First off, I don't know anything about tires. please help! I have a 2000 Jeep Cherokee. The rear right tire is low, i will fill it up with air, and approx 2 days after, it always goes low. So I need to replace. Now, all the tires on the vehicle now are P255/65/16. The spare is a P245/70/16. So I'm assuming I just can't throw on the spare due to the different sizes. I don't have the money to replace all 4 with new ones. Can I just buy another tire matching the spare size and throw on the rear left? So the rear tires are the same size, and the front tires another size. Or can I just throw a can of that sticky stuff into the low tire and wait till I can afford all new tires? Thanks.