Most common downtube diameters?

[recumpence]

I want you guys to measure the diameter of your bicycle frame downtubes for me. I have an idea for a drive clamp that can flex a bit around various diameter frame tubes, so I do not need to machine a bunch of different size clamps. But, I need to know the range of tube diameters of the most common bike frames (downtube diameters).

Matt

 

[Zoot Katz]

If you look at the Tange catalogue, even in the same series of steel tubing sets, the down tube sizes go from 31.8mm to 34.9mm for mountain bikes.
For road bikes they're pretty much all listed as 28.6mm. Their OS series offers 30.0mm and 31.8.
The builder selects tubes to match the riders weight and expected service of the bike.
All of my bikes (except the choppers) are double or triple butted chrome molybdenum steel. The road bikes are around 28.5mm. The mountain bikes are more like 32 mm.
HTH

 

[Grinhill]

For the dummies, that's the diagonal one from the front of the bike to the bottom bracket, not the one the seatpost slides into right?

My MTB has a tube which is round at the front of the bike and gradually squashed into on oval shape where it is welded to the bottom bracket.

EDIT: OK if its around 32mm you must be talking about the vertical one. :?

 

[recumpence]

I am talking about the tube from the bottom bracket up to the head tube.

Matt

 

[Zoot Katz]

For the dummies, that's the diagonal one from the front of the bike to the bottom bracket, not the one the seatpost slides into right?

My MTB has a tube which is round at the front of the bike and gradually squashed into on oval shape where it is welded to the bottom bracket.

EDIT: OK if its around 32mm you must be talking about the vertical one. :?

No, the vertical one is the seat tube. I'm talking about the down tube.
There's also a 700C cro-mo mixte frame here thats down tube is oval vertically at the head tube and it gradually becomes a horizontal oval at the bottom bracket shell. It has no round sections throughout its length.
I've got a hi-ten kids bike that's 42.5mm. It's squahsed vertically into an oval where it meets the head tube. (the one the fork steerer comes through)
I just measured a generic Al hadtail and its down tube is 52.6mm. It's squashed at both ends to fit the head tube and bottom bracket.
A cheap hi-ten CCM comfort frame here is 37.2mm. It's downtube is curved.
Many inexpensive steel bikes used way oversize hi-ten tubing to simulate the larger tubing sizes commonly found in aluminium frames.
It's purely a marketing thing though there's no doubt that the large diameter tubing is stronger than a smaller tube of the same material.

 

[swbluto]

My diamond-back response bike has an unusually large "down tube" and it's shaped in an elliptical way. It has a circumference of about 6.5" or 165.1 mm, or it seems to be about 2" along its diameter or about 50.8 mm. It's an aluminum frame.

 

[Toshi]

My diamond-back response bike has an unusually large "down tube" and it's shaped in an elliptical way. It has a circumference of about 6.5" or 165.1 mm, or it seems to be about 2" along its diameter or about 50.8 mm. It's an aluminum frame.

i seem to recall that my (aluminum) klein quantum race's downtube was 61mm in diameter. moral of the story: steel tubes are of much smaller diameter than aluminum ones in this application.

 

[GGoodrum]

It looks like most of the "standard" sizes are based on inch values: 28.6mm = 1-1/8", 31.8mm = 1-1/4", 34.9mm = 1-3/8" and 38.1mm = 1-1/2".

-- Gary

 

[Russell]

My DOWNTUBES measure as follows:

Kona (steel): 32.0mm

Cannondale Caad2 AL road frame: 41.5mm

Raleigh touring/hybrid AL frame: 44.0mm


-R

 

[Russell]

It looks like most of the "standard" sizes are based on inch values: 28.6mm = 1-1/8", 31.8mm = 1-1/4", 34.9mm = 1-3/8" and 38.1mm = 1-1/2".

-- Gary

Those are standard sizes for SEATTUBES

-R

 

[GGoodrum]

Those are standard sizes for SEATTUBES

Whatever, these also are the same as some of the the downtubes on my bikes.

 

[Drunkskunk]

I have like 7 ridable bikes. None have the same size downtube. or even the same shape, and half of them have unconventional tapers and shapes. Only my Schwinn LaTour has a constant width 30.(?)mm tube. everything else is in the 50 to 80mm range.

 

[GGoodrum]

Not sure why everyone seems focused on downtubes-only. On my bikes, that would not be an optimum location. Seat tubes are better for me.

-- Gary

 

[MitchJi]

Hi,

Just checked my Haro. Its about 2".

Tentatively planning to get a Kona Dawg which has a non-round down-tube and the size varies:

Gary:
I plan to mount on the bottom of the down-tube to maximize the space inside the triangle available for batteries.

 

[spinningmagnets]

1.65" tall/1.45" wide, my downtube is oval in cross=section. As it moves up to the head-tube it flares wider/taller. My wife's bike is a different brand, but next to the BB, they are both the same size and shape. ladies Scwinn Sidewinder, and mine is a cheap Wal-Mart Mongoose XR-200 MTB w/front disc