Can I change the Original Equipment (OE) Tire size of my Infiniti G20?

Your G20's OE tire size is P195/65R15 89H not "195/65R15". Yes, you need to use the whole description. Here is why...

These other tires are probably P185/65R15 86-somethings. They are smaller in diameter (throws off speedometer and odometer readings and gearing for reduced gas mileage). They have a smaller and narrower contact patch for reduced traction, braking and handling. They have a lower load carrying capacity (to the tune of about 75 lbs/tire) which could result in the tires overheating and blowing out.

And oh yeah, the may have a lower speed rating which further reduces braking and handling capability, reduces traction and have less heat resistance.

No shop that has a clue what it is doing will put these on for you due to the potential liability. If they will, they have no integrity or expertise and you shoudl shop elsewhere. Otherwise, it's a great idea.

EDIT:

Now you went and screwed me up. OK, if your real OE size is P195/60R15 87H then most everything above still applies except that you can get around the load carrying capacity problem by increasing inflation pressure by 3 psi front and rear.

You can change them, yes. It will make your speedometer off a little. It will also change the shift points in your transmission, which can be damaging. You will need to make sure the shop that does the mount and balance also has the means to recalibrate for the new size.

in case you are able to no longer locate the properly suited tire length interior the automobile door in basic terms call a tire broking or an Infinity broking. they're going to have the flexibility to tell precisely what the applicable tires are on your sort. -f

yes you can use those on it ,it will make the speedometer just little off in it,maybe a 1-3 miles per hour off,but other than that it wont hurt nothing ,you wont notice anything out of the ordinary with it either,the gas mileage it will affect very little,so you,ll be alright with that .good luck with it.

Yes. Your speedo will be off and your mileage will be less.