hitting potholes: steel vs carbon

[Climb01742]

somewhat involuntarily lately i've been doing a bit of product "testing". i've hit enough potholes and badly broken pavement the last two weeks to keep my dentist busy for a long time replacing my loose fillings. one thing seems clear (though why i'm not sure):

steel is better for whacking a pothole than carbon is. personally, i find carbon (both in a fork and an entire frame) is more to my liking for absorbing or muting the normal buzz of coarse pavement. but an interesting thing happens when you whack something bigger.

when an all-carbon frame (a hampsten-parlee Z1 in my case) hits a good size pothole, it gets airborne. it jumps up, with a jolt. hit the same size pothole with a steel-forked steel frame (like an MXL) and it rolls over and through it.

it feels like carbon handles vibration better (to me, anyway) but steel handles jolts or big hits better. my lame, unscientific guess is that steel bends (deflects?) and carbon doesn't. when a whole bunch of force (a pothole) hits carbon, that energy or force is transferred in a linear manner (hence the goin' airborne jump), while the same force bends steel a bit, so the whole bike (and rider) aren't thrown around as much.

brainiacs, am i even close? :confused:

i love my parlee and i love my MXL. but it's fascinating how they react differently to the same input. judging by how some teams are modifying (or abandoning) their carbon frames for roubiax today, hitting big bumps hard is a very specific application. neat.

[1centaur]

So carbon bikes are for people with decent bike handling skills :)

Seriously, I think your description is about right, but with the following caveat - as CF bikes get lighter and lighter, they are getting stiffer and stiffer, and in their stiffness they react to potholes as you describe. My aluminum Klein and my CF Orca have that big bang on hitting potholes, while my Calfee Tetra Pro reacts with more equanimity.

Wheels can change the equation markedly. Topolinos change my Six13 from jarringly stiff to nicely plush; on my Crumpton the double vibration reduction is, arguably, too much.

If I were choosing a bike for medium rough roads it would be CF for the common vibration damping and somewhat compliant wheels for pothole resistance. Steel, in my experience, is inferior as a pothole shock disipator to medium weight CF with compliant wheels.

[David Kirk]

Hey.....

I think one of the difficulties with this question is that it assumes that all steel or all carbon bikes ride the same as each other or at least somewhat similarly.

It seems to me that one can make a carbon/steel/ti/wood etc. bike feel a number of different ways depending on the design. Therefore it seems that making generalizations about ride qualities of a given material might not be so good...........comparing one frame against the other makes much more sense to me.

Time for a quick ride before PR come on the tele..........

Dave

[Climb01742]

So carbon bikes are for people with decent bike handling skills :)

while i'm not the best handler :beer: a lot of my miles lately have been commuting to work. with a lot of cars on my left, choosing your own line is harder. hitting a pothole seems softer than hitting a pick-up truck. ;)

i'd be curious about your take on your topolino's. reaction seems to be mixed. some folks quite like 'em; others not so much. and what are you running on your crumpton? (nick is a cool guy, isn't he?)

[1centaur]

After I wrote that post I went out for 76 miles on the Crumpton with Topolinos.

The combo did not feel too soft to me this time - first time this year on the Crumpton - maybe because New England road are so frost heaved that every bit of vibration damping is welcome. The Topos consistently seem to ooze quality construction to me, but I sometimes hear noises that don't sound right but I can't diagnose them since they are only noticable when pedaling, not freewheeling or spinning the wheel in the stand (and they're hard to hear over the wind in my ears). The non-metal spokes make a different noise cutting through the wind, and I keep wondering if I am hearing a little hub noise or just the wind noise. Sometimes I hear nothing at all. Finally, it feels like the wheels just HAVE to be soft because of their construction, so I get the feeling when standing and cranking a hill that I'm flexing them, but again that could be sound more then motion.

My bottom line is I need to ride them more both on the Crumpton and the Six13 this year to know if I love them or like them. If they were silent I would think they were awesome - light, spin up quickly, easy to change tires on, etc. The noise has me considering options for my next incoming bike. Who makes the smoothest, quietest hubs in the world?

Yeah, Nick's a great guy and I was frequently impressed while climbing yesterday at how efficiently I was transmitting power to forward motion. I would buy from him again.

[RPS]

David makes a great point in that design can make a significant difference.

Vertical compliance of conventional frames -- regardless of material -- is so limited compared to the combined compliance of the tires and wheels that it shouldn't make much difference when hitting a large pot hole.

I've been test-riding road frames with rear passive suspension for a while and have concluded that the ones with greater compliance handle large bumps better, regardless of the material.

My carbon frame does a great job at isolating low-applitude high-frequency road buzz, but my titanium frame which has the greatest vertical compliance does a better job at isolating shock from larger bumps. Material differences between steel, carbon, and titanium have been less significant than suspension travel when it comes to riding over large pot holes.

Fortunately a frame with as much vertical compliance as an accomplished rider would want to ride can be designed using any one of these materials.

[tch]

happened in the "best bad road bike" thread. I have a Rivendell Ramboulliet with steel fork and a Concours with carbon fork. The Concours rides MUCH smoother and without the big-bang effect. But Ray interestingly diagnosed the issue as perhaps more to do with weight distribution than fork/bike material -- and after some thought and some more riding, I am prone to agree with him. I think that material is one element -- but that design (which includes things like fork rake, angles, and weight distribution) is another, and perhaps much more important.

And...add to this the element of the wheels, and there are no absolutes, just combinations of solutions and feels.

[jl123]

RPS,
What sort of passively suspended bikes have you been riding? Do you consider DKS or Moots style rear suspension passive?

Tch,
I think your right about the overall design of bikes affecting their feel/balance, only I don't think its the long chainstays in and of themselves that cause the imbalance for most of the riding you do. I've spoken with numerous riders of older French Randonneuring (spelling?) bikes which also have long chainstays but much different geometries than most US touring bikes, and they are almost universally praised for there comfort and balance. JL