43 replies to this topic

[MclarenF1]

Does anyone know why CFRP frames are not used in these motorcycles? I had heard that the frames are designed with intentional flex in certain areas, why could the same not be done with CF?

[imaginesix]

I didn't think CFRP was used in any racing motorcycle. Am I wrong?

[MclarenF1]

I don't know of any team using CF but some have experimented with them . "Biaggi tested a carbon framed/swingarmed Priller 250 and couldn't get it to handle properly , so they went back to Al." Why, exactly, they chose not to pursue this option is a mystery to me however.

[moog101]

Yamaha had a CF frame GP500 for Rainey (?) I believe. It suffered from high speed chattering in fast corners. This problem has since been attrbuted to it being too stiff. It seems that the suspension cannot react to high frequency movements, and transfers them to the frame without absorbing them. An ally frame does this by flexing, a CF frame does not. The result is a loss in rider confidence and reduced contact patch at each tyre.

I reckon it is only a matter of time before they get it working, they probably would have already if they needed too, but ally frames are a reliable, known quantity already, and work well too.

[desmo]

IIRC Honda mucked about with the idea for a time, perhaps as part of the NR500 project and I believe the ELF 500GP bike of the '80s with the novel center hub front suspension, the tank under the engine and the expansion chambers routed above did as well. And I think the teams had a bit of a time figuring out welding sequences and heat treatments for the early Al alloy frames before they would emerge from the process dimensionally resembling the blueprints. Al alloys don't like to be cold set.

I think that when the bike encounters surface irregularities whilst really heeled over the angle the loads are fed into the suspension prevent it from working as designed to some extent and that some designed in "lateral" flex in the frame translated to better tire contact being maintained under those conditions. Sounds dodgy to me, but how do you design a suspension to be ideal for both straight up and heeled over given the quite differing forces acting upon it under those conditions?

[Ben]

There were some fully CF monocoque bikes in the eighties, the Heron Suzuki springs to mind.

I don't think they were ever a significant improvement.

Ben

[AS110]

The Britten didn't seem to have many problems,not a GP bike of course,but still leading edge technology at the time.

www.britten.co.nz

[Bluehair]

Desmo raises a very interesting question. Were it not for the weight and bulkiness, I would suggest some sort of a swing arm within a swing arm, to deal with multi-directional dampering. However, I don't see why the swing arm can't remain as is, and other parts of the frame be made from carbon based materials. Every year, street bikes claim to be x-percent stiffer, so carbon fiber seems to be a nice solution if that is the desired direction. Vibration must be the drawback.

[RJL]

From what I've read, I'd say that Desmo has it pretty much right. Once the bike is leaned over far enough, road surface iregularites are fed into the suspension at such an extreme angel that it cannot do it's intended job. Honda was the first to go to "tuned flex" style frames I believe. I also think that, in time, those clever engineers will find a better way of dealing with this issue than flexible frames. Perhaps some sort of controlled suspension motion ACROSS the motorcycle, in addition to the existing stuff? I dunno, just a thought. Maybe a frame material with superior damping properties? Whoever finds the way will immediately go quicker than the others, so they'll emulate him.

[rdrcr]

Just took a glance at the Britten... Note the composite fabrication includes Kevlar to give the chassis and other components a bit of flex. This chassis is probably hand done in sections and then laminated together and bagged. I've never seen one, but it must be a beautiful piece.

desmo and Moog are on the money when it comes to the handling characteristics relating to stiffness of the chassis. I theorize that most manufactures haven't constructed an all composite chassis and using them currently, because of these vibration problems and the overly stiff characteristics they have. The flex and torsional attribute that an aluminum chassis naturally exhibits are more cost effective to date.

I don't think it will be too much longer though before we start to see the CF components, swing arms and the like and perhaps entire chassis in the next few years. The R & D of tooling, setup and acquisition of a proper autoclave are the biggest expenses associated with such a project, IMO.

[desmo]

When I first heard about the problem of "excessive" lateral stiffness in GP500 frames years ago, I did some drawings of a design with a Belleville spring mounted axially on each side of the swing arm bearing set and a lateral damper to try to provide some degree of tunability to this phenomenon, but it seemed like a lot of bother for perhaps a questionable result so I gave up and threw them out. I am quite sure I am not the only one who thought of a similar "solution."

[MclarenF1]

My roommate is friends with Dr. Rob Tuluie, he designed his own race bike which you can see by following this link.
http://venus.13x.com...r00/tularis.htm
Anyway, the response he gave as to why teams do not use CF is because the overall weight savings are minimal (about 2 lbs) once all the aluminum inserts are installed. And that if and when the rider crashes the bike it is very difficult to find/repair any delamination damage. Whereas an aluminum frame can easily be x-rayed for any cracks. He did not say much about the stiffness of the chassis other than that a Ducati race bike (he wouldn't say what type or for which team) is extremely stiff from the rear engine mount back, and flexible by the headstock.

[imaginesix]

Originally posted by MclarenF1
My roommate is friends with Dr. Rob Tuluie, he designed his own race bike which you can see by following this link.
http://venus.13x.com...r00/tularis.htm
Anyway, the response he gave as to why teams do not use CF is because the overall weight savings are minimal (about 2 lbs) once all the aluminum inserts are installed. And that if and when the rider crashes the bike it is very difficult to find/repair any delamination damage. Whereas an aluminum frame can easily be x-rayed for any cracks. He did not say much about the stiffness of the chassis other than that a Ducati race bike (he wouldn't say what type or for which team) is extremely stiff from the rear engine mount back, and flexible by the headstock.

Ahhhh yes.
The truth is like an drug, and this is my hit for the day. Thanks McLarenF1.

[AS110]

Thanks mate that was delicous

Now I'm going to curl up in a corner for some serious digestion.

[desmo]

I'd read that article a couple of years ago, and was very much impressed with the design and the process of ideating and developing the concept from scratch. Any more recent news on it's racing results?

[MclarenF1]

I honestly don't know too much about it's racing success/failures. I will ask my roomate about it if I ever go home. (at school too much)

[scarbs]

Successful Carbon framed bikes I can recall are...

Armstrong GP 250/350 Rotax from the 80's, Had a carbon twin Beam frame and Cantilever swing arm, Scottish Rider Niall McKenzie rode it with some success.

Cagiva GP 500 from the 90's, had a full carbon twin beam frame and swing arm, rider Randy Mamola noted the frame was "too stiff" and the bike suffered from excessive front end chatter, he bike was campaigned for several season and hence some of the handling issues must have been resolved.

The Heron Suzuki GP500 (already mentioned) had a monocoque type frame and was developed from an alloy honeycomb version and later full carbon version (more like a twin beam frame) was built and never raced as the team collapsed.

Aprilia GP250 run with a "huge" carbon swing arm and a structural carbon rear seattail unit.

Hejira, a small British firm have made some Carbon frames for Club racing (mainly for single cyl' bikes I believe)

In general the GP teams have not developed bike with the approach of F1 or car racing teams, engines are the key area for development, with geometry coming second and other design issues are not given a large amount of time. The suspension is looked after by the damper manufacturers. Often smaller specialist manufacturers (e.g. Harris) have made frames the rider preferred or the team have resorted to previous seasons frames for better handling. the teams use carbon as a general material and rarely for structural purposes, there's still a lot of fiddly alloy and steel work holding bits on or together (fairing, airbox and radiator mounts).
The quick to build-easy to fix and modify factor is quite large in MotoGP, major geometry changes (headstock angle, swing arm position) occur during the season this is easier if rewelding alloy, re moulding a carbon frame would be costlier in both money and time.

[Timm]

Here's some info and pictures of the CFRP arm on the Team Roberts machine.........

http://www.grandprix...ft/ftpw013.html

[D. Heimgartner]

I was watching the Donnington race today and began wondering what type of chassis (err, I mean frame) these bikes have. Are they steel/aluminium tubes or a carbon fibre space frame? I know this sort of question should be in the Technical Forum... but alas...



Speaking of frames, did anybody see that hottie that was holding the umbrella for... Jeremy Williams, I believe. She was blond and had on a black, skin tight top that had only one strap, which went over her left shoulder, and drooped very far down on her right breast...




There! That should assure this thread a continued placement in the RC.

[klthomas]

This is taken from Aprilia's website about their motogp bike:

Engine type:
four stroke, three cylinders in line; four-valves per cylinder timing with pneumatic return; sealed circuit liquid-cooled; forced lubrication with extraction pump and dry crankcase; aluminium alloy engine block and cylinder head/cylinders.

Displacement:
990cc

Max power/rpm:
more than 220 HP at more than 15,000 rpm

Fuel injection/ignition:
Aprilia digital electronic injection/ignition system,

Gear box:
six-ratio aluminium alloy box with front couplings, completely removable

Frame:
aluminium dual beam frame

Suspension:
upside-down Öhlins fork, 42 mm dia., double hydraulic regulation Aluminium or carbon swingarm with differentiated design arms APS progressive system with fully adjustable Öhlins shock absorber

Brakes:
Brembo. Front: double carbon disk, 290/320 mm diametre.
Rear: single disk, 218 mm diametre

Wheels:
in magnesium alloy or carbon, 16.5”/17” front and 16.5” rear

Dimensions:
weight more than 135 kg,
length 2,030 mm +/- 30 mm, wheelbase 1,410 mm +/- 30 mm

Tank capacity:
24 litres

[D. Heimgartner]

I suppose the governing body doesn't allow carbon fibre frames?

[nicholasc]

I can't remember where I read it - probably in an old atlas thread - that CF is too stiff for the bikes and transmits too much vibration. The flex in an alum. frame helps with steering. Motorcycle frame building is still a bit of a black art, much the same as an F! chassis, as the likes of JAG and BAR have discovered...

[Dynojet]

Just a think:

Why isn't there any carbon fiber and honeycomb motorcycle frame? Neither on motorsports or expensive exotics?

[desmo]

Motorcycles are never off-topic here!

I've merged this thread with an earlier one on the same topic.

[MoMurray]

I was a mechanic on the Silverstone Armstrong 250GP team in the mid eighties. The team used beautiful carbon fiber honeycomb twin spar chassis with a swinging arm of similar construction. Aboslutely a beautiful piece. It was designed by Mike Eatogh who I believe now works for Harley Davidson (consultant at least). It was very light and very rigid in all the right areas. We used Rotax 256 tandem twin engine which was not up to the challenge of the factory Yamaha and Honda engines that had just arrived. The team also had little in the way of a development budget and so were not able to take the concept or the engine powering it to the next level. Donnie MacLeod and Niall McKenzie were the riders and finished first and second IIRC in the British championship but GP results were more difficult to come by. The best result for the team using that chassis was a second place at Spa in 1986 (MacLeod). I was the #2 mechanic on MacLeods bike and my opposite number on the McKenzie bikes was a big Geordie known as Crusty. Geoff Crust went on the become team manager for the Marlboro Yamaha MotoGP team running Biaggi.

One little interesting tidbit is that while the frames were very strong in certain planes they were very weak in others. This was accounted for in design and was not a problem under normal running. However, the side fairing mount was a simple half inch by four inch aluminum tube. Unfortunately, even just the weight of the bike was enough to push this tube through the side of the frame spar and so even a slow speed get off often had the annoying and very time consuming effect of destroying a chassis. We had a lot of late nights... It was fun though.

Mo.

[LandOfSnow]

I've heard rumours that Ducati GP bikes (a steel trellis frame) have removable tubes to adjust the chassis flex...

[jgm]

Actually it puzzles me as to why racing bikes have frames at all. If you're designing the engine / transmission unit from scratch why not incorporate integral attachments for the steering head at one end and the swinging arm at the other end. The engine / transmission then becomes the frame /chassis - like F1. I know this has been tried on a few bikes but nobody seems to have perservered with it.

[MRC]

Doesn't the new Ducati MotoGP bike constructed this way? I was reading through cycle world or something like that and they had an article on it. They said there was a bracket connecting the steering head to the engine and then the swing arm attached right to the engine.

[MclarenF1]

In these pictures you can see a red trellis structure. It is difficult to determine how the swing arm attaches to this structure.
http://www.sportbike...icture_ID=45184
http://www.sportbike...icture_ID=41280

[Mark Beckman]

Originally posted by jgm
Actually it puzzles me as to why racing bikes have frames at all. If you're designing the engine / transmission unit from scratch why not incorporate integral attachments for the steering head at one end and the swinging arm at the other end. The engine / transmission then becomes the frame /chassis - like F1. I know this has been tried on a few bikes but nobody seems to have perservered with it.

Bikes need aprox 3mm vertical flex/movement between the headstock and swingarm pivot.
The manor and position of this flex is critical to handling and is a black art as much as a science. Lateral movement is a no-no and this is why today the wide twin spar alloy frame with massive swingarms is the most common base although obviously Ducati makes the trellis tubular frame work to their requirements.
Engine torque has an effect on the vertical frame flex to a degree that engine repositioning movements as small 1mm can make or break a bikes handling and often does and this is one of the reasons that a perfect handling frame goes 'off' during the course of a season as more torque is found thru engine development.
CF frames are too stiff, simple as that.

[desmo]

Anyone care to speculate why motos might require a degree of vertical compliance in their connection between the headstock and swing arm pivot? I can't see it really. Wouldn't it necessarily be more advantageous to have an essentially rigid connection with an adjustable degree of sprung and damped compliance assuming one understands why such compliance is useful?

Secondly how can a catagorical blanket statement such as, "CF frames are too stiff, simple as that." hold true given that a CFRP, like an Al or steel for that matter, frame can within reason essentially be as stiff or flexible as the designer desires it to be?

[Wuzak]

Here is the Britten V1000







The Britten was radical in a couple of ways.

Firstly, the bike did not have telescopic forks on the front suspension. It used twin wishbones with a coil over shock.

The engine was a fully stressed frame member. A carbon fibre head stock bolted to the engine to mount the steering and front suspension.

Britten lists its chassis dat as:

Fully stressed engine with ducted under-seat radiator. Top chassis, girder & swing arm all constructed in carbon/kevlar composites.

Front Suspension: double wishbones with girder.

Rear Suspension: swing arm with adjustable three bar linkage.

Shock Absorbers: Ohlins

Rake: adjustable

Trail: adjustable

Front Wheel: 3.5" x 17" in-house carbon composite

Rear Wheel: 6.0" x 17" in-house carbon composite

Front Brakes: Twin 320mm cast iron rotors with opposed 4-piston Brembo callipers

Rear Brakes: 210mm rotor with opposed piston Brembo calliper

John Britten, the creator of this bike, died in 1995 from cancer.

http://www.britten.co.nz/


Also, Ducati has used the engine in their bikes as a stressed member for many years. Until the latest bikes (the 999,998, and all their predecessors), the rear suspension mounted on the back of the gearbox/engine unit. Now, I believe, there is actually some frame there.

[Wuzak]

The seat unit is, I believe, self supporting, not requiring a separate support frame.

The spring/shock at the front of the engine is the rear suspension unit, and is operated through links.

The fuel tank is beneath the engine.

Also, I have read that the Honda NR500 GP bike from the early '80s, the last of the 4 stroke 500s from Honda, was a monocoque chassis.

[Wuzak]

Just a thought........

Could the apparent requirement for some flex in a motorcycle's chassis be a compensation for the suspension system used?

In particular, the front suspension with the telescopic forks?

If the frame is too stiff, would that cause problems with the forks??

[Greg Locock]

I'm following this with interest, without being able to add much.

In cars we generally aim to have as much stiffness in the body as we can get away with - I can't remember being asked to reduce the body stiffness, or for that matter a bush stiffness, by the Steering and Handling people.

So, for some reason they want an (effectively) undamped compliance between the two sets of hardpoints in the vertical direction.

My first thought is that the front forks are not truly vertical, so this may provide a specific vertical compliance to allow for vertical motion at the contact patch. I don't like this as an explanation, since the telescopic will happily handle vertical deflection, it just gives you some longitudinal motion for free. Car suspensions do the same, to reduce impact harshness.

My second thought is that the resonant frequency associated with this is likely to be quite high. Perhaps it is designed to cope with high frequency inputs that the telescopics can't handle, as by then the deflections are so small that there is too much stiction for them to break free.

There is a directly analogous issue on cars, that is why production car shocks have rubber at each end (usually) - this allows HF to be absorbed/controlled in the rubber, with the shock locked, while LF is absorbed/controlled in the shock in the normal fashion.

Now, this is a dangerous approach for a shock absorber - by softening its mounting points you have DEGRADED its ability to handle small inputs - the rubber moves instead of the shock. Careful tuning of the rubber part is required. The last time I did this was a long time ago. John Miles was the driver and evaluator, I was the techno-boy in the passenger seat!

Given the inherent problems with putting vertical compliance into the telescopics while retaining any steering precision, I suspect this is part of the answer at least.

[Wuzak]

Just looking at the Britten picture again, it appears that he lower wishbone, at least, is connected directly to the engine.

[12.9:1]

Good discussion !
I'm leaning toward the idea that Moto GP and F1 are more alike than we had thought.
In that; At the limits of traction or maximum tire loading, they both generate and must deal with powerful - tire, suspension, and chassis oscillations.
This is well known in Moto GP and may be one of those "dark secrets" of F1, certainly of tire manufactures.

To illuminate the dynamics involved, mental as well as vibrational, at least on the moto side -

Here another fine essay by Kevin Cameron, pub- CYCLE WORLD dec. 2002


Flexi-Flyers

Kevin Cameron

FLEXIBLE VEHICLE STRUCTURES DE-
form under operating loads. An example
is found in the Space Shuttle's controlled
rate of main engine cut-off. At eight-
and-a-half minutes offlight, the engines
are operating at 65 percent thrust to
limit Orbiter acceleration to 3 g. Veloci-
ty is close to 26,000 feet per second.
Instead of simply shutting down the
turbopumps supplying propellants to
the main engines, the liquid oxygen
flow is reduced at a controlled rate, to
limit thrust reduction to a rate of
change of 700,000 pounds per second.
It takes roughly 1.3 seconds to reach
zero thrust at this rate.
Why bother with such a complexity?
The answer is that the thrust of the three
main engines puts considerable strain
into the Orbiter's structure; that is, it de-
flects it like a spring, storing significant
energy in the strained parts. If all that
stored energy were released at once, the
structure would "ring," or vibrate, pos-
sibly damaging itself. The controlled
rate of thrust reduction allows natural
damping within the structure to absorb
this energy harmlessly.
Consider a racing motorcycle. For-
mer roadracer Dale Quarterley de-
scribed his Kawasaki Superbike of the
early 1990s as needing restraint during
hard maneuvering.
"They make a big deal about chas-
sis stiffness today," he told me then,
"but when you ride them hard, you
can feel all the parts winding up and
unwinding,"
He said the 750's chassis was so flex-
ible that you had to wait for it to finish
"unwinding" from one move before you
could start another-or there would be
handling trouble.
Think of what this means. When the
rider applies steering pressure on the
bars to make the machine roll over for a
turn, first the front tire's tread starts to
lay down footprint in the new direction.
As it does so, it generates stress in the
tire sidewalls, tending to pull the rim
sideways to move in the new direction.
This force on the rim passes through the
slightly flexing wheel spokes and axle,
and acts next on the fork legs, bending
them in the new direction that the tire
tread has taken. This force travels up to
the steering head region of the chassis,
twisting it slightly with respect to the
rest of the motorcycle. Now all these
parts-tire, wheel spokes, axle, fork legs
and steering head-are deformed like
springs, holding energy within them-
selves. As the tires drive out from under
the bike, making it roll over, the energy
in all these springs has to rebound. If the
rider allows it to happen suddenly, it
would be as if the Space Shuttle's en-
gines had cut off instantly, allowing the
accumulated strain from 900,000
pounds of thrust to be released sudden-
ly, vibrating through the structure,
causing oscillations and high local ac-
celerations. The motorcycle would
wobble as all its parts snapped back to
their unstressed positions and vibrated
afterward.
So Quarterley and other top riders in-
stead release those stored energies at a
controlled rate. A good word for this is
"grace"
Cycle World's Off-Road Editor Jim-
my Lewis has speculated about how
one dirtbike, with quick steering geom-
etry, may nevertheless seem sluggish in
its response compared with another,
similar machine with rake and trail fig-
ures that ought "by the numbers" steer
more slowly. He believes this kind of
surprise may be explained by differ-
ences in component stiffness. When
you put steering pressure into the bars
and the above sequence of events is set
in motion, it takes time for tire flex to
build up force on the rim, for wheel and
axle flex to build up force on the fork
tubes and so on. The sum of all these
delays must be added to the time it
takes the rider to turn the bars against
gyro and trail/self-centering resistanc-
es, and to the time it takes for the ma-
chine to physically roll over once the
applied forces have developed. In the
case of a structurally "soft" machine
with quick steering geometry, versus
one with slow geometry but greater
stiffhess, it may be the slow-but-stiff
bike that reacts faster.

Back on asphalt, this is complicated
by the perceived need to make chassis
less stiff, to enable them to act as sup-
plementary suspensions when the ma-
chine is leaned far over in turns. In this
condition, more flex helps to keep the
tires in road contact, while greater
stiffness leads to what Wayne
Rainey once called "chatter, hop
and skating." The soft, slower-re-
sponding bike that results from re-
ducing stiffness to avoid such prob-
lems must then be speeded-up in its
responses by giving it quicker steering
geometry.
All these flexible parts can be regard-
ed as oscillators with very little damp-
ing. A more flexible fork or a twistier
steering head may solve one problem
but create another. The aforementioned
tire chatter, largely a racetrack phe-
nomena, is made much more likely
when two or more of the motorcycle's
natural oscillators-the vertical bounce
of the front tire and the back-and-forth
bending of the front fork, say-come
into step with each other. This allows
the system to store so much energy in
oscillation that the natural damping
present-the friction between fork tubes
and the crowns that clamp them, or the
flex of rubber in the tire-can not absorb
it fast enough. Small driving forces in
the system such as tire variation (out-
of-round or out-of-balance) put energy
into the oscillators, perhaps sufficient
to make the front tire begin to bounce
up and down. If everything is oscillat-
ing together, the bounce builds until the
rider sees double and the harder he
twists the throttle, trying to accelerate
out of the turn, the less time the tire
spends on the pavement.
This is why racing engineers are no
longer describing chassis stifiness in
terms of deflection versus applied force,
or chassis twist per foot-pound of
torque, but in terms of oscillation fre-
quency. Tuning fork, anyone?

[JwS]

"CF frames are too stiff, simple as that."
You know Desmo, I hear things like this all the time. I think the problem may be that there is not enough damping in CF, so if the frames spring rate is correct it doesn't have the damping it would need (unlike steel, ducati frames)
You hear the same thing in bike frames etc., and then everyone repeats it and it becomes 'common wisdom'
JwS

[Mark Beckman]

Originally posted by JwS
"CF frames are too stiff, simple as that."
You know Desmo, I hear things like this all the time. I think the problem may be that there is not enough damping in CF, so if the frames spring rate is correct it doesn't have the damping it would need (unlike steel, ducati frames)
You hear the same thing in bike frames etc., and then everyone repeats it and it becomes 'common wisdom'
JwS

If you wish to belittle people then at least do it with sound facts and not guesses.

While you do I'll be out in the shed tending to my racing bikes which I build myself, not all of us sit around just talking about it.

12.9:1 - That article is at least 20 years old regardless of when it was printed, ask JwS the resident expert how I know that as the answer is in the print clear for all to see.

[Mark Beckman]

Desmo you remind me of my workplace where when I tell an Engineer "it wont fit" they go into a tirad saying I wouldn't know or I'm not fitting it properly and how it fits perfectly on their computer program until they come into the workshop and actually try it themselves and after considerable effort they give up and say "it wont fit".

Find Tony Foales webpage for some more reading on bike frames or buy his books.

http://www.tonyfoale.com

[Wuzak]

Originally posted by Mark Beckman
While you do I'll be out in the shed tending to my racing bikes which I build myself, not all of us sit around just talking about it.

May I ask what your frames are constructed from, and how you come about your geometries, etc?

Is it experience?

[JwS]

"If you wish to belittle people then at least do it with sound facts and not guesses."
I don't, my point was that when I hear you say "CF is too stiff" without any reasoning to back it up
I have to ask myself why???? and alot of times I don't get a good reason

"While you do I'll be out in the shed tending to my racing bikes which I build myself, not all of us sit around just talking about it."
I have raced motorcycles for 7 years and do all my own development.

"12.9:1 - That article is at least 20 years old regardless of when it was printed, ask JwS the resident expert how I know that as the answer is in the print clear for all to see."
He does mention a kawasaki of the 90's, that says 10 to me, what did you see?
JwS

[JwS]

And sorry to say, I am one of those stupid engineers, but I am also the machinist, assembler and field service guy. And I have designed and built parts for my race bike, and put my own ass on the line testing them!!!
JwS

[desmo]

Originally posted by Mark Beckman
Desmo you remind me of my workplace where when I tell an Engineer "it wont fit" they go into a tirad saying I wouldn't know or I'm not fitting it properly and how it fits perfectly on their computer program until they come into the workshop and actually try it themselves and after considerable effort they give up and say "it wont fit".

Find Tony Foales webpage for some more reading on bike frames or buy his books.

http://www.tonyfoale.com

I think you misunderstand me. I am a frequent proponent of the empirical over the theoretical, and further I am in no way an engineer. The school of bloody knuckles is indeed one of the best for mechanical engineering. Still, I assume you would concede that it would be possible to construct a frame in CF that would be insufficiently stiff?

And thanks 12.9:1 for finding and sharing Kevin Cameron's (very much a graduate of the school of bloody knuckles as well as an insightful and articulate writer) on point little essay on frame and component flex. Whenever it was actually written, the insights it contains are timeless.