Is there supposed to be an advantage to Compact Frame Geometry?



R

Ron Ruff

Guest
Mark Hickey wrote:
> Ahhh, but the seat tube/top tube/seat stay junction has to be stronger
> than on a traditional frame to handle the longer lever-arm of the
> longer (heavier) seat tube. Hence, the compact frame either uses the
> same tubes and is weaker in this area (relative to the forces
> produced) or uses heavier tubes and is as strong (also negating any
> miniscule weight reduction).


It seems like that would be true, but I haven't heard of compact frames
having a failure problem in that area and I don't think they do
anything special... at least with the metal frames.
 
J

jim beam

Guest
Colin Campbell wrote:
> I don't like the look of the compact frames, and my cynical take on them
> is that manufacturers like them because it reduces the number of frame
> sizes they need to make.
>
> A compact frame is likely a bit lighter than a "standard" frame, but
> doesn't the extra long seat post negate most of that advantage?


this is a troll. you pose a question, then answer it with your own
prejudice.

bottom line, compacts save weight [a little] and may also do a little to
address shimmy since shorter tubes are stiffer.

it's stupid when aesthetic arguments are used against technical rationale.
 
C

* * Chas

Guest
"Michael Press" <[email protected]> wrote in message
news:[email protected]
> In article
> <[email protected]>,
> "* * Chas" <[email protected]> wrote:
>
> > At various times compact frames have been popular because they are
> > slightly stiffer due to shorter tubes which is beneficial especially

in
> > short duration competition like track racing, criteriums and time
> > trials.

>
> I want to see documentation for this, because I do not
> think compact frames are stiffer. What a rider sees as
> stiffness is reduced flex at the bottom bracket under high
> pedal forces. This is almost entirely a function of the
> joints at the bottom bracket, particularly to the chain
> stays.
>
> --
> Michael Press


No need for documentation, it's a simple matter of physics and basic
engineering. I did a quick Google search on moment, angle and bicycle
but didn't find an appropriate reference example for you.

Consider this, the main "triangle" is rather an irregular 4 sided
polygon than a triangle in most bike frames. The smaller the frame size
in modern bikes, the closer they become to a triangle and the more
resistant the shape becomes to distortion.

I think that most people use bottom bracket flex as a measure of
"stiffness". Bike frames flex on a number of planes. The rear triangle
flexes up and down as well as side to side along with the bottom
bracket. The fork blade flexes up and down and to a small degree side to
side. The head tube flexes back and forth and side to side.

I watched a segment of the TDF on TV today. Every rider I saw was riding
a compact - in my opinion - frame. They were using a riding posture that
would have been limited to track or time trial racing a number of years
ago: long seat posts, low bars, short top tubes. Look at photos of Eddy
Merckx and others of his era and check out their frame sizes. Here's his
world hour record bike:

http://en.wikipedia.org/wiki/Image:EddyMerckxHourRecordBike.jpg

30 years ago, I rode a 54cm road bike with a short top tube and stem and
the seat up about 8" (200mm) and all the way back. Now I look for
comfort in a road bike and I ride more upright on 55 or 56cm frames with
more relaxed angles. It's a lot easier on my hands and butt.

Chas.
 
C

* * Chas

Guest
"waxbytes" <[email protected]> wrote in
message news:[email protected]
>
> I have short (relative to my torso) legs. It wasn't until compact

frames
> that I could get a bicycle that I could ride comfortably and still

stand
> over without singing falsetto. I like the look of traditional geometry
> but compact framing has won my vote, for strictly fit reasons. As far
> as stiffness and weight go I don't think the differences are
> significant comparing bikes of same make and material similarly
> equipped. The number of size increments made in a model of bicycle is

a
> manufacturing decision and has little or nothing to to with the merits
> of any particular frame design.
> --
> waxbytes
>


I'm in a similar situation. I'm 5'10" with a 28" inseam - long torso,
short arms and legs. I used to ride 54cm road bikes for the clearance.
Now I'm riding 55 or 56cm road frames because they are a little more
flexible and comfortable and I don't mean side to side bottom bracket
flex.

Chas.
 
Q

Qui si parla Campagnolo

Guest
Kurd wrote:
> "Qui si parla Campagnolo" <[email protected]> wrote in message
> news:[email protected]
> >
> > poppycock...it's like the shoe store only having shoes in whole
> > sizes...some may fit, some may not...I guess stuffing some tissue in
> > the toe. HOW compact, 4 size makers, say their bikes 'fit more
> > people'..well they gotta but fit fewer well.
> >

>
> I agree that it's not nessessarily better for the customers to only have 4
> sizes. It's a calculated loss for the manufactuer and the dealer to only
> have to worry about 4 or 5 sizes. Lower inventory and fewer SKUs make most
> dealers happy. Very similar comparison to shoes.


BUT, along the way, making it tougher to fit properly the, you
know-CUSTOMER!!

Not there to make bike shops or manufacturers 'happy'...there to fit
the customer, so that they ride the thing, often and for a long time.
 
Colin Campbell wrote:
> I don't like the look of the compact frames,


I don't particularly like the looks of lots of things other people like
the look of. And I'm sure the opposite is true too. Imagine if
everyone only liked the looks of blonde haired girls. The dark haired
girls would all be old maids. That would not be good.


and my cynical take on them
> is that manufacturers like them because it reduces the number of frame
> sizes they need to make.
>
> A compact frame is likely a bit lighter than a "standard" frame, but
> doesn't the extra long seat post negate most of that advantage?


I reckon seatposts are actually lighter than the seattube tubing it
replaces.

One big advantage of compact frames is a person with short legs but
long torso, my brother, can get a properly fitting frame without going
custom. Due to a childhood accident my brother ended up with short
legs. He needs a standover height of about 29" but a top tube of about
56cm. A compact such as the Litespeed Ghisallo in M/L size would fit
him perfectly because it has a low enough standover to give the 1" of
clearance and the top tube length he needs. If you look at the
horizontal top tube bikes made by Litespeed, he would need the 57cm
size for proper top tube length. But it would have 2" too much
standover height. Compact or custom is the only way to get a properly
fitting bike for him. I mention the Ghisallo model because my brother
loves light weight bike parts. I like light weight bike parts too.
But cheapness is my first love so I end up with 20-23 pound road bikes.
All horizontal top tubes of course since I hate the look of compact
frames.
 
S

SMS

Guest
Qui si parla Campagnolo wrote:

> BUT, along the way, making it tougher to fit properly the, you
> know-CUSTOMER!!


They are willing to lose an occasional customer if it saves them money
overall. In some cases they can make it fit, in a less than optimal way,
and in some cases they can up-sell the customer to a different model
that has a proper size.
 
Q

Qui si parla Campagnolo

Guest
[email protected] wrote:
> Colin Campbell wrote:
> > I don't like the look of the compact frames,

>
> I don't particularly like the looks of lots of things other people like
> the look of. And I'm sure the opposite is true too. Imagine if
> everyone only liked the looks of blonde haired girls. The dark haired
> girls would all be old maids. That would not be good.


But nobody is saying that blondes are 'better' somehow-like the compact
frame makers 'claim'.
>
>
> and my cynical take on them
> > is that manufacturers like them because it reduces the number of frame
> > sizes they need to make.
> >
> > A compact frame is likely a bit lighter than a "standard" frame, but
> > doesn't the extra long seat post negate most of that advantage?

>
> I reckon seatposts are actually lighter than the seattube tubing it
> replaces.


Reakon wrong methinks...a seatpost will all the hardware to hold the
saddle I think would weigh more than longer aluminum tubes...
>
> One big advantage of compact frames is a person with short legs but
> long torso, my brother, can get a properly fitting frame without going
> custom. Due to a childhood accident my brother ended up with short
> legs. He needs a standover height of about 29" but a top tube of about
> 56cm. A compact such as the Litespeed Ghisallo in M/L size would fit
> him perfectly because it has a low enough standover to give the 1" of
> clearance and the top tube length he needs. If you look at the
> horizontal top tube bikes made by Litespeed, he would need the 57cm
> size for proper top tube length. But it would have 2" too much
> standover height. Compact or custom is the only way to get a properly
> fitting bike for him. I mention the Ghisallo model because my brother
> loves light weight bike parts. I like light weight bike parts too.
> But cheapness is my first love so I end up with 20-23 pound road bikes.
> All horizontal top tubes of course since I hate the look of compact
> frames.


Hmmmm...light isn't necessarily expensive. We sell a really nice steel
frame, a Waterford, that weighs about 3.2 pounds....the resulting bike
is 17 pounds...

But yer right, light weight is vastly overplayed. A $3000 frame that
weighs 1.5 pounds less than a frame that costs 1/3 as much makes no
sense to me.
 
P

Pat Lamb

Guest
[email protected] wrote:
> Colin Campbell wrote:
>>
>> A compact frame is likely a bit lighter than a "standard" frame, but
>> doesn't the extra long seat post negate most of that advantage?

>
> I reckon seatposts are actually lighter than the seattube tubing it
> replaces.


It can't be by much, if that's true at all. Those big, heavy seat tubes
are maybe 1 mm thick (probably less, if the designer was concerned at
all about weight). Last time I looked at my seat post, that
featherweight thing had to have 3 mm thick walls, if not more. Let's
see, OD of the light part = ID of the heavy part. Light part 3x thicker
than heavy part. Are you sure those adjectives are where they belong??

Pat
 
P

PUSHERBOT

Guest
On 19 Jul 2006 05:47:31 -0700, "Qui si parla Campagnolo"
<[email protected]> wrote:

>
>[email protected] wrote:
>> Colin Campbell wrote:
>> > I don't like the look of the compact frames,

>>
>> I don't particularly like the looks of lots of things other people like
>> the look of. And I'm sure the opposite is true too. Imagine if
>> everyone only liked the looks of blonde haired girls. The dark haired
>> girls would all be old maids. That would not be good.

>

Compact frames, like blondes are cheaper to make....
 
Pat Lamb wrote:
> [email protected] wrote:
> > Colin Campbell wrote:
> >>
> >> A compact frame is likely a bit lighter than a "standard" frame, but
> >> doesn't the extra long seat post negate most of that advantage?

> >
> > I reckon seatposts are actually lighter than the seattube tubing it
> > replaces.

>
> It can't be by much, if that's true at all. Those big, heavy seat tubes
> are maybe 1 mm thick (probably less, if the designer was concerned at
> all about weight). Last time I looked at my seat post, that
> featherweight thing had to have 3 mm thick walls, if not more. Let's
> see, OD of the light part = ID of the heavy part. Light part 3x thicker
> than heavy part. Are you sure those adjectives are where they belong??
>
> Pat


If you are using the same seatpost in both frames, then the horizontal
frame will be heavier. So unless you cut off all excess seatpost, then
the compact frame with seatpost will be lighter. Due to getting the
post for $25, I have a 400mm post in my horizontal top tube bike. Same
uncut post in a compact frame would be lighter. I could easily cut the
post since its aluminum, but I haven't. If you're using something like
a carbon Easton EC90 post, fairly light, I don't think it comes in too
many lengths in a size like 31.6. Lets say it only comes in 400mm
lengths. Are you going to cut off the excess carbon seatpost to reduce
its weight? Or just carry the extra weight inside your horizontal top
tube's seattube? Most aren't going to cut off the carbon post.
 
M

Mark Hickey

Guest
[email protected] wrote:

>If you are using the same seatpost in both frames, then the horizontal
>frame will be heavier. So unless you cut off all excess seatpost, then
>the compact frame with seatpost will be lighter. Due to getting the
>post for $25, I have a 400mm post in my horizontal top tube bike. Same
>uncut post in a compact frame would be lighter. I could easily cut the
>post since its aluminum, but I haven't. If you're using something like
>a carbon Easton EC90 post, fairly light, I don't think it comes in too
>many lengths in a size like 31.6. Lets say it only comes in 400mm
>lengths. Are you going to cut off the excess carbon seatpost to reduce
>its weight? Or just carry the extra weight inside your horizontal top
>tube's seattube? Most aren't going to cut off the carbon post.


Ummmm, why wouldn't someone with a bike with a horizontal top tube
just buy a (lighter) 235-250mm post instead of a MTB post and be done
with it? Your logic kinda escapes me here...

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame
 
P

Patrick Lamb

Guest
On Wed, 19 Jul 2006 18:56:34 -0700, Mark Hickey <[email protected]>
wrote:

>[email protected] wrote:
>
>>If you are using the same seatpost in both frames, then the horizontal
>>frame will be heavier. So unless you cut off all excess seatpost, then
>>the compact frame with seatpost will be lighter. Due to getting the
>>post for $25, I have a 400mm post in my horizontal top tube bike. Same
>>uncut post in a compact frame would be lighter. I could easily cut the
>>post since its aluminum, but I haven't. If you're using something like
>>a carbon Easton EC90 post, fairly light, I don't think it comes in too
>>many lengths in a size like 31.6. Lets say it only comes in 400mm
>>lengths. Are you going to cut off the excess carbon seatpost to reduce
>>its weight? Or just carry the extra weight inside your horizontal top
>>tube's seattube? Most aren't going to cut off the carbon post.

>
>Ummmm, why wouldn't someone with a bike with a horizontal top tube
>just buy a (lighter) 235-250mm post instead of a MTB post and be done
>with it? Your logic kinda escapes me here...


I'm confused, too. You could build a bike with solid steel cranks and
cogs, and put on racks and fenders, but why would you if you're trying
to save a few ounces of weight with a compact frame?

Pat

Email address works as is.
 
R

Robin Hubert

Guest
[email protected] wrote:
> Pat Lamb wrote:
>> [email protected] wrote:
>>> Colin Campbell wrote:
>>>> A compact frame is likely a bit lighter than a "standard" frame, but
>>>> doesn't the extra long seat post negate most of that advantage?
>>> I reckon seatposts are actually lighter than the seattube tubing it
>>> replaces.

>> It can't be by much, if that's true at all. Those big, heavy seat tubes
>> are maybe 1 mm thick (probably less, if the designer was concerned at
>> all about weight). Last time I looked at my seat post, that
>> featherweight thing had to have 3 mm thick walls, if not more. Let's
>> see, OD of the light part = ID of the heavy part. Light part 3x thicker
>> than heavy part. Are you sure those adjectives are where they belong??
>>
>> Pat

>
> If you are using the same seatpost in both frames, then the horizontal
> frame will be heavier. So unless you cut off all excess seatpost, then
> the compact frame with seatpost will be lighter. Due to getting the
> post for $25, I have a 400mm post in my horizontal top tube bike. Same
> uncut post in a compact frame would be lighter. I could easily cut the
> post since its aluminum, but I haven't. If you're using something like
> a carbon Easton EC90 post, fairly light, I don't think it comes in too
> many lengths in a size like 31.6. Lets say it only comes in 400mm
> lengths. Are you going to cut off the excess carbon seatpost to reduce
> its weight? Or just carry the extra weight inside your horizontal top
> tube's seattube? Most aren't going to cut off the carbon post.
>


Cowards.


Robin Hubert