Fluted seat post... Why?
 

Hi,

I recently bought an older road bike (mid 80's), and it has a nice alloy seatpost on it, with finely machined flutes up the side. I've seen this style before, but I don't understand it.

Why flutes? Appearance? Grip? Anti-seize? Weight Reduction? Aerodynamics? Its a neat seatpost, and I've got no problems with it, I'm just curious as to the engineering choice...

peace,
sam

My roommate just got a late 80's Cannondale with one of these fluted seatposts too. I'd love to know why they did it too... presumably it's not for grip because it reduces the surface area of contact between the seat post and seat tube.

My guess would be either appearance (they are beautiful) or a half-baked weight reduction attempt.

During that era flutes were popular as a weight reduction technique. Other parts, like brake levers commonly had a neat series of holes drilled in them for the same reason. Some guys would amuse themselves by drilling little holes in their brake calipers, derailleurs, chainrings etc. It is a lot of work to get all of the holes evenly spaced and it didn't remove all that much weight either.

Exactly so! Lots of structural integrity loss for virtually no weight savings. It sure sold well, though! :p

I have a pair of "safety" brake levers from that era with lots of little holes drilled in the lever. What I'm wondering is, if they wanted to lose weight, why not just lose the stupid extension lever :)

Yeah, when Campy came out w/ Super Record that was the only difference in the brakes; little holes in the levers. They would whistle from the air going through them when you rode.

Holes were big in chainrings, too.

I'm reminded of homer simpson using a pickaxe to jab "speed holes" in his car to make it go faster. ;)

Anyway, I'll enjoy my flutes, but I don't think I'll be taking the dremel to my bike today. :)

peace,
sam

:lol: Classic!

FWIW, flutes are an engineering trick to make tubes stiffer while reducing weight.

A good example of this is match-grade rifle barrels (for them, the additional surface area of the flutes also facilitates cooling, not an issue for most riders).

Another $0.02 worth...

Air cooled seatpost :) Awesome... now I have a good place to carry around spare uranium fuel rods with me.

My '84 Trek 520 had a fluted seatpost. I liked it because it looked classy. Maybe it'd be less likely for the seatpost to bind in the tube (steel)? Sounds like a reach, though, doesn't it?

Another example is the "blood groove" in a hunting or fighting knife. Contrary to popular belief, it has nothing to do with relieving suction by allowing blood to flow, and everything to do with stiffness. Like an I-beam.

Bingo.
A knife with a blood groove is weaker than an identical knife without one if the groove is made with a grinder (material removed), however if the fuller/blood groove is made via forging, the material is simply pusher away from that area, which equals a stronger knife.

Weight weenies will be happy to note that a fuller also lightens the blade and increase the stiffness/weight ratio.

If I ever need to stab a cager with my seatpost, I'll be glad my seatpost has been structurally enhanced with flutes. :)

peace,
sam

The flutes act in the same principle as the corrugation of cardboard in a cardboard box. The flutes add strength. One other point is that if the seat tube wall thickness is uniform throughout it's circumference, the flutes also add weight. Why? Because the total linear measurement of the tube circumference is greater when it's fluted. It could also be that the seat tube maker was using a "thinner" than usual alloy and employed the flutes for strength. In this case many would say that the flutes reduced weight. Not true though, it is the thinner alloy that reduced some weight, but the flutes cancel some of that weight savings. This is similar to tubes that are butted. A tube maker uses a thinner tubeset. That reduces weight. But to add strength to the thinner material they butt the ends. This increases the tube thickness, adding weight. But, many would say that butting reduces weight. Not so. The thinner tubes provided a weight reduction, and some of that weight savings is cancelled by the neccassary butting.

Maybe it'd be less likely for the seatpost to bind in the tube (steel)?

This makes a lot of sense to me. They would be easier to adjust because there is less friction area when moving the post up or down.
My old Fuji has the flutes, and I just think they are attractive.

Removing material reduces weight. The wall thickness of a fluted seatpost is not uniform throughout its circumference it's a tube with grooves machined out of it.

Butted tubes are not thickened at the ends, they're thinned at the center.

Silly boy.

This is just so wrong. Have you ever actually seen a fluted seatpost?

He/she was alot closer than you were. :rolleyes:

I think this is a "glass half empty"/"glass half full" argument...

One of you is saying that a butted tube is a thick-walled tube that has been thinned in the middle.
The other says that a butted tube is a thin-walled tube that has been thickened at the ends.

Unless you're in the tubing business, who cares which it is :)? The point is that a well-designed butted tube can achieve a desired strength with less weight than an unbutted tube (of the same length and diameter).

PS- The way a butted tube is made isn't by actually adding or removing material from a unbutted tube. I believe the way they do it is by putting a mandrel with slightly tapered ends inside an unbutted tube. Then it's drawn through a die to squish down the ends against the mandrel. See this thread: http://groups-beta.google.com/group/...ec5ff948d5f3ec

Not closer. Dead on.