Attn Mick Potter. Frames and handling..

Great Mick .... My 001 has 37kg on the front and 39kg on the rear - what would you think is ideal(?) for a bantam
and what would be your chosen wheelbase?

Also assuming the same tyres front and rear, what would different rims do ? ie WM1 front WM2 rear ?

Cheers Mike

If it is in part 4 disregard this post but I think something about gyroscopic effect will help. Not a big factor with the size wheels we use but still important.

Hi Mike.
I don’t think you read my last post correctly. If you weigh the same as me (63 KG in clothes) then your bike is 11 KG by the weights you have quoted. As a MOT tester I have to weigh the bike being tested with me sat in the normal riding position. Some but not all sports bikes have more weight on the front wheel than the rear, remember that these are road bikes not those that have been lightened for racing. It’s not just the bike but the bike and rider that contribute to the loading on the tyres. Every bike is different, it depends on where the c,of,g of the bike is (front to back) compared to the c,of,g of the rider in their normal cornering position. Usually the riders c,of,g is rearward of the bikes, so increasing rearward bias but not always. Only weighing front & rear ends with rider on then off the bike will tell you.
Increasing the rim size for a tyre (only do this if the manufacturer states that is an allowed rim if not ideal) will move the contact patch away from the centre line & increase the size of the contact patch. But the angle of lean before you run out of tyre will be reduced. A choice between better grip and greater lean angle. Rear tyres have more contact because they need to transmit the power coming out of the corner. As with all things to do with handling it’s a compromise.

Mick.

Gyroscopic force of the wheels was mentioned before Ted! As with that dreaded flywheel topic it is the dia and weight to be the factors of the force with dia being prominent when weight is at the rim(as with Tyres): James Cook pointed out a good video on it you could call up on here and I spoke about my experiment(s) with it on Icarus-2 which upset Wobblyman no end and frightened me poohless at Brands.
Ken Sprayson said things (handling-feeling things) would always feel more comfortable if a line drawn thro´the steering head crossed above the bisection of the Rolling Radius (vertical line down from wheel spindle centre) by about half-an-in inch. This can be achieved by altering the relationship fork Rake angle to steering head angle with suitably machined `slab´(?) yokes.....

I made it half inch under the halfway point of the Rolling Radius and Icarus-2 FLOPPED into the corners. It was a disturbing experience -- well, frightening then!! It is understandable when you think of the total (bike & rider) weight being thrown (distributed) forward on decelearion when entering the bend with the weight having more leverage over the front wheel angle -- than when the bisection is half inch lower!!

I guess it is the gyroscopic action that allows the rider to remain upright with feet on the pegs....

Cheers!

PS Why does "g" -- the Force of Gravity -- hurt more at Snetterton than at any other circuit?
Is it something to do with height above sea-level???

Oh right you are, so bike and rider need a 50/50 % Front/rear weight -ish

And i'm guessing bike only wants a 55/45 % weight distribution ? looking in books ?

Here's some BSA Diagrams for std 175 frame - sorry numbers not readible...

Ted.
You are right & I will mention it in next post.

Mike.

Correct, the difference between the two values will give you lead to how much you need to increase the wheel base or move the riders weight forward (very unlikly on a Bantam).

I'm on holiday from Thursday for a week so no more post's until I return.

Mick.

Hi Mike.

Just rmembered somthing that happened at work today that may be of interest. I had to MOT a Yamaha R6 (the same model that won this years world supersport championship). Total weight with me on it sitting in the normal riding position 230 KG. Balance of bike 1 KG heavier at the rear (less than 0.5% differance). Out of interest I weighed the bike on it's own. Balance of bike 11 KG heavier at the front. Hope this stirs the grey matter in everyone.

Mick.

From the dim past comes that Humphrey R... one of our club´s IoM, TT replica award winners and a DegreeMan at that, reckoned the wt distribution -- rider up, fully race-shod -- should be 60/40 - heavier at the back -- because of race-braking being nearly "g" -- 32ft/sec²...
H... argued on (with the famous engineer, Dr Lowe) in MC journals that deceleration during braking, to the maximum (at that late 50´s time) would result in a switch of those percentages to 60/40 heavier weight distribution to the front ...

Well, when watching GP racing over the years, seeing the back wheel rise clear of the tarmac during braking I´d say there was 100% of total weight on the front tyre patch so both of these clever geezers got it a bit wrong ---
--- did they? OR didn´t they?
Otherwise we have a new way of flying -- hmmm!?

--- daft thing I just said, it is a form of flying....

But like you said Mick -- it is all down to where the centre of gravity is...

... or sits??

If the wheelbase was 100inches (never that long, of course...) and the wt distribution was 60% rear then the CofG -- lengthwise -- will be 40" from the
rear spindle ... won´t it?

I imagine that if the CofG is forced higher by other factors (as Mick said) the distance of the CofG
from rear spindle has to increase to counteract that change (maybe lengthening the wheel base) and the wt distribution will consequently be altered.

Can do it with a diagram by taking moments about each tyre patch and KNOWING exactly where the CofG is --

--- but I guess it can be done practically -- perhaps by suspending from different locations on the bike (with rider aboard) and plumb-bobbing centre-lines ... which when bisected determine the CofG point....
-- hanging from a substantial ceiling, of course!!

--- there must be an easier way -- Mick??

All interesting stuff? Perhaps it's time for me to consider - lenghting the
swinging arm and shortening the fork offset/ steepen head angle ?

Looking forward to next installment... great reading...

001 in for repair 2009

I rode my 1927 Triumph 500cc "Model TT" around Cadwell and Brands (not raced because it was still hand-change
and kept jumping out of gear) and finished halfway down the field so I feel sure I was going faster than on the
Bantam.
Point I am making is that the Triumph was girder fork front and solid rear end ---
-- so, shouldn´t a solid rear end be alright with a Bantam??

... get ready to duck John-Boy....

Good evening Gents,
Have not missed any of the recent postings but have resisted the temptation to reply.
This is a cracker.i have had long conversations with Mick on this subject and have a similar background to him.
i also feel that alot of time can be gained with your optimum set up.Always remember that its the riders confidence that will produce the best lap time so when considering a radical change you may not produce the same time until you are used to the new set up.This is what sets club racing apart from the professional arena. those guys have the skill and budget to push to the limit and beyond to find what they want plus a bike stuffed with electronics to measure all the different perameters its not all by feel! The data does not lie.
I also think our bikes tend to be to heavy over the rear wheel and even mentioned it to Mike some time back (do you remember Mike)i have also been looking at various wheels base lengths ,steering head angle ,fork off set and evening took the liberty of measuring ians bike one day at Toms.
Another observation i witnessed this season was the pace of Michael Brown at the start of this season it was not what it was last year and i know he ran his new frame with last years engine so was this a confidence thing , set up or just a case of getting dailed into it ? Let us know Micheal or Rob.
To finish i like the frame jig thing Mike i believe that is at the Mecca of bantam building ?
All the best Nick

Bravo! Don´t be shy, Nick...!
Splendid observation & conclusion Nick -- A rider with great confidence can ride a heap of junk to some degree of success
and put a whimp on a champ´s bike and he´ll come back whining summatt´s wrong.

Like you said JB, look what my hero Mike Hailwood could achieve on his return on machinery Sheeny whined about !
But being an average rider I still think Bantams have adequote handling.
We lengthen Bushman swinging arms on trials bikes but for slightly different reasons. It does keep the front end down, gives better rear wheel traction; especially on steep uphill turns, but also works the longer shocks more.
I have Bultaco TSS front end on my watercooled racer, this has shallow offset and leading axle forks, on the standard Bantam steering head trail is a bit short.
On my 175 I have some B44 forks, 60mm shorter and with spacer below top yoke to maintain greater distance between yokes. The shallow yoke offset gives almost 100mm of trail and steeper setup. Turns in really quick and I am using back brake less.

Odd, when I look at my trials bike and racer side by side the geometry for modern uses is getting very similar

Mike,
with your welded up subframe do you still use standard Bantam swinging arm pin set up; if so how do you get it out to remove the swinging arm ?

I agree Nick -- the Bantam with its approx 12ft-lbs of max torque does not need to be heavy on the back which also agrees with Mick´s 50/50, R/F weight distribution -- as against what I said about the Humphrey (IoM TT replica personage) contention of 60/40 R/F but, of course, H... was talking about a heavier road racer than a Bantam. Even with the modern disc front brake the weight transferred to the front wheel during braking does not appear sufficient to go for 60/40 F/R set up.
Even at a full `g´ deceleartion it would not be enough to lift the back wheel off the tarmac -- that is assuming the C of G of a 440lbs total weight (rider full shod plus bike) to be 1,5 -1.6 feet above the ground.

I won´t bother anyone with the calculations that verify that latter statement --most have a "feel" for it anyway!!

Hi nick

As most of you all know my old frame used to handle like a dog and had nearly reached the potential the bike had to give I knew the engine i had was quick and after a ride on ians bike a cadwell I was amazed at how his bike handled so through the winter we got started on a new frame well as you all probably know it takes ages to get a bike to handle right and through out the season we were changing bits to see if they would help but also dealing with the good old reliability of a bantam you say you observed my pace through out the year but I don't think you realised lap times altho my bike wasn't handling as well as it could I was still matching or beating my old lap times as u probably know there was a few good riders that joined us last season which I'm sure we were all pleased with and because of this and a few other riders getting faster bikes I may of looked slower but according to lap times what I would go by I wasn't and though I would clarify this with you all

Michael

Hi Micheal & all,
thanks for that, very pleased to know your lap times are improving & i hope that continues
throughout 2012.
Another thing thats interesting is how the moto gp riders all tend to favour one particular
bike over another. I believe these bikes can have the exact same set-up , and obviously are built to a level of accuracy that we are unable to achieve, so it brings me back to thinking that it is a mind set thing and just a matter of gaining the confidence with that chassis.
It would be interesting to know from Mike , Ian or anyone else as to their favoured frame/set up.I have not had the chance to ride one of the sms framed bantams so can not make any judgement about their handling characteristics but what i would say is that the more standard type frames tend to have good turn-in feel but seem to have a more nervous feel on fast sweeping bends and lack a little straight line stability,this confirms a few things to me .
Good steering head geometry for turn-in but slightly lacking weight over the front end (sitting to far back)
A little to short in wheel base length, possibly to steep a steering head Angle ?
Your coments please.
Nick

You´ve touched on the very thing I was thinking of mentioning (Again??) about one-man´s-meat-being-another´s-poison, Nick.
I´ve already told the story of how I built Icarus-2 (second cocky Bantam!) -- following a talk by Ken Sprayson on frame design -- with a low bisection of the rolling radius by a line from the the steering-head at its rake angle -- and I shall have to get the diagram on here to show what that means but what it meant out on the circuit to The Wobblyman, Colin Aldridge, and myself was total opposite in rider confidence: poison to Wobbly, meat to me. The steering head rake angle was 63 degrees(from horizontal) as was the fork angle using equal yokes and trail was 4.2" ....

I suppose some would say it was "twitchy" I described it as "flopping into the bend"
which, probably, the experts would say is `oversteering´.
The feeling was that as the bend approached and braking and gear changing done- with a mere twitch of the clip-ons and the whole plot would be leaning at a more acute angle than necessary for the radius of curvature which meant my natural (Freddy Frith) tendency to lean upwards would automatically switch in and I´d feel fully under control.... I can understand the difference for Colin who´d raced 500s and bigger... earlier with that tendenmcy to climb-off would be quite disturbing!!?? .

I tried sending the diagram and lost everything and had to do the above again -- so I think I shall have to e-Mail the diagram to Eddie again...

Eddie!? is it OK?

John,

Email what you want and i will see if i can sort it (especially as you called me Eddie as i hate Ed!)


Kind Regards



Eddie

My first name is Edwin but my Mum won the day `cos everyone calls me John!

I tried to send the b.... diagram -- I just dunno what to do when it doesn´t go...

I´ll try again,

Thanks Eddie,Cheers,
JayBee.

John first SMS frames had std s/a pin with a complicated pair of tapered allen cap screws
in the outrigged subframe points. However all? I think now have separate 'trunions' which
run inside the bushes. the whole set up has a 3/8"shaft running through :- subframe-trunion-
frame-trunion-subframe, nuts at both ends. Hope that makes sense? (Pic 2009 repair)



Nick std 175 frame is 27degree (from diagram) and SMS frame is 27degree from jig.
However dont know as to std 175 frame on its tyres? And although my bikes 27degrees
on there tyres Ians and Snowy have 30degrees (but they all came out of the same jig -27)
Ian's 2 bikes are different again as they have yokes with different offsets.

Ian only raced his 005 once last year (a race you will remember Nick )

I raced both my bikes which are nearly identical and same chassis set ups
Difference is weight distribution 001 F 37kgs R 39kgs 003 F 38kgs R 38kgs.

My first choice bike is the original Pete Styles 001

Came in German John




Eddie

Thank you Eddie!

Gross ERROR! the "63°" SHOULD BE 27° -- 63° from horizontal -- Whoops!


I also realise: AFTER 39 YEARS! that the diagram is not to scale: the wheel is too small for starters and the Y yokes distance fork centre to steering head centre too large for seconds.
But it is a good indication of the "feel" of understeer and oversteer caused by front end differences.

See where the line from the steering head cuts the Rolling Radius -- vertical -- under the midway point?
by about half-an inch ?
This gives more wheel-and-forks weight leverage forward of the pivot-axis which not only has the gravitational effect but also increases the gyroscopic response to movement of the clip-ons (or rider twitch??) . These two plus leaning-in make the response to rider reaction very sensitive. BUT if the rider keeps his own CoG in line with the plane of the wheels the centrifugal force & vertical weight function cancel these out -- IT IS ONLY WHEN LEANING AWAY FROM THE WHEEL-PLANE: up or in --that these factors have any effect.


If the distance `Y´ on the yokes is reduced, the steering-head rake line cuts above the midway point on the rolling radius but the trail increases too much so the answer is to steepen the angle (as Nick spoke of... but a limit is suggested of 25° ...) or to make the `Y´ on the yokes different from each other thus keeping the required trail and having the rake line come above the midway point -- thus reducing both the effects mentioned above and making the steering less senstive to the rider´s "twitch" or hanging-out lean.


I´ll try another diagram to make that clearer...


Cheers!

Good morning all,
To John S ,Tom also does a nice mod to the swinging arm pivot on the more standard frames it is a press in pin arrangement , drilled to 3/8 and being the same width as the rear mounting lug, he then has 2 trunnions (top hat type) that fit in the original bushes these are made to a high tolerance and take out any side play within the arm.Then bolted up as standard .I Dont know their material but they are very hard,hope this is a reasonable description.
Mike ,thanks for that ,Who has 001 now, is it Chris ? very interesting that it was your favoured chassis, was it a particular aspect that was better ,perhaps you could let us know.
John ,great drawing and well described i can almost understand the maths.
how about some diagrams of leading and trailing link fork arrangements i know there not in current use but very popular in the old days.(right up your alley i hope)i think some exaggarated diamensions
would show exactly how things are happening.
Cheers Eddie for the help.
Nick