It looks like I am the odd ball here. In my shop stocking tires is an absolute necessity. I stock roughly 2,000 units and it works very well for me. Tires can be quite lucrative if you can do them in volume and having the ability to stock them allows you to take advantage of good buying opportunities when they come along. The goal in warehousing tires is to make as much money as possible when you buy them to keep investment costs to a minimum. For example, I am currently averaging $23.57 cash back on every Michelin and BFGoodrich I purchase. $13.83 on every Toyo, $11.03 on each Yokohama, and $14.05 on every Continental and General. That is cash back from the manufacturer and the supplier combined, some of which is paid to me monthly and some of which is paid quarterly. The dollar figures are smaller for other brands such as Cooper, Mastercraft, Pirelli, Hankook, Kumho, Nitto, and Sumitomo, but I earn cash back every time I purchase one of them as well.
Whether or not stocking tires can and will work for you will take some time to figure out and there are many variables that come into play. If you feel that you are only able to sell a few sets a week then it is almost certainly not beneficial to stock any, but if you believe you have the potential demand to move three or four sets a day then it is definitely worth taking a good long look into growing that area of your business. Some questions you will have to ask yourself.
How much demand are you experiencing from your customers?
Do you have the required space to warehouse them?
Do you have enough cash to invest in them?
Do you participate in any manufacturer incentive programs?
Do you have a good working relationship with a large supplier?
Do you have the right equipment to begin doing more?
If you have the demand, space, and cash then you should almost certainly investigate further. If you can develop a good working relationship with a supplier like Carroll, TCI, or ATD and move enough units to participate in a manufacturer program such as Michelin MAST, Continental Gold, Yokohama Advantage, or Toyo Driven you can get a better buying price and earn money when you buy them. One potential drawback that comes with doing more volume in the tire business is the associated equipment and supplies....more capable tire changers and wheel balancers, TPMS diagnostic/reprogramming devices and sensors, wheel weights, etc.
On the positive side, the more I stock the more I sell. I have found that the more options I give customers the more likely I am to have something on the shelf that appeals to them on some level. This is simple consumer psychology. Many consumers make impulse buys and most consumers love to have options and the "perceived" value of a rebate or sale available to them. If a customer walks into a shop and asks for price and availability on a set of P215/55R17 you are much more likely to make a sale if you can provide estimates on three or more products, which provides the consumer with choices. One of those choices is eligible for a manufacturer rebate or is on sale, which provides perceived value. And you can have any one of them installed in about 45-90 minutes, which provides the opportunity to buy on impulse.