Frame geometry / layout / design

[Al]

Anyone done any work on, or have knowledge of; frame layout etc.
I am going to make some changes to the J frame over winter and want to know more about what i am doing first.
Books, internet sources or any other thoughts /leads appreciated.

AL

[ADRIAN H]

http://www.tonyfoale.com/

[Jay1969]

http://z1ownersclub.co.uk/forum/viewtop ... t+geometry

[malmojoe]

http://www.tonyfoale.com/

here's a look inside the book at google
http://books.google.ca/books?id=84hF-qoR5I8C&pg=PA1&source=gbs_selected_pages&cad=2#v=onepage&q&f=false

[Al]

Thanks Jay i did read that when originally posted and made a mental note of one item.

Adrian and MMJ, thank you, i have been reading that book on another link but with (annoyingly) many pages blanked out.
I think Tony Foal is probably a tormented genius, would like to be in a room with him and Alan Milyard discussing motorcycle design. Fierce i reckon.
The Tony Foal book is good but always seems to come to the same conclusions; here is a problem with no solution,....no wait,.... use one of my bizzare designs to resolve it.
There was one of TF's bikes at Cadwell last month. The one with the handlebars sticking vertically out of the top of the fuel tank!!!!!! Most odd.
Unfortunately didnt see it out on track though.

This was my starting point and i have several issues to address;

Need more weight over the front wheel.
Need more ground clearance
Having jacked up the back end i need to put the swingarm back between the sprockets again.
Need to steepen the steering head angle.

Solution; cut out and move the front swingarm pivot point down by about 3/4 inch



Some of the dimensions above have now changed and some are just plain wrong.

AL

[garyd]

The one with the handlebars sticking vertically out of the top of the fuel tank

I had one of them...it wasn't blue with a Z1R engine was it.

It actually rode really well. Tony was quite e decent chap but did take an awful long time to make the bike...typical of your one man barn industry.

[Al]

Gary i think it was one of these but didnt see the engine as it passed behind other bikes. Was transfixed by the sight of what i did see though!



AL

[jimmock]

Anyone done any work on, or have knowledge of; frame layout etc.
I am going to make some changes to the J frame over winter and want to know more about what i am doing first.
Books, internet sources or any other thoughts /leads appreciated.

AL

Bring back the head tube by approx. 45 degrees.

Extend the forks by approx. 600mm.

15inch front wheel.

22inch rear wheel.

They are the basics of what I always start with.

[Al]

Thank you Jim an inspiration and a gold mine of innovative and helpful suggestions as always. We'd be lost without you.
I have just been down to the garage and done as you said but the front discs were rubbing between number two and three carbs so moved the engine to on top of the seat with the chain running vertically downwards.
Handle bars are attached to the battery and you have to use the left rear indicator stem to change gear.
Will test drive in the morning and let you know how it goes.

AL

[jimmock]

Thank you Jim an inspiration and a gold mine of innovative and helpful suggestions as always. We'd be lost without you.
I have just been down to the garage and done as you said but the front discs were rubbing between number two and three carbs so moved the engine to on top of the seat with the chain running vertically downwards.
Handle bars are attached to the battery and you have to use the left rear indicator stem to change gear.
Will test drive in the morning and let you know how it goes.

AL

Sounds good.

Let me know how your road test goes.

[coldsummer]

Hi Al, very interesting questions, I'm afraid I don't really know the answers but it does remind me of something I've often wondered about and I hope you don't mind if I raise it here, hopefully you or someone else will enlighten me.

When I was building a project bike a few years ago I used a zrx1100 swinging arm and initially mounted the shocks on the original mounts. However this resulted in them being too upright which not only looked horrible but it also jacked the rear end too high. I had the lower mounts removed and refitted further back on the swinger.

During this process whilst trying to decide how far back to place the brackets I wondered where the optimum mounting point would be. It seemed to me this would be at the point where both top and bottom shock mounts would be equidistant from the swinging arm pivot point giving the most natural arc of travel. However, I noticed a lot of 'special' builders fitted their shocks in a more extreme position, often moving the top mount to a point further forward giving a much smaller angle at the lower mount point. I wondered how they knew how far to place the mounts before the geometry of the suspension was too compromised to be effective?

I suppose I wondered about the science of it, or if people simply went by gut instinct and hoped it would work if it looked OK? I did ask a couple of the guys who posted their builds in the projects section but they never replied so I suspect it is often the latter.

[markz9]

unfortunately as most things in life frame design/suspension /steering angles etc are a compromise so for example modern bikes have a relatively steep steering angle however they also have smaller wheels and more compact and narrower engines thus allowing a lower centre of gravity (better handling) all the things we dont have on an old zed. I recently raced a bike at spa classic this year which built from a collection parts from lots of bikes it should have been awful but getting the right info and help, harris braced frame and moved shock mounts etc, maxton rear shock and racetech the front forks it was one of the best handling bikes ive ridden but again this is on a race track not public roads
ring them up and ask for some help you will be amazed
Mark

[Al]

Simon i dont know the answer but what i can say is that moving the bottom shock mount forward, as in my case artificially hardens the spring rate (less mechanical leverage) and reduces the available travel at the wheel spindle.
Moving the top shock mount forward in the special builders' case, will increase the theoretical travel available to the wheel but artificially lower the spring rate making it sit high and be softer on the ride.
Or vice versa
You get a similar effect from the front end.
This from The Tony Foale book and others.
-------------------
I dont use the bike on the road now its' really track only so little chance to test it on The Queens Highway but with track use you read the tyres and sense what the feel of the bike is telling you.
Initially i had no idea what was happening. Bliss.
Now, i have no idea what is happening, but see the signs and cant make head nor tail of them.
Thats not strickly the whole story but when i made changes last winter i didn't know what effect they might have.
Some have been good and some bad.
Having made the majority of cosmetic and practical changes and witnessed the results i can now see that the little room for adjustment i had left myself has not been enough in some areas' hence the need for some further tinkering.
The J1 frame is the laziest of the J derivatives with a sunken back end and a very lazy flat steering head angle.
The proposed change to the swingarm front pivot point addresses several issues to do with ground clearance / chain alignment, but will also steepen the steering head angle without the need to change yolks.
One of the details in the Harris article Jay posted mentioned having the pivot point as near as possible to the G/Box sprocket.
I have an over length swingarm and a long wheel base so will look to set these against each other in the change and may move the pivot point forward a little too.
My comment about having not enough weight over the front wheel above comes from; some of the changes (lighter front wheel and discs, lighter mudguard, removal of lights and clocks, having fitted longer / stiffer front springs) and finding that there is no front end steering at all and no readable tread pattern on the front tyre but the back tyre had melted even though the bike's weight balance is within 1 kilo front to rear.

markz9; are you Whitchurch Hants or one of the other ones???

AL

[ADRIAN H]

I recently raced a bike at spa classic this year

Mark was that your Suzuki GS at Debben Performance, about a month back ?

[markz9]

hi zorded yes whitchurch actually its freefolk priors which is very close but no one has heard of it
mark