So i'm trying to learn more about tires and rims and so far i know that i want to get some larger tires that are offset (bulge out a little more) for the rear. I was thinking and trying to read other forums but they just give numbers like 215/55-50 or something and you're supposed to know exactly what's goin on, could you clarify or point me somewhere?

I want to go for this kind of wheel on the rear and keep the front stock

 

the first number is the width of the tire, in millimeters. the second is the sidewall ratio to the tread. so if its 55% of 215, it basically notates the height. the last number is the rim diameter, in inches. for a stock 280zx, with stock rims, you can run a 225/60/r14 up front, and a 235/60/r14 out back, and have a decent footprint on the ground. btw, stock is 195/70/r14. hope that helps a bit.

 

you should probably learn about wheels too. they are usually attached to rims.

 

Let's look at a tire size...

215/55R16:

215 = Tread width in milimeters

55 = Aspect Ratio (Sidewall height as a percentage to tread width as measured from the rim seat bead to the tread. In this case, the tire sidewall is 55% of the width which means the sidewall is 118.25 Milimeters tall).

R16 = fits a 16" wheel (The "R" designates that it is a Radial tire)

As you can see by this example, as you increase width you must lower the aspect ratio to sustain overall diameter. In other words, a 225/55R16 is both WIDER and TALLER than a 215/55R16 because 55% of 225 is more than 55% of 215 (123.75 Milimeters VS. 118.25).

Wheel diameter is important to note as well here. As you increase wheel diameter you also increase the overall height... Thereby making the "Aspect Ratio" an even more important player in the final equation to maintain proper "Rolling Radius". You don't want the final combination of wheel/tire to be significantly "Taller" or "Shorter" than the original else you will suffer from an inaccurate speedometer and your final drive ration will change (meaning a different RPM level to maintain speed which could lead to the engine working harder than it should or poor gas mileage etc...)

So, if you go from the stock 14" wheel to say a 16" wheel, you need to significantly lower the Aspect Ratio of the tire to accommodate for that 2" in diameter increase.

This thread: https://www.zdriver.com/forums/general-tech-info-all-z-car-years-272/tire-sizes-15618/ That I started a long time ago has two PDF files showing options for tire sizes that will closely match the stock Rolling Radius. It would have been a good place to start your quest for knowledge

Take note of the closeness in overall diameter between the various sizes listed despite the fact that the wheel sizes and tire widths are all drastically different.

Anything Else you need cleared up?

For our next lesson, we'll discuss "Wheel Offset"


CLASS DISMISSED!


Rod.

P.S. Here is an updated ratio guide to include an 18" option: