dabern

Check the tubes on this Koga - makes the Cannondale look scrawny! Also attaching link to story at Cyclingnews:

https://www.cyclingnews.com/tech/2005...ults/london054

dabern

A nice seat tube sticker on that Koga:

absntr

I've seen that frame here in Chicago at Upgrade Cycleworks. It's ovalized. If it weren't for the teardrop shape towards the upper (inside the triangle), it'd be quite similar to the Cannondale.

rithem

looks a bit like my Russ Denny / ovalized = stiff

gregg

Spicer has a similar downtube on one of his track frames:



@ spicercycle.com

jonb

i like the koga/spyker bike in the article you linked...

FarHorizon

And the question of note is:

Why is the DOWNTUBE such a large diameter? The downtube, on a diamond frame bike, is in TENSION - not in compression! If fact, one manufacturer eliminated the down tube all together, substituting a length of CABLE!

For strength and rigidity, the top tube, seat tube, and seat stays are the tubes that should matter, yes? This is why Specialized uses different materials on the sections mentioned in the previous sentence on their best road machines.

taras0000

[QUOTE=FarHorizon]And the question of note is:

Why is the DOWNTUBE such a large diameter? The downtube, on a diamond frame bike, is in TENSION - not in compression! If fact, one manufacturer eliminated the down tube all together, substituting a length of CABLE! [QUOTE]

Just because the down tube is in tension doesn't mean that it doesn't help other parts of the bike (the seat tube) from resisting torsion. The bottom bracket on a bicycle , when under pedalling forces, actually twists side to side. So as your right foot moves from the 9:00 position to the 3:00 position, the right side of the bottom bracket moves forward. At the same time, the left side moves backwards. This causes the seat tube to twist. The right side of the bottom bracket "compresses" the right side of the downtube, and the left side of the bottom bracket "pulls" on the left side of the down tube. Slingshot's design could've been stiffened up by using two cables and attaching them as wide as they could onthe bottom bracket. The wider your downtube, the farther out it attaches to the bottom bracket, giving it less leverage to twist about the seat tube. This is why Columbus came up with the Esspresso bottom bracket shell. This is the one that is CNC'd out of a block of aluminum and shaped like a wedge. This allows you to weld a wider downtube to the bottom bracket, enveloping the seat tube, and giving more surface area for the weld, making a more solid bottom bracket junction and a stiffer frame. If you want to see a really big downtube/bottom bracket junction, take a look at Guru's prototype track bike as ridden by The Track Team ( https://www.thetrackteam.ca/ )

taras0000

By the way, Guru used tandem down tubes for the down tube and seat tube of that bike. About 45 mm wide and have internal ribs running down it's length.

queerpunk

<grammarbot>
quoting strongbad, "ooohhhh, if you want to be posessive, it's just I T S, but if it's supposed to be a contraction than it's I T apostraphe S.... SCALLAWAG!"
</grammarbot>

Fugazi Dave

where's Trogdor when you need some burnination?

icithecat

Why is the downtube so large?
The answer is simple. That is where the brandname goes.
Marketing 101.

jamey

that's what she said.

Fugazi Dave

*rimshot*

Serendipper 

Reading further into the article, Kinesis claims that a beefier downtube allows for stiffer steering, presumably for sprints, when the rider is applying more force to the cockpit.
Makes sense to me.
Kinesis 'Winter/Summer' bike is the best street/track fix I've seen coming, BTW.
Doesn't look like a gimmicky road conversion, like other '06 bikes.

LóFarkas

My *warning, disturbing material ahead* geared bike has a frame made by Kinesis for Magellan-a Hungarian maker. Best bang for the buck around here.