Topic: Structural integrity of Stock forks w/ out fender?

[754]

Why are you using a Triumph disc..

 Easy test, put fork against frame stop.. get a bar that fits where the axle goes, but extending out a foot. then pull with spring scale, with and without brace, and measure deflection..

[mlinder]

Nikki, the brace works in conjunction with the triple tree and axle.

Please see the image below. This image ignores the triangulation which exists by nature in a tube and clamp situation. Since both ways have that equally, it is a null factor in this discussion:



Figure a and b ignore triple tree and axle rigidity, since they exist equally on both setups.
Figure A is without a brace. The only structural rigidity are the tubes themselves. In figure b, we see the triangulation via a form of gusseting that occurs with the brace. I'm sure I don't have to explain the benefits of triangulation. I haven't added all the lines for triangulation, because it decreases greatly due to distance between, say, top of left stanchion to the two mounting points on the right fork lower, and the design of the stick brace isn't really the best at dealing with that direction of force in the first place

The other 'group' benefit can be shown in c and d.
Boxes aren't the most structurally sound shape. of course, the longer one side of a box there is, the more leverage a force has on it. By adding the brace, we reduce the size of the boxes, and reduce that leverage.

Again, this is simplified. I don't have my cad program installed here at work, and drawing it all in, basically, mspaint, would take too long.

Hope this helps explain why your tests are not indicative of actual benefit, and hope it helps people understand more why a brace does help.

[Nikkisixx]

Mlinder - I know why a brace helps, and  I'm not trying to debate the value of a brace.  Nor am I defending the flawless nature of my test. We can agree that the test I performed was rudimentary and coarse.   However, it does show that as a "brace" the fender adds very little to the system.

I challenge you to perform a test to quantify the value of a piece of 12 gauge steel as a "brace" within a system consisting of 35mm steel tubing, an upper and lower tree of considerable heft, and an axel that is what 15mm?  It must also consider the load exerted by several hundred pounds as the bike corners.   

My interest in this debate goes beyond the necessity of the fender or is the fender a structural member.  It has been noted that some CB's hit harmonic vibration points at various speeds.  I've noticed this myself, and in trying to track down the source I've hypothesized that the "springy" nature of the fender may contribute.  I have only anecdotal evidence to support my theory, so I hesitate to boldly proclaim that the fender is the root of harmonic vibration.  Just a hypothesis at this point. 

[mlinder]

Mlinder - I know why a brace helps, and  I'm not trying to debate the value of a brace.  Nor am I defending the flawless nature of my test. We can agree that the test I performed was rudimentary and coarse.   However, it does show that as a "brace" the fender adds very little to the system.

No. The brace itself is not a 'system'. The triple tree, the brace, and the axle together are a 'system'.

Three structurally weak rods make a wonderfully strong triangle.

I challenge you to perform a test to quantify the value of a piece of 12 gauge steel as a "brace" within a system consisting of 35mm steel tubing, an upper and lower tree of considerable heft, and an axel that is what 15mm?  It must also consider the load exerted by several hundred pounds as the bike corners.

Don't have time or equipment. Why do I need to quantify common sense and similarly tested common engineering knowledge and basic physics.

It's like asking me to quantify and defend the relations of mass, energy and speed. No need, already been done.

My interest in this debate goes beyond the necessity of the fender or is the fender a structural member.  It has been noted that some CB's hit harmonic vibration points at various speeds.  I've noticed this myself, and in trying to track down the source I've hypothesized that the "springy" nature of the fender may contribute.  I have only anecdotal evidence to support my theory, so I hesitate to boldly proclaim that the fender is the root of harmonic vibration.  Just a hypothesis at this point. 

I don't see why it couldn't be, but doesn't mean it is. Have you removed the little bushings between cooling fins?

[Nikkisixx]

Yes, it is easier to sit at a computer and pontificate than to test an assumption.  It is cold in the garage, and nice and comfy inside.   The world is flat, the moon is made of cheese, and nothing travels faster than sound. 

Pity you won't pick up the challenge.  You seem a bright fellow and I'd have liked to see what you came up with.  Cheers!

[mlinder]

Yes, it is easier to sit at a computer and pontificate than to test an assumption.  It is cold in the garage, and nice and comfy inside.   The world is flat, the moon is made of cheese, and nothing travels faster than sound. 

Pity you won't pick up the challenge.  You seem a bright fellow and I'd have liked to see what you came up with.  Cheers!

Sorry, Nikki. I shouldn't be required to 'prove' that a triangle is more structurally rigid than a rod.

[srook]

Please show us how the front forks form a triangle.  You can add any lines you want to your fork outlines, but they remain rectangles.



Scott

[mlinder]

Please see figure B :/

Christ.

[KingCustomCycles.com]

So why aren't these illegal?  I'm just sayin' 

[mlinder]

So why aren't these illegal?  I'm just sayin' 

Nobody said anything was illegal.

Nobody said you'll instantly die from running without a brace.

Why do people need to over-exaggerate a statement someone made to try to state the opposite?

Oh yeah, it's because their argument doesn't stand up to the real counterpoint, so they have to make up something...

[mlinder]

By the way, classic strawman.

"Since these forks aren't illegal" (see, you can't disagree with that) "then a fork brace must not be better than no fork brace." (which is false, but you make it appear true because you've used an illogical strawman argument.)

Some things work. Some things work better.

[Joksa]

This is what I call a fork brace:

[Goofaroo]

Now there's an example of a component being designed strictly for utility with absolutely no consideration given to aesthetics.

[Markcb750]

This is what I call a fork brace:

Up-sprung weight and it detriment to suspension response comes to mind...but I'll bet it is stiff.

[mlinder]

I gotta say, this is pretty much why I stopped posting in this part of the forum as soon as the hipo section was formed.

No one actually interested in performance and safety at accelerated speeds would consider arguing the against the benefits of a fork brace, against the detrimental effects of removal of integral frame sections, or ignore the statements of people such as Hondaman who has been racing, building, and/or riding these particular bikes since they were released.
Only a fool would say that increased use of larger forks and most substantial fork braces over time was some kind of fashion statement, and that the reason people like Yoshi strengthened or braced sections you guys are trying to remove structural components from was because he got a wild hair up his ass and wanted to add weight.

Get on back to giving bad information to each other, I'll leave ya'all alone.

[Joksa]

Up-sprung weight and it detriment to suspension response comes to mind...but I'll bet it is stiff.

Aluminum parts are hollow and those pipes are not so thick walled. I like when form follows function and I was very happy finding this period accessory.

[MCRider]

Up-sprung weight and it detriment to suspension response comes to mind...but I'll bet it is stiff.

Aluminum parts are hollow and those pipes are not so thick walled. I like when form follows function and I was very happy finding this period accessory.

I was going to say its probably lighter than it looks.

[Goofaroo]

They definitely have a frim grasp on the top of those fork legs. Any idea of their origin?

[mick750F]

I gotta say, this is pretty much why I stopped posting in this part of the forum as soon as the hipo section was formed.

No one actually interested in performance and safety at accelerated speeds would consider arguing the against the benefits of a fork brace, against the detrimental effects of removal of integral frame sections, or ignore the statements of people such as Hondaman who has been racing, building, and/or riding these particular bikes since they were released.
Only a fool would say that increased use of larger forks and most substantial fork braces over time was some kind of fashion statement, and that the reason people like Yoshi strengthened or braced sections you guys are trying to remove structural components from was because he got a wild hair up his ass and wanted to add weight.

Get on back to giving bad information to each other, I'll leave ya'all alone.

 

[Joksa]

They definitely have a frim grasp on the top of those fork legs. Any idea of their origin?

I found it on ebay.de - cannot recall if it had any markings.

[Retro Rocket]

Wow, sometimes i don't think there is much common sense in some of these threads. My Father raced cars, i liked motorcycles so i have had an interest in handling since i knew how it all came to help faster lap times and made cars and bikes easier to ride or drive fast. You could say i was a bit of a lunatic on the road as a young bloke. I had mates that raced these bikes and very early on i learned the value of good suspension and also engine work on these bikes, i bought my first RC crank and rods in 1980, i was 17. The very first time i went for "form over function" i bought a sharp looking fibreglass fender for the front, it looked great. I had it on for 2 days and i can tell you that it made my bike feel like it had hinges in the front end but it effected the feeling of the whole bike, i was stubborn and didn,t click straight away of its lack of effect in stabilising the front but it came off anyway because it had broken where it was clamped to the forks, this must give you lot some idea of how much flex is in the front of these bikes without that front brace, regardless of how flimsy you think it is. I was on my way home with a mate, both on 750's and doing around 160k's {100mph} when some idiot pulled out in front of us, i slammed on the brakes knowing i had room to avoid the idiot and my friend was doing the same on my right so my path of escape was limited to the left shoulder. No sooner had i hit the brakes, the front end started a massive tank slapper that was that violent my wrists ached so did my thumbs as they were continuously slammed into the tank, i assume that this is when the fibreglass guard broke. Anyone that thinks that the front brace does nothing is full of #$%* and has no real world experience, i have ridden a lot of well set up bikes in my time and my mates called me " the last of the late brakers" because that is where i liked to over take, going into a corner under brakes, i would and could not ride that bike like that, it was scary so the original brace went back on and i also fitted a steering damper and have used them ever since. The suspension shouldn,t flex, the frame should, these days flex is designed into frames because they DO need some give, {you can use google to find out about this}, NO bench test especially without any predetermined parameters is worth its weight in sand , go do a track day and try both the brace and none and then try tell me that it does nothing.....Its even worse on the street....

I gotta say, this is pretty much why I stopped posting in this part of the forum as soon as the hipo section was formed.

No one actually interested in performance and safety at accelerated speeds would consider arguing the against the benefits of a fork brace, against the detrimental effects of removal of integral frame sections, or ignore the statements of people such as Hondaman who has been racing, building, and/or riding these particular bikes since they were released.
Only a fool would say that increased use of larger forks and most substantial fork braces over time was some kind of fashion statement, and that the reason people like Yoshi strengthened or braced sections you guys are trying to remove structural components from was because he got a wild hair up his ass and wanted to add weight.

Get on back to giving bad information to each other, I'll leave ya'all alone.

I would love to see the responses in that section Mlinder, i feel compelled to answer here so some of these lesser informed guys don't make stupid changes to their bikes, some of the info in these threads is just plain dangerous....


Mick

[mlinder]

Well, I'm the one the moved this thread to the regular forum from the HiPo forum. Maybe I should have left it there, though the original question wasn't really geared towards 'HiPo' applications.

[Markcb750]

I still say the airplane takes off.   

[mlinder]

Thats' because it does.

[Markcb750]