Race chassis

[Hilleye]

This style of spine frame is normally used to house sizable lumps such as fours and Vincents harleys etc.

I used to own one of those, it was actually for a bucket and i think the spine was made out of the drive shaft of a car. It was made by a m/c engine builder based in Te Atatu and from memory it was all braized together. Didn't weigh much at all. Unfortunately never got the chance to ride it with an engine in (he bought it back off me before I could get a CB125T into it) so can't testify to its rigidity.

[F5 Dave]

Nice pics
mmm, almost zero swingarm droop & 30 odd degree steering head angle. Should handle like its on rails.


Literally.

[husaberg]

Nice pics
mmm, almost zero swingarm droop & 30 odd degree steering head angle. Should handle like its on rails.


Literally.

27.5 degrees according to the blub for faster steering response. than std.
The Egli frames were originally i believe designed for hill climbing Road racing was banned in Switzerland from memory as Interferes with the cuckoo clocks or something.
In the other pics with the engine in and the wheels on the ground it does have surprisingly little droop though.
They were renowned i believe for their stability.
But this one looks like it could do with longer shocks.
Which could account for the lazy looking head angle.
But a quick note remember these old bikes ran rear tires equivalent to a front tire on a rs125 front tire(probably skinnier) and most likely in triangular profile so the steering is probably a little quicker than it looks.
It has a 4 inch spine and is 1.8mm wall thickness rather than the std 2.4mm road version.
The gearbox plates for the Norton/AMC transmission used are 9/16 (14mm?) 7075 T6 Aluminum.
So someone had hacked off the Vincent gearbox previously.
What you can't see in the picture is the beautiful engine turned finish on the gearbox plates.
Oh how i adore it.

[husaberg]

Some interesting stuff here about properties and design.
You will also notice the NWS boys look a bit crazy in this pic as well.
Beautiful work as always though.
The tagline for the company was pure fabrication.

I do note now swingarms are supposedly designed to have a certain amount of lateral flex to limit the chances of a highside and improve feel.

[Grumph]

Fitz Egli and terry Prince - whose idea that frame was anyway - always had strange ideas on geometry. Terry got into frame building doing sprint frames so straight line stability was high priority....One race test of an Egli I've got describes the footrest placement as a hamstring stretching exercise. Whatever fits the builder I suppose.

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.

[husaberg]

Fitz Egli and terry Prince - whose idea that frame was anyway - always had strange ideas on geometry. Terry got into frame building doing sprint frames so straight line stability was high priority....One race test of an Egli I've got describes the footrest placement as a hamstring stretching exercise. Whatever fits the builder I suppose.

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.

[Brian d marge]

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.

The 91 Cr was probably the best frame , was a goodun that one, not so sure about the latest crop...anyway Hysterisis ( no Im not hitting spell check , knackered brain aint working and its beer time ) but I cant remember what the britain had , Carbon Fibre swing arm ? frame , headstock , completley different hyterisis pattern to steel ( a wonderful product may I say ,,,3 cheers for steel hip hip !!!) I do believe the ducati is sharing the similar problem.

In an earlier post it was said that by winding up the rear? damping , the front end chatter dissappeared , would like to follow this up , what was the cause ? My feeling damping was masking another fundemental problem ?

Stephen

[husaberg]

The 91 Cr was probably the best frame , was a goodun that one, not so sure about the latest crop...anyway Hysterisis ( no Im not hitting spell check , knackered brain aint working and its beer time ) but I cant remember what the britain had , Carbon Fibre swing arm ? frame , headstock , completley different hyterisis pattern to steel ( a wonderful product may I say ,,,3 cheers for steel hip hip !!!) I do believe the ducati is sharing the similar problem.

In an earlier post it was said that by winding up the rear? damping , the front end chatter dissappeared , would like to follow this up , what was the cause ? My feeling damping was masking another fundemental problem ?

Stephen

Yeah McGrath allegedly only used one model frame (91 I think) Honda allegedly used to dress up the old models he so preferred to look like the latest current model. whether it is a urban myth or maybe he was superstitious i don't know. Certainly no one can argue with his results and while he was winning i guess they would give him what he wanted.
But the story goes he left when the alloy frame came along because they couldn't get away with it anymore and hated the alloy frame no doubt he was offered a lot of money as well to leave Honda.
Could be total crap but it is an interesting story nevertheless.

Aluminum,steel and Carbon fibre as well as titanium all have very different properties and the design of the frame does not readily translate to the other. As BSA found out to their peril no mater how much money they threw at it.

I seem to remember the Carbon frame may have been the cause of some electronics issues on the Britten as well with the ignition talking to the ECU and other electronics.
Sure was and still is pretty though.

[Brian d marge]

Yeah McGrath allegedly only used one model frame (91 I think) Honda allegedly used to dress up the old models he so preferred to look like the latest current model. whether it is a urban myth or maybe he was superstitious i don't know. Certainly no one can argue with his results and while he was winning i guess they would give him what he wanted.
But the story goes he left when the alloy frame came along because they couldn't get away with it anymore and hated the alloy frame no doubt he was offered a lot of money as well to leave Honda.
Could be total crap but it is an interesting story nevertheless.

Aluminum,steel and Carbon fibre as well as titanium all have very different properties and the design of the frame does not readily translate to the other. As BSA found out to their peril no mater how much money they threw at it.

I seem to remember the Carbon frame may have been the cause of some electronics issues on the Britten as well with the ignition talking to the ECU and other electronics.
Sure was and still is pretty though.

I can sort off confirm the mcgrath storty , have it from 2 separate honda sources .... ( but not from the horses mouth) oh and that Access card frame , from bsa , ( access your flexible friend ) nice try , but different materials need a different design approach , still its how we learn , by cocking up ,,,,,

Honda have made some howlers,

Ducati is in the middle of one ( stoner said "stiffer" , nice try but ...the Italian entry , "pas de points")

Stephen

Ps , you can squash thing and stretch things , but they bounce back when you bend, em . except silly putty , which is ... silly

[Grumph]

The 91 Cr was probably the best frame , was a goodun that one, not so sure about the latest crop...anyway Hysterisis ( no Im not hitting spell check , knackered brain aint working and its beer time ) but I cant remember what the britain had , Carbon Fibre swing arm ? frame , headstock , completley different hyterisis pattern to steel ( a wonderful product may I say ,,,3 cheers for steel hip hip !!!) I do believe the ducati is sharing the similar problem.

In an earlier post it was said that by winding up the rear? damping , the front end chatter dissappeared , would like to follow this up , what was the cause ? My feeling damping was masking another fundemental problem ?

Stephen

The Britten arm was a foam filled carbon fibre shell. Fairly late in the piece Murray redesigned it as they'd picked from pictures that it was flexing more than they'd thought. I'd suspect that if they'd had an experienced conventonal suspension guru on tap quite a lot of their problems could have been solved earlier.

The front end chatter problem referred to was just the opposite to your memory....specific to spine frame Aermacchis with the motor rotating backwards - too much spring or compression damping at the rear causes front end patter. Read a track test of Dick Linton's bike by Crashcart who found exactly the same thing - I just laughed and said...been there.

[F5 Dave]

27.5 degrees according to the blub for faster steering response. than std.
. . .

Put tassles on it, that's a cruiser.

[Brian d marge]

The front end chatter problem referred to was just the opposite to your memory....specific to spine frame Aermacchis with the motor rotating backwards - too much spring or compression damping at the rear causes front end patter. Read a track test of Dick Linton's bike by Crashcart who found exactly the same thing - I just laughed and said...been there.

my memory is crap at the best of times
no , the question I was asking is WHY, was the suspension " jacking " up ie not returning fully in operation, moving bike cog Back a bit
add a reverse engine, , less weight on the front, prone to patter?
just curious....
stephen

[Grumph]

I can only make guesses as to why this particular layout is prone to this problem.

Most if not quite all macchi singles use Ceriani forks - the 35mm standard spring is quite light - don't have precise figures sorry.
Given that most twin shocks as bought have spring and damping rates appropriate to somewhat heavier bikes it's not surprising we see mismatches front/rear....

"backwards" engines - Surtees who rode nearly everything reckoned they should have the shortest possible wheelbase so as to compensate for the lack of torque - induced front end weight transfer....that was his theory for what it's worth...
Most Macchis are around 52 - 53in and it's harder to get them shorter.

[Ocean1]

I'd suspect that if they'd had an experienced conventonal suspension guru on tap quite a lot of their problems could have been solved earlier.

But would they have ended up using conventional suspension?

Dude, someone's got to make the mistakes, otherwise we'd never find the non-intuitive solutions you don’t get using iterative development processes.

[husaberg]

I can only make guesses as to why this particular layout is prone to this problem.

Most if not quite all macchi singles use Ceriani forks - the 35mm standard spring is quite light - don't have precise figures sorry.
Given that most twin shocks as bought have spring and damping rates appropriate to somewhat heavier bikes it's not surprising we see mismatches front/rear....

"backwards" engines - Surtees who rode nearly everything reckoned they should have the shortest possible wheelbase so as to compensate for the lack of torque - induced front end weight transfer....that was his theory for what it's worth...
Most Macchis are around 52 - 53in and it's harder to get them shorter.

I had a quick look for the front spring rates for a machi couldn't find them in any articles plenty about rear.
I did not Cathcart said the triangular Dunlops were a help on the island as they were springy allowing the bikes to run relatively harder spring rates with an acceptable ride comfort than they would have otherwise.

Re Daves bit yes they do have a lazy head angle but not really chopper like. Imagine if they had modern geometry with the old skinny tires and inefficient suspension. The old bikes weren't necessarily crap they were limited by the suspension and tire technology of the time.
Remember too although a big lump heavy the Vincent engine i hazard a guess is a bit narrower than a lot of modern engines as well.

I also note the racing Rocket Threes and Tridents. (The real Rob North/Hele works ones) head angle was 28 degrees. Well it was, after they fixed the first batches made wrong anyway.
The Triumph Bonneville was mostly around 28 also and the famed Featherbed was well depending who you talk too around the same.
Opinions differ but Sprayson says 27.5. The Commando arround the same as well. I bet they all had shorter wheel bases though.
The bevel Ducatis would have had far shower steering head i hazard a guess.
If it makes you feel better all the modern Egli Replica's have more modern steering geometry but they also have more modern tires and suspension.

For Brian the funniest Honda story i have read is what Gardner swears happened (he was there) that made them finally realise the upside down bike was a piece of crap and that they were on the wrong trail pushing the center of gravity down and down. Now that's a funny story.

I have a story which says each ti frame made fir BSA cost 3000 pounds they ordered 20 so what did 3000 pounds buy in 1966
Well heres a clue the average price of a UK house in 1966 was 3800 pound.So that one dear frame let alone twenty of them and they didn't even generally last a race meeting.

Below the finished bike one of the few Egli's I have seen with a tank that doesn't look awful.

Here is a link to a more modern Egli like Vincent replica in Stainless steel.
http://weldingweb.com/showthread.php?t=46896