New tire help

I've been looking around for some new tires for my '93 XLT and I'm a little confused with the sizes. Some of the websites I've been looking at say that 235/70 and 235/75 fill fit. I'm currently running 235/70. Now I've been looking around on this forum and have seen people running 255/70.
First what is the difference between the 235/75 and the 255/70? Which is bigger?
Second is there another size that I can get to fit without a lift?
I'm mainly looking the biggest tires possible. Also how is the ride with the bigger tires, I've heard people saying the ride isn't as smooth.

Thanks for any help.

 

[JDraper]

The tire size is a ratio. 235/75-15 means a 15" rim with a tire that has a 235mm wide tread. The 75 is called the aspect ratio. It means that the sidewall of the tire is 75% of the width. For example a 235-75-15 tire has a rim diameter of 15". Add the sidewall height (235 x .75 =176.25mm=6.94") twice and you get a rough tire height of 28.9". The 255/70-15 tire has a height of 29.05" when you do the math. The difference is that the tread width on the 255 is .79" wider than the 235" tire. All other things being equal, this should produce better cornering and traction because you have a larger contact area.

As for the largest tire you can fit on a stock vehicle without rubbing or modification, I believe it is a 31x10.5 tire.

 

[duke16]

Ok, I think I understand all that. But then what does the 31x10.5 tire equal in the other form?

 

[CHH777]

Originally posted by duke16
Ok, I think I understand all that. But then what does the 31x10.5 tire equal in the other form?

Try this:

http://therangerstation.com/Metric_To_Inch_Tires.html