can I put 235 size tires in place of 255 size tires?
Yes they will fit but they will effect your odometer and speedometer. See how much by entering the info in this calculator. --- http://www.miata.net/garage/tirecalc.html
In a word, NO. The vehicle was designed for the 255 width tire, and you will lose serious amounts of highway traction with a tire that is 20 mm narrower.
Michael, having 255 tires doesn't mean it was a stock tire size!!
First thing to do is check the diameter of each size tire to see how much it will throw off your speedometer and anything else that depends on registered speed. Second thing to do is check the load bearing weight of each tire to see if the 235 is at least equal to the 255. Many states that have yearly inspections require alternate size tires to have at least equal weight bearing tires. Third thing to consider is how will it alter how the car handles. Car suspensions are set up for the original tire size. A low profile tire handle a lot different than a high profile tire. Unless you have a good reason to alter tire size stick to the size located on the sticker drivers side door.
I don;t know why you would want to put a smaller tire on your expedition. If you have any doubt as to what size tire is the factory original, look at the door panel for the info or in the owners manual. Most reputable tire dealers WILL NOT put on and other tire than the manufactures specified tire. Unless you just happen to have a set of free 235's, you will find there is little difference in the cost of the 255's and then. GO WITH THE FACTORY SPECIFICATIONS
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