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Here's an attempt at adding a method to allow controlling of the maximum 
radial value displayed in a polar plot. In axes.py, I added the following 
method to the PolarAxes class. I basically copied the code from 
autoscale_view() and made some minor changes. If I can figure out what 
each step actually does I'll add some comments.
 def set_rmax( self, rmax ):
 rmin, oldrmax = self.rlocator.autoscale()
 self.rintv.set_bounds(rmin, rmax)
 self.axesPatch.xy = zip(self.thetas, rmax*ones(self.RESOLUTION))
 val = rmax*math.sqrt(2)
 self.viewLim.intervaly().set_bounds(val, val)
 # Re-create the radial ticks and labels.
 ticks = self.rlocator()
 self.set_rgrids(ticks)
 for t in self.thetagridlabels:
 t.set_y(1.05*rmax)
 r = linspace(0, rmax, self.RESOLUTION)
 for l in self.thetagridlines:
 l.set_ydata(r)
It sorta works but it definitely has a lot of problems. Here's a sample 
script:
from pylab import *
figure( figsize=( 5, 5 ) )
theta = arange( 1, 6, .1 )
r = 10 * theta
polar( theta, r )
show()
Then try:
gca().set_rmax( 30 )
show()
1) I don't really want to call set_rgrids() because you lose any 
modifications the user has made to the radial grid. If I don't call this, 
the radial grid doesn't update though so it looks crazy. What would be 
nice is to duplicate the behavior of X/Y plots. For example, if I set x 
ticks to be at 1,2,3 and then set the x limit to be 1->2, I don't see the 3 
tick somewhere off to the right of the plot.
2) There seems to be some kind of update problem w/ the theta labels. Even 
though they're locations are being reset in the set_y() call, they don't 
appear. However, if I use the pan button in the GUI and lightly tap the 
screen, they'll show up in the right locations (forget for a moment that 
panning is kind of a stupid thing to do in polar plots).
3) There is definitely some kind of data clipping problem. The curve is 
not being properly clipped at the plot boundaries after calling set_rmax().
I'm sure all of these are problems w/ my set_rmax() routine but I'm not 
sure where to start with them. Does anyone have any pointers for me to 
start with?
Thanks,
Ted

Hi,
It seems there is a little bug in axis.py, line 543 (in Axis.draw()).
The legacy Tick.set_label() is used instead of set_label1 and
set_label2 (a few lines above, the analogous code for major ticks uses
set_label1 and set_label2).
This causes minor tick labels not to be drawn when using tick_top(), as
shown in the attached example (+ two lines patch).