Tires: Tire size, Tire Size

Question
I have a 1996 Roadtrek RV that is built on a Dodge 3500 Maxivan.  Roadtrek specs call for a 225/75/16 but i wouldn't mind having a little more ground clearance.  The Dodge Maxivan Heavy Duty model calls for a 254/75/16 so i was wondering if i could use a 235/75/16 tire or would it mess up the transmission shift points?

Answer
Brent,

You have to be very carefull here.  There are letters in front of the tire size and they are important.

Go look at your current tires and you will see the letters "LT" in front of the tire size.  While you are at it, look at the sidewall and notice the maximum load and maximum pressure.  The sidewall will probably say Max Load 2335# and max pressure 65 psi.

Now go look at the spec sfor the 235/75R16 - max load 2094 max pressure - (Well it will probably say 44 psi, but there is some variation)

It's a bit more complex than this, but obviously the "LT" tire is built differently.  You need to have tires with the letters "LT" in front of the size.

Also, go check for the vehicle placard.  It is usually located on a doorpost or in athe glove box, but on an RV it could be almost anywhere.  It will list the original tire size and the proper pressure fopr that size.  I'll bet it says LT215/85R16 at 70 psi front - 65 psi rear.

Here are some other complications - there has to be enough space between the dualled rear tires to prevent touching when loaded - and of course when you hit a bump.  Your vehicle is set up for the LT215/85R16's and I'll bet there isn't enough room between the duals for anything else.

So I think you need to get what the vehicle placard says.