Sloping top tube geometry

[jim beam]

Tim McNamara wrote:
> In article <[email protected]>,
> jim beam <[email protected]> wrote:
>
>> Qui si parla Campagnolo wrote:
>>> On Apr 7, 12:16 pm, [email protected] 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.

> 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...

>
> 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.

 

[jim beam]

M-gineering wrote:
> jim beam wrote:
>
>>>> 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.

 

[M-gineering]

jim beam wrote:
> M-gineering wrote:
>> jim beam wrote:
>>
>>>>> 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

 

[Paul Cassel]

jim beam wrote:

>
> 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

 

[John Forrest Tomlinson]

On Sun, 08 Apr 2007 14:04:11 -0600, Paul Cassel
<[email protected]> wrote:

> 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
****************************

 

[Michael Press]

In article <[email protected]>,
"Tim McTeague" <[email protected]> wrote:

> 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?

 

[Lou Holtman]

Michael Press wrote:
> In article <[email protected]>,
> "Tim McTeague" <[email protected]> wrote:
>
>> 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)

 

[A Muzi]

> jim beam wrote:
>> 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 wrote:
> 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

 

[A Muzi]

John Forrest Tomlinson wrote:
> On Sun, 08 Apr 2007 14:04:11 -0600, Paul Cassel
> <[email protected]> wrote:
>
>> 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

 

[Bill]

"John Thompson" <[email protected]> wrote in message
news:[email protected]...
> On 2007-04-07, [email protected] <[email protected]> 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
>
> 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 protected])

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

 

[James Thomson]

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

> 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

> 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"?

> 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.

> 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

 

[James Thomson]

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

> 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

 

[stevek]

On Apr 7, 2:16 pm, [email protected] 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

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.

 

[Michael Press]

In article <[email protected]>,
Lou Holtman <[email protected]> wrote:

> Michael Press wrote:
> > In article <[email protected]>,
> > "Tim McTeague" <[email protected]> wrote:
> >
> >> 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.

 

[M-gineering]

James Thomson wrote:
> "M-gineering" <[email protected]> a écrit:
>
>> 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

 

[Skippy]

"Tim McNamara" <[email protected]> wrote in message
news:[email protected]...
> In article <[email protected]>,
> jim beam <[email protected]> wrote:
>
>> Qui si parla Campagnolo wrote:
>> > On Apr 7, 12:16 pm, [email protected] 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.

>
> 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


>
> 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.

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

 

[Paul Cassel]

John Forrest Tomlinson wrote:
> On Sun, 08 Apr 2007 14:04:11 -0600, Paul Cassel
> <[email protected]> wrote:
>
>> 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.

 

[Paul Cassel]

A Muzi wrote:

>
> 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

 

[Qui si parla Campagnolo]

On Apr 8, 10:00 am, jim beam <[email protected]> wrote:
> Qui si parla Campagnolo wrote:
>
> > On Apr 7, 12:16 pm, [email protected] 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. 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.

 

[Nigel Cliffe]

Paul Cassel wrote:
> A Muzi wrote:
>
>>
>> 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/