Well.... I had my first operational design issue. Since I put the fenders on I have not been above 65 MPH (just realized that when this event occurred) as I have been riding the quieter blacktop two lane roads and not the super slab.
I was driving the bike to the saddle shop on a freeway and within a mile or two broke free of rush hour congestion and opened her up. When I hit 70 the fenders started a hard oscillation banging into and off of the tire. The sound scared the hell out of me at first as I thought the calipers had come loose or???? Then I saw it. The LH fender was trying to flap like a wing. I pulled over and inspected things. No breaks, cracks etc.... So I pulled off at the next exit. No problems. Got back on the highway and cranked it up. 50 MPH NP, 60 ..same... 65...same... 70? BANG BANG BANG.... :gah:
So, It appears as if airflow and/or nodal vibrations (harmonics) in the structural elements have an issue at speeds above 70.
Good News - I can pull the fenders off and keep riding
Bad news - Engineering a modification/repair likely means a re-paint for the fenders (Damn)
One of my theories is the gap between the tire and fender (~0.250") is too tight and the fender is lifting off the tire. Think about how those tires shed water from the tread pattern... air is a fluid too... so at speed they could be creating an air flow that lifts the fender. The solution for that fix could be swapping the MT 29x18 R15 tires for 28x12 R15 tires. That would give me 0.500" vs 0.250 clearance and perhaps provide an exit for the airflow. I lose width but save the paint.
It is just a theory though
The other fix would be to increase the stiffness of support structure by moving from 1/2" to 1" round bar in the fender frame. Essentially rebuilding the fender. I would also have to thicken the bracket and beef up the attach points as I would move that bending load someplace else by stiffening the uprights. But I could also add the clearance of the smaller tire at the same time and retain the tire width I like ...
So gotta make a choice
First thing is to remove the fenders.... I will be able to think better when I am ridingorag:
Not so crappy ... hoping you get the springer on this one ...
Man, I've not been to this thread in a while.
CONGRATULATIONS! Good to read you're out enjoying the wind on your sweet ride!!!
Looking forward to your new build. Kevin
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