I have a set of Yokahamas that have less than a 100 miles on them. They look new and have been in my garage. Thing is I bought them about 5 or 6 years ago. I want to have them mounted and use them, but am I asking for trouble doing this?

Common word is six years. If they have been in the dark, i'd say you have a year left IMO, especially on a light weight car. Guess it depends on what your gonna do on them

6 yrs.

But, if the tires have been in a dark garage and not around running electric motors (with semi stable temps) you might want to give it a whirl, especially as they are so low mileage.

If they sat in the sun, or have been exposed to ozone, trash em.

I was told 7 years but 6 is a good round number. Better safe than sorry.

every nut bolt and screw on your car is designed to optimize how it relates to the road. all this technology connects via your tires.
...think of a super computer...on dial up
because they are round and black does not mean it's still a tire. sell them cheap to some broke guy that needs tires just to get by. my guess is that if you didnt really care you would not be asking us and you would not be driving a Porsche

what type of driving do you enjoy in your Porsche

They may be within the useful limits - if the sidewalls haven't started cracking from sun, ozone, etc. as the others have mentioned above - but only a max. of about 1-2 years or so of safe use, depending on whether you use the 6, 7, 8, 10 or other max. age you want to use, & when they were made - as opposed to when you bought them.

HOWEVER, even though you bought them 5-6 years ago, they could be even older by date of mfgr., so you need to look at the DOT date code on the sidewall to determine the exact age of the tire. Most tire retailers & mfgrs. have similar info. to this on their websites, but you can see reading sidewall for mfgr. date & life of tires links here for the 6-10 yr. range:
http://www.discounttire.com/dtcs/infoHome.do

Read up, get the mfgr. date of the tires (all of them, since each can vary), & inspect them for cracking by bending both of the sidewalls hard inward all around while looking for cracking on the outsides & repeat opposite direction to check the inside walls, & look down the tread grooves all around (even hairline is the start of bad news); then decide if they're even in the ballpark for your use.

If so, then try mounting them (oldest if different ages to spare) & inspect them first with max. inflation on the sidewall (not the vehicle max.) & "loaded" with the car on the ground & inspect for sidewall cracking & in the grooves/sipes between the treads (over inflation with stretch the treads outward to expose cracking there); then deflate a bit & do the same at a relatively low temperature (18-20 lbs.) to flex the sidewalls for cracking (low pressure over stretches the sidewalls) & treads again; then if no cracking shows at either of the two; try it all over again inflated to the proper 914 pressure specs. on the label at the gas filler/evap. tank & reinspect for cracking at sidewalls & treads.

If they all check out okay (including the spare) & is within the 10 year max. which most tire mfgrs. recommend, then try them out on the car for awhile, but be careful to check them all every 100-200 miles for cracks for a couple of thou, then every 500-1000 thereafter.

Also mark a date on a calendar or somewhere you won't forget to replace them on the date which the oldest mfgr. date tire reaches 10 years, & do replace them by that point or before.

Sean, I am with you. I am concerned about the age. I guess four hundred bucks on new tires is alot cheaper than taking a chance and having a tire go south and tear up the car.

Tom, are you trying to say I should not use the original 36 year old spare in the front trunk!

Ummmm......yeah Jack - that's only for CW show now buddy!

Those Yoko's MAY be okay for a year or 2 if cash is tight - depending on their true age, but a new set at $500 or more all in & mounted - with a new spare too - is a safer bet.

Hey, you can still get new old school Michelin XWX 185/70VR15's like the M-471 package came with at Lucas Tires special order - but they'll set you back $407 EACH last I looked - plus mount & balance, tax, shipping if not near Lucas in SoCal or Ohio, etc.!!!!!

If anyone is interested in those as a total CW - PM me for their contact info, cuz I'm not tracking this thread, just checked back this once.