Tuesday, July 8, 2008

Crustacean part 1

The project: Create Crusty a randonneur/gravel frame & fork based on his Cannondale, Caad9. I think I got it all, but the fork's axel to crown isn't adding up. Tomorrow I'll have to get a physical measurement instead of dimension manipulation. One problem is they don't give you the frame size center to center, instead they give you the size center to top of top tube. However they tell you the stand over height is 822mm to the center of the sloping top tube. All my other measurement work out. It's that axel to crown measurement that is wrong in my drawing.

These are my tentative plans for the new frame & fork. One liberty I took was to lay the head tube back 1/2 degree to 73 . . . I might some more depending on what happens when I get a look see at the real axel to crown measurement.

It's pretty simple. I just need to take the Caad9 dimensions and make accommodations for Jack Brown 33.333c tire and fenders.

For the tires and fenders it's going to take longer chain stays, and longer fork blades. To maintain the same bottom bracket height with the big tires, I had to lower the bottom bracket. Lowering the bottom bracket also shortens the head tube.

The head tube is also going to be affected by longer fork blades. Also the Cannondale has a internal headset. Most headsets have a lower stack height of 13mm.

I had to shove a few other dimensions around . . . well you can see for yourself.

Once I get the dimension ironed out I can select the tubing. . . . Yep not straight guage 4130 like my last 3 frames, but tubing design specifically for bicycles. I see Dedacciai or True Temper in Crusty's future.

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