Vallie Components - bicycle part and accessory design

The testing:

The simplest way to do this, will be to anchor the two faces where the dropout meets the rest of the frame. Next I'm going to put a very slight axle groove in the top of the dropout so that the forces of the axle can REALLY be localized. (as opposed to applying force along the entire upper edge of the dropout) Remember, I'm trying to simulate an axle impacting this thing.


Okay, let's assume our Proj-B test rider weighs about 190lbs. If he hits an object (like a wheel swallowing pothole in the South Bronx) then the force on the axle is going to be several times his mass.

We don't actually need to use any particular value here, because I'm going to use the same value to test the dropout with and without the fancy cutouts, but let's assume that the force is twice the rider's weight, thats 1690N being applied at the upper edge of the dropout.

SolidWorks has a handy stress analysis tool that allows one to calculate the Factor of Safety (FOS) of a part. Simply put the FOS is the Material's yield strength divided by the equivalent stress at a point.

-An FOS less than 1.0 at a location indicates that the material at that location has yielded.
-An FOS of 1.0 at a location indicates that the material at that location has just started to yield.
-An FOS larger than 1.0 at a location indicates that the material at that location has not yielded.

So, for the Plain old dropout, and a 1690N force, we get a FOS of: 5.25102
No problem. I would ride this all day.

The Von Mises stress distribution on the model look like this:

Let's repeat that test for the Fancy Cutout version:


Here our FOS is 4.43389 That's 15% less strength!

These pictures show the model in a total deformed state, though thats not actually the case for these applied forces. The dropout will NOT deform under these conditions. Solidworks just uses this to illustrate how the stresses are distributed.

So what can we tell from this?

Well, it's certainly more colourful. You can see where the stress is concentrated in this last picture. That lower crescent and the little arrow head appear to be areas of concern. It seems the cutout dropout is only 85% as strong as the solid one. Whether or not that is 'strong enough' is entirely subjective. Much like my opinion of the aesthetic design of this particular dropout.


I started playing around, finding the maximum force before the material would actually deform. It seems the solid dropout could withstand a force of 9kN or 2020lbs before it would yield.. and even then, just barely.

When that same force is applied to the cutout version, we see a couple more areas of deformation.

Most notably is that little pointy arrowhead tip again.

I guess today I've learned that fancy cutouts aren't really as bad as I thought they were. I've also learned how easy it is for me to get sidetracked into theoretical testing and hypothesizing simply by staring at a picture of a bicycle for too long.

If any of this bicycle's designers are reading, please don't feel too slighted by my words. (I didn't even touch upon your PBR bike!)

I am only doing this because I wish i was doing what you are doing.

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