Race chassis

[TZ350]

Late model NSR125 die cast frame sides bolted up around the headstock.

[Michael Moore]

Offenstadt and Shepherd did cast frames and swing arms, and the small block Guzzis came with cast swing arms.

[Frits Overmars]

Late model NSR125 die cast frame sides bolted up around the headstock.

That Honda frame looks an awful lot like an Aprilia frame.

[F5 Dave]

Both designed and made in Italy.

[Flettner]

You know, you could sand cast that quite easily for a bucket sized frame. Cast in CC601 then heat treat to T6. But a set of press tools with sheet would work very well also.
I'm assuming the bushing (bearing housing) that is bolted into the head stock could be offset bored for head stock angle adjustment?

[Grumph]

You know, you could sand cast that quite easily for a bucket sized frame. Cast in CC601 then heat treat to T6. But a set of press tools with sheet would work very well also.
I'm assuming the bushing (bearing housing) that is bolted into the head stock could be offset bored for head stock angle adjustment?

My thought on the adjustment was, if the piece is symmetrical top/bottom, but the steering axis is offset 1 degree from C/L, inverting the bolt in piece gives a 2 degree variation in rake. That's usually enough.

[Flettner]

I'm thinking frame stiffness, north to south real stiff, east to west some compliance? Or has this already been covered. These frames shown above are wide to go around carbs etc on four cylinder engines. If your engine is much thinner ie single or V twin the spars do not need to be pushed out so wide?

[Grumph]

I'm thinking frame stiffness, north to south real stiff, east to west some compliance? Or has this already been covered. These frames shown above are wide to go around carbs etc on four cylinder engines. If your engine is much thinner ie single or V twin the spars do not need to be pushed out so wide?

Compliance has been mentioned...I've quoted the Roberts team as knowing what stiffness parameters they wanted - and in which planes - when they ordered up the frames for the triple.
Got shot down - in a good way, LOL - as it would seem the opinion is that stiffer is better, at least for small homebuilts.
I'd really like the chance to back MIke Sinclair into a corner and hammer out some guidelines as he appears to have measured the stiffness of nearly everything he's ever worked on.

In my experience with larger heavier bikes, there's enough unwanted compliance from flexible wheels and forks that making it as stiff in the chassis as possible will at least make it rideable.

[husaberg]

Compliance has been mentioned...I've quoted the Roberts team as knowing what stiffness parameters they wanted - and in which planes - when they ordered up the frames for the triple.
Got shot down - in a good way, LOL - as it would seem the opinion is that stiffer is better, at least for small homebuilts.
I'd really like the chance to back MIke Sinclair into a corner and hammer out some guidelines as he appears to have measured the stiffness of nearly everything he's ever worked on.

In my experience with larger heavier bikes, there's enough unwanted compliance from flexible wheels and forks that making it as stiff in the chassis as possible will at least make it rideable.

http://www.cycleworld.com/2015/10/16...g-races#page-3

“Chatter, stability, chassis flex, and engine characteristics are mysteriously entangled. There is no textbook.
As tires evolve, chassis must evolve. When Michelin brought a big new rear tire in 2006, it set every chassis to chattering. The usual emergency fixes (like lead-filled axles to tune out certain flex frequencies) worked for Honda but not for Yamaha. Valentino Rossi was stopped by chatter for four races, and only reverting to the 2005 chassis enabled recovery. Chatter, stability, chassis flex, and engine characteristics are mysteriously entangled. There is no textbook. The ’06 championship was lost.

No chassis can be perfect—just better or worse. Motorcycle roadracing might have once been a noble contest of engine power and durability, but with engine development now frozen in-season it has become a struggle to produce chassis properties that riders can use to race hard all the way to the last lap. Chassis and suspension function as a filter system, softening or stopping inputs that fatigue the tires, letting through inputs that riders need to know where the edge is.

In 2007, the problem was Casey Stoner on the 800cc Ducati with revolutionary Bridgestone tires. When Rossi switched to Bridgestones, weight had to be shifted rearward on the Yamaha and its center of mass raised to transfer weight forward quickly on braking. Yamaha’s 2008 chassis’ lateral stiffness cut another 10 percent (making it now just two-thirds as stiff as the 2004 baseline), and with refined electronics and Bridgestone tires Yamaha riders dominated 2008–2010

http://www.insidemotorcycles.com/blo...in-motogp.html

In the current issue of Inside Motorcycles, I wrote about the 2012 MotoGP bikes and touched on chatter and chassis flex. I addressed chatter in my previous blog, and will go into more detail about chassis flex here. Chassis designers have long known that some flex is a good thing as it acts as the motorcycle's suspension at extreme lean angles. With tires getting grippier and wider over time, motorcycles are getting increasingly more lean angles and the importance of chassis flex increases accordingly.
Incorporating flex into a chassis is not easy, as strength and stiffness are still desired in some directions while flex is advantageous only in certain directions. Typically, manufacturers express chassis rigidity in three ways: vertical, lateral and torsional. The chassis is generally desired to be stiff vertically, to absorb braking and acceleration forces, while some flex is desirable in the lateral direction to act as suspension. Torsional stiffness keeps the wheels in line, but some twisting can also translate to lateral movement at the contact patch. Yamaha published a graph showing the M1's changing chassis rigidity over the past few years, with vertical stiffness increasing and lateral stiffness decreasing - just what you would expect as tires get stickier and the bikes lean further.

https://motomatters.com/analysis/201...mosedici_.html

As tuneable flexibility has become increasingly important, the attractiveness of alternatives to aluminium has also grown. Traditional aluminium has the benefit of being light and easy to work with, but as MotoGP chassis designers push the limits, they also run into a few limitations. Engineering in flex is a matter of designing chassis elements with a specific thickness and shape, but the underlying properties of aluminium mean that at some point, achieving the precise amount of flexibility required means sacrifices strength. The way to get around this problem is by making elements longer, allowing a mass (usually, the mass of the engine) to use the greater leverage provided by a longer element (such as an engine spar connecting the engine to the main chassis beam) to provide the flexibility without sacrificing rigidity.
When the rest of the world switched from perimeter steel tube frames to aluminium twin spar frames, Ducati took a different but still ingenious approach. Instead of wrapping the engine in aluminium box section, Ducati welded up short sections of light steel tubing to create a trellis frame. The advantages were that the chassis was relatively easy to tune, by changing the diameter and position of the individual tubing sections and redistributing the load and the flexibility, and Ducati persevered with the design for six years until they dropped it in favor of carbon fiber.

The problem is not that CF is too stiff, but that the feedback it provides differs so completely from conventional aluminium. The property most often quoted is hysteresis, which in this instance, refers to the rate at which absorbed energy is returned. One of the benefits of CF is the fact that it can be made to damp vibration, its hysteresis meaning that the energy absorbed from an input (such as striking a bump) is released in a much more controlled fashion. Tap an aluminium tube and it rings like a bell; tap a CF tube and it emits a dull thud.
This is a property that Ducati had hoped would help them solve the problem of chatter (or extreme vibration over bumps) but it had an unintended side effect. Just as with the original attempts at using carbon fiber for chassis, starting with the Cagiva back in 1990, the damping also removes some of the feel from the front end. When used to build swingarms - as Aprilia had been doing for their 250cc racers for several years - this damping helps remove unwanted vibration, but at the front of the bike, that vibration also contains valuable information. As Guy Coulon once explained to me on the subject of unconventional front suspension systems, what is required of a racing motorcycle is that the information from the tarmac should pass directly into the rider's brain with as little interference or loss of data as possible. Any system which removes or alters that information means that the rider has to learn to interpret the feedback almost from scratch. All of the experience gained in his many years of racing is of little value in interpreting what he is feeling.
This is what caused the Cagiva to fail back in the early 1990s. The riders, brought up on a generation of steel and aluminium chassis, simply could not understand the feedback they were receiving from the machine. And this seems to be at least one part of the problem with the Ducati Desmosedici: the carbon fiber subframe connecting the front forks to the front of the engine may be damping the vibrations too much, reducing the amount of information traveling from the front tire up into the rider's brain. Alternatively, it may be returning too much information, providing more feedback than most riders are used to receiving. Filtering out this new (and not necessarily useful) information may be what is confusing the riders about the feel.

http://motodna.net/motogp-tech-talk-swingarms/

The chassis should bend like a tree according to Yamaha legend Engineer Masao Furusawa.
A longer chassis creates a long lever, which allows flex to be designed more gradually, accurately and effectively.
So just how do MotoGP Engineer’s work out the right amount of strength, stiffness, flex and in what plane or direction?
Well, Engineers increasingly evaluate huge amounts of data in MotoGP, which can be measured, quantified and related to the bikes performance.
However it’s difficult to quantify what the rider feels and it’s this conundrum that ensures race engineering remains a balance between an empirical art and science.
Subsequently the factories go through an incredible amount of research and development to settle on the motorcycles overall handling performance.

Flex is the chassis ability to absorb force, bend in different directions and return to its original position.
Lateral means sideways, so lateral flex is bending in the side or the bikes vertical plane namely when the bike is cornering on extreme lean angles

Lateral stiffness is a trickier one to balance; too much and the bike will suffer a lack of grip at extreme lean angles. RSV4 frame has more lateral flex than the RSV-R for this reason.

https://www.kiwibiker.co.nz/forums/s...post1130236080

I'd argue that a fexible arm actually makes a bike more prone to highside...until they redesigned it the Britten arm was very flexible.
After so many years, Andrew or one of the others may be prepared to go public on what we regularly saw when they tested at Ruapuna.
The only thing that saved innumerable highsides was the ability to keep the rear spinning...if the rider was brave enough.

Not a flexible arm in itself but a small amount of only lateral flex. The idea as i understand it is to both be able to feel the limit and absorb some of the force rather than have it break fee on the limit and then slide and catch which is the start of most classic highsides.
I am not saying they dont make them strong what i am saying is what i understand they don't try to achieve ultimate rigidly against sideways force.Like they did in the 90's.
All the alloy MX frames are also designed with flex in them as well for a less rigid feel from what i understand as well.
After riding a 97 CR250 framed bike i can understand the MX bit. Every bike subsequent to this model has been progressively pared done for more flex.
Although this saves weight and helps the suspension work better no doubt as well.

When Kenny Roberts junior went to Suzuki he tested the bike and asked for a less stiff chassis
Suzuki obliged
he tested it and it was worse
Willings asked if they had tested the stiffness Suzuki said no. So they tested it.
It turned out the less stiff chassis was actually considerably stiffer.

[Frits Overmars]

I'm assuming the bushing (bearing housing) that is bolted into the head stock could be offset bored for head stock angle adjustment?

That is what we tried on an Aprilia RS50 moped frame. Worked well.

Chassis designers have long known that some flex is a good thing as it acts as the motorcycle's suspension at extreme lean angles. With tires getting grippier and wider over time, motorcycles are getting increasingly more lean angles and the importance of chassis flex increases accordingly.

Everybody calls it flex; I'd rather call it lateral springing. And springs have a tendency to spring back, bringing an unwanted resonance into the frame.
What's needed is lateral suspension, i.e. springing with damping. If you can incorporate that, the frame and wheels can and should be as rigid as possible.

[guyhockley]

Offenstadt and Shepherd did cast frames and swing arms, and the small block Guzzis came with cast swing arms.

I slightly helped out a racer called Danny Pullen at a couple of belgian classic meetings. At the time he had a Shepherd Suzuki (GT250 based frame) and a TZ with a Shepherd cast frame. If I remember correctly, he said he was in partnership with frenchman and they had started to reproduce the cast frames but were having trouble getting the swinging arms to come out properly. Think they may have had the original moulds, but I'm not sure. Anyway, this was a few years back, I don't have any contact details and Google came up with very little except he now seems to be racing road bike based 250 and 500 Suzukis. Not heard of any new Shepherd frames...

[husaberg]

Here is the Husaberg cast swing arm 2001
Don't be fooled by the pic its all one piece made by renthal (in Ireland i think.)
quite a few cracked (due to a poor material batch) and were replaced under warranty

With the 1kg heavier traditional fabricated 2000 version.


I would say KTM ones are made the same as the cast Husaberg.


Yip http://motocrossactionmag.com/bike-t...-fun-of-racing

Swingarm updates were made possible by an updated manufacturing process called “single component casting,” which eliminates welding. Additionally, KTM refined the swingarm’s flex properties and its shock mounting position.

[Ocean1]

Flex is the chassis ability to absorb force, bend in different directions and return to its original position.
Lateral means sideways, so lateral flex is bending in the side or the bikes vertical plane namely when the bike is cornering on extreme lean angles.

Not sure that makes perfect sense. But I'll just point out that the XB swingarm I posted earlier was mounted on the engine, which was isolated from the frame via rubber mounts and some tricky wee tie rods.

I wonder if that's why, with no linkage and nothing special by way of a rear shock that back end performs remarkably well....

[Muciek]

Hi, I have a question regarding tires in bikes, we race here mostly with 18" rims (classic bikes) and is there any rule of thumb how to choose tire for a bikes? For example 90-110 kg and 30-40 of hp? Is there a benefit to use for example rear 120 tire instead of 90? Any info or guidelines would be appreciated. Cheers

[guyhockley]

Here is the Husaberg cast swing arm 2001
Don't be fooled by the pic its all one piece made by renthal (in Ireland i think.)
quite a few cracked (due to a poor material batch) and were replaced under warranty


I would say KTM ones are made the same as the cast Husaberg.


Yip http://motocrossactionmag.com/bike-t...-fun-of-racing

That's really nice work. I presume the holes are for the cores. My neighbour's daughter has a KTM road bike and that has a cast arm but quite different (and easier/cheaper to make, I guess).
Picture stolen from Ebay.