Part science, part "art", part VooDoo...  Tires.

I still had lots of life left in my factory installed Good Year GS-A tires when a tame off-road trip went bad.  We were going along a rutted dirt road where some water collects.  This spot is muddy and we usually plod through with no problem.  On this day, the puddle was nearly dry and we could see the ruts and the high spots in the middle and on both sides.  So I decided to straddle the ruts and ride on the crown and one side of the road.

About half-way through, we lost a little traction and the back wheels slipped sideways back into the ruts.  It was not very dramatic as we were only going about 3 m.p.h.  I just continued on through the shallow mud and started up the road when I heard a swish-swish-swish sound and felt the rear-end kind of sloppy.  A quick check revealed the problem:  The left-rear tire was going flat.  So I pulled up to a level spot and, using the bottle jack, popped the wheel and tire.  There on the inside side-wall was a 2-inch gash.

The spare was brand new - still had the little mold injector projections on it.  So I installed it knowing that the tire I removed was toast.  Not knowing what caused the flat, I had to decide how I was going to get back out - the way in is also the way out.  If I wasn't careful I could get another flat in the same spot and be out of spares...

The last thing I needed was another flat on the way out.  So I took down my shovel and drained what remained of the water in the puddle.  That took some time....  I couldn't find anything obvious there to explain the cut in my tire, so I filled in the ruts as best I could and drove back out without incident.

On the way home I started considering my options.  Before this happened, I had decided that I was going to use the factory tires and wheels until the tires wore out, then get new tires one size larger and with some more aggressive tread.  I still had about 20,000 miles to go.  I wasn't planning on new wheels in the near future.  I didn't want to get a tire that was any larger than 30 or 31 inches.  I was not ready to get involved with lifts, gears, and all the rest of it. (Note:  Some time later all of these other things I didn't want came to be...)

When I got home, I checked the rest of the tires.  I found that another tire had a pretty good cut in the side-wall and probably would not be safe to continue driving.  So now I am down to three tires: two that have 20,000 miles left on them and one brand new one.  I was sure that I did not want to go out and buy two new GS-A's, so I made the rounds of the used tire stores and found nothing worth buying.  That was when I decided to get the new tires early.

I shopped all the brands that offered 30 x 9.50 x 15 light truck, all-terrain tires.  I wanted to have a good compromise between highway handling and off-road capability.  After a process of elimination, I settled on the Pirelli Scorpion A/T 30 x 9.50" x 15.

They are actually about 29.6 inches high.  This is roughly 3/4 of an inch taller than the Good Year 225/75-15's that I had.  This should give more ground clearance but I am not seeing any measurable difference. 

I made the mistake of measuring bumper height on both corners of the rear before I had them mounted.  I should have measured clearance below the differentials to see what I got before and after. 

When I made the pre-installation measurement, I had an empty gas tank and an spare tire with no air in it.  After the tire installation, the tank was full and I had a larger spare with air in it.  This extra weight probably accounts for the net change of zero inches.   But I know I am riding a little higher because I now brush a canvas sign in the parking garage that I never touched before.

The speedometer is reading a little lower, and I now use 1st gear (it used to be too low to bother with.)  The first trip on a familiar trail, I noticed fewer clunks and bumps on departure from obstacles, and improved traction.  So this change did give me a mild off-road performance increase.  Fifth gear still reads about 2200 rpm at 60 mph so I think there is no need to do anything with gears etc.

On the highway I feel confident when I say that they are better than the Good Years.  I have been out in driving rain, traveling at about 60 m.p.h. and got good steering response, without any vagueness.  Starting from a stop in the wet, traction is positive, even with slightly aggressive pedal pressure.  In dry conditions, they are very stable.  I don't notice any noise increase.

The "art" in this is the appearance.  They are good looking tires.  There is an aggressive tread pattern, beefy foot-print, and clean side-wall.  I chose to have the white letters inside with black lettering out.  I don't like the way the white letters look once they have been scuffing around in the woods for a few months.  They self-clean mud from the tread pretty well too.  They should last about 40,000 miles.

Update: 5/13/02  I have about 30,000 miles on these tires and probably about 1/3 of their tread life left.  If I did nothing but drive on-highway, the tires probably have 1/2 of their tread life left.  I don't think the tires will be very good off-highway when the tread depth gets a few more 32^nds worn.  But so far I have been pleased with the tires except for a couple of extreme circumstances where, combined with driver error, they did not perform as well as I would have liked.  

I rotated and balanced the tires, including the spare, along with having the front end aligned, following a spring installation.  I should be good for another 10,000 miles maximum.  Probably by December 2002 I will be ready for more tires.

Update: 7/19/02 - I installed InterCo TrXuS tires.  The Pirellis served me well and I would recommend them highly.  It was just time for me to try a tire more biased for trail use!   These tires were retired with plenty of tread left of street-only use - approximately half of their life still left!