On my 1982 Westy, I currently have tire size 195/70R15.  My wheels are not
original.

I take most of my vacations up on rough, rock Forest Service roads,
pretending I have 4WD, and though I drive slowly, it's hell on tires.  One
of my Nokias developed a slow leak after my most recent foray and Big O
showed me that it has multiple tiny leaks and said it shouldn't be salvaged.

Can anyone make a recommendation as to a really strong tire that can take
this kind of abuse?

In addition, I have calculated that my speedometer and odometer read about
5% low (65 MPH is actually over 70, etc.).  This alone wouldn't concern me
terribly much.  I can make the adjustment, if I'm getting new tires all the
way around anyway, I wondered if I ought to try to get the originally
specified size which would make the speedometer read correctly?

Thanks for your recommendations.

Paul in Colorado