Is it possible to put a 15" tires on the standard TL, which has 16" tires originally.... ?? Just wondering... I heard the smaller the tires are, the faster it is... however, I also heard there is some kind of ratio u have to keep... like smaller rims with thicker tires...
let's say if a 15" tires fit, how thick should it be?

 

Really unsure of what you're trying to accomplish; most people increase their wheel size!
The so-called "ratio" would be the overall height of the wheel/tire combination. Your set of replacement wheels need to be close to the stock height which is 25.7". Too small and your speedo will read faster than your actual speed while too large would have the opposite effect.

 

i suppose you could but what would be the point???

 

I'll sell you mine!

 

The fact is I have a set of snow tires but they were for my accord, and they r 15". I was thinking using it on my TL. However, I notice that the break is pretty much full in our 16" rims. Can a 15" rim fit on it?

 

okay... are you trying to save $$$ by using those 15" snow tires and therefore going with 15" wheels? I don't think you can fit 15" wheels on TLs but... the question is: WHY would you in the first place? I say... keep the 16" wheels you have now... and get some 16" snow tires for them, if you must have snow tires in the first place. And another thing... if you live anywhere, where you need snow tires... I don't think speed should be a concern...