godspiral

Which would you expect to be more comfortable?

Steel frame with 23mm tires?
alumnium frame (crmo fork) with 28mm tires?
alumnium frame (carbon fork) with 32mm tires?

If the alumnium bikes are 2lbs lighter, would you expect them to be faster?

barba

It is hard to say, as geometry will have a large part to play in comfort. My guess would by the AL frame with 32cm tires. Air is a great shock absorber and the carbon fork will help, as well.

fmw

I would expect the steel frame to be more comfortable - noticeably more comfortable. 2 lbs. doesn't make any difference to your speed - sorry.

-=(8)=-

Hmmmmmmmm.........
Although I think long wheelbase and steel should be the
most comfortable I will go with carbon fork and 32's for
the choices you offered.

johnny99

Comparing frame materials alone is silly. Some steel frames are very compliant. Others are very stiff. Tubing diameter and tubing thickness make a huge difference. Some steel frames with oversized tubing are designed to be just as stiff as aluminum frames. Some aluminum frames with standard sizes tubes are very flexy. Frame angles and wheelbase also have a large impact. Shorter wheelbases generally mean stiffer frames, but more responsive steering.

godspiral

Thanks to everyone for trying to answer, or expose potential problems with the question.

The one aluminum bike with carbon fork I rode was incredibly harsh on cheaply paved but good condition road. Road texture was causing discomfort not bumps or cracks. Do carbon forks have a rep of being more comfortable than steel? I had expected the opposite effect of smoother response to vibration, but supposed harsher reaction to potholes.

I asked the speed question because the thinner tires could make up for higher weight (i dont really know)... assuming not too difficult hills.

johnny99

No. Carbon is lighter, but "comfort" depends on the design of the fork.

Tire air pressure will make a bigger difference.

dutret

carbon dampens too. You can make a carbon part that will be more comfortable(less jarring) then an equivalently stiff steel or al part. So yes it is safe to say that carbon has a rep of being more comfortable then steel.

That said riding my dads e1(which is completely carbon) is alot more jarring then my old steel miyata so design plays a large part as well. With 32mm tires(hypothetically since they would never fit) that E1 will be even smoother then pretty much anything with 23mm tires on it.

Without knowing the specific bikes I think in general for bikes built with similiar goals in mind some generalizations can be made. The AL with a carbon fork 32mm tires will give the smoothest ride. Not only is there more air in the tire to absorb shock but you can run a much lower pressure without having to worry about pinch flats. Keep in mind this lower pressure is going to make you a bit slower.

-=(8)=-

I think the tires make the biggest difference.
I have loaded my fixed track bike up with a
tiny little frame bag but between the tube, flat kit, pump
and multi-tool Im sure it boosts the weight of the bike
to 19lbs. I commute on this bike expensively and can
tell no difference at all with the 3lb's or so added weight.
I have 32's on the geared bike that do absorb bumps better
but still much prefer the 23's.
Less rolling resistance is what makes the
difference more than the weight to me. Once the weight
is in motion I beleive it to be much less of a factor than the
constant resistance a wider tire will give.
Just my .o5 !

johnny99

I don't buy that argument. You can also make a steel part that is less jaring than equivalently stiff carbon part. The only reasons that steel is not popular now are weight (vs. carbon) and price (vs. aluminum).

I do agree that wider tires are more comfortable, but mostly because you can run a lower tire pressure in a wider tire without risking pinch flats.

mowhitesnake

Man, my mustang doesnt even have tires that wide.

dutret

Tap a steel frame and a CF one with a key. Hear how one rings and the other doesn't? That is because vibrations aren't damped in the CF but allowed to resonate in the steel. Still don't believe me take a steel and CF fork or similiar stiffness and bang them on the ground hard. You'll feel it.

An argument could be made that this damping in CF means that there is more power loss do the same amount of flexing. But that is another story entirely and would take a very very sophisticated study to show.


BUT? aren't you agreeing with me regarding tire pressure?

Tom Stormcrowe

Originally Posted by godspiral
Steel frame with 23cm tires?
alumnium frame (crmo fork) with 28cm tires?
alumnium frame (carbon fork) with 32cm tires?

I just noticed that, I hope you mean mm wide?

DrPete 

And if hitting a bump in the road were the same as making your frame ring with a key, that argument might make sense. But let's go with it for a sec--if you tap a CF frame with a key and it doesn't ring, doesn't that mean the vibration was damped?

Actually, since resonance has absolutely nothing to do with shock absorption, no, that argument wouldn't make sense anyway.

DrPete

dutret

sorry
s/aren't/are

It would because it is related to the ability of cf to transmit vibrations from the road to your hands/ass. How far a shock in one part of the tube gets transfered to others be it from an uneven road from the dropouts or a key in the middle can tell us alot about the properties of that tube. That the key shock can tavel back and forth through the tube hundreds of times in the steel tube but not the CF is a good measure of how smooth the ride will be.

Either way the 32mm tires are going to blot out the differences between materials in almost any situation.

DrPete 

I'm glad we agree on the tires, because I'm quite sure your point about resonance as it applies to shock absorption is dead wrong. The fact that the vibration DOESN'T travel through the CF frame is the very definition of damping. And again, the amplitude and frequency of road shock has nothing to do with the amplitude and frequency of a sound made by hitting metal on metal, and these properties at one amplitude/frequency say nothing about another amplitude/frequency.

If a pretty sound were the goal of a bike frame, we'd make them all out of crystal, wouldn't we? That would last all of one bump.

DrPete

dutret

indeed see my previous correction regarding replacing aren't with are. I'll edit the original post if that makes more sense to you.

To make it more clear. Aren't was a typo. the sentence should have said that vibrations are damped in the CF. I'll edit the post since you are still talking about a typo.


frequency and amplitude don't matter.
How long a tube resonates after a single shock(infintitely small frequency) tells you something about how that tube transfers shocks from one end of it to the other. Provided you use the same amplitude for both tubes you are still gaining useful information regarding the properties of the tube that will hold for any other amplitude. If you don't believe me try the impact test or just ride a moderately stiff CF bike and compare it to an OS steel frame.

slowandsteady

I ride an aluminum frame with carbon forks and seat stays with 23c tire(Fuji 1.0 WSD), and it rides smoother than my CroMoly MTB with 26x1.25 slicks and front suspension did on the same lousy roads full of potholes, bumps, cracks and tar & chip surface. It really needs to be compared on a case by case basis.