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

[Retro Rocket]

Spot on Ron.....

Mick

[MCRider]

Spot on Ron.....

Mick

Thannks RR  

Here's a high performance tweak bar made for me by a machinist. It clamps the tube on the inside first, than draws down on the outside. Fine piece of work. I decided against using it though as I can't get to my fork lock and this project is to be a street machine. I had a brace made for the lower legs instead.  I can use the tweak bar on the 750F project, slide it right up under the lower tree.

[scottly]

Attached is a pic of two 750 fender mounts; K1 on the left and K7 on the right. The K1 was bolted on rigidly, while the K7 was bolted to the right leg through the rubber grommets. The other pic is an aftermarket brace I took off a Kawi 550: the clamps fit the top of the fork lowers, but I had to elongate the holes where the top plate bolts to the clamps, as the Honda forks are slightly narrower.

[MCRider]

That's what we have to do sometimes, be creative with an already existing piece. My brace was from a GL1000. $20 from eBay. The machinist had to sleeve it down for the smaller legs, raise the center section to clear the tire, and made some tops that look like stock, to hold the dust covers.

I see you've mounted your needle fender to the brace. Good idea. I've mounted my fender to the brace as well, gets rid of hardware.

[turboguzzi]

just to add a balanced view here, it's not a clear cut issue. The mechanics are quite clear, the link at the top of the legs creates a stiff rectangle but...., current bikes with USD forks, motogp included have no bracing with only the spindle as a sort of stabilizer, though usually the axle diameters now are about 25mm against a sohc's 15mm and the 41 to 48mm  legs are stiffer too due to the USD design.

back to our 35mm forks, i have a tarozzi stabilizer on my racer. Tried to twist the fork through the handlebars by holding the wheel between my legs, the difference with and without the stabilizer was quite amazing. you can try it yourself. so to me it was a no brainer, added it and doing so also on my next racer build. that said, some winning guys in my class run without a stabilizer. so go figure.

TG

[754]

The drag race style brace I made is very stiff... very handy too..for loading the bike , lifting wheel etc...

 plus you can make most of it yourself at home with  hand tools..

[srook]

mlinder,
You figured me out.  I was so ashamed to admit it to you that I don't run the stock brace it caused me to react personally.  Cmon.  In my post I provided examples of similar styled telescopic forks in high performance applications that did not fold up on themselves or result in catastrophic failure becuase of the lack of a stock style fender mount.  You insinuated that to run without the fender mount was to invite death due to weakend forks.  On top of that you said that anyone who didn't admit to everyone else their complete lack of common sense was somehow a poseur.  That is what I reacted to.  And yes I do take it personally when the safety police (you) tells me that to run anything other than stock is to compromise my safety and performance.  Guess what, its my safety and I will compromise it whenever I see fit.  Thanks for your concern.

Mick,
I think you misread my post.  I did not one time ever say that the forks would work better without the fender mount.  I simply stated examples where the mount was not used and their was no catastrophic failure as a result.  The people who omitted the mount were trained engineers and were way past "physics for dummies".

No one who races these bikes these days does so without a brace, our understanding of suspension performance has gone through major changes since these old bikes were made and my concern is the same as mlinders,

M3 CR750 that Adam Popp rode to many AHRMA victories and dominated the Formula 750 class for years.  Note the fiberglass fender held on by side plates and the lack of the CB750 stock style fender mount.  The forks are 37mm from a 1982 dohc CB750F2.



BTW are we all so wrapped up in our own genius that we believe people will trust us blindly becuase we say things on a message board?  I stand behind my comments that to remove the stock fender mount, in and of itself, will in no way lead to catastrophic failure and that many have done so in the past and continue to do so.  My opinion only.

Scott

[mlinder]

mlinder,
You figured me out.  I was so ashamed to admit it to you that I don't run the stock brace it caused me to react personally.  Cmon.

Aren't the intarwebs wonderful?

In my post I provided examples of similar styled telescopic forks in high performance applications

Which you said yourself were summarily upgraded to having some sort of fork brace because they perform better, work better, and by proxy, are safer.

that did not fold up on themselves or result in catastrophic failure becuase of the lack of a stock style fender mount.

First, no one said they fold in on themselves. Stop exaggerating things to try to make a point. Second, I didn't say the stock brace was required. I said a brace of some sort was better than none, and a good aftermarket brace better. You cannot argue this point.

You insinuated that to run without the fender mount was to invite death due to weakend forks.

It's absolutely safer to run with a brace than to run without.

 On top of that you said that anyone who didn't admit to everyone else their complete lack of common sense was somehow a poseur.

No, I didn't. I said to tell people that it makes no difference is irresponsible.

That is what I reacted to.  And yes I do take it personally when the safety police (you) tells me that to run anything other than stock is to compromise my safety and performance.

No, I told you not to tell other people missinformatin.

 Guess what, its my safety and I will compromise it whenever I see fit.  Thanks for your concern.

Do as you like, you're a big boy. Just don't tell other people to do things that aren't in their best interest.

BTW are we all so wrapped up in our own genius that we believe people will trust us blindly becuase we say things on a message board?

It's not my genius. I'm not relying on opinion. I'm stating fact on mine, and other peoples with far grater experience than mine, common sense, and simple engineering practices.

 I stand behind my comments that to remove the stock fender mount, in and of itself, will in no way lead to catastrophic failure and that many have done so in the past and continue to do so.  My opinion only.

Scott

Nobody mentioned catastrophic failure. But when you hit a fast uneven road and your wheel starts pointing a different direction than you point it, and then starts pointing slightly different directions very quickly, it's not the forks that will break.

[stueveone]

Attached is a pic of two 750 fender mounts; K1 on the left and K7 on the right. The K1 was bolted on rigidly, while the K7 was bolted to the right leg through the rubber grommets. The other pic is an aftermarket brace I took off a Kawi 550: the clamps fit the top of the fork lowers, but I had to elongate the holes where the top plate bolts to the clamps, as the Honda forks are slightly narrower.

Hondaman talks about this in his book BTW. Anybody know if the k1 style will fit later years directly including fender?

[Retro Rocket]

I think you misread my post.  I did not one time ever say that the forks would work better without the fender mount.  I simply stated examples where the mount was not used and their was no catastrophic failure as a result.  The people who omitted the mount were trained engineers and were way past "physics for dummies".

Srook, i don't wish to continue this any further because you are twisting everything we are saying. And if you had read my post in full you would see my reference to "advances in frame and suspension" you are still quoting 40 year old technology and comparing it to what we know now, engineers must evolve or they are worthless. As TG said, it is really easy to find flex in an unbraced front end and if the bike is ridden  on the street {race tracks are far smoother and predictable than the street, you won't find a pot hole on the track} you have a good chance of finding out the limitations of an unbraced front end like i have in the past and is easily rectified with a brace and even a steering damper. Form over function is a choice that you make for yourself, don't try and convince anyone else that an unbraced front end is better or as good because it is not. Sorry mate but when everything is weighed up your opinion is flawed...Don't take it personally because that is not my intention...

Mick

[srook]

No, I told you not to tell other people missinformatin.

You told me?  Again with the commands.

It's not my genius. I'm not relying on opinion. I'm stating fact on mine

Yes because you have given us factual data on CB750 forks and how they react to different road conditions with and without the fender mount.  Well I am man enough to tell you that my posts were my opinion.

Just don't tell other people to do things that aren't in their best interest.

What??  Did I tell anyone to do anything?  You have been telling me what not to say for the last 2 posts.  I think it would be in your best interest to stop. 

I didn't say the stock brace was required. I said a brace of some sort was better than none, and a good aftermarket brace better. You cannot argue this point.

Yes, I can and have been.  Since it is my opinion I can argue whatever I want.  That's really what your issue is here.  Someone challenged you.  Aside from the original post about why Airtech has a disclaimer about removing the stock fender mount you can't believe someone could argue against your opinion that the stock fender mount is essential.  Then you turned it into some function v. form issue where anyone who removed the stock fender mount should admit that they aren't a "real" rider and are only concerned with asthetics.  Have fun with the quote button mlinder.  Like Mick, I'm out of this one as well.

BTW the Adam Popp bike was run from 1997 to 2004 not 40 years ago.  I trust Mark McGrew knows more about suspension than all of us.

Scott

[mick750F]

  Okay, I'm going to lend something to this thread even though what I have to offer is purely empirical...I have a '78 750F with stock fender. Many years ago I found someone on ebay that was selling NOS, from the "day" fork braces. After following the bugger's sales for a while I ended up with a nice NOS brace at a decent price by bidding at the right time..in the early AM hours..US time. Adding the brace to my stock fender situation...it clamps to the top of the lower tubes, right above the stock set-up, I immediately noticed far better handling. I don't race but I "push" it all the time. As far as I'm concerned...this is my own humble opinion, removing the original fender/forkbrace is a huge mistake if you are at all interested in handling.That's all I got...

Mike

[754]

If the 78 F (stock fender)has rubber on the mounts, it was not stiffening it anyway..

[KingCustomCycles.com]

Good to see you all can't get along, even when I am not involved.  I see fork braces on magnas and Goldwings out of the factory, I trust Honda engineering.  I see rubber mounted front fenders on our CB750's, not fork braces, I trust Honda engineering.  Personally, I have never seen, or felt, any difference with, or without, any fender or fork brace.

[cobrajunkie]

I got this off of Airtech's Website:

CR7504
Front Fender
This is the front blade that replaces the steel front fender. Honda engineers designed the front forks on your motorcycle to work with that heavy steel brace on the front. Do not run your front forks without the steel brace, severe wobbling will occur. Simply take your stock fender and drill the rivets out to remove the steel fender from the fork brace and the front and rear hoops and reattach this fender onto your steel hardware. This lightweight fiberglass piece actually takes a lot of weight off your front fork assembly and helps the suspension reaction and makes your bike handle better.

Any idea how accurate that statement in red is?

I've seen a lot of people not use a fender at all and many with modified fenders so I'm curious. I'd at least like to know before I go chopping up the original one or swapping it out.

Not sure if you're just looking for a naked look or weight savings or both but this thread indicates that adding a lower fork brace like the aluminum Fast piece below helps to tighten up the front end. I just ordered one but not here yet.

[cb650PK]

Does Tarozzi make fork brace for 750 K6? And I absolutely can tel the difference fork brace makes on 35mm Honda forks. I cannot feel the difference on 37mm GS forks however.

[mlinder]

No, I told you not to tell other people missinformatin.

You told me?  Again with the commands.

I'm not telling you what do with your own bike.

It's not my genius. I'm not relying on opinion. I'm stating fact on mine

Yes because you have given us factual data on CB750 forks and how they react to different road conditions with and without the fender mount.  Well I am man enough to tell you that my posts were my opinion.

I sure have. We've established that damn near everyone ended up with a fork brace on their race bike, and street bikes, from factory.

Just don't tell other people to do things that aren't in their best interest.

What??  Did I tell anyone to do anything?  You have been telling me what not to say for the last 2 posts.  I think it would be in your best interest to stop.

Sorry, I misspoke. You didn't tell anyone to ride without a brace. You just posited that a brace made little to no difference.  

I didn't say the stock brace was required. I said a brace of some sort was better than none, and a good aftermarket brace better. You cannot argue this point.

Yes, I can and have been.  Since it is my opinion I can argue whatever I want.  That's really what your issue is here.  Someone challenged you.  Aside from the original post about why Airtech has a disclaimer about removing the stock fender mount you can't believe someone could argue against your opinion that the stock fender mount is essential.  Then you turned it into some function v. form issue where anyone who removed the stock fender mount should admit that they aren't a "real" rider and are only concerned with asthetics.  Have fun with the quote button mlinder.  Like Mick, I'm out of this one as well.

Let's try this one more time.
Let me get this straight. Please tell me, is it your opinion that a brace adds no structural stability to the front fork? Yes or no?

BTW the Adam Popp bike was run from 1997 to 2004 not 40 years ago.  I trust Mark McGrew knows more about suspension than all of us.

Scott

I can actually see a race bike doing better without a brace than a street bike, assuming the suspension has been upgraded in some way.
Tracks, generally speaking, are far smoother and less likely to upset a less rigid front end by nature.

Let's try this again, Scott. I'll try to be less combative.

The omission of a fork brace will not spell immediate and unavoidable disaster as you scoot around town. It can, however, get you into trouble under conditions where a fast road may also have surface irregularities that cause faster and more extreme forces on the front suspension.

Often, tracks have much better surfaces than public roads, so the effects of a fork brace may be less noticeable under those conditions.

Since I don't know how everybody rides, or how they will ride, I can only give advice based on how I ride. I, and almost all of my friends, often see triple digit speeds on less than optimal roads with our 30 to 40 year old, already inadequate suspensions, and compromising what little integrity they have would be dangerous for us.

Since the fork brace makes things safer for us, it obviously makes it safer for other people, especially should they decide to open it up a bit on an unfamiliar, less than optimal road.

So, even though I never said that no brace = instant death, to try to get along with you, I'll concede that a brace isn't necessary to ride your bike.

[mlinder]

If the 78 F (stock fender)has rubber on the mounts, it was not stiffening it anyway..

This isn't true.

Possibly slightly less, but not "not stiffening it anyway". If you look at the simple image I made, you'll see that even a 'rubber mounted' system will still add rigidity.

[bollingball]

Honda must have made a change in (78). My 750K8 front fender has no rubber on the mounts it seems to be stock and fairly rigid.

[MCRider]

In the case of the M3 CR750 of A Popp, do we know if AHRMA allowed a fork brace in the rules for that class? Just curious.

[mlinder]

Doesn't say they aren't in formula vintage, from my quick perusal of the 2011 rulebook.

[754]

 Face it, stock forks are not very god anyway.. early ones were often verry worn internally.

 You are limited to what you can expect of them, there is lots of other stuff out there that works better.

 Myself, I will try Ceriani forks( better clamping), with a 2 bar brace.... I dont have much lean angle anyway, so hard cornering is not an issue..

[mlinder]

Face it, stock forks are not very god anyway.. early ones were often verry worn internally.

 You are limited to what you can expect of them, there is lots of other stuff out there that works better.

Exactly. Why make them even worse?

Myself, I will try Ceriani forks( better clamping), with a 2 bar brace.... I dont have much lean angle anyway, so hard cornering is not an issue..

Whatever's clever.

[Goofaroo]

A quick look at a parts diagram reveals that my brace and fender stays mount rigidly to the fork (72 CB500). It appears that for some reason on later models the brace and the stays are mounted on rubber bushings. My best guesses would be that the newer design transferred a little less stress to the fender and possibly allowed the fork legs to work a bit more independantly. It might have added a bit of smoothness to the ride quality. It could be that they were concerned about the old configuration being a bit too stiff in conjunction with the flex designed into the frame and the fork. Either way, there is a reason that we love these old Hondas and in their original state they are well engineered machines. To second guess their original design seems to me like an excersize in futility.

We do however know that advances have been made in motorcycle technology since these bikes were produced but in my opinion, the charm of a vintage bike is in it's original design and function. To get these bikes back to their original handling characteristics there are a few things that will have to be addressed. Bearings, bushings, suspension springs and damper units are all items that will have to be addressed to regain the proper handling characteristics. This is where the puzzle begins. Even from the showroom floor, these bikes were not setup to accomodate all riders. In fact they were probably set up to be a close fit for 5'5" asian guy that weighs 140 lbs. Even moderm motorcycles that I have owned have required me to increase spring rate, firm up dampening, and if it has a windshield, it will never even come close to fitting a big goofy 6' 225lb white kid like me. So that being said, now we are talking about taking a well engineered motorcycle that is 35-40 years old and trying to bring it up to spec and make it more suitable for our needs. If you are 140lbs and ride like Valentino than your needs are noticibly different from a guy like me that is of a reasonably aggressive riding ability but also likes to be able to carry a load and take extended weekend trips. In other words, my setup will not be the same as Rossi's would be.

So now we need to begin fitting our bikes to ourselves by modifying the original beautifully engineered design. Part of our decisions will be made for function but almost always, aesthetics will be involved as well. To begin, we know that there are basic things that have to be done to get the bike to suit us. First and foremost, the original forks and shocks are an area that time has not been kind to. The shocks are most certainly shot and require replacement. They are simply not serviceable and the springs have lost their effectiveness. No big deal because they didn't fit most of us anyway. Simply replace them. The forks on the other hand can be modified to work reasonably well and regain their original glory. At the very least, we can replace the springs with some that fit our weight and riding ability and control the dampening to our tastes by using different weights of suspension fluid. That in itself is a safe upgrade that will do nothing but improve the handling and overall enjoyment we get out of the bike. If the rest of the components are left in place (including the fork brace) the bike will be as safe if not safer than it was before the modifications. Where the disagreement seems to begin is when we begin to alter the original design by actually removing some of the original components of the stock forks. In my opinion (so disagree but don't get mad at me) the original brace is sufficient to retain the original handling, charm, and safety of the design that the Honda engineers came up with and that we love so much. I would not remove the brace any more than I would remove half of the spokes or cut off a few frame tubes. On the other hand, I'm not convinced that a more substantial fork brace will do much to improve the action of these forks.They are some rather spindly legs coupled to a relatively small front axle. Maybe the rubber bushings on the later bikes' fork braces was to allow more independant movement of the individual fork legs. Maybe they determined that a more rigid brace would transfer too much stress to the fork legs. Either way, I like the original design and I am not qualified to second guess the engineers that designed them. Putting a more substantial brace on there may very well improve the handling somewhat but only trial and error will tell.

[Retro Rocket]

Look, if you are a sedate rider and never push the bike hard then the stock set up is fine, if its a bobber with no rear suspension then who cares but i can say this with all the confidence in the world, i used to ride my old Honda's very hard, wearing footpegs out and even scraping the alternator cover and side stand mounts, i can tell you guys that when the front suspension is loaded up braking heavily into a tightening radius corner and you hit a bump of any size you will be glad that there is some kind of brace on the front of your bike. I only ever had one bike i put a cool looking fibreglass fender on and i broke it the same day and it made my front end feel like spaghetti. I used to beat most guys braking into corners and still do, i get comfort knowing that my forks will stay close to the same plane while "making a move" on a mate......You guys can do what you like but your bike is better with the brace or better again with a "proper" brace, and if you really want to lessen the chances of an unstable front end then add a steering damper. This is taking into account that you have good tyres and good fork oil, these will also help the situation...Comparing race bikes just doesn't work, they have different springs, different valving for rebound damping and other changes that benefit handling, not to again mention the lack of hazards on a race track.
Ride both an unbraced bike and a braced one hard and you will be amazed at the difference......Thats all i got...

Mick