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id honestly say. its minimal at best. most likely almost useless as a fork brace considering the forces involved. i mean, i have a freakin fibreglass fender for crying out loud. dosnt seem to make a difference one way or the other. i get beat by guys with them, i get beat by guys without them. whoop de doo. personally, i think a fender, especially a ss, alum, or chrome one on a racebike makes it look cool.


http://caferacer.net/mossportnew/013.html
 

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quote:Originally posted by 736cafe

most fenders act as a fork brace on the bikes that we talk about here. motorcycling is dangerous enough; why make it more so by removing the safety features of your machine? darwin effect?
So did my 550 even hint at headshake or any other form of high-speed instability the last time you rode it? Yeah, didn't for me either...

I started typing this big convoluted thing about how the lower end can only deflect the amout of the running clearance in the bearings w/o flexing the axle and that most of the deflection in the front end is usually caused by worn inner bushings and that a brace is a band aid in that you can make the lower tubes run parallel w/each other but that has nothing to do with the slop and potential bindage on the inner tubes and I that sincerely doubt you're going hard enough on the street to deflect the inner tubes w/o being a front runner for the Darwin Award yourself, but like I said it was convoluted.

What I know for sure;

Front fenders are unsprung and the stock one on my bike was fookin' heavy. On forks w/basically no low-speed damping circuit I'm way more conerned with unsprung weight than I am with any potential aerodymanic effects.

I put a Telefix brace on my RZ350 a hundred years ago. Made it ride like shit. I know now why, but don't think a brace in itself can't cause problems.

I have never once got caught in the rain and thought "this wouldn't suck if only I had a front fender".
 

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here is how a proper lower leg fork brace can cause problems, somebody thinking they know how to set up a front end subscribing to the "eyeball close, front ends, and good enough for hand grenades school of thinking" not realizing that ain't good enough

yeah that got fixed

quote:Originally posted by Ratty-550



I put a Telefix brace on my RZ350 a hundred years ago. Made it ride like shit. I know now why, but don't think a brace in itself can't cause problems. <I now know why, but think a brace can cause problems???>

 

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Which is why, when putting your front wheel back on, you tighten the axle clamp on the axle nut side first. Then bounce on the front end for a bit, then tighten the axle clamp on the other side.


But yes, fork braces can introduce more problems if they aren't made and installed correctly. The better way to reduce the front wheel deflection is to use a larger diameter axle and wider lower fork axle clamps. Modern dirtbike axles/forks are a good example of this.
 

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the one shown about was simply not spaced correctly and was done so with hardware store washers instead of precision machined spacers

10 thou error between those two spans means quite a bit more at the axle

buy a pair of calipers large enough to measure and you'll likely be surprised at how few are spot on

those are 12 inch calipers

fwiw.... it allegedly passed tech at some new england track with that error, and many many others

the least of which was not one of the rocker boxes touching the bottom of the glass tank and engine mounts so sloppy that careful use of a 2' prybar could actually move the lump more than 60 thou of an inch with the fasteners brought just snug and designed as such that having them fully torqued only required more force to result in such a movement
 

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I woulda rotated each fork leg 180 degrees one at a time and taken measurements at the top of the sliders again to make sure it wasn't a bent tube :)
JohnnyB
 

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that's why I'd come sweep the floor in your shop and would allow you to do the same in mine

why hail farr, I'd skip that and direct you to any of the serious metal munchers you fancied

they were quite straight and it would seem the less than ten miles they had covered didn't manage to tweak them
 

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I have had 35mm fork tubes flex enough under hard braking to cause the front tire to rub the front of a full fairing when static there was 2" of clearance. This was on a CB550F with Ceriani tubes in stock sliders. With a stock front fender bracket and a fiberglass fender, at least the deflection was straight back. I wonder how it would have been in the turns or breaking without the brace?
 

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mr. sex
are you saying that the tubes are deflecting 2" due to braking forces? i'd think the fork compression has to account for 1 3/4" of that clearance being gobbled up. but maybe i'm naive.
-parks
 

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Parks,
That is what I am saying. At full compression, there was 2" of clearance between the lower fairing and the front tire in a static situation. At the end of the back straight at Road America when it was hard on the brakes into turn 5, the front tire would just rub the fairing. This is on a CB550 with an Action Fours 590 kit, cam, Jerry Branch ported head and CB750 carbs, Lester wheels and dual drilled discs. It probably topped out at about 130 MPH. The Cerianni fork tubes were supposed to be the hot ticket, back then. This was about 1979 or 80.

Ken
 

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Ahh.... I've heard that the newer Cerianni repro forks sold by a company in NJ that we all know and love used some rather thin fork tubes, making them junk for anything other that sitting still and looking pretty with a fancy name on them.

You'd think that bending 2" would cause the tubes to kink. Or at least I would. But I also think I look hot in a speedo, so what do I know.
 

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Maybe the repro's are not such bad copies after all...cause I hear they do the same thing.

Usually flexing like that a few times and it will start shedding chrome in flakes off the front of the tube by the lower clamp.

Or maybe the frame was flexing too. Like a hinge at the neck.

Sometimes at warp speed the rear of the front tire will slow faster than the front of the front tire causing a matrix shift in the McGanzer Grid and the rim becomes egg shaped.
JohnnyB
 

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ive heard the original cerianis were the bomb. the roadracer setups. not the street forks. i liked seeing zachs fender sawn in half at summit after the front tire expanded enough. that was cool. not.
 

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quote:Originally posted by Ratty-550

quote:Originally posted by 736cafe

most fenders act as a fork brace on the bikes that we talk about here. motorcycling is dangerous enough; why make it more so by removing the safety features of your machine? darwin effect?
So did my 550 even hint at headshake or any other form of high-speed instability the last time you rode it? Yeah, didn't for me either...
Your obviously not pushing it hard enough.
On Honda CB550, I found you get a major head shake between 115 to 118mph, smooths out again over 120mph and is flat out at 127mph
Even with (maybe because of?) braced swing arm and good fork brace they hinge in the middle.
The paint cracks just under nose of seat/rear of tank, the axle plates on swing arm around welds and swing arm pivot area.
As you reinforce one area, somewhere else gets more stress.
BTW, mine had a home brewed 591cc 'kit' (similar to those marketed as 605cc conversion), cam, porting, exhaust, etc.
As to question,
I'm ambivalent about fenders, personally, I run them , tried without, when its raining, much better with.
Never run without a decent fork brace, tried once, real scary.
Even stock ones help handling.
Try this.
Stand in front of bike, grip front wheel between knees and ankles, turn bars left/right.
It flexes a lot more without any bracing as its relying solely on axle to keep things lined up.
PJ
 

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there area a few exotic alloys which would result in extremely light weight fork 35-37mm tubes that would also be of adequate strength for a 425 pound 130 mph racer

but a set of tubes from those would cost several hundred thousand dollars, maybe millions

I can't imagine even very high grade stainless steel heat treated to work like a spring moving that much and not deforming but at the same time

there forces involved at even slower speeds and less weight are quite huge

maybe the fairing shifted a bit under braking, maybe the headstock did as well, maybe there was a bit more travel before coil bind hidden in reserve

check out the testing that was done when they were developing PWA (pratt whitney aircraft) 1480

I think just a 1/8" bolt of it cost several many thousands of dollars but my guess is one could whip out a pair of 15mm onion skinned fork tubes out of it, and a few other similar materials, that would be much stronger than many huge conventional tubes
 

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Come to think of it...with a 2" flex in the tube. I'd imagine one of two things would definately happen.

A. All the flex within an inch or so of the bottom fork clamp...fork would bend, and stay bent.

B. The flex in a gentle arc from the bottom clamp to the slider...result...slider would sieze.

The slider can't slide up a bent/flexed tube...and the tube is starting to flex at the same time as the slider coming up to compress the forks. Seems like that much flex would basically cause the fork to sieze and you probably would have noticed if you lost all suspension in the front end.
JohnnyB
 
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