A question on bike frame design
09-11-15, 08:23 AM
#1
Senior Member
Thread Starter
Join Date: Jun 2008
Location: Central NJ
Posts: 576
Bikes: MGX MTB, Fuji Supreme, Miyata 90 and a Trek 700 in the works
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 16 Post(s)
Likes: 0
Liked 2 Times
in
2 Posts
A question on bike frame design
In the old days bike frames had a slim down tube.
Bikes still worked as expected and I am not aware of bikes prone to fail at down tubes due to tube diameter.
Then why most newer bikes are built with very large diameter or flattened profile down tubes?
Is the added rigidity etc. really that beneficial over the slim tube down tube?
I find the fat down tubes really ugly.
Bikes still worked as expected and I am not aware of bikes prone to fail at down tubes due to tube diameter.
Then why most newer bikes are built with very large diameter or flattened profile down tubes?
Is the added rigidity etc. really that beneficial over the slim tube down tube?
I find the fat down tubes really ugly.
09-11-15, 08:26 AM
#2
Senior Member
Join Date: Jun 2013
Location: Bozeman
Posts: 4,094
Bikes: 199? Landshark Roadshark, 198? Mondonico Diamond, 1987 Panasonic DX-5000, 1987 Bianchi Limited, Univega... Chrome..., 1989 Schwinn Woodlands, Motobecane USA Record, Raleigh Tokul 2
Mentioned: 25 Post(s)
Tagged: 0 Thread(s)
Quoted: 1131 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
Today we use lighter materials which require thicker walls and bigger tubes to have the same strength/rigidity. Steel did not need that.
09-11-15, 09:02 AM
#3
Banned
actually things happened with how and where things got made like steel to aluminum ,
and manufacturing went overseas..
the Taiwan Contract companies spent their Profits on making things better and faster, for less ,
and the brand importers took advantage of those techniques, sending designs there ..
Hydroforming as a way to shape frame tubes , is fairly recent , in the Bike Frame making. It works especially well in Aluminum .
and manufacturing went overseas..
the Taiwan Contract companies spent their Profits on making things better and faster, for less ,
and the brand importers took advantage of those techniques, sending designs there ..
Hydroforming as a way to shape frame tubes , is fairly recent , in the Bike Frame making. It works especially well in Aluminum .
09-11-15, 09:03 AM
#4
Senior Member
There's a school of thought in bike design that a stiffer frame will enhance power transfer from human to road. The larger junction at the BB/DT join isn't so much for structural reasons of keeping the bike together, but mainly to stiffen the frame up.
09-11-15, 04:52 PM
#5
Senior Member
Join Date: Feb 2012
Location: Rochester, NY
Posts: 18,075
Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Stewart 650B ATB
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4201 Post(s)
Liked 3,859 Times
in
2,307 Posts
Agree with the above replies but will add the marketing aspect. Bigger is better as started in large number by the ATB bike advent. Very soon ATB bike design led road bike expectations to the masses. As to if the larger diameter or shaped tubes are of real performance advantages- you'll get different arguments from different people. I feel that a bike can be too stiff for efficient long distance riding. Andy.
09-11-15, 07:38 PM
#6
Senior Member
Join Date: Apr 2009
Location: New Rochelle, NY
Posts: 38,712
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Mentioned: 140 Post(s)
Tagged: 1 Thread(s)
Quoted: 5781 Post(s)
Liked 2,577 Times
in
1,428 Posts
Agree with the above replies but will add the marketing aspect. Bigger is better as started in large number by the ATB bike advent. Very soon ATB bike design led road bike expectations to the masses. As to if the larger diameter or shaped tubes are of real performance advantages- you'll get different arguments from different people. I feel that a bike can be too stiff for efficient long distance riding. Andy.
Fashion and marketing are as important as engineering in modern frame design, and the large flattened section of downtubes is a case in point.
Frames already have more than enough rigidity within the plane because of the diamond truss configuration. Tubes with a large cross section in this direction are already is use with single tube frames, such as many folding bikes, and "Y" frame mtn bikes.
If BB or lateral rigidity were the goal the tube section across the plane (fatter crosswise) would be used. In fact, we often see both seat and down tubes flattened in that direction where they meet the BB.
So, one can take a few minutes to eyeball oval or flattened frame tubes, and consider the effects and decide for themselves if it's science or marketing (or often some of both).
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
09-11-15, 08:08 PM
#7
Senior Member
Join Date: Aug 2005
Location: Pittsburgh, PA
Posts: 33,656
Bikes: '96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '20 Surly Midnight Special, All are 3x10. It is hilly around here!
Mentioned: 39 Post(s)
Tagged: 0 Thread(s)
Quoted: 2026 Post(s)
Likes: 0
Liked 1,096 Times
in
742 Posts
Has the increasing emphasis on stiffness for it's own sake gone too far? Probably so for most riders.
09-11-15, 08:15 PM
#8
Senior Member
Go Cannondale.......smaller downtubes. 
