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

[Free Booter]

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.

[myhondas]

I think that it would depend on what type of riding you are planning on doing. If it includes high speeds or running the twisties, I would be inclined to go with some sort of fork brace. If you are going to be using it as a daily rider in town without a lot of heavy riding/turning, it should be ok. Even with a fender, some bikes require an additional fork brace to eliminate the fork flex that can be be quite a problem in racing.

[mlinder]

Removing the front fender, and therefore the forkbrace, without adding another fokbrace, does indeed reduce stability.

[754]

Also if your treees have been chromed, it will be less stiff. unless no chrome is on the  bores..

[scottly]

The stock "fork brace" on the K7 front end I just fitted to my Seeley was mounted to one fork lower on rubber grommets! It's a fender mount, not a brace..

[mlinder]

The stock "fork brace" on the K7 front end I just fitted to my Seeley was mounted to one fork lower on rubber grommets! It's a fender mount, not a brace..

I don't know anything about your personal bike. I do know the big brace under the fender on a stock setup is, in fact, a brace.

[Retro Rocket]

Any idea how accurate that statement in red is?

Accurate, it should actually be stiffer in my opinion. You have one disc for a start so centrifugal force is trying to twist the front end without braking. If your front end gets a wobble it can and will spit you off because there is no brace to hold everything tight. I NEVER ride without some sort of front brace and more often than not i use a better brace.I have had some really bad "tank slappers" with the standard brace, would not want to try and control an un-braced one. You will get a lot of guys say that you don;t need one but they aren't paying for your medical........

Mick

[Free Booter]

Here's one from Cycle-X:

[dave500]

if its a brace its a flimsy one,i can bend them with one hand,the axle is clamped fairly solid,the trees are fairly solid,so a piece of tin half way down is going to make or break you?

[Retro Rocket]

That is basically a fork tube brace for extended forks on choppers, different to the lower mounted fork braces that sit between the top of the fork lowers. That type of brace is not really any good for standard forks because iyt has to sit up against the lower fork clamp which is already doing the job in that position..

Mick

[Retro Rocket]

Dave , its the twist between the bottom clamp and the axle thats the problem mate, remember that the wheel acts like a gyro and wants to go round in circles side ways while we want it to go straight, adsd a disc to one side and it gets worse, any brace is better than nothing but a good one is best...

Mick

[Goofaroo]

Any idea how accurate that statement in red is?

The statement is accurate. However, it sounds to me like your question is about chopping your fender. You can chop it all you want. You can make one out of popsicle sticks or paper mache if you want (depending on your local fender laws), but you need to leave the original brace on the forks. It alone is what provides the needed rigidity and it will still function regardless of your fender design.

[swellguy]

if its a brace its a flimsy one,i can bend them with one hand,the axle is clamped fairly solid,the trees are fairly solid,so a piece of tin half way down is going to make or break you?

That's my thinking on it too. We aren't talking about forks that are 18" over stock length.

[dave500]

im still not convinced retro,its a mudguard mounting bracket held on by pissy 6mm screws,honda might call it a brace,if you had a decent heavy clamp on the lowers sure,i might take mine of next weekend and if pine creek rd is open(mud and rockslides)ill try and do my best time up it and see if it feels wobbly,ill also fang along one of the long straight rds out that way and see i get wobbles.

[KRONUS0100]

OK...............pictures?   I have never seen this so called fender/fork brace on any CB750..  Mine has never had one, either with the stock, the trashed 78, or the current Gl1000 front ends.  So what does this piece look like?

[Kong]

It is very difficult for me to think of my front fender's mounting bracket ('77 550k) as a fork brace.  If it was designed by the factory to be a fork brace then I'd like to know why its bolted on through 4 throughly flexible rubber grommets.

[srook]

"Any idea how accurate that statement in red is?"

Airtech is attempting to insulate themsleves from any possible lawsuits with that statement.  Airtech isn't concerned with your front forks anymore than you are concerned with my front forks. 

Food for thought:  How come many of the cafe racer kits of the 1970s used fiberglass front fenders and got rid of the stock setup?  The CR750 kit used a fiberglass fender with mounting plates that bolted to the fender on each side rather than a stock style mount.  Many of you are overstating the effect of the fender mount as a brace.

CR750 Fender


Scott

[Steve_K]

I have a 77 CB550k and a 76 550k.  I took the fender and brace off the 76 and put the wheel between my knees and tried to twist the fork by the handle bars.  The 77 was much harder to twist. Without the brace it was much easier to cause defection in the forks(76).  Note the 77 fork lowers are longer and may be more rigid.  If you want to keep pin point handling, I would have a fork brace.  I am sure that a better brace can be found or made. 
Steve

[754]

WHAT IT REALLY MEANS..;

 We have not figured out a way to make an all fibreglass fender that will not crack at mounting points, due to forks flexing.

 Athough a proper engineeered solution would be to make an aluminum brace similar to the stocker, but at about the third of the stock weight, we are not willing to do that..

 We are fibreglass workers, fast and easy, not taking the longer more permanant metalworking route, because that is not what we do.

[Goofaroo]

I'm not familiar with other models but my 72 CB500 came with the brace shown in the photo. It is certainly not rubber mounted to the forks. If yours is rubber mounted it is most likely a "mod" by a previous owner. The pins that hold the fender to the brace are notorious for getting loose and rattling at idle so maybe they were trying to isolate the fender from the engine vibration and eliminate the rattle. If so, I'm guessing it didn't work.

Anyway, in my opinion, there is absolutely no question that it is a brace and should be left in place. When bolted properly into position it adds considerable rigidity to the flimsy forks that come on these bikes. It also greatly reduces the forks resistance to "twist" which would be the primary problem if it was removed. The single disk configuration on these bikes certainly doesn't lend itself to removing the brace either.

If for some reason you want to run without a fender, then just remove the fender from the brace and put the brace back on. It's not uncommon to see that look. It would look pretty cool powder coated in black.   There is a huge aftermarket industry around replacing the factory brace with a more substantial one but I'm not sure if there are any available for these old Hondas. My BMW came with a brace very similar to the one on the Hondas but I found a more significant one through aftermarket sources. I can't say that it is a lot more effective than the factory one but it looks really cool.

[Kong]

I'm not familiar with other models but my 72 CB500 came with the brace shown in the photo. It is certainly not rubber mounted to the forks. If yours is rubber mounted it is most likely a "mod" by a previous owner. The pins that hold the fender to the brace are notorious for getting loose and rattling at idle so maybe they were trying to isolate the fender from the engine vibration and eliminate the rattle. If so, I'm guessing it didn't work.

Anyway, in my opinion, there is absolutely no question that it is a brace and should be left in place. When bolted properly into position it adds considerable rigidity to the flimsy forks that come on these bikes. It also greatly reduces the forks resistance to "twist" which would be the primary problem if it was removed. The single disk configuration on these bikes certainly doesn't lend itself to removing the brace either.

If for some reason you want to run without a fender, then just remove the fender from the brace and put the brace back on. It's not uncommon to see that look. It would look pretty cool powder coated in black.   There is a huge aftermarket industry around replacing the factory brace with a more substantial one but I'm not sure if there are any available for these old Hondas. My BMW came with a brace very similar to the one on the Hondas but I found a more significant one through aftermarket sources. I can't say that it is a lot more effective than the factory one but it looks really cool.

Parts number 1 and 2 in the schematic linked below, used on all 6 mounting points.
http://www.bikebandit.com/houseofmotorcycles/1977-honda-motorcycle-cb550k/o/m9448#sch405591

[bwaller]

Anything bolted between the forks may help, but it's a fender bracket.

RR mentions the axle and that's what gave the CR's the rigidity a larger axle with a four stud clamp.

[Goofaroo]

I stand corrected. Mine didn't have the rubber so it has apparently been "modded" by a previous owner. I will bolt it back in like it was although I doubt that I'll get a significant reduction in twist over the stock rubber mounted configuration.

[mlinder]

You can not be convinced all you like, however:


You are talking about being able to flex the brace as in figure 'a'.

Yes, you can. This direction doesn' matter, as this isn't a direction that the forks would try to go anyway. Nothing really to counteract in this directon.

However, I seriously doubt you could flex the stock brace in figure 'b' by hand, which is an important brace, as without the extra bracing, the only thing keeping the forks compressing and extending at the same rate and distance would be the axle and an inch or so of aluminum that is held together with bolts at the end of the forks.

And please see figure 'c'. With the 4 mounting points at the corners of the brace (blue dots), getting it to flex would be extremely difficult. However, without the brace, it would be extremely easy to get the forks to 'twist'. This area of flex is extremely dangerous, and couneracted quite well witht he stock brace.

[Goofaroo]

Great explanation and illustration. I'm sure the guys at Honda wearing the lab coats engineered a certain amount of flex into the brace to reduce stress that a more solid brace could put on other components. Given the nature of these forks I would be most inclined to leave the original brace in place and look for handling improvements with a set of springs and suspension fluid better suited to my weight, riding ability, and intended use of the bike.