatpost is just neat.

BobbyG

I mostly commute and own three 700c road bikes in my "stable". My 1984 Nishiki International, a 2006 Felt F-65, and a 2015 Charge Plug. The steel Nishiki with its thin seat and chain stays and tapering, rim brake front fork The Nishiki has lovely, comfortable frame flex, but was a little harsh with the original 23mm tires that it had when I acquired it in 2009. Rattled a bit with the 23s and still with 25s. At some point I put 700x28s on it and even at 90psi it now rides like a dream, At 75psi, it's really sweet, but a little too mushy. (I tried 32s but they would rub the fork crown)

A year and a half ago I bought a 2006 Felt F-65, which has an aluminum frame and bars, but carbon-fiber seat and chain stays, thisk, stubby fork, seat post and cranks. 700x25 seems to be the max tire size. I also fill the tires to 90psi. The whole set-up has noticeably compliant ride, but not as much as, and different from the Nishiki. The Nishiki feels "flexi", the Felt feels "smooshy", but not in a bad way. Kinda like it has bushings vs springs.

My main commuter is a steel 2015 Charge Plug but stouter (and heavier) than the NIshiki. The Plug has a thicker, disc brake front fork, and thicker chain and seat stays. Very, little flex, but there is a hint. I run the 700x38 tires at 90psi. With its rack and fenders, the bike tend to rattle slightly on rough pavement and over bumps. With its longer wheelbase and more relaxed geometry, the ride motions are slower than the two other bikes. It's comfortable, but is missing the extra comforting flex of the other bikes. Lowering the psi in the tires does nothing to soften the ride. But the Charge Plug is a fast, comfortable cruiser, especially because of the slower ride movements.

My old commuter is a stiff-framed 1997 Nishiki Blazer, and fatter 26x2.125 tires make all the difference in comfort...with racksm fenders and folding baskets, it rattles.

My 2007 20" Dahon Boardwarlk folder (steel) has some frame flex, but, kinda lateral, not the good kind. The long aluminum seat post provides some flex, but it's a little weird. With bull bars and 20x1.75 Schwalbe Marathon Racers it's comfortable, but slightly bizarre.

My 16" Dahon Getaway (steel) project bike is a rickety mess and not really comfortable. But it is the old frame design and folds really small. It serves a purpose, and I have been updating the gearing and brakes for speed and safety. But it will never not be rickety.

I might also add that all my bikes have padded seats, and padded Bars, but not as much as before.

Iride01 

Doesn't matter what the bike frame is made from. You'll find bikes that ride poorly and bikes that ride well. It's not just the geometry of a bike, but how the tubes and other structures are designed and built to take the forces of riding.

If the vibration you are talking about is road feel, then the tires you put on your bike as well as the amount of pressure you fill them with will make a difference. Better tires that cost more generally do give a better ride feel.

For some of us, a certain amount of vibration is desirable. It lets us perceive how well our bike is handling and gripping the road when we are riding fast and going through turns. So to mute that too much would be like losing another sense.

Jughed

I've had just the opposite experience with similar sized aluminum frames. A 1997 CAD3 and a 2021 Trek ALR 5. Both bikes are close in geometry, with the ALR being slightly more relaxed. The old bike ran 23mm and the new bike came with 25mm. I keep my tire pressures high.

The ALR 5 is worlds smoother than the CAD3. The ALR is stiff in terms of power delivery, but the road buzz and harshness are just eliminated. Differences in the geometry are understood - but the bikes are worlds apart.

I also had an old steel Trek 330 and currently have a steel 2001 Lemond Zurich. Both older steel frames - night and day difference. Both are smooth, limited road buzz... the 330 was like riding a wet noodle. Frame flex, BB flex, no real feel to the bike - I could make the chainring rub the front mech under heavy loads, the bike was a noodle. The Lemond is smooth and stiff at the same time, the bike is worlds better.

I also have a CF cyclocross frame, a Giant TCX - the bike, even on 37mm tires with a flexy seat post, is brutal. Stiff, harsh, road buzz...

indyfabz

I had one of those Schwinns. The internal seal post bolt kept allowing the seat to slide down a bit, and the wheels had to be warrantied after only a few months. The last straw was when the bearings started falling out of the cassette as I was riding it back to my apartment up a long hill in Pittsburgh.

Worst bike I ever owned, IIRC, it was built with Sun Tour GPX.

delbiker1 

I love riding my carbon fiber Orbea Avant. It has a fine ride and handling with impeccable balance. It also has more noise than any of my other 4 bikes. I have eliminated most of what used to really irritate me with re-cabling including slick lube liner through the entire frame, new Shimano bb and crankset to replace the original FSA, and fiddling with the cable/housing positioning from the 5700 brifters.
The drivetrain still creates some resonance through the cf frame, and there is still very minor rattling on rough pavement, but I don’t notice it much anymore after being on the bike for a while.

70sSanO

The carbon bike rattles not because of the frame material, but because you don’t maintain it properly.

The frame itself doesn’t rattle, it is all the stuff that is attached to it.

John