Race chassis

[Grumph]

The Question is:

Will it be lighter than a Tube steel fame?

Possibly - but the devil is in the details - Light forks, light swingarm, think light.....I was surprised to find that instead of the common 6mm fasteners everyone uses, John Britten used 5mm. How much saving ? don't know, but you get the idea...

How thick does the Ali have to be?

Depends if it's going to be formed like the Ossa or a straight sided box...Michael has already quoted gauges for a bonded and rivetted box. If it's formed and welded I would use 2mm. Largely depends too on what you can source if it's got to be formed into a shape. Soft 1.6mm is readily available here but i don't know about thicker gauges.

I think a tank / seat unit is a good idea. I do like to have a tank under me.

In principle for a bike monocoque I'd always advise a separate tank. It's hard to keep a welded monocoque "watertight". Which leaves either a separate tank outside or a bag tank inside. Bonded and rivetted ones always require separate tanks. Pretty sure your bro Kev will know where to source bag tanks...

[Grumph]

Actually, Rich's project raises a question in my mind - frame stiffness Vs feel. Any monocoque he makes is potentially anyway going to be stiffer torsionally than a tube frame. How stiff is desirable ?
Talking to Mike Sinclair a couple of weeks ago (yes, name dropping..) he confirmed what i thought - it is possible to go too stiff. He had numbers which he'd collected over the years from good and bad frames. The trouble is that as tyres change, so does the desirable range of chassis stiffness...
Asked, he said that the figures that they'd based the Modenas frame on, would not be relevant with the current tyres. He told me to have a talk to Magee who was there also. Mike said he's one of the best chassis setup guys he's struck. I didn't manage that but if they're all at the upcoming Auckland meeting, Rich might...

Then there's the question of kart track use Vs big circuits...Very different rider inputs required so you'd assume different chassis stiffness would be wanted.

Frits - We know that in the 50cc and 80cc classes, manufacturers went monocoque then back to tube from year to year. Did anyone actually come up with any hard data as to which was preferred - and why ?

[Frits Overmars]

richban, your design looks familiar. FWIW, Tony Foale had a chance to talk to Eduardo Giro who confirmed that at least some of the frames (I can't recall if it was all of them) were welded Mg sheet, not aluminum.

To the best of myknowledge Giro used electron sheet for the Ossa monocoques.

Frits - We know that in the 50cc and 80cc classes, manufacturers went monocoque then back to tube from year to year. Did anyone actually come up with any hard data as to which was preferred - and why ?

Van Veen Kreider started with tubular frames and never tried anything else. Derbi tried everything, going forward and backward (but then they were Spanish).
Jamathi started tubular, then went monocoque and never went back. The Piovaticci, Bultaco, Minarelli and Garelli 50cc and 125cc bikes all were monocoques.

Hard data, as in hanging measuring equipment on a bike? Nah. Putting the likes of Nieto, Lazzarini and Cadalora on a bike: yes. Those guys could really tell what was happening. They all had previous experience with tubular frames and they all wanted to stay with the monocoques. They all became world champion with 'm.

[richban]

Putting the likes of Nieto, Lazzarini and Cadalora on a bike: yes. Those guys could really tell what was happening. They all had previous experience with tubular frames and they all wanted to stay with the monocoques.

Thats a good bit of data right there. I have riden Steel frames with lots of flex and (feel). Feel as in like you could feel the front end flexing. And really stiff Ali beam frames with lots of feel. ( that feel meant you new what the trye was doing.) I prefer that later. If I build this thing I will not think to hard about it. I will simply try and find the cheapest easiest way to do it. 2mm sounds heavy. I will have to mock up a cutting list from a sheet and see what it weighs. 2mm full sheet weighs almost 14kg.

[Michael Moore]

Greg, I think that stiffness thing depends so much on the rider. I doubt that any frame could be too stiff for me as I generally can't tell if the tires have got a reasonable amount of air in them until they are about half flat. Everything feels strange for 15 minutes when I get on a different bike and then it seems normal and like I've never ridden anything else.

Building a bike for a sub-50th percentile rider opens up many options, because the bar is soooo low. It is (almost) all good.

Things that contain liquid are probably best kept easy to remove, clean, fix, and isolate from vibration. But I am tempted to do a fuel-bearing welded steel or aluminum frame some day.

Frits, isn't elektron a Mg/Al alloy? There may have been a little translation problem between Mg and Mg/AL and AL sheet by the time the info trickled down to my level.

richban, I was doing some weight comparisons yesterday, if you can remember the weight per foot/sq ft and that steel is 2.9X heavier than AL it is then easy to scale up/down as needed for different thicknesses:

1 foot of 1" x .062" wall is .626 lb
1 foot of 1" x .05" wall is .508 lb
1 foot of .75" x .062" wall is .459 lb
1 foot of .75" x .05" wall is .3748 lb


.080 wrought AL 1.123 lb /sq ft
.080 steel sheet 3.267 lb/sq ft

[Grumph]

Greg, I think that stiffness thing depends so much on the rider. I doubt that any frame could be too stiff for me as I generally can't tell if the tires have got a reasonable amount of air in them until they are about half flat. Everything feels strange for 15 minutes when I get on a different bike and then it seems normal and like I've never ridden anything else.

Building a bike for a sub-50th percentile rider opens up many options, because the bar is soooo low. It is (almost) all good.

You're not wrong Michael...Short story.
Some years back, first season of what became a very well known special here (Tony McMurdo's pink thing for the Kiwis..) When he got to the NZGP meeting I got a chance to ride it in practise as did the rider of my bike in the same class - F3. I'd built the motor for it.
My works rider thought it was great - he was lighter than Tony. I found it flexed most unpleasantly - I'm about 30Kg heavier than Tony...
So older slower - but heavier - rider could show up something that Tony only found at the extreme limit.
Solved with a shitload of aluminium welding...
Maybe all works bikes should be tested by a fat rider.....

[mr bucketracer]

You're not wrong Michael...Short story.
Some years back, first season of what became a very well known special here (Tony McMurdo's pink thing for the Kiwis..) When he got to the NZGP meeting I got a chance to ride it in practise as did the rider of my bike in the same class - F3. I'd built the motor for it.
My works rider thought it was great - he was lighter than Tony. I found it flexed most unpleasantly - I'm about 30Kg heavier than Tony...
So older slower - but heavier - rider could show up something that Tony only found at the extreme limit.
Solved with a shitload of aluminium welding...
Maybe all works bikes should be tested by a fat rider.....

mine are tested by fat riders lol , i'm learning all the time (-;

[husaberg]

Bultaco built a variety of 360s. Or 363 cc to be precise, with 85 mm bore x 64 mm stroke (yep, way oversquare, exactly what I would not recommend today).
Based on the Bandido engine, they also made the TSS350 roadracer (picture below), with straight-cut primary gears and a five-speed gearbox.
I had to make do with the MX-bike's four gears but mine was better in acceleration anyway .
Attachment 327975

My bike more or less survived. It's resting in my brother's haystack (because I haven't got a haystack of my own). The handlebars are missing because I used them on my 750 cc Kawasaki H2 triple.
The engine broke itself to pieces. Once I had convinced the crankshaft bearings to stay where they belonged, and the clutch to grab instead of slip, I could finally dial in some power and then the gearbox shafts got twisted to pieces, pushing the cases apart in the process. That was more than I could finance at the time.

I think i posted some stuff a while back on the ese thread about Bert? Floods el bandito.
Do you have any pictures of the engine and carb.

There were a lot of those big Bultacos sold in Aussie - but not NZ - and a few were raced I believe. If you'd been in Aussie, your visually similar Holden would have had a 3 litre six in it to carry you to interstate meetings....

Tony Tomasi used to race an el bandito in the early days of cams.
it had a double sided SLS front brake of a laverda or Moto Morini or similar.

[Grumph]

mine are tested by fat riders lol , i'm learning all the time (-;

Ever tested the stiffness of yours against one of the RS125 frames ?

[F5 Dave]

Thats a good bit of data right there. I have riden Steel frames with lots of flex and (feel). Feel as in like you could feel the front end flexing. And really stiff Ali beam frames with lots of feel. ( that feel meant you new what the trye was doing.) I prefer that later. If I build this thing I will not think to hard about it. I will simply try and find the cheapest easiest way to do it. 2mm sounds heavy. I will have to mock up a cutting list from a sheet and see what it weighs. 2mm full sheet weighs almost 14kg.

Perhaps 3mm steel sheet might be more in keeping. Scaling things appropriately. . . . I'm just saying

[TALLIS]

Ever tested the stiffness of yours against one of the RS125 frames ?

We have found the honda rs125 and Yamaha tz125 frames are quite a bit easier to get a grinding disk thru. Unsure how that transitions to frame flex on the track.

[Grumph]

We have found the honda rs125 and Yamaha tz125 frames are quite a bit easier to get a grinding disk thru. Unsure how that transitions to frame flex on the track.

bloody heathens...you could at least test the next one BEFORE cutting it up.....

[F5 Dave]

Regan's tested at least one. Think the result was Earth1: HRC nil

[mr bucketracer]

Regan's tested at least one. Think the result was Earth1: HRC nil

lol yes clean break , he sold it with new frame and jay snaped that one to , like you said i would go 3mm alu ,already started a sheeted frame

[trevor amos]

When designing the monocoque structure of the Ossa, Eduard Giro, with his formal back ground in aviation, specified magnesium alloy sheets not available in Spain, but was denied an application for their import from another country. Such was the oppressive and paranoid regime of General Franco. Not to be deterred, he arranged the “clandestine import” of the material on the backs of mules using a smugglers route over the mountains from France. Don`t know if this tale is true or not, but if so then its another inspiring example of putting one over on the dictators of this world, and of a small team with limited resources achieving great success against the mighty Japanese factories!
Frits, perhaps you might be able to confirm or dispel the reality of this tale, and might I be able to detect some small influence from the Ossa concept in your own creations?

Cheers, Trevor