70 replies to this topic

[jatwarks]

It's a given that a competition chassis should be as torsionally rigid as possible in order for the suspension and tyres to perform to their design optimum, without random additional flexing from the chassis platform.

However, it was interesting to hear Steve Parrish suggest that the Ducati MotoGP bike suffers from too stiff a chassis. His explanation, if I understood it correctly, was that when cornering on the limit the stiffness of the headstock causes the front tyre to tend to skip (momentarily lose grip), while a slight amount of flex would allow the tyre to maintain good contact.

I can understand that single track vehicles that lean through corners could benefit from this slight amount of torsional flex at the front end, but could multiple track vehicles ever have a chassis that is too stiff?

I suspect not.

[cheapracer]

It's a given that a competition chassis should be as torsionally rigid as possible in order for the suspension and tyres to perform to their design optimum, without random additional flexing from the chassis platform.

However, it was interesting to hear Steve Parrish suggest that the Ducati MotoGP bike suffers from too stiff a chassis. His explanation, if I understood it correctly, was that when cornering on the limit the stiffness of the headstock causes the front tyre to tend to skip (momentarily lose grip), while a slight amount of flex would allow the tyre to maintain good contact.

I can understand that single track vehicles that lean through corners could benefit from this slight amount of torsional flex at the front end, but could multiple track vehicles ever have a chassis that is too stiff?

I suspect not.

Motorcycle chassis flex is a black art and has been baffling them forever, a small change such as a power curve change can require a totally different frame and that's why every year obviously as they upgrade engines or change the power delivery they are left chasing the chassis as well - how many times over the years have you seen a team go backwards and complaining about the frame or the latest frame not working although last years bike was brilliant...

The chassis needs to be rigid in a horizontal plane and torsionally but to flex in a vertical plane - where and how much is the key and why you have not seen highly successful carbon fibre frames in GP racing, it's difficult to control it's stiffness especially with the endless engine upgrades where a new frame needs to be developed or changed rapidly. Casey Stoner winning on the CF framed Duke seems to be just one of those combinations that just worked out, happens in racing history occasionally going against the norm.

Good writeup here ...

http://www.gizmag.co...truction/11456/

[gruntguru]

Sounds like racing motorcycles need an additional adjustable compliance mode. A "hinge" in the headstock with adjustable springing and damping? Ditto for the rear?

[desmo]

When a motorcycle is nearing its cornering traction limit the suspension travel is obviously at a less than ideal angle relative to the road surface. I once tried sketching some mechanical solutions but they were all less than elegant. Karts do pretty well once they're sorted using flex without conventional springs and dampers. If I were a racing bike designer I'd probably throw the whole mess at the tire engineers and say, "Fix this please."

[meb58]

I think that trail and frame/fork stiffness are all teathered. I don't ride motorcycles but I spent about 12K miles a year racing bicycles and frame feel is so important but incredibly elusive.

[murpia]

It does surprise me, given the capabilities of modern software like MSC.ADAMS, that pedal bike frames, motor bike frames and kart chassis can't be put on a more analytical footing the same way race car suspension has been over the last few decades.

The metrics should be straighforward: torsional stiffness plus bending stiffnesses in the lateral and vertical planes for bikes. Torsional and bending stiffness in the vertical plane for karts. Plus some measure for damping in those degrees of freedom.

I guess the damping is the hardest aspect to specify - what units would be appropriate?

Regards, Ian

Edited by murpia, 16 August 2011 - 10:18.

[24gerrard]

Working out the effects of 'lean' on the bikes front forks would be the difficult part.
It is one reason hub center steering was factored in to our project 425 with Lotus.

http://oi34.tinypic.com/fw820o.jpg


Although it was not designed to lean much anyway.

[meb58]

How so? I am interested because I feel the fork - on pedal type machine or motor driven - is critical to how both feel and react through a turn. Of course a road racing bicycle has only its pneumatic tire as its suspension. Cross terrain and moutain bicycles are different...perhaps more like a motorcycle frame.

[Fat Boy]

How so? I am interested because I feel the fork - on pedal type machine or motor driven - is critical to how both feel and react through a turn. Of course a road racing bicycle has only its pneumatic tire as its suspension. Cross terrain and moutain bicycles are different...perhaps more like a motorcycle frame.

I bet it's actually quite similar to what is felt on a road bike. Some of the bigger manufacturers seem to be getting a pretty good grasp of the effects of stiffness in different modes (Specialized). It's amazing that a bike with no suspension can feel so much different from another bike with no suspension. It's the same with karts.

[24gerrard]

I bet it's actually quite similar to what is felt on a road bike. Some of the bigger manufacturers seem to be getting a pretty good grasp of the effects of stiffness in different modes (Specialized). It's amazing that a bike with no suspension can feel so much different from another bike with no suspension. It's the same with karts.

More attention is being given to frame and chassis stiffness.
The problem on bikes is measuring the effects of lean on energy input to the forks, which goes from maximum linear input when the bike is vertical to non existant linear input at full lean.
How do you calculate where in their travel the forks lock up due to side loads when they are off vertical?

Karts have the added problem of calculating in the movements of the driver and the variations to C of G that result.
Most kart racers use their weight to alter handling.

Edited by 24gerrard, 16 August 2011 - 12:58.

[murpia]

More attention is being given to frame and chassis stiffness.
The problem on bikes is measuring the effects of lean on energy input to the forks, which goes from maximum linear input when the bike is vertical to non existant linear input at full lean.
How do you calculate where in their travel the forks lock up due to side loads when they are off vertical?

Karts have the added problem of calculating in the movements of the driver and the variations to C of G that result.
Most kart racers use their weight to alter handling.

I agree that bushing stiction on mountain & motorbike forks might be a difficult thing to model. In recent times (racing) Mac struts have benefited enormously in recent times from low friction linear bearing technology instead of bushes. What do high-end motorbike forks use?

Also, motorbike racing probably has the most extreme variations in driver movements & therefore C of G.

But since the area of interest is grip over bumps & kerbs surely the rider can be assumed to be static and the bumps become the input to the analysis?

Regards, Ian

[24gerrard]

I agree that bushing stiction on mountain & motorbike forks might be a difficult thing to model. In recent times (racing) Mac struts have benefited enormously in recent times from low friction linear bearing technology instead of bushes. What do high-end motorbike forks use?

Also, motorbike racing probably has the most extreme variations in driver movements & therefore C of G.

But since the area of interest is grip over bumps & kerbs surely the rider can be assumed to be static and the bumps become the input to the analysis?

Regards, Ian

I dont think riders shift their weight much front to rear and the side movement should be fairly easy to calculate with no load transfer side to side.

The kart is subject to C of G movement both front to rear and also from one pair of tyres on one side to the other.
Corner to corner stiffness is a major factor. It allows the drive axle to work without tyre drag for a start. (no diff)

[cheapracer]

I dont think riders shift their weight much front to rear

Like hell they don't, it is quintessential to bike control.

[jatwarks]

I haven't yet found the video Steve Parrish used to illustrate the problem on the BBC TV coverage; it's quite an eye-opener.

It shows Casey Stoner on the limit cornering at Brno at the weekend, in slow motion. The bike is almost horizontal, with the tyre contact patches way up on the sidewalls.

The fatness of the rear tyre is all that's keeping the bike off the ground.

The graphics Parrish added to the video show the vertical axis of the bike is at 87 degrees (IIRC) to the vertical; Stoner's angle of lean off the inside of the bike has him actually below horizontal!

The grip offered by the tyres, considering that the cornering forces are virtually devoid of any vertical component, is incredible.

If anyone here can find that video I urge them to watch it and be impressed.

[bigleagueslider]

It's a given that a competition chassis should be as torsionally rigid as possible in order for the suspension and tyres to perform to their design optimum, without random additional flexing from the chassis platform.

However, it was interesting to hear Steve Parrish suggest that the Ducati MotoGP bike suffers from too stiff a chassis. His explanation, if I understood it correctly, was that when cornering on the limit the stiffness of the headstock causes the front tyre to tend to skip (momentarily lose grip), while a slight amount of flex would allow the tyre to maintain good contact.

I can understand that single track vehicles that lean through corners could benefit from this slight amount of torsional flex at the front end, but could multiple track vehicles ever have a chassis that is too stiff?

I suspect not.

jatwarks,

Race bikes are different from cars with regards to torsional stiffness. As dirt-trackers like Kenny Roberts first showed, having a road-race bike chassis that gives a controlled slide in the corners is a fast chassis. Thus a chassis with consistent stiffness is more important than one with ultimate stiffness.

slider

[Lee Nicolle]

Interestingly in years past some of the Commodore Cup cars actually cut diagonals out of the cage to make the cars handle better. Though that was probably more to do with the control springs and shocks they had to use.

[24gerrard]

I dont see a great deal of front to rear body movement in these moto GP slow Mos cheapy.
Plenty of side to side.
I do agree that front to rear body weight transfer is used a lot in off road bike riding.
I cant remember moving front to rear on my old Norton and that could be lent over onto the side of the tyre.
If I remember Avon made tyres then that had a 'rap around' tread right onto the tyre walls.
Leaning circuit bikes was the way then, it is more rider lean today, because of the higher power to get down.
However Stoner obviously has the skill to lean when he can.

[blkirk]

The grip offered by the tyres, considering that the cornering forces are virtually devoid of any vertical component, is incredible.

The laws of physics are not easily fooled. If you sum the forces acting on the bike, you will find that the full weight of the bike and rider are still acting vertically on the contact patches no matter what the angle of lean. There are three things that could potentially reduce the contact patch loads. The first is bumps which will cause variations in the contact patch load, but on average it should still come out pretty close to the weight of the bike and rider. The second is changes in the angle of lean. As the center of mass of the bike+rider moves up and down, the contact patch loads will change. They will increase as the lean decreases and they will decrease as the lean increases. The third is the rider dragging a knee which will support some of his own weight and remove it from the contact patch. If this ever becomes a significant fraction of the rider's own weight it's called a low-side and the rider will not be on the bike anymore.

[GrpB]

The fundamental problem is that engineering 'feel' at the limit does not have a defined, quantitative, empirical methodology. To improve traction/drive in a certain part of the corner, to regain a hp deficit, or to improve specific fuel consumption are clear directives with known tradeoffs. To improve feel, to make changes that provide consistent, clear, subjective rider feedback at the traction limit – with minimal performance degradation, is not a well defined process, and cannot proceed with easily defined tradeoffs and incremental steps.

Fixing something related but even more straightforward like chatter is hard enough when the spring IS the damper (as the motorcycle approximates at full lean). To do it analytically, that sort of forced response analysis is hard enough for something similar like valvesprings which have simple geometry, easily defined system inputs, and straightforward physical correlation. To do the same for a full motorcycle boggles the brain. It certainly believable that it's more realistic to find a fix with experiment instead of analysis. Although it is amusing to think that for a chassis issue the most relevant investigations have been done for engine compoments.

The easy fix of course would be to make the magic deal and get Stoner back…

[24gerrard]

It certainly shows that chassis and frame flex is an ongoing problem not completely solved.

[sherpa]

I think designing a moto gp chassis would be a very difficult task, as the bike changes considerably throughout a corner. As the bike enters the corner the forks will be compressing , thus changing the steering head angle and trail measurement, midway through the corner I remember reading that the chassis flexes up to 20mm at the midpoint. As the rider exits the corner the front forks extend under power and again changes the head angle, trail and the wheelbase. Add to this the variable centre of gravity, ie the rider moving, and the inevitable wheelspin and you can see why this is indeed a black art. The riders weight transferences may not be obvious but they are essential to the package going fast. The rider can pull up on the bars exiting a corner and almost instantly put 100% of the weight on the back wheel as the front wheel is just kissing the track, and the same going into a corner , the front end is loaded up to the point where it will have 100% of the weight as the back wheel skips off the ground. I cant imagine cars having to deal with these extreme changes in weight distribution and geometry through a corner. The Ducati problem seems to be related to the motor being a stressed part of the carbon fibre frame, and as a result not providing that all important 'feel'. The Japanese bikes all have conventional cradle frame, which the engine sits in. What I cant get my head around is why Ducati cant build flex into the carbon fibre chassis, Many things are made of composites these days that are required to have some built in Flex eg tennis racquets, push bikes etc, you would think there is enough information out there for Ducati to get it right
Cheers Greg

[24gerrard]

I think designing a moto gp chassis would be a very difficult task, as the bike changes considerably throughout a corner. As the bike enters the corner the forks will be compressing , thus changing the steering head angle and trail measurement, midway through the corner I remember reading that the chassis flexes up to 20mm at the midpoint. As the rider exits the corner the front forks extend under power and again changes the head angle, trail and the wheelbase. Add to this the variable centre of gravity, ie the rider moving, and the inevitable wheelspin and you can see why this is indeed a black art. The riders weight transferences may not be obvious but they are essential to the package going fast. The rider can pull up on the bars exiting a corner and almost instantly put 100% of the weight on the back wheel as the front wheel is just kissing the track, and the same going into a corner , the front end is loaded up to the point where it will have 100% of the weight as the back wheel skips off the ground. I cant imagine cars having to deal with these extreme changes in weight distribution and geometry through a corner. The Ducati problem seems to be related to the motor being a stressed part of the carbon fibre frame, and as a result not providing that all important 'feel'. The Japanese bikes all have conventional cradle frame, which the engine sits in. What I cant get my head around is why Ducati cant build flex into the carbon fibre chassis, Many things are made of composites these days that are required to have some built in Flex eg tennis racquets, push bikes etc, you would think there is enough information out there for Ducati to get it right
Cheers Greg

I am not sure flex in the frame is the way to go.
Most of the movement is in the front and rear suspension, the frame is mainly just a support girder.
If you consider the frame and rider as the central platform with a moveable mass (varying with rider weight), it should be a good start point.

[sherpa]

I agree, from an engineering point of view you would think rigid is better[by the way I am an engineer] but as a person who has competed on motorcycles for way to many years, I can tell you flex is important, its the same with push bikes and tennis racquets. I to have trouble understanding why stiff frames don't feel as good and obviously I am not alone. I know they have gone to a great deal of trouble to reduce stiction in the forks and rear suspension to eliminate some of the handling issues, but as I said before I still think its a black art that not to many people understand.
Cheers Greg

[jatwarks]

I am not sure flex in the frame is the way to go.

The problem with flex is that it implies a lack of ultimate control over the characteristic, and that suggests inconsistency. True, all spring operation is based on material flexing, but you would rather be able to control the point at which displacement occurs and the axis of displacement.

That's why suspension uses rigid components, joints with single axis movement and separate spring units. Flex brings live-axles and leaf-springs to mind!

I guess that, in fact, what we are discussing is just what the role of suspension is on a bike cornering at the limit.

With the suspension compressed by cornering forces resisted by tyre grip the bike can be considered pretty rigid. If the track surface isn't billiard table smooth then, presumably, some controlled lateral movement is required to keep grip consistent over bumps, movement that isn't wanted when the bike is upright.

Surely, the best way of achieving that is with the tyres?

[sherpa]

Would it be reasonable to assume that while cornering if the frame is in the process flexing then the full 'sideways' force is not transmitted to the tyres until the frame has reached its maximum displacement.
This would give the rider some 'warning' or 'feel' as to when the bike was about to slide. Remember the Moto gp tyres are almost V shaped and would offer very little sidewall flex in comparison to a F1 car, any thoughts, Greg

Edited by sherpa, 26 August 2011 - 04:10.

[MatsNorway]

Flex is everywhere. Its used with benefits on skateboards. There was a alu board once but it had no "pop" you use the flex to ollie (jump) higher.



Flex is also used on RC cars with full duble wishbone suspension and kinda simple dampers.

http://www.teamxray....c31f7c55757a052

XRAY Multi-Flex Technology™
One of the more legendary and certainly one of the most innovative set-up features in touring car designs in the last few years is without a doubt the invention and introduction of XRAY Multi-Flex Technology™ which was brought forward into the T3 platform. This smart system allows the setting of different flex characteristics for different track conditions. This extremely effective set-up feature has been updated for the T3 platform to allow for easier flex adjustments by using the multiple positions on the top deck only. No matter whether you drive on asphalt or carpet thanks to Multi-Flex Technology™ you can set the flex – soft, soft-medium, medium-stiff, stiff – or anywhere in between to best suit your track conditions.

Lots of good answers about RC car chassie flex here: http://www.rctech.ne...assis-flex.html

Edited by MatsNorway, 26 August 2011 - 05:32.

[Spoofski]

I dont see a great deal of front to rear body movement in these moto GP slow Mos cheapy.

It's subtle but there. Front/rear movement can be a much slower process, being used to compensate for unequal tyre-wear as the race goes on, or grip levels as the race evolves. That's in addition to the faster movements used to counter wheelies and to weight the rear under braking.

Isn't Dani P's relatively poor performance under braking attributed to his low mass and consequent inability to move it rearwards under braking? Might explain why the first part of his starts are usually OK (wheelie limited as he can't get enough weight forward) but the later parts are mighty as his low mass and better drag shape become significant.

[jatwarks]

Remember the Moto gp tyres are almost V shaped and would offer very little sidewall flex in comparison to a F1 car...

I don't think so.

Years ago (40?) GP tyres had a triangular section, but not any more. If you look at the various videos of MotoGP bikes cornerinmg you will see that the cross section of the tyres is mostly round; the contact patch can be anywhere from the centre of the tread to the sidewall. The squashiness of the tyre rubber produces the contact patch.

Before control tyres were introduced the tyres even had different rubber compounds on each side for clockwise and anti-clockwise laps; softer on the less used, and so less heated, side.

One problem in MotoGP now is that they have adopted single-supplier control tyres; the problem is that the bike must be developed to suit the tyres, rather than the other way round.

Incidently, I believe that control tyres are the biggest cause of the lack of overtaking in all forms of motorsport; they set the performance limit and so competing cars / bikes all have the same performance. The overtaking opportunities seen in F1 this year are purely down to wear rates that cause variations in performance.

While I believe that the solution to Ducati's problem lies with the construction of the tyres (to give the necessary flex discussed) that is not an option unless the tyres suit all the teams.

[24gerrard]

I don't think so.

Years ago (40?) GP tyres had a triangular section, but not any more. If you look at the various videos of MotoGP bikes cornerinmg you will see that the cross section of the tyres is mostly round; the contact patch can be anywhere from the centre of the tread to the sidewall. The squashiness of the tyre rubber produces the contact patch.

Before control tyres were introduced the tyres even had different rubber compounds on each side for clockwise and anti-clockwise laps; softer on the less used, and so less heated, side.

One problem in MotoGP now is that they have adopted single-supplier control tyres; the problem is that the bike must be developed to suit the tyres, rather than the other way round.

Incidently, I believe that control tyres are the biggest cause of the lack of overtaking in all forms of motorsport; they set the performance limit and so competing cars / bikes all have the same performance. The overtaking opportunities seen in F1 this year are purely down to wear rates that cause variations in performance.

While I believe that the solution to Ducati's problem lies with the construction of the tyres (to give the necessary flex discussed) that is not an option unless the tyres suit all the teams.

[24gerrard]

http://www.teamxray....c31f7c55757a052

Scale model car racing flex chassis.

[murpia]

I am not sure flex in the frame is the way to go.

The problem with flex is that it implies a lack of ultimate control over the characteristic, and that suggests inconsistency. True, all spring operation is based on material flexing, but you would rather be able to control the point at which displacement occurs and the axis of displacement.

That's why suspension uses rigid components, joints with single axis movement and separate spring units. Flex brings live-axles and leaf-springs to mind!

I guess that, in fact, what we are discussing is just what the role of suspension is on a bike cornering at the limit.

With the suspension compressed by cornering forces resisted by tyre grip the bike can be considered pretty rigid. If the track surface isn't billiard table smooth then, presumably, some controlled lateral movement is required to keep grip consistent over bumps, movement that isn't wanted when the bike is upright.

Surely, the best way of achieving that is with the tyres?

Years ago race car chassis & suspension arms flexed and the dampers that interconnect them were under-developed technology.

Nowadays race car chassis & suspension arms are essentially rigid, and dampers are sophisticated and well understood.

If a bike requires lateral flexibility in order to cope with bumps while leaning, surely that could be developed as one or more rigid structures with dampers between them? The obvious places to em would be the steering pivot and the swingarm pivot.

Surely an FE or ADAMS study could start with an existing flexy frame then design a rigid frame plus joints that mimics it?

Regards, Ian

[24gerrard]

The problem with flex is that it implies a lack of ultimate control over the characteristic, and that suggests inconsistency. True, all spring operation is based on material flexing, but you would rather be able to control the point at which displacement occurs and the axis of displacement.

That's why suspension uses rigid components, joints with single axis movement and separate spring units. Flex brings live-axles and leaf-springs to mind!

I guess that, in fact, what we are discussing is just what the role of suspension is on a bike cornering at the limit.

With the suspension compressed by cornering forces resisted by tyre grip the bike can be considered pretty rigid. If the track surface isn't billiard table smooth then, presumably, some controlled lateral movement is required to keep grip consistent over bumps, movement that isn't wanted when the bike is upright.

Surely, the best way of achieving that is with the tyres?

Years ago race car chassis & suspension arms flexed and the dampers that interconnect them were under-developed technology.

Nowadays race car chassis & suspension arms are essentially rigid, and dampers are sophisticated and well understood.

If a bike requires lateral flexibility in order to cope with bumps while leaning, surely that could be developed as one or more rigid structures with dampers between them? The obvious places to em would be the steering pivot and the swingarm pivot.

Surely an FE or ADAMS study could start with an existing flexy frame then design a rigid frame plus joints that mimics it?

Regards, Ian

I agree that much more is known about suspension, however in F1 the mechanical suspension is today compromised in every way to accomodate aero needs. IMHO F1 suspension is crude compared to what it could be with a major reduction in Downforce.

The bike debate on this issue is brilliant and I hope more of those clever engineers out there will contribute.
It looks like tyres are (as always) the major influence.

[bigleagueslider]

A GP bike chassis is more about weight distribution, moment of inertia, and engine throttle response. A modern MotoGP bike produces way more power than it can put down to the pavement effectively during acceleration. These bikes put 100% of their power into the rear tire during acceleration, and almost 100% of their stopping torque into the front tire during braking. Unlike an F1 car with aero downforce, a MotoGP bike can only produce as much traction force at the tire contact as the weight of the bike and rider creates.

The key to turning a fast lap on a MotoGP bike is mostly due to rapid weight transfer in the corners. And this requires a chassis with a low polar MOI. Absolute chassis stiffness in torsion or bending is not so critical.

[jatwarks]

If a bike requires lateral flexibility in order to cope with bumps while leaning, surely that could be developed as one or more rigid structures with dampers between them? The obvious places to em would be the steering pivot and the swingarm pivot.

It was reported during coverage of qualifying from Indy that Ducati are experimenting with collars / spacers in the headstock.

Incidently, I hadn't realised until today that the current Ducati Series 11.1 uses the engine / gearbox as a fully stressed member, with the headstock and swinging arm attached directly.

[24gerrard]

So why not just lean the driver and frame/powerunit and leave the wheels more unright?
It can be done with hub center steering.
Then the suspension would work better and be easier to set up.
It would also be easier to apply power on corner exit.

Edited by 24gerrard, 29 August 2011 - 15:07.

[cheapracer]

and almost 100% of their stopping torque into the front tire during braking. Unlike an F1 car with aero downforce, a MotoGP bike can only produce as much traction force at the tire contact as the weight of the bike and rider creates.

No, a rider acts greatly as an air brake during braking and not just the front contact patch. A rider also transfers heaps of weight front to rear and side to side transfering the weight around the contact patches as well as weighting or deweighting those patches as required.

Absolute chassis stiffness in torsion or bending is not so critical.

You can not be serious.

Maybe Loris can change your mind ... (July 2011)

Ducati's first MotoGP race winner, Loris Capirossi, insists that Ducati must abandon tradition and build a conventional aluminum frame for Valentino Rossi to win.

"The problem with the Ducati is the rigidity," Capirossi said. "The most important part is the middle of the frame and this (on the Ducati) is the engine and you can’t change the rigidity.

"You can work a little bit with the front and rear but you can do nothing with the engine. There is no flex in the middle part of the bike."

Capirossi won Ducati's first ever MotoGP race, the 2003 Catalunya Grand Prix, riding the 990cc, trellis-framed Desmosedici.

In five seasons as a factory rider Capirossi won seven GPs on Ducati 990s.

He is currently riding a carbon-fiber framed GP11 for the Pramac Ducati team and like Rossi has been unable to come to grips with the bike.

Edited by cheapracer, 29 August 2011 - 15:08.

[kikiturbo2]

So why not just lean the driver and frame/powerunit and leave the wheels more unright?

eeeeeerrrrrrrr, maybe because moto GP tyres and wheels can't acctually transmit any side force worth mentioning.. ? (+ a host of other reasons.. incl CG height in corners etc etc... )

[PhilG]

The whole rigidity issue in motorcycle frames is about giving the rider feel when on the side of the tyre, so slides and the like can be corrected . With no 'feel' you cant push to the limit because you get no warning of it, you just crash.

Most of the worst bike designs have come from car people not grasping this , and making them too stiff, and then nothing works.

For Ducati to do this, bearing in mind historically that their steel trellis frame gives the best handling bikes on the road , makes it even more strange.

[24gerrard]

eeeeeerrrrrrrr, maybe because moto GP tyres and wheels can't acctually transmit any side force worth mentioning.. ? (+ a host of other reasons.. incl CG height in corners etc etc... )

If the wheel leans over it has to support the rest of the bike through the spindle to the tyre contact patch.
Perhaps flexible wheel design is Ducatis answer.

With hub center steering it is easy to lean the chassis-frame-rider independent to the wheel angle.
In fact it can be designed with a lower CofG height in corners.

[PhilG]

If the wheel leans over it has to support the rest of the bike through the spindle to the tyre contact patch.
Perhaps flexible wheel design is Ducatis answer.

With hub center steering it is easy to lean the chassis-frame-rider independent to the wheel angle.
In fact it can be designed with a lower CofG height in corners.

Its been done, with the ELF 500 Honda back in the day, and the main issue was grounding out before you reached the edge of the tyre. It will never feature on a MotoGP bike

[cheapracer]

Its been done, with the ELF 500 Honda back in the day, and the main issue was grounding out before you reached the edge of the tyre. It will never feature on a MotoGP bike

Man do I ever miss the days of the Bol'odor 24 hours and all the experimental bikes - equate it to Mariner's hillclimb specials.

Honda spent an absolute fortune to win the Bol'odor with conventional looking bikes to make the others look like a waste of time, it worked sadly.

At least BMW are brave enough to go with the Telelever and the Duolever although not brave enough to sell it to the hardcore Hyperbike buyers using standard style forks - but it will happen when they finally get the message through on there sports touring models.

Ducati could do themselves a favour and go to the Duolever setup (Hossack suspension) as it would relieve a lot of reliance on the chassis as it removes almost all stiction from the front end but then there's the marketing problem and admitting BMW was right - certainly the reason you will never see it on a Japanese bike (unless of course they "reinvent it" cough, cough).




Actually it's interesting reading so go here ... http://www.carbibles...ible_bikes.html
... and scroll down to Front Duolever and below that the Norman Hossack article as well as his website here ..
http://www.hossack-design.co.uk/
I didn't realise he was ex McLaren.

Edited by cheapracer, 29 August 2011 - 18:41.

[Tony Matthews]

http://www.hossack-design.co.uk/

Is that Hossack Cycle drawing done from the rear, or does it rotate ant-clockwise? Not that it makes much difference, I suppose.

[cheapracer]

Is that Hossack Cycle drawing done from the rear, or does it rotate ant-clockwise? Not that it makes much difference, I suppose.

I don't understand sorry?

[desmo]

That Hossack design seems more a development of what used to be called a "girder fork" than anything groundbreaking. They have moved the steering axis outboard of the suspension arms though.

[cheapracer]

That Hossack design seems more a development of what used to be called a "girder fork" than anything groundbreaking.

Read his website, he's actually adamant it is not related to girder fork principles. I admit to thinking so what, it's just a girder when I first saw it years ago.

They have moved the steering axis outboard of the suspension arms though.

Yes he did, eliminating a lot of steered mass, weight and unsprung weight along the way.

[Tony Matthews]

I don't understand sorry?

[cheapracer]

Oh you mean the engine, anti clockwise and makes a difference in relation to when the exhaust port opens.

It probably has a little more combustion duration than a 2 stroke but the complication (sealing, balancing) isn't worth the hassle.

[GrpB]

Man do I ever miss the days of the Bol'odor 24 hours and all the experimental bikes - equate it to Mariner's hillclimb specials.

Honda spent an absolute fortune to win the Bol'odor with conventional looking bikes to make the others look like a waste of time, it worked sadly.

At least BMW are brave enough to go with the Telelever and the Duolever although not brave enough to sell it to the hardcore Hyperbike buyers using standard style forks - but it will happen when they finally get the message through on there sports touring models.

Ducati could do themselves a favour and go to the Duolever setup (Hossack suspension) as it would relieve a lot of reliance on the chassis as it removes almost all stiction from the front end but then there's the marketing problem and admitting BMW was right - certainly the reason you will never see it on a Japanese bike (unless of course they "reinvent it" cough, cough).

BMW and others don't race only conventional front ends for lack of bravery, rather they are facing up to reality: Racing is for marketing, but marketing is of little value without winning. All top riders know only the feel of conventional forks, top teams/crew chiefs only have experience/notes with conventional forks, top racing suppliers only know what works with conventional forks, and perhaps most important, sponsors only throw money behind what they know and feel comfortable with. Other suspension designs may have technical advantages, but without the top riders, top teams, best suppliers and adequate sponsor support, they would be backmarker oddities at best.

Britten's (RIP) modified Hossak design probably had the best racing success of an alternative suspension design in the modern era, but success at the BOTT national level is different from consistent international success with FIM or Dorna. That bike in it's initial form with conventional forks was (to his credit) about the same on paper as the current Ducati chassis, but I don't think anyone would argue that a V1000 with alternative front end could be updated with a modern 1000cc V4 for '12 and use it's supposed technical advantages to actually be competitive - on a spec tire. Nor for Moto2 does any current chassis builder believe it would be realistic to actually sell anything other than a conventional, alloy twin beam, telescopic front, linkage/swingarm rear chassis to the teams/sponsors participating in that class.

The current Ducati, an essentially conventional bike whether 11 or 11.1, probably behaves about the same as the M1 or the RC212 on a macro level, similar front/rear suspension movement, similar attitude change and response to throttle/brake/body postition, and still whatever element of feedback is lacking is losing them 1 sec per lap or more. The more interesting engineering project wouldn't be to design a 'better' suspension or chassis for the Ducati, it would be to define and correlate the objective/subjective parameters that define 'feel'. With the former, you might fix one bike, with the latter, you could 'fix' all bikes.

[murpia]

I agree that much more is known about suspension, however in F1 the mechanical suspension is today compromised in every way to accomodate aero needs. IMHO F1 suspension is crude compared to what it could be with a major reduction in Downforce.

I disagree. Just because current F1 suspension cannot be seen to move very much, does not stop it exercising very precise control over tyre contact patch forces.

In particular the axle roll moment distribution with lateral force and the damping & control of pitch / heave coupling are very highly developed.

Neither of those effects are affected by the jacking forces from the front wishbone angles needed for good aero.

Can you show me a non-aero formula that has highly developed 3rd elements as F1 does?

Regards, Ian

[cheapracer]

Apparently Rossi raced last weekend with "aluminium section" apparently replacing the front carbon fibre half on the Ducati.

As I mentioned before with the ever evolving engines in the search for power resulting in new chassis virtually every year and more, when they made this major change to the chassis they actually had to change the engine to suit as the one that suited the carbon fibre chassis doesn't suit the aluminium - amazing stuff, would love to know the technical reasons behind all of it.