How to hold head tube rigidly on a flat table for flex test?

Yes for sure! But I’m a software guy so just pressing a few buttons in SW is easier than doing actual hard math :smiley: I design in CAD anyways.

I’ve decided to standardize on swing arm pivot - which is similar to a BB in my case anyways. Seems like my front triangle is extraordinarily flexy (roughly 20N/mm deviation at the headtube) which seems very high compared to other known rigid road bike frames. Of course this is not a road bike - but seems like to ride like one it’ll need to be as stiff as one.

Had two plates with a big flat 2mm thick shim out of Delrin with a bolt running through a bearing on top of the plates and screwed into the bottom plate. Adjusted the tension on the shim with the bolt and used a locknut to lock it off. From memory. It was about 23 years ago now. I tried to design it so that teh rear ‘shuttle’ would slide a little as when you flaxed teh frame sideways you shorten the wheelbase fractionly. I was trying to emulate the real world of no constraints on the frame other than fiction from tyres on the road. The next level would have been to allow the rear to rock side ways as well but fark!…….how far do you take it?

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Makes sense!