what causes frame flex


What causes frame flex and then tire rub in a Mountain Unicycling frame? Is it the type of tubing or the design of the frame?


Often if its a good frame, it probably wont get bent out of shape, Your problem is probably your wheel If it is not true, it could have parts that rub the frame.
-David Kaplan

Additional note: even if its not such a good frame, your problem is probably the wheel.
-David Kaplan

In my experience flex that I thought was being caused by the frame was actually being caused by a bearing slipping side to side on the axle. It only takes a little bit of movement of a bearing to cause what feels and looks like frame flex. In cases where I have had flex that caused the tire to rub the frame it was actually caused by a bearing slipping on the axle and not actual frame flex.

On most standard unicycles the bearing is press fit on the hub (the Profile hub is the only exception that I know of). The only thing keeping the bearing from sliding side to side on the hub is the press fit. If the press fit gets loose the frame is not going to be strong enough or stiff enough to keep the bearing from sliding on the axle under hard pedaling.

I usually use Loctite sleeve retainer or bearing retainer to secure the bearings on the axle. The Loctite retainer products are designed to better secure press fit parts. Keeping the bearings secure on the axle is key if you want to eliminate excessive flex in the frame.