sweetspot

It seems that bike makers have mainly two options:
Thin and long seat stays mounted on the level of top tube (like salsa warbird) or short seat stays mounted way below top tube (like new specialized diverge). In your opinion and from your experience what is a better solution in terms of rear end comfort? What are pros and cons of each solution? Or as makers of True grit have told nothing beats 40c tire clearance?

Nessism

There is very little vertical flex in the back end of the common double triangle frame. I suppose a frame with thin and small diameter stays, mounted as high up the seat tube as possible, would hold some small advantage but I wouldn't expect much in the world of real world difference.

unterhausen

40mm tire definitely has more effect on comfort. If you had a bike with significant flex in the seat stays in combination with rim brakes, you wouldn't like it. Even curvy Hetchins style stays don't flex very much.

squirtdad

there is the kirk terraplane stay Terraplane Seat Stays | Kirk Frameworks

Andrew R Stewart 

Ah yes, the bike industry is cyclic, rehashing previous designs.

The amount of tire compression/deflection when riding over bumps is so much greater an amount then the seat stay compression that , IMO, comparing the two is questionable. Andy

Abu Mahendra

yeap. This point was made by Sheldon many moons ago, and it still mskes sense today. Tire deflection Will be orders of magnitud greater than the frame. This is probably true for discrete bumps which can be modeled as impulses (damped, under-damped and over-damped). A separate issue is constant micro-bumps or road chatter which can be modeled as a high frequency signal. Here the material properties will trump geometry (if we ignore resonance). Geometry is primarily about handling, comfort and secondly about dampening.

sweetspot

and what Will be better in terms of dealing with Micro bumps: Steel or carbon with additional compounds like look or lapierre are making?

fietsbob

putting a suspension seat post on is quite effective..

an elastomer 'rubber' block under compression within a mono seat stay design
has been utilized ..

Trek made some frames for Paris Roubaix Race , like that .. chainstay flexes ..




...

Brian25

Longer chain stays. To exaggerate my point, try captaining a tandem. On a tandem the captain is on a really long truss, the rear wheel is so far back that it makes for a smooth ride for the captain when you hit bumps here and there.
Even a single bike with somewhat longer chain stays, and the rear wheel further back will give a slightly softer ride.

unterhausen

I say that's just confirmation bias at play

Brian25

Let me clarify: If you run over a 3/4" bot dot on a bike with a single bike with 16.5"/ 42cm chain stays The bottom racket will go up about 1/2" with you above it. Compared a tandem, you hit a bot dot and now your rear wheel is about 30" farther back, the length of the lever is greatly longer and I would be surprised if the captains bottom bracket would go up more than a 1/4". longer chain stays = smoother ride.

Abu Mahendra

I don't know, but it is something that a materials lab can test, and quantify.

David Tollefson

This works pretty well...

TiHabanero

I have tested tire width/profile and pressures on my touring bike and confirm that tire pressure and tire width/profile make very noticeable differences. Not sure chain stay length or curls make any difference at all to the rider. I am sure someone has quantified it in a lab, but out on the road it is all about the tires.

Andrew R Stewart 

+100. This is one reason why I never have followed the trend to having the least long chain stays. I like a smooth chain run with less chain/tooth meshing noise and find that really short stays are worse in this.

The single biggest difference one change can make is with the tires. This was common knowledge back in the 1970s (and likely long before that) and only seems to be understood again recently. My cynical side wonders if the industry fashion is more the push or will the next 10 years see a push back to skinny tires (I can see the ads now "less weight" "stiffer side walls" "more aero") Andy

mikeread

I recently owned an alloy framed bike for a very short time, it was far too harsh and I sold it after a few months. It completely took the fun out of riding.

Even with wider tyres at significantly lower pressures than I usually run (20psi or more lower) it was still uncomfortable,compared to other bikes I ride (steel and titanium)

So in my opinion the frame does make quite a significant difference, the seatpost too.

At the front end I am convinced that the fork and in particular, the bars together make about as much difference as the tyres. You only have to push down on a pair of lightweight bars to see how much give there is and straight bladed forks, beefed up for disk brakes are so unforgiving the might as well be made from scaffold poles.

Nessism

Yeah, frame flexibility can affect comfort, but most of the useful flex occurs in the front triangle, not the rear. And aluminum frames are typically quite stiff.

In order of importance to ride quality...tires (size/pressure), fork stiffness, frame (front triangle). Bar tape and seat cushion can also help. Rear triangle stiffness (vertical) offers minimal opportunity.