Friends, riders, fellow SOHCers, let me begin by saying that a brace is a thing of beauty and a joy to behold. I myself have an aftermarket piece fixed to my own cycle and I am quite happy with it. Also, let me say that I don’t take offense to anyone’s opinions or comments. I’d be quite happy sitting down, having coffee, talking bikes, and having this conversation in person. It would be a darn site easier. One more thing – while you sit and read this sipping your coffee in your PJs or a beer in your boxers, please remember that I was in the garage wasting my time when I could have been working on my bikes
The original post is as follows:
“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 don’t presume to know what other people think, and there aren’t any Honda engineers who worked on that project present. Too bad, we’ll never know for sure if that statement is accurate. Perhaps contact Airtech and find out where they got that information?
Since one can’t know what the intention of that extra steel under the fender is for sure, it would be interesting to test the validity of the statement. Therefore, I post the following hypothesis:
The stock fender of a Honda SOHC provides sufficient input to be considered a “BRACE” where a brace is defined as a structural member that improves the stiffness of the front suspension more than 5%.
For the sake of discussion, I tested the rigidity of a stock CB500 fender. While it has been pointed out that a fuse tested in isolation will not indicate the potential speed of the motorcycle, it is useful to know if that fuse is capable of carrying the load of its intended circuit.
Clamping the left mounting tabs in a vice, I dangled a weight from the right tabs and measured the deflection of the fender. The weight (now accurately measure at 2 lbs 3 oz) deflected the fender .050 of an inch. That is about the thickness of a quarter.
It was then suggested that the test be performed in a different plane. Done, with the same result:
This test was quickly disputed as invalid. While it is only circumstantial to the stated hypothesis, it is telling. Neither the material of the fender nor its shape provides the rigidity of items that are commercially available as a brace. I assure you, two pounds does not deflect this item 0.050:
The free floating fender rigidity test was deemed inconclusive. “The fender in isolation is not a true test of its prowess.” Fair enough. For the rest of the test I pulled out the front end from a ’76 CB750F. It is in good shape, and I intend to use it on my current project.
Does the fender provide a significant force to aid in keeping the fork slider parallel? To find out I bolted up the hub and axel to the sliders tubes. This assembly was fastened to the press to hold it steady. A dial gauge and the 2lb3oz weight from the first test were put into service.
With no fender adding 2 lbs to a specific point on the tube resulted in a deflection of 0.015 inches
Installing the block for the brake caliper and rigidly (no rubbers) bolting up the fender I tested again.
With or without the fender, an equal force resulted in an equal deflection. Installing the upper clamps might seem the next logical step. Doing so, I could not apply enough force to push the sliders out of parallel without fear of bending tubes.
Does the fender provide enough structure to keep the sliders even or the handlebars and axel parallel? To test this everything was tightened to spec, and a piece of pipe fitted between the clamps to simulate the neck.
I fitted the entire assembly in a press. One of the axel caps was position in such a was so that force was applied to one side of the front end
A point was marked on each slider and both sides of the lower clamp, and a measurement was taken. At rest, the lower clamp was positioned 3.25 inches from the sliders on both sides.
The fork was compressed until the loaded side reached 1.30 inches. At this point the unloaded side read 1.34 inches. A difference of 0.040 inches.
The process was repeated with the fender bolted in place. The results were the same: 0.040 deflection.
No other forces were tested. Does the fender keep the wheel in check around the steering head? I would say any force that can twist the wheel in that direction would simply move the handlebars. Can the fender keep the sliders from rotating around the axel? Movement in this plane would not change the geometry between the handle bars and the axel.
I can’t make the fender provide a 5% delta. I’m leaving the conclusions up to ya’ll. My opinion won’t sway you one way or the other. I will say that the front end is pretty darn stout all things considered. A fender keeps the rocks and rain off you and the bike, provides a place for the speedo and brake lines, and gives you one more thing to polish (or not).
