Sloping top tube geometry

Tim McNamara said:

In article <[email hidden]>,

jim beam said:

Qui si parla Campagnolo said:

On Apr 7, 12:16 pm, [email hidden] wrote:
> >From personal ride experience, could someone help outline whether
>
> there is a real advantage to horizontal top tubes in terms of
> weight distribution and handling as opposed to sloping tubes. Say
> I'm looking to buy a modern steel alloy frame for racing and
> riding. Would a horizontal top tube serve me well? - R.G
First recognize it was a way for Giant(the 1st) to save money on
models. Like so much else 'bike', it was foisted as some sort of
performance advantage, when of course, it is not. IF sloping top
tube, either from lowering the seat cluster or making the headtube
longer, makes the bike fit you-great idea. Mostly for those who
want standover clearance(shortish riders) or those that want a more
upright position, great ideas. For the majority of riders, it is
marketing, nothing more.

no, there's sound engineering behind it.

The designer of the Giant TCR was Mike Burrows, who also designed the
Lotus track bike that Chris Boardman rode in the Olympics. He also
designed the Windcheetah tadpole trike, the RatCatcher recumbent, and
the 8-Freight cargo bike. Burrows sold off the first and continues to
manufacture the other two. All of them are based on glued-together
frames as Burrows can't weld, apparently.

eh? that's gratuitous slander.

Quoted message said:

However, their owners are
generally quite enthusiastic and there don't seem to be reports of
problems with the bikes. Burrows was also working on a city bike made
of plastics for Giant when their relationship ended.

there's the end of the setup...

Quoted message said:

Burrows is not an engineer, and although that doesn't automatically mean
his designs are without merit it also calls into question whether you
can call it "sound engineering."

and there's the discreditation.

<snip remainder>

timmy boy, a shorter tube is stiffer than a longer tube, all other
factors remaining equal. any engineer can understand that. most
without engineering degrees understand that too. projecting /your/ lack
of engineering comprehension onto anyone without an engineering degree
is as insulting as it is wrong.

M-gineering said:

jim beam said:

Quoted message said:

> A sloping frame isn't as torsionaly stiff as a frame where the
> seatstays are attached higher up. But not by much and nothing
> sensible tubeselection can't cure.

Ok, I'm confused. Why do shorter tubes and smaller triangles result
in reduced tortional stiffness?

they're not - he mis-spoke. shorter tubes are stiffer, all other
factors being equal.

True if you would scale down the frame, but not if you use the same
wheelsize. Then the forces in the triangle and the deformation of the
seatstays increase as the triangle gets shallower and the geometry changes

that's too simplistic and assumes point geometry. that's not the case.
if you think about it logically, tubes are subject to buckling
stresses ["pre-buckled" tubes are exploited to "soften" the ride in some
bikes like cannondale], twisting stresses and the joints are subject to
all those, plus bending. shorter tubes lessen bending leverage, are
stiffer in torsion, etc., etc. and again, this is not a point geometry
exercise - it's a complex 3d model.

jim beam said:

M-gineering said:

jim beam said:

>> A sloping frame isn't as torsionaly stiff as a frame where the
>> seatstays are attached higher up. But not by much and nothing
>> sensible tubeselection can't cure.
>
> Ok, I'm confused. Why do shorter tubes and smaller triangles result
> in reduced tortional stiffness?

they're not - he mis-spoke. shorter tubes are stiffer, all other
factors being equal.

True if you would scale down the frame, but not if you use the same
wheelsize. Then the forces in the triangle and the deformation of the
seatstays increase as the triangle gets shallower and the geometry
changes

that's too simplistic and assumes point geometry. that's not the case.
if you think about it logically, tubes are subject to buckling stresses
["pre-buckled" tubes are exploited to "soften" the ride in some bikes
like cannondale], twisting stresses and the joints are subject to all
those, plus bending. shorter tubes lessen bending leverage, are stiffer
in torsion, etc., etc. and again, this is not a point geometry exercise
- it's a complex 3d model.

So what, because of all these red herrings you can ignore a cosine?

I still stand by what I wrote, and so does my 1000 pound surface plate
and dial indicators

--
---
Marten Gerritsen

INFOapestaartjeM-GINEERINGpuntNL
www.m-gineering.nl

jim beam said:

want a recommendation for "advantage"? go with an aluminum frame. i'm
a big guy and i ride in all weathers. a decent aluminum frame offers
comfort, reliability, corrosion resistance and shimmy resistance. and
yes, i'm talking from experience. i own good quality custom steel,
including a full custom della santa with a deda "baseball bat" tube set
which is about as good as you can get. and i still say, a good aluminum
frame is better. my current faves are my bianchi ev3 and my cannondale
synapse.

Mostly due to providence, we're an all Al riding family here. I bought
what I thought was a good deal (road and mtn) as did my wife (road only)
and they all happened to be Al bikes.

Yesterday, I and my wife were in an LBS because she was in the market
for new shoes. I browsed around the bicycles seeing what's changed and
what's new while she did the shoe show.

As far as I could make out, the entire upper end of bicycles was either
plastic or Ti. I do not think there was an Al bike or any metal bike not
Ti in the entire store. By upper end, I mean bikes which were retailing
above $900.

Now I'm not saying 100% there wasn't an Al bike, but I sure didn't see
one. Advising the purchase of a nicer bike in Al would seem to me to be
advising a used purchase.

-paul

Paul Cassel said:

the entire upper end of bicycles was either
plastic

What bikes are made of plastic?
--
JT
****************************
Remove "remove" to reply
Visit http://www.jt10000.com
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In article <[email hidden]>,

Tim McTeague said:

While production bikes with sloping top tube may exist to ease manufacturing
costs many custom builders use it for fit reasons. New stem and headset
styles lack any real adjustability and carbon fork steerers limit stack
height. Builders such and Serotta and Seven use sloping TTs to facilitate a
decent handlebar height. Sloping the TT by pivoting the tube in the middle,
front up a bit and back down, ensures that the bar is not too low and you
still have good stand over clearance.

I do not follow this. Would you explain more details, and perhaps
contrast with a horizontal top tube configuration?

Michael Press said:

In article <[email hidden]>,

Tim McTeague said:

While production bikes with sloping top tube may exist to ease manufacturing
costs many custom builders use it for fit reasons. New stem and headset
styles lack any real adjustability and carbon fork steerers limit stack
height. Builders such and Serotta and Seven use sloping TTs to facilitate a
decent handlebar height. Sloping the TT by pivoting the tube in the middle,
front up a bit and back down, ensures that the bar is not too low and you
still have good stand over clearance.

I do not follow this. Would you explain more details, and perhaps
contrast with a horizontal top tube configuration?

You can 'slope' the top tube by lower a horizontal toptube at the
seattube side. Same toptube length and more standover clearance for
people with a normal torso lenght and short legs. Or you can lift the
toptube at the headtube side. Same toptube lenght and longer headtube so
you can raise your handlebar without the ugly stack of spacers or a
ridiculous upward stem.

Lou
--
Posted by news://news.nb.nu (http://www.nb.nu)

Quoted message said:

jim beam said:

want a recommendation for "advantage"? go with an aluminum frame.
i'm a big guy and i ride in all weathers. a decent aluminum frame
offers comfort, reliability, corrosion resistance and shimmy
resistance. and yes, i'm talking from experience. i own good quality
custom steel, including a full custom della santa with a deda
"baseball bat" tube set which is about as good as you can get. and i
still say, a good aluminum frame is better. my current faves are my
bianchi ev3 and my cannondale synapse.

Paul Cassel said:

Mostly due to providence, we're an all Al riding family here. I bought
what I thought was a good deal (road and mtn) as did my wife (road only)
and they all happened to be Al bikes.

Yesterday, I and my wife were in an LBS because she was in the market
for new shoes. I browsed around the bicycles seeing what's changed and
what's new while she did the shoe show.

As far as I could make out, the entire upper end of bicycles was either
plastic or Ti. I do not think there was an Al bike or any metal bike not
Ti in the entire store. By upper end, I mean bikes which were retailing
above $900.

Now I'm not saying 100% there wasn't an Al bike, but I sure didn't see
one. Advising the purchase of a nicer bike in Al would seem to me to be
advising a used purchase.

In all fairness, you may not have much of a sample as shops vary greatly
in their emphases and selection. Here for example all the AL bikes are
$299, $399, $499. Mix of plastic/steel/Ti up to $3000, almost all steel
over $3000, YMMV. At other shops you might see other selections. I have
no particular point about what's good, just that shop owners display
their preferences and reflect a local market.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

John Forrest Tomlinson said:

Paul Cassel said:

the entire upper end of bicycles was either
plastic

What bikes are made of plastic?

Kestrel, Trek, Walmart. . .

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

"John Thompson" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Quoted message said:

From personal ride experience, could someone help outline whether
there is a real advantage to horizontal top tubes in terms of weight
distribution and handling as opposed to sloping tubes. Say I'm looking
to buy a modern steel alloy frame for racing and riding. Would a
horizontal top tube serve me well? - R.G

No. Sloping top tubes are intended for manufacturer and shop
convenience, not riding quality. A sloping top tube allows the
manufacturer to spec fewer frames sizes and the shops to stock fewer
frames sizes while still managing to accommodate most people.

--

John ([email hidden])

I may be missing the point here. But it seems to me that most bicycle
manufacturers, including lots of perceived high end ones, maintain the same
angles through a several centimeter size range. With the advent of very
rigid light longer seatposts and stems with angles other than -17 degrees it
is possible to achieve the same position and weight distribution with fewer
frame sizes. If you can get past the idea that a horizontal top tube is not
your aesthetic ideal what's not to like? Bike shops can "correctly" fit more
customers with fewer sizes in stock. If the manufacturer and shop win with
the unintended consequence of a win for the consumer is that a bad thing?
fBill

"Tim McNamara" <[email hidden]> a écrit:

Quoted message said:

The designer of the Giant TCR was Mike Burrows, who also
designed the Lotus track bike that Chris Boardman rode in
the Olympics. He also designed the Windcheetah tadpole
trike, the RatCatcher recumbent, and the 8-Freight cargo
bike. Burrows sold off the first and continues to manufacture
the other two. All of them are based on glued-together frames
as Burrows can't weld, apparently.

The 8Freight has a welded frame. You can clearly see the head tube welds
here:

http://www.velovision.com/mag/issue9/8freight.pdf

Quoted message said:

Burrows is not an engineer, and although that doesn't automatically
mean his designs are without merit it also calls into question whether
you can call it "sound engineering."

If he's not an engineer (and I won't ask for a definition), then does it
follow that what he does (designing, building, testing, redesigning,
rebuilding, testing), is not engineering? I'm not a mathematician, but if I
perform a valid calculation or proof, does that mean it can't be called
"sound mathematics"?

Quoted message said:

Burrows's book on bicycle design has been rather strongly criticized
for being short on specifics and long on generalizations.

That's a criticism I've made, and it's a point of view I think most
rec.bicycles.tech readers might share, but mostly I think I just wasn't the
book's target audience.

Quoted message said:

The British cycling press tends to see him as an eccentric genius.

"Genius" is a word that journalists tend to overuse. He's certainly a smart,
creative thinker who, working largely on his own, has put a number of
original designs into production.

James Thomson

"M-gineering" <[email hidden]> a écrit:

Quoted message said:

I still stand by what I wrote, and so does my 1000 pound surface
plate and dial indicators

Could you describe your tests in more detail?

James Thomson

Quoted message said:

Quoted message said:

From personal ride experience, could someone help outline whether

there is a real advantage to horizontal top tubes in terms of weight
distribution and handling as opposed to sloping tubes. Say I'm looking
to buy a modern steel alloy frame for racing and riding. Would a
horizontal top tube serve me well? - R.G

Up until last fall I was a dyed in wool traditionalist. No sloping
top tubes, no aluminum for me. It came time to replace my 1985 steel
frame (Columbus SL and SP). I decided to go with a custom built
frame. Decided also to go with aluminum (can't necessarily resist the
times forever). But I wasn't going to go for one of those new fangled
sloped geometries. There have to be limits somewhere!

The builder drew up plans with a horizontal top tube. However, poor
back flexiblity on my part meant the stack height on the steer tube
had to be rather large (verging on unsightly) or I was going to have
severe stand over issues. The builder proposed a frame with a slight
slope to the top tube which allowed him to reduce the stack height and
have adequate standover. I decided to trust the builder's judgement.
In the end I have a new bike that rides as smoothly as the steel bike
but is stiffer climbing. I've heard that almuminum can be harsh so I
went for a Reynolds Ouzo carbon fiber fork and Campy carbon fiber seat
post -- those things probably contribute to the smooth ride. The
overall combination exceeded my expecations and is a joy to ride.

The frame builder, David Tiemeyer, would have built the bike either
way -- sloped top tube or level. I'm glad I followed his
recommendation. The bike looks nice (even to a traditionalist like
me) and rides great.

In article <[email hidden]>,

Lou Holtman said:

Michael Press said:

In article <[email hidden]>,

Tim McTeague said:

While production bikes with sloping top tube may exist to ease manufacturing
costs many custom builders use it for fit reasons. New stem and headset
styles lack any real adjustability and carbon fork steerers limit stack
height. Builders such and Serotta and Seven use sloping TTs to facilitate a
decent handlebar height. Sloping the TT by pivoting the tube in the middle,
front up a bit and back down, ensures that the bar is not too low and you
still have good stand over clearance.

I do not follow this. Would you explain more details, and perhaps
contrast with a horizontal top tube configuration?

You can 'slope' the top tube by lower a horizontal toptube at the
seattube side. Same toptube length and more standover clearance for
people with a normal torso lenght and short legs. Or you can lift the
toptube at the headtube side. Same toptube lenght and longer headtube so
you can raise your handlebar without the ugly stack of spacers or a
ridiculous upward stem.

Check. Thanks.

James Thomson said:

"M-gineering" <[email hidden]> a écrit:

Quoted message said:

I still stand by what I wrote, and so does my 1000 pound surface
plate and dial indicators

Could you describe your tests in more detail?

James Thomson

clamp headtube to table, fix dropouts to axle, which can slide on the
table and rotates on an axle intersecting the front dropouts. Add 50 Nm
and try to build a stiff FS frame among other things

--
---
Marten Gerritsen

INFOapestaartjeM-GINEERINGpuntNL
www.m-gineering.nl

"Tim McNamara" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

In article <[email hidden]>,

jim beam said:

Qui si parla Campagnolo said:

On Apr 7, 12:16 pm, [email hidden] wrote:
> >From personal ride experience, could someone help outline whether
>
> there is a real advantage to horizontal top tubes in terms of
> weight distribution and handling as opposed to sloping tubes. Say
> I'm looking to buy a modern steel alloy frame for racing and
> riding. Would a horizontal top tube serve me well? - R.G

First recognize it was a way for Giant(the 1st) to save money on
models. Like so much else 'bike', it was foisted as some sort of
performance advantage, when of course, it is not. IF sloping top
tube, either from lowering the seat cluster or making the headtube
longer, makes the bike fit you-great idea. Mostly for those who
want standover clearance(shortish riders) or those that want a more
upright position, great ideas. For the majority of riders, it is
marketing, nothing more.

no, there's sound engineering behind it.

The designer of the Giant TCR was Mike Burrows, who also designed the
Lotus track bike that Chris Boardman rode in the Olympics. He also
designed the Windcheetah tadpole trike, the RatCatcher recumbent, and
the 8-Freight cargo bike. Burrows sold off the first and continues to
manufacture the other two. All of them are based on glued-together
frames as Burrows can't weld, apparently. However, their owners are
generally quite enthusiastic and there don't seem to be reports of
problems with the bikes. Burrows was also working on a city bike made
of plastics for Giant when their relationship ended.

You omitted the Half-Way single sided folder. Not a bad little bike.

Quoted message said:

Burrows is not an engineer, and although that doesn't automatically mean
his designs are without merit it also calls into question whether you
can call it "sound engineering." The TCR was designed to allow Giant to
make only three frame sizes, using seven different lengths of seat posts
and adjustable stems to fine tube the fit. One of the marketing goals
was for parents to be able to have the same bike fit their growing child
for a number of years. Manolo Saiz and ONCE adopted the bike for racing
but required that Giant make seven different sizes for their team. The
bikes seemed to work well enough for Laurent Jalabert and Alex Zülle.

The 3 sizes thing was quite possibly to make it more cost-effective to tool
for monocoque composite frames. remember the MCR?

http://www.businessweek.com/1998/02/b3560041.htm

Quoted message said:

Burrows's book on bicycle design has been rather strongly criticized for
being short on specifics and long on generalizations. The British
cycling press tends to see him as an eccentric genius. I think he's
rather interesting, seemingly eccentric and perhaps not a genius per se
but willing to think outside the usual.

The book is a little lacking in depth. RBT types are not really the target
audience.

Quoted message said:

The question is whether there is real benefit in terms of performance.
This remains speculative at best.

John Forrest Tomlinson said:

Paul Cassel said:

the entire upper end of bicycles was either
plastic

What bikes are made of plastic?

Any of the 'carbon' bikes are fiber with resin or plastic.

A Muzi said:

In all fairness, you may not have much of a sample as shops vary greatly
in their emphases and selection. Here for example all the AL bikes are
$299, $399, $499. Mix of plastic/steel/Ti up to $3000, almost all steel
over $3000, YMMV. At other shops you might see other selections. I have
no particular point about what's good, just that shop owners display
their preferences and reflect a local market.

Of course, I've not sampled all LBS's but I have two. Also I didn't
really examine closely all bikes, but I did have about an hour to look
at the racks. Then too, it may be a local thing. LBS's are, well, local,
and the local prejudice may be toward carbon / plastic bikes instead of
Al or steel.

I'm only discussing adult road bikes. The mtn bikes had some metal (Al
or steel?) and the kids bikes were probably all steel. I was somewhat
surprised at what to me is the sudden emergence of all this carbon way
down in the price ranges.

-paul

jim beam said:

Qui si parla Campagnolo said:

Quoted message said:

>From personal ride experience, could someone help outline whether

Quoted message said:

Quoted message said:

there is a real advantage to horizontal top tubes in terms of weight
distribution and handling as opposed to sloping tubes. Say I'm looking
to buy a modern steel alloy frame for racing and riding. Would a
horizontal top tube serve me well? - R.G

Quoted message said:

First recognize it was a way for Giant(the 1st) to save money on
models. Like so much else 'bike', it was foisted as some sort of
performance advantage, when of course, it is not. IF sloping top tube,
either from lowering the seat cluster or making the headtube longer,
makes the bike fit you-great idea. Mostly for those who want standover
clearance(shortish riders) or those that want a more upright position,
great ideas. For the majority of riders, it is marketing, nothing
more.

no, there's sound engineering behind it. hopefully, there's no argument
about a shorter tubes being lighter. torsional benefits may be less
noticeable, but are still real. standover benefits are not disputable.
and now that we have better seat post materials [carbon], compact
geometry is much more viable - compared to dodgy old cast aluminum posts
at any rate.

As I've said, it is a fit issue. 'Shorter tubes being lighter', yep,
except that a 400mm+ seatpost is heavier than a 200mm one. Compact
geometry is an answer to a not asked question by cyclists. One asked
by bean counters and marketeers but not by road cyclists.

Paul Cassel said:

A Muzi said:

In all fairness, you may not have much of a sample as shops vary
greatly in their emphases and selection. Here for example all the AL
bikes are $299, $399, $499. Mix of plastic/steel/Ti up to $3000,
almost all steel over $3000, YMMV. At other shops you might see
other selections. I have no particular point about what's good, just
that shop owners display their preferences and reflect a local
market.

Of course, I've not sampled all LBS's but I have two. Also I didn't
really examine closely all bikes, but I did have about an hour to look
at the racks. Then too, it may be a local thing. LBS's are, well,
local, and the local prejudice may be toward carbon / plastic bikes
instead of Al or steel.

I'm only discussing adult road bikes. The mtn bikes had some metal (Al
or steel?) and the kids bikes were probably all steel. I was somewhat
surprised at what to me is the sudden emergence of all this carbon way
down in the price ranges.

Carbon frames lend themselves to mass production; set up the mould tools and
churn out in high volume.

Given the premium price that anything which is carbon can attract in road
cycles, its not surprising that makers are using it.

- Nigel

--
Nigel Cliffe,
Webmaster at http://www.2mm.org.uk/