View Full Version : bicycle design
gt6267a
10-19-2006, 10:04 AM
The thread on forks and custom frames has me thinking about bicycle design in general. DK put forth some great ideas about forks and their impact on a bicycle. He also stated that these are just pieces of the puzzle and I am interested to hear more about the big picture including trail, front and center, and other factors that are important when designing a bicycle.
Without trying to muddle the discussion, or maybe just give a little direction that is of specific interest to me: my Serotta fit points me to a bicycle that is 53 x 53. When I look at purchasing a second bike, almost all non-custom bicycles are around 53 x 54.5. I am told the 53 x 54.5 setup is to get the correct front and center. I am interested to know what changes and/or sacrifices are made to make a 53 x 53.
Thanks and regards,
Keith
obtuse
10-19-2006, 10:13 AM
top tube measurements are almost always a result of setback, front center, seat tube length and the like on a properly designed race bike. it should not be the measurement that determines the rest.
obtuse
Grant McLean
10-19-2006, 10:38 AM
Obtuse speaks the gospel truth.
Contact points, contact points, contact points, contact ponts, contact points.
Are what matter for fit. The placement of the wheels is the magic for
the framebuilder wizards.
g
Jeff Weir
10-19-2006, 10:40 AM
How much does that bike weigh?
Grant McLean
10-19-2006, 10:44 AM
How much does that bike weigh?
it depends on your size.
:)
g
sspielman
10-19-2006, 10:50 AM
it depends on your size.
:)
g
...a Colnago C-Nothing, ATMO
fiamme red
10-19-2006, 11:00 AM
http://www.geocities.com/verdrahciretop/invisibike.html
atmo (http://www.atpm.com/9.10/images/design-gestalt.gif)
David Kirk
10-19-2006, 11:20 AM
Me thinks Grant nailed it. I've always (well not always but for the last 20 years anyway....before that I had other things on my mind..... like candy) taken the 3 contact points and suspended them in space and then put the wheels under the rider where they need to be to give the proper handling and then let that generate things like top tube length and the such. There are no charts or tables or established etched in stone values for for front center or BB drop. Every design should be looked at as a whole from the beginning and everything should balance.
To better answer your specific question...what is done to give a bike with a 53cm top tube enough front center? Mainly the head angle will be relaxed and the fork rake increased to match the head tube. It's a win-win thing in that the shallow head angle will need more fork rake to maintain a given trail AND it makes the front center longer at the same time.
Kapeesh?
Dave
Grant McLean
10-19-2006, 12:46 PM
atmo (http://www.atpm.com/9.10/images/design-gestalt.gif)
sweet.
g
nick0137
10-19-2006, 12:51 PM
Ok. Guess the rider. Last one's Ale-Jet for sure. Anyone spot the others?
sspielman
10-19-2006, 01:04 PM
Ok. Guess the rider. Last one's Ale-Jet for sure. Anyone spot the others?
The first one is Grant Peterson.....Definitely....
nick0137
10-19-2006, 01:30 PM
Is the 2nd one a Robbie McEwen uphill-wheelie-special being made by Ridley for when he goes over the top of an HC climb in next year's Tour?
The first one is Grant Peterson.....Definitely....
No way - Grant's always been a STRONG advocate of lots and lots of saddle setback for almost everyone. He does some bikes with 71.5 degree seat tubes. The bars might be about right, but not the seat.
-Ray
Geoff
10-20-2006, 08:39 AM
taken the 3 contact points and suspended them in space and then put the wheels under the rider where they need to be to give the proper handling and then let that generate things like top tube length and the such. There are no charts or tables or established etched in stone values for for front center or BB drop. Every design should be looked at as a whole from the beginning and everything should balance.
Dave
THis seem exactly right to me. My question is doesnt this largely depend on weight distribution of the rider? And if so what is teh best way to determine a riders center of gravity. Also what is the ideal front/rear wheel weight distribution?
G
J.Greene
10-20-2006, 09:35 AM
Obtuse speaks the gospel truth.
Contact points, contact points, contact points, contact ponts, contact points.
Are what matter for fit. The placement of the wheels is the magic for
the framebuilder wizards.
g
Your missing something here grant...The bike also needs to be geared a certain way, determined by if it is a planing or non planing bicycle. Not to mention that 45c tires on 650b wheels should be used because they roll better. Or so says my favorite french tabloid. :D
JG
who is just kidding
mosca
10-20-2006, 04:47 PM
it becomes a simple matter of connecting them all together.
Of course, extensive finite element analysis is required to optimize the load paths and maximize planing.
slowgoing
10-20-2006, 05:06 PM
This is the funniest thread I've read in a long time.
taz-t
10-20-2006, 05:32 PM
Can I change my name to 'Slicky-G' ?
Taz-T
whippettanker
10-20-2006, 08:03 PM
Obtuse speaks the gospel truth.
Contact points, contact points, contact points, contact ponts, contact points.
Are what matter for fit. The placement of the wheels is the magic for
the framebuilder wizards.
g
Whoa, that's kinda technical. Can you break it down for non-engineers in the crowd.
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