Tires: Tires, proper inflation pressure, 6 wheels

Question
Hello Barry,
I have some questions regarding tires that no one can seem to answer for me.

I have an 1989 Chev silverado 3500 4x2 dual wheel pick up. No Abs brakes.

My front tires are LT245/75R16. My Rear tires were the same...however they were not as wide (so the tires dont rub under weight)

About half the shops I talk to say I cant use an LT245 on the rear, the other half says I can.

I've also been given 4 other possible allowable tire sized for the rear, they are
235 85r16
225 75r16
215 85r16
245 75r16

Which is the best legal size to have ?

Also regarding tire numbers
245 75r16  

is the 245 the height? the higher the number the higher the tire?

75 is the thickness? higher the number the thicker?

16 is the rim size?

Thank you very much!
Patrick

Answer
Patrick,

First you need to visit the web site listed below.  It will tell you more than you need to know but will be able to answer many of the questions you asked and some you didn't.  I'll start you out with the sizing question.

http://www.tirerack.com/tires/tiretech/general/size.jsp

I'll wait while you do that.

Mmm.   Mmmm.  Mmmm.  Whssss. Whsss.  Mmmmm.

Back so soon?

My book is a little unclear about what tire size originally came on your vehicle, but my best guess is LT225/75R16.  

You should verify this by finding the placard, which is usually located on the door post or in the glove box.  While you're there, check for the proper inflation pressure for that size.  I think it will say 55 psi front and rear.

IMHO that is the correct size.  If I remember correctly the offset on the wheels means you are in danger of the duals kissing if you use an LT245/75R16.  This would be a bad thing, but you might not be able to see it happening because it would occur when the tire hits a bump.  

Besides your vehicle came with 6" wheels and an LT245 needs at least a 6 1/2".

If you want to get wheels from a newer model that originally came with LT245's, then you could use that size.  You need to find 7" wheel off a dually - 2001 and newer.  You may have to do a trial fit to see if you have enough room, but knowing that GM is generous, it probably will work.

Hope this helps.