Lets try to explain this out for our OP.

For this math we will be assuming that a 28" tire is actually 28" exactly and so on.

With a 28" tire the circumference (distance around the tread) is 88"

with a 30" tire the circumference is 94"

So with the 28" tire on the front one rotation of the tire travels 88" and with the 30" tire it travels 94". Of course your front axle and your rear axle can not travel different distances because the front and rear are fixed together by the chassis and suspension so what happens is either the tires slip on the ground (best case scenario) or and much more likely one of your differentials breaks (usually the front one) and you get to spend $1,000 and still replace the tires. While some may thing that "OK so my front tire will just travel less distance" it doesnt work that way. The tires have to move at the same speed across the ground so in doing so there will be constant binding between the front and rear.

You had referenced the wheels were 14" and yes that is true. but the tires are the "final drive gear multiplier" in your drive train. Wheel size could be 12" on the front and 14" on the rear and the machine wont care in the least as long as the OVERALL tire HEIGHT is the same. See the picture below on plus sizing wheels

Lets do a little bit of basics on tires while we are all here just to make sure we all understand what those numbers mean. First we will focus on the our UTV/ATV tire sizing standards. For this we will use the tire size 26x9x14 tire. 26" is the over all height of the tire. 9" is the width of the tread of the tire. and 14" is the wheel diameter that that tire fits (this wheel diameter does not include the lip of the wheel). If you want a bigger (taller) tire you could go with a 27x9x14 and the tire would net you 1/2" more ground clearance (only 1/2" because you gain 1" in diameter and only 1/2 of that is below the center line of the axle. Thus the other 1/2 is at the top of the tire and not actually helping with clearance). But to do that and not snap important drive pieces you would have to do all 4 tires at that size. If you just wanted a wider tire you could do a 26x11x14 and you would gain 2" of width (what most do on the rear) this is ok to just do on the rear as you do not change the overall height/gear ratio of the tire. If you wanted bigger wheels with less sidewall you could go with 26x9x15 and your wheel would be one inch larger but the overall tire size would be exactly the same so no issues there.

Now CAR TIRE sizes are much different. We will work with 225/75/R15 as a tire size. 225 is the width of the tread in MM (notice the width is in a different place in the number sequence). 75 is the sidewall height and it is a percentage of the width. So in this case it is 75% of 225 MM which comes out to 168.75 MM. The R means it a radial. the 15 is still the wheel diameter in inches. I know that can be confusing but in the ATV/UTV world we dont have to deal with that LOL.

I hope this helped some and explains WHY its a HORRIBLE idea to mix and match overall tire heights and the damage it can cause.