It's more than a "spare tire"... more like a parachute. If you need one and don't have it, bad preparation.
I'm no expert, but there are a lot of reasons to carry a spare magazine, especially with a 6 or 7+1 round Kahr. I'll just mention a few. I'm sure that others can add more.
First, magazines fail. We've had newbies come here almost in tears or hysterical that their ONE magazine broke... and in some instances, their TWO mags broke! I have 10 or more mags for .380 through .45. I recently had all 9 of my PM45 mags that were replacements from Kahr fail with shattered springs or the wrong springs... too weak... in my 7-rounders. I did have two replacement springs and followers, so I was able to keep the PM45 in service until I received replacement springs from Kahr. NOTE: You may have noticed that I said 9 mags after espousing 10 or more. Believe me, I have many more... two more Kahr and some 1911 Officer mags for it as well.
Secondly, in an altercation the magazine in the pistol may be lost due to a struggle or the loss of fine motor skills from the adrenaline rush encountered in fight or flight scenarios. Don't discount that if you haven't been there, because it's not like at the gun range with no stress. Whatever the reason, it would be nice to have a backup magazine in a carrier that allows all-aspect access... possibly during a struggle, or while trying to seek cover.
Thirdly, you might actually need the extra ammo, especially if you make it to cover and there are two or more assailants. Cops and good guys alike have blown through high-capacity 15-20-round mags at close range in gunfights, with little or no hits. You aren't prepared for much if you expect to take out the bad guy(s) with 1 or 2 "well-placed" shots... as your 2-inch groups at the range show you're capable of... but not when"your hair's on fire and you're up to your ass in alligators", as some gunfight veterans have described their feelings at the time.
I carry a standard, flush-fitting mag in my Kahr in an IWB holster and a 'high-cap" 7 or 8-round Kahr mag opposite side in an OWB holder. I also carry a spring-assisted Gerber FAST Draw on my weak side for a backup.
I don't expect trouble, but if it finds me, I would rather be "over-prepared" than a complacent victim. Carrying an extra magazine is just part of my carrying a concealed weapon... part of my everyday kit.
Wynn
USAF Retired '88, NRA Life Member. Wife USAF Retired '96
Avatar: Wynn re-enlists his wife Desiree, circa 1988 Loring AFB, ME. 42nd BMW, Heavy (SAC) B-52G's
Frédéric Bastiat’s essay, The Law: http://mises.org/books/thelaw.pdf
Thomas Jefferson said
“A government big enough to give you everything you want, is strong enough to take everything you have.”
and
"Peace is that brief glorious moment in history when everybody stands around reloading".