Frame Bracing.

[Ausben]

Thought you might like some pics on bracing gsframes.
Found these online,cant guarantee effectiveness.

[sharpy]

God try BUT the first pic the pipes,airbox and tank wont fit if its a street bike. Just being picky lol. Have a look in here for more stuff....http://www.tonyfoale.com/Articles/index.htm or download this as its a bible for motorcycle handling....http://www.demonoid.com/files/details/1816951/775222/

[Dave8338]

God try BUT the first pic the pipes,airbox and tank wont fit if its a street bike. Just being picky lol. Have a look in here for more stuff....http://www.tonyfoale.com/Articles/index.htm or download this as its a bible for motorcycle handling....http://www.demonoid.com/files/details/1816951/775222/

Yeah but he's running pods, 4-2-1 exhaust (with turbo) 22psi boost, 1100 bored and stroked and correct me if I'm wrong...isn't that a 550 frame?

I like it. Build it and someone will come.

[posplayr]

Question

This is the second frame I have seen recently that doesn't include the classic "OSS_C" bracing as described over at OSS.

As described by that author, "OSS_C" bracing is the minimum and yet here is a second example of leaving it out.

Somebody want to explain ?

EDIT:
I added the following Free body diagrams of the OSS frame so we can do eyeball integration to understand why the bracing works. A Freebody diagram looks at the structure from all external forces whereas the original diagram highlighted areas of internal stress. I did add additional emphasis to the rear triangle area and the cantilever support for the passenger weights.







Pos

[Dave8338]

I think it's overkill. You could plate the entire frame if you wand a truely "ridgid" set-up but at what point do you draw the line. The 'C' brace, as shown is on a tighter radius than the bend in the tube, just ahead of it. If it were me...I'de brace the middle (in the example you shown) and not worry about the down force where the 'C' brace is concerned.

[posplayr]

NOTE all bracing references are with respect to the OSS picture.

Well I guess I should be more clear. The point of most frame bracing for high performance cornering is concerned is to maintain alignment between the headstock and the swing arm pivots. Fork and swing arm stiffness are important as well but not a part of frame bracing.

Just doing an eye ball calculation the point in the middle seems to be the weak point which is the purpose of the "C" brace to improve.

For example, it is hard to see that there is much improvement to be gained by bracing the headstock in "A" without the "C" brace as the smallest flex at "C" will cause much more head to pivot deflection than a much larger headstock deflection. Movement at the center is magnified by the distance to the end points of the frame. Couple this with the bracing already in the stock frame at the headstock , and I'm confused why "C" is left out.

Attached is a very nice example of "C" bracing. Also shown is a "E" and "D" cross brace. BTW hat builder also did all the other OSS bracing except "F"

I know i have spoken to others that only do "E" bracing, but if you are going to do A,B,D, and E why leave out C?

Pos

[Dreef1999]

Definitely seems like you are right posplayr.

The torsional weakspot of the frame does 'look' to be right where the 'C' gusset is being welded in the OSS frame. They even helped by defining the load path they are using by coloring in the frame members blue, green, and yellow.

Why is 'C' the weakspot?
It is the narrowest point on the frame and it has no vertical bracing. All of it's strength is in the horizontal axis with nothing in the vertical.

This seems to assume though that the frame beneath the engine provides virtually no strength to the swingarm.

Maybe i will read through that paper after work.

[mark_vaughn]

This is a topic I was going to ask about before I send my frame off to paint.

Is there a need for bracing for the typical rider on these bikes? I am not going to be racing the bike in any measure.

[posplayr]

Is there a need for bracing for the typical rider on these bikes? I am not going to be racing the bike in any measure

Probably not, it is only a subject that comes up when you start putting braced swingers and larger wheels and tires with more engine hp.

[tone]

Ahem excuse me guys if you want an honest opinion on frame bracing why not ask someone who's been doing it for racers & road bikes since 84

tone

[salty_monk]

Cough up then... don't just tease them

80GS1000 says he can feel a "wobble" through the middle of the frame if a bump (or his knee) upsets the bike when leant over in a turn...

I guess his front & rear are about as stiff as they get (ooh er )

Might want to get his input on it too......

[posplayr]

Ahem excuse me guys if you want an honest opinion on frame bracing why not ask someone who's been doing it for racers & road bikes since 84

tone

Tone,
U always have an open invitation to comment . So what is the relative benefit of the various frame bracing indicated in the OSS picture?
Pos

P.S while I may not be posting from experience, I have accumulated a bit on info as gleaned from those that have.

So post up so I can glean somemore

[tone]

Cough up then... don't just tease them

Oh go on then you persuaded me

Before i start can i point out i did start bracing & modding frames in 84 when i was given a drawing of how to do it by a top uk racer of the time the first was my own gs7/10 road bike, i still do 2 or 3 a year for for both road riders & racers plus my own stuff of course

In Ausben's pics the brace marked E is in the wrong place it should be lower, preferably between the top rear engine mount points, as it is its doing little more than adding weight, The x bracing marked D should also be as low as possible & a vital piece on the frame shown is missing completely

If you refer to the pic shamelessly nicked from the oss site you will see a brace marked C, this brace is the one that has most effect on the frames stiffness as it covers the weakest part of the stock frame, If you leave it out any amount of steelwork added to the rest of the frame will have little effect & if you are going the monoshock route you will be putting extra stress on this area ..... well done posplar for spotting it

Again refering to the oss pic the braces you NEED for a nice stiff frame are C, D & E i also sometimes add B but only if a RACER insists imo as with the other braces shown they are not needed & just add unwanted weight

For materials i use 1"OD lightweight tube for all exept C, for that i usually use 3"x 1" lightweight box cut to shape

Just to put the record straight if anyone it doing this type of bracing i can tell you all your stock parts with the exeption of the airbox WILL still fit

This is just a quick guide from me so anyone with specific questions on this please feel free to shout up either on here or via pm & i'll help where i can
Cheers tone

[jwhelan65]

Ahem excuse me guys if you want an honest opinion on frame bracing why not ask someone who's been doing it for racers & road bikes since 84

tone

And who might that be? Let's hear it...

[tone]

Tone,
U always have an open invitation to comment . So what is the relative benefit of the various frame bracing indicated in the OSS picture?
Pos

P.S while I may not be posting from experience, I have accumulated a bit on info as gleaned from those that have.

So post up so I can glean somemore

Hi pos
you posted as i was writing the above short novel
the aim of the oss type bracing is to address the weak points of any stock 80's frame namely the the swingarm pivot area & the point where the tubes meet under the tank the bracing shown in the pics & mentioned in my previous post do this well without adding too much weight, if you also add more modern running gear the differance is well worth the effort but even on a stock gs it removes a lot of the OE wollow & weave associated with these bikes when pushed hard

cheers tone