Attn Mick Potter. Frames and handling..

Hey Nick!

Eddie can show the pic of Andy Boyle´s GP5 replica which has funny forks, leading-link like Earles, I think -- I sent the photo as a test
for my PC sending pics -- it was a Ken Sprayson job. Andy does work with him and the Gardner Carb bloke...

If the pic of Andyßs bike is there ... then perhaps more learned/experienced experts can explain the advantages etc...
for my part, the diagram I showed of normal teledraulics has a lot of weight forward of the pivot axis (bit of the wheel plus forks weight) which doesn´t cause any bother until you hang-out, lean-out or `lean-up´.

Because I had a tendency to `Lean-Up´ the set-up I showed suited me...
Not for Wobblyman though, he tended to shift his weight in toward the centre of the bend -- came from riding bigger bikes before Bantam, I guess...

That backs the point you made about gaining confidence in a set-up -- I was more confident at a higher speed with my second Bantam than with the first, the trouble with Icarus-2 was its pistons didn´t last and then, of course, I got that fantastic job offer in Canada (greedy gitt) -- enormous salary and status lift -- ruined my chance of becoming club champion!!!????

Cheers!

JB's Modified

Nick I own 001 !!
and 003!

Chris has 002
Phil Betty 004
Ian Scutt 005,007(yet to be used) and 008
006 scrapped Snowy 009(re-framed 006)
Michael Brown 010.

Ref - preference- more 'confidence' in 001 27yrs spent racing it, 003 only 10yrs??

oh yes mike,the penny should have dropped i spent enough time looking at that number on your seat cowl this year
Have been thinking about the differances built into the sms frames and wondered what the jig is like to hold the frame whilst brazing them back together could you let us know.
Does Tom have lots of distortion problems, as you probably know when the tubes are heated and expand they always contract by a greater amount so you will always end up with an amount of built in error.
The old frame builders would re apply heat in certain areas to correct the errors ? is this the method Tom uses ?
cheers Nick

Nick frame jig is very heavy duty and has a base made out of girders! Some angle iron goal posts
to hold Swinging arm pivot and a pillar and collars set at 27degrees to hold the steering head.
Just scanned through my pic's but none of the jig...
I have been involved(cutting filing cleaning) with the making of 003,
006 and many repairs... but always had a top class welder(and former bantam champion) Pete Styles
on hand with torch and rods. Fair amount of distortion? Pete sorts it? Not sure how....

Yes just to confirm Tom fabricated the jigs but Pete did the hot gluing in the team.
001 and 002 had different forks, front hubs and rear suspension. Pete had Girlings I can't remember the name of the rear units I had but they were supposed to be the mutts nuts so I wanted them ! I believe the geometry of both bikes was identical. Having done a few laps on both bikes I cant say I noticed any difference in the handling. Pete was happy with the handling from day one but it took me a while to get used to it, they seemed more top heavy than I was used to. And not being able to sit up and steer them without my hands on the bars was completely alien.

Mick P thanks for your input, very interesting and enjoyable reading.
Have I totally misunderstood or would it be a case of the heavier the rider was the more weight would be transfered to the rear. And because the front would become lighter there was more justification in the heavier rider moving his weight about ?

Just the point I was making Ned -- moving the weight about makes that latest mass I´ve shown in red in the modified diagram much more sensitive -- or effective is the better word. As I said it before -- if the rider keeps his own CoG in line with the CoG of the bike that red mass doesn´t matter: it was blokes like Wobbles and me with 3 stone more flab who had the difficulties. Colin used to hang out -- or is it "IN"?? and on Icarus-2 he had a hard time whereas my Freddy Frith style suited Icarus-2....

Modified diagram. If you imagine the Rake (steering head) centre line being moved forward so that it cuts the RR above the midway point (as was my first Bantam, Icarus-1) by say 1/2 an inch then there is less torque (weight of forks and part-ofwheel multiplied by a lesser x lever arm) that gets out of control with rider twitch and you get the message Ken Sprayson was putting across at that talk he gave -- the sensitivity to rider reaction is less -- i.e. feels more comfortable and controlable. I think it was because I carried my grass habits into road and although I was trying to rid myself of that "lean-up" I felt better trying to pull Icarus-2 upward all the time.

Re the "Slip Angle" -- used a bit too loosely here -- it is in plan view the distortion of the tyre as it is forced to follow a track that is not the curvature of the radius of the bend so the tyre contact patch is virtually twisted thro´a small angle -- which both (front & rear) tyres expereince during cornering. (When cornering the front wheel is inclined to the radius of curvature track more than the rear wheel is...) This tyre distortion -- or Slip Angle is the basic cause of oversteer or understeer. Here, it is that although the distance of tyre patch to steering axis will be greater the distance x will be less -- hence the torque of the forks & wheel portion will have less influence on the slip angle than it does when in the set-up shown.

Ned! If you´d known about my bad riding habits in `81 would you have still lent me your lovely Bantam to almost destroy....??

My last bit on front end stability is that the Rake angle reduces the gyroscopic effect (from that of the rake angle being zero -- vertical).-- i-e. a horizontal twitch of the hands to the left creates a wheel-kick-slant of the wheel to the right but even though the rake reduces it, the effect is still there and is worse when the rake-line cuts through under the RR bisection and shown in the Icarus-2 -B diagram.

Ahh-men!

Thank you again Eddie, for showing diagram Icarus-2 - B...

Since Nick has requested a review of other fork options would you please show
the pic I sent of Andy Boyle´s GP5 Royal Enfield -- which has a leading link, similar Earles (I think) front end -- which really looks good yet I have not heard any mention of its adavantages or otherwise.

I wonder about the damping??

There´s a thought I had that´ll probably have everybody going hysterical -- it seems that "recognised" pattern suspension units and forks are fitted and then
the damping rates adjusted one way or another which means conmparison is made against an already varying variable.

What if the bike was first tested with a rigid units on the rear?
The first test riding to settle the front end spring-rate & damping -- tested with a solid back end. This way getting an optimum front end before concentrating on the rear suspension? Then with the rear working well the front would probably need some adjustment followed by fine tuning of back and front because they obviously affect each other....?

I say that because thundering around Brands and Cadwell with my old Triumph
-- girder forks and solid rear end -- was amazingly comfortable ...??

Hey Mick Potter... --- HELP!! I think I am out of my depth.

Cheers!

There you are Nick!
I didn´t get Andy´s permission to show it -- but if he gives me a good kicking I´ll pass it onto you.

cheers!

Ned - just for your info - circa 1984

001 RD200 Forks and brake assy Girling shocks

002 GT185 Forks and brake assy Koni shocks

Mike

Oh Ye! Thanks for jogging the old grey cells Mike.

"John" Edwin I notice the exhaust and rear chain were removed before you were allowed to sit on that Royal Enfield.
Why on earth didn't I think of that

Hi everyone, back from my holiday & trying to catch up on the latest posts.

Ted. I’ve been thinking about your post & I have spoken to some people about it. It’s well known that fitting lighter wheels help handling because of the reduced unsprung mass. The effect of gyroscopic progression when leaning into a corner however gave rise to much debate (as I expect it may hear). The consensus was that as a bike’s size increases the rear wheel rotating mass increases in relation to the front wheel. But at the same time the rotating mass of the front brake increases therefore keeping the relative rotating masses near to constant. If I remember my physics lessons correctly two rotating masses rotating in the same direction cancel each other out. Obviously the front wheel doesn’t have exactly the same gyroscopic effect that the rear has & the rear is fixed wear the front is not. But no one I have spoken to has ever read any papers or publications on the subject. I await enlightenment on the subject.

Ned. You are quite correct. A heavier rider on a standard Bantam will move the c,of,g back & up. Moving the c,of,g up mean’s less lean angle at the same speed but it will mean the heavier rider will need to move his body weight forward to regain an equilibrium of balance (assuming both riders sit squarely on their bikes).


Mick.

Whilst you were away I have hogged this topic -- sorry Mick.

It was because I had taken that bit about gyroscopic couple effect to heart and when Wobbly Aldridge
took me to a Ken Sprayson talk in Coventry my whole thinking -- about bike handling, went inside-out,
upside-down and I built Icarus-2 with an experimental front end which was very sensitive yet which I
could feel comfortable with and Colin Aldridge could NOT.

I must admit my first test run at Brands had me worried -- I went very wide (on
the grass at Paddock) but once I got used to the "Icarus-2 Flop" I enjoyed riding my second Bantam more than the first.

I have a good article about gyroscopic effects by Vic Willoughby where he says the same thing James
Cook has said*** -- if you´d like to see it I´ll try Eddie´s patience again and get him to post it on here.
My wretched German PC won´t obey my commands -- much like the situation when I was riding Bantam -- so I have to e-Mail docs & pics to Eddie who then sticks them on here..

*** James put a video on here earlier which shows that the rider hands-twitch to the left results in a bike
tilt to the right -- and vice versa -- which is what we do automatically, the article says...
... and which many do NOT believe.

Ned´s theory of sitting hands-off to steer a bend would surely be querying the notion. (Uh oh! I´d better creep into my corner again...).

Apologies to all the readers here for repeating this tale again and again!!

Made another discovery where I get Logged-Out of this website -- and I cabnnot get back in -- it is the using of Capitals to log-on -- upsets the BRC software. Thanks again Alan. "Caps Lock" Alan said which had me puzzled but is simply CAPITALS LOCKED!!??
Cheers!

Nobody´s perfect Wobblyman said, in disgust, when he gave me back Icarus-2 -- piston seized again....

john bass wrote:

*** James put a video on here earlier which shows that the rider hands-twitch to the left results in a bike
tilt to the right -- and vice versa -- which is what we do automatically, the article says...
... and which many do NOT believe.

Ned´s theory of sitting hands-off to steer a bend would surely be querying the notion. ..

Not necessarily John. When we ride no handed, peddle or motor bike we continually move our weight to correct the line. So it's quite possible we subconsciously shift our weight in the opposite direction first.

Yup! you are right Ned. That was my argument, that although we mightn´t slide our posteriors across the seat --all that much -- we do, automatically move our body-weight about just as much as we might automatically move the handlebars (clip-ons, I mean) the opposite way to the bend to initiate the lean angle.

So I am all for arguing that both ways work but would ask -- which do we actually use when desperately rushing into a bend?

I would like to show the difference of Wobbleyman´s `style´ from mine where
Wobbleyman didn´t have to angle bike over as much as I did to drive hard thro´the curve.

I´ll try and draw pics of our differences...

Just remembered this photo -- shows difference of style.

Sorry! didn´t function...

Hi John,

Send what you want to show and if anybody is interested then i will post it up.


Eddie

Hi John.

The afect of moving the handelbars to the right to tern Left is called counter stearing and it is the only way of iniating a turn. We all do it without thinking.

Hi, all.

Frame flex, & why it applies to a Bantam.

I hope you are all reading the racing pages of whatever publication you subscribe to & watching moto GP & WSB, ect. If you are, many a time you will have come across people referring about frame flex & how it affects handling. A certain Mr V, Rossi has had problems with the handling of his Ducati. I (and many people I know) have believed that the engineers at Ducati have completely misunderstood what is required. How many times have various manufacturers engineers produced a new chassis only to have it rejected by the riders. Firstly contemplate a motorcycle travelling across a ripple in the race track when vertical (let’s assume the deviation is 25mm). The suspension Front & rear will move vertically 25mm as the wheels move over the deviation. Now contemplate a motorcycle travelling across the same ripple at a lean angle of 90 deg (it’s impossible). To insure that the tyres stay in contact with the ground the wheels have to move sideways in relation to each other. Now think about a Bantam (or any bike) at a 45degree angle of lean while cornering, in comparison to the same bike in an upright position. The suspension movement will be almost completely used up because of centrifugal forces & gravity meaning that the 25mm deviation in the surface results in a small deflection of the suspension (because the movement is not in line with the suspension) and a flex in the frame that corresponds to whatever is needed to keep the tyres in contact with the ground. The greater the angle of lean, the more the frame flexes in comparison to suspension movement. In corners of high G force, possibly the bottom of paddock hill bend at Brands Hatch or Mansfield’s at Caldwell the only suspension movement may be frame flex. The Ducati had a very short frame that connected the top of the engine to the steering head (obviously the engine can’t flex); the engineers calculations said it was OK. The riders said it didn’t work. Now Ducati are trying a longer frame that the riders are happier with. This example proves that an engineered solution to handling doesn’t mean it will feel right to the rider. I believe Ducati made the mistake of trying to get their flex into to one part of the bike rather than whole bike. Every bike has to flex otherwise it will give the rider no feedback and the rider will have no confidence in the feel of the bike. In order that a bike feels good when on the limit, the wheels must stay upright in relation to each other but be able to flex left to right (easier said than done). The standard Bantam frame is as we know very simple. When stressed more than its original specifications it will flex. Instead of the front wheel moving from side to side in parallel with the rear wheel the frame will twist, resulting in the front wheel leaning at an angle in relation to back wheel. The result is a very bad handling bike that may shake its head violently. Also the frame can bend into a Banana shape therefore inputting steering effect not wanted by the rider. Under breaking the wheel base can also shorten irrespective of suspension movement. These three types of (bad) frame flex are the Bain of frame designers. With all the compromises that a designer has to make it’s no surprise that no one has yet produced the perfect frame. Over the year’s most riders have modified the frame of their Bantam to improve its handling. Anything that you can do to reduce the bad types of flex (wheatear one or all three) will improve handling but try to retain the left to right flex in order to maintain rider feel. If you compare many modern frames of sports bikes over the last ten years (whatever the type of construction) on average the frame spar/spars move from the swing arm pivot towards the steering head parallel to the line of the bike, then turn at 45deg into the steering head. By looking at outer types of frame construction it may give us ideas of how to improve our own bikes. Before any modification is made consider what effect it will have on the handling.

I hope this stirs more grey matter.

More ranting to follow.

Mick.

Countersteering -- that´s the word I forgot.

What started a flurry on here about Rossi and his Ducati was that Rossi had apparently said (after bringing Casey Stone down) that the flywheels were too light and that had me thinking about Son Slick and his expereiences with Carl on the Ducati, WSB Superbike. I wonder what differences the GP Ducati of now has over that of the Ducati Foggy won 4 world titles on???

Point of all fuss I made about the front end geometry being special to a style of riding was reinforced by what you said about rider confidence. Taking it as read that countersteering is what we do automatically -- and could well do it, No hands Mum! no teeth! by a quick lean left, to go right -- I got into the idea of showing my Freddy Frith, body `lean UP´ and The Wobbleyman (Colin) Alfridge´s `lean-in´
styles and had started doing sketches -- when --

--- and it occurred to me that a photo -- taken from an unusual angle -- existed of us at Llandow complete with Max Ridge: all three exhibitting different body lean...

We are on different parts of the bend but the differences show. Max, in front has
screwed his spine so that the top part of his body is well inside the curve and his CofG is way off the centre line of the bike -- inwards of the bend.
Colin, at the rear, has slid his bum off the saddle to hang his flab inwards...
And I, in the middle, am for once not doing my lean-up á la Mr Frith. I was at that time on Icarus-1 with the preferred steering geometry.

So, I shall again send Eddie the photo to show what I mean.

Cheers!

Hi Mick! I am hesitating going on with my bit about the front end and how that affects the rider´s style (and confidence) because Mike Powell addressed this Topic to you -- and I feel I have been hogging the pitch, too much, whilst you were taking a break --

-- but before quitting -- at least for a while -- I´ll change tack just for a quick moment and light upon what you said about that certain Mr V. Rossi and his complaining about the GP Ducati´handling and frames flexing -- although by what Mr Powell said I could have sworn he (Mike) had it that Rossi was on about his flywheels being the problem. I do believe -- now -- that was a `con´ by Mr powell to get some of us going yakkitty- yakk about the flywheels (and I fell for it!!).

In all the times I went to see my lad with Carl Fogarty racing Ducati I never saw the Ducati naked -- i.e. less its fairing -- so I had no idea how the frame and engine go together but I just came across a picture of Fabio Taglioni (Ducati´s former frame designer) holding the frame of a 600cc Pantah V-Twin and if the GP Ducati has that sort of frame design it doesn´t surprise me in the least that Rossi, after having raced a duplex tubed frame machine, found the Ducati´s handling dodgy. Like you said, a rider gets used to how a bike feels at racing speeds and obviously Rossi immediately fell foul of the difference from the Yamaha and Honda of his earlier GP racing ...
It was the other way about with Carl Fogarty when he went from Ducati to Castrol Honda for a season -- he seemed a different rider altogether -- maybe proving that point to the full; the Ducati suited Carl and the Honda did not....

Mick! Do you know the differences of the WSB Ducati of the late nineties -- from the GP Ducati of today?
The engine still forming part of the frame´s rigidity??

The Pantah frame is all welded tube joints and virtually two triangulated box constructions coming together at the top where a single horizontal cross-tube forms their connection -- leaving a large triangular gap -- ^-- for the engine to connect to -- such that the engine is holding the plot together, of course.
It seems to me -- and I could be criticised here -- that where the engine mounts have movement in their mounting fastenings (even precise machined bolt-housing will still move....) this will be magnified to the front and back end of the frame -- thus making the banana shape you mentioned and probably causing yaw -- particularly with the torque the Ducati puts to the back wheel.

Another thought occurs before closing. Is it possible a frame can be too rigid?
That the rider does not get a PROPER FEEL for back-end and front-end movement
because of too much rigidity? Was that so with Lugged frames? It might explain why Carl was top dog with the Ducati and the following season with Honda playing second fiddle to Aaron Sleight.


Cheers!

Hi john.

Ducati first used a ladder trellis frame on its Pantah engine road bikes. From the second generation Pantah and until two years ago on the Moto GP bikes, they have used a fully triangulated trellis steel tube frame. The frame mounted onto the front of the crankcases and to the rear of the crankcases, just above the swing arm pivot. The swing arm pivoted directly into the rear of the crankcases. For the last two years at least, Ducati have returned to a frame design that to my knowledge has not been used since The Vincent. The Vincent as I am shore you remember had an oil tank that was referred to as the upper frame member. The Ducati Moto GP bike of the last two years has mounted the rear suspension and rear sub frame directly to the rear of the crankcases. The steering head had the air intake passing through it into the air box and that constituted the whole of the frame. The air box/frame was about 30-35cm long and connected to both cylinder heads of the V4 engine. Firstly the frame was aluminium and then changed for carbon fibre. Most other manufacturers have developed aluminium beam frames. In developing road bikes for use in WSB & BSB many teams have not fitted one or two upper engine mounting bolts (depending on manufacturer 2, 3 or 4 upper engine mountings are used), because the riders preferred the feel that resulted. Ducati are now experimenting with the aluminium frame concept. Only one person has been able to get good results from the old air box frame (Casey Stoner) and when he crashed he always lost the front end. As you said some people can ride anything, but most need a bike that responds in a way that they are happy with. Basically a bike has to inspire confidence in the rider. The only way a rider can find out what they like is to change what they have and/or ride a different bike. Until comparisons are made there is no way anyone can know what they they prefer?

Mick.

Thanks Mick -- I had no idea so much had gone into Ducati frame design...

And that was the other bit that has made me regetting not haviing more time with Bantam Racing and the BRC and that is that I was just discovering with Icaus-2 what I really needed and not getting any good results because of lack of engine reliability when greed for money and status took me off to Canada. I feel I missed
out on what could have been the better part...

When I started Bantam racing I wondered WHY? because it just did not suit my temperament. On grass and speedway I was used to lots of torque, no brakes and flinging the plot down to scrub away speed and virtually steering on the back wheel sliding coming out of bends, where with the road Bantam it was much more refined and sitting patiently waiting for the signs to come up for when to brake etc.. etc....

What I have yet to see in any review of MC Handling is the effect of rider´s CofG relative bike CofG -- how the interaction effects the steering and how much the rider does move his weight about....

I have just been informed its time to get myself ready to go out so I shall leave you. Mick -- and the rest who may be interested -- in this little bit of subjective science to ponder on:

Many decades ago Science Magazine presented this: hold a cat upside down -- feet upwards -- and when thrown high in the air the cat will always land on its feet. Unlike a diver who gets his impetus from his feet on the springboard the cat has to manipulate its body -- somehow -- about its CofG whilst without any obvious means of support ...

... now! I wonder just how much of the cat the road racer needs to have in manipulating the tracks of a motorcycles wheels to do his bidding???

Cheers!

PS don´t go telling me you heard Mike Powell purrr when he´d won....!!!