I never had any "problems" with the stock IRCs.  But once the rear got slick, I bought the Dunlops to replace.  WOW, what a difference.  It feels like a completely different bike, with regard to handling in turns, rain grooves and otherwise crappy road surfaces.  With the IRCs some of the raingrooves were absolutely white-knuckle.  No problems whatsoever now.  Maybe I'll go with some Metzlers next time around and get another epiphany.  The Dunlop is a little wider than than the IRC, too.

Interesting about the tire width.  All are the nominal 140 mm width, but IRC GS-18 lists their rear tire's actual width as 128mm (5.04"), and Dunlop D404 is listed as 5.85".  I don't know if they're measuring at the same point.  Pirelli lists the maximum width of their 140/90-15 MT66 Route tire as 151mm (5.94"...can that be right?  Their 150 is listed as 157 mm).  Metzeler does not list a width for their ME 880 Marathon.  By the way, Metzeler is a Pirelli brand,  bought out in 1986.

A couple of interesting pages on the Metzeler web site about tire pressures and tire upgrades:
http://www.us.metzelermoto.com/web/products/tire_pressures/default.page
Quote:


Then, they show recommended tire pressures for the ME 880:
ME880      Solo      2 Up Light      2 Up Heavy
Front      38-40      40-42      40-42
Rear      44-46      46-48      48-50
But, the IRC GS-18 has a max pressure of 41 psi.

About tire upgrades:
http://www.us.metzelermoto.com/web/products/upgrade_options/default.page
Quote:


Except they don't recommend an undersized wheel, and both Pirelli's 140 and 150 have a recommended wheel width of 3.0"...our rear wheels are 2.75" wide.  Also keep in mind that a bigger diameter tire will give an effective higher gear ratio.  The stock GS-18 140/80-15 has an outside diameter of 612mm.  The MT66 140/90-15 has an O.D. of 629mm, and the 150/90-15 has an O.D. of 653mm, about 7% bigger for about a 7% reduction in engine rpm and about 7% reduction of power (very rough estimate of the power loss).  Top speed may not be helped if our bikes run out of power before they run out of rpms.

By the way, here's what the tire sizes mean for anyone who doesn't know:  
140/80-15 M/C 67H
140 = the nominal width of the tire body in millimeters.
80 = the percentage of the tire body height to the width.  (70 is a lower tire of the same width, 90 is a taller tire of the same width, etc.)
15 = the wheel diameter in inches.
M/C = Motorcycle tire
67 = Load Index = 677# for these tires
H = speed rating, not over 130 mph for "H"
Also, the last four digits of the DOT code impressed into the sidewall of the tire show the week and year of manufacture.

I prefere the dunlop 404s I had before. I think the wider tires made tight corners feel more "smooth". With the cheng shins im running now it feels kind of twitchy in a hard corner.

Although my Savage is my "daily rider" (I don't own a cage), I put less than 2000 miles on it a year (I use it strictly for local duty - most trips are very short).

If you're like me, you may want to consider just staying with the OEM IRC tires.  If I get a high quality tire, it will age out before I can wear it out.  That would be a waste of rubber.

"By the way, here's what the tire sizes mean for anyone who doesn't know:  H = speed rating, not over 130 mph for "H"

Hey, ya'll let me know when the tire needs to be anything over a 110 rating for our Savage!  

Recently I had my AC unit break down, and here that is a big deal in summer, so the tire purchase is on hold for a bit.  But I sincerely appreciate all the feedback, and printed it out for the purchase reference.