gotcha.

 

Are you positive about this? Most people with 20's I've seen run 245/35/20 in front. With the rears, it's fine to run 275/30/20 since it's a wider tire therefore the side wall ratio should be fine. I can't comment on the 255 or 285 widths since not that many people run them with 20" from what I've seen.

 

Yes I am positive. People who run 245/35/20 are running the WRONG SIZE. Just plug it into a tire size calculator and you'll see why this is a poor option. A stock 225/40/19 has a diameter of 26.1", a 245/35/20 has a diameter of 26.8", a 2.6% difference. A 245/30/20 has a diameter of 25.8" or a 1.1% difference from stock. To make the problem even worse, a 275/30/20 has a diameter of 26.5", which would make the front tire even taller than the rear tire, totally killing the stock height stagger. 255/30/20 is the best match, at 26.0", and my personal choice for 20's, but some people like to run a narrower tire. So the point is, just because most people do things doesn't make it right. Do you own research rather than listening to others who may not know what they are talking about. http://www.miata.net/garage/tirecalc.html

 

^By using the calculator I agree with what you're saying but there's a lot of things the calculator does not take into account such as wheel width. Some people I've seen run stretch wheels to fit their application. Others run a certain brand of tires since side walls height varies from make. You're right with doing your own research but I'm one of those who likes to go with the flow and get what others have if it has worked. Good info on the tire sizes though.

 

Unless you are planning on only stretching the front tires, the same issues are going to come up with the front and the back, sidewall heights may vary, but if they tend to be short, they'll be short across all the sizes, so you'll end up with the same problems. 245/35/20 is not the right size with matching rear tires in any application. Just because it works doesn't make it the right setup.

 

255/30 & 285/30 is your safest option

 

Time to sell those tires then...

 

For a 10.5 wide rear rim, you should want the 285's anyway. Some tire manufacturer sizes do vary. The initial Nitto 555's that I had on my 10.5's were more stretched than the BFG KDW2's on the same rim. Both tires were 285/30/20. The BFG is still a little stretched but not as much as the Nittos.