You can precisely define the value of any element's movement. After pressing G, S or R and selecting the desired transformation axis (press x,y or z) you may input the number from the numerical keyboard. As pictured below I selected the edge of the spoke, pressed G, then Y and then 0.2
Select all the spoke's edges and press Shift+S-->Snap-->Cursor to Selected. It will place the cursor in the center. Set the pivot point type to a 3D Cursor. Press S and input the desired transformation value. You may also enable the Snap Tool (click the magnet icon, and change the snapping type to Increment). It will allow you to increase the spoke's lenght very precisely while scaling (hold Shift while scaling and you'll be able to change the lenght's value in smaller increments).
Now change the pivot point type to Individual Origins.
Press S and input the desired value to make all the spokes scale the same way.