Went to a wakeboard tour this last weekend & the Mastercraft trailers where sporting some 18” wheels. 255x55x18. I’d like to update the look of my trailer with possible some 16” wheels vs the standard 14”. I assume I would need to go down to 60 or 65 series tire to keep the height the same. I’ve read the Chevy S-10 (5-4.75) or Ford Ranger (5-4.5) wheels will work but as you can see the spacing is slightly different on the Chevy wheel? Also these wheels are 7”wide vs stock 14” wheels @ 5.5”. Will most boat trailer fender accepts a 7” wide wheel?

You should find out what your wheel offset is. A wider rim with the same offset will have more backspacing. If you change the offset, you will change how much weight is put on your hubs and axels, so try to put wheels on it with the same offset (ET). The best way to find out if it will fit, is simply to measure. If you keep the same offset, the 7" inch rims will be 3/4" wider on each side. Also, the shoulder of the tires, if you go wider, can create more problems than your rims. How much wider are you going tire wise, and what tire size are you running now?

If you have more space on the inside of your fenders than on your outside and VV, with the combo you have now, you can change your ET a little (+/- 1/5"), but stay as close as possible, especially if you are close to your trailers max load.

I'm running a 205/75R14 now & after measuring the rim it seems to be a 7" wide rim already. The outside of the rim is recessed about 3". Does this mean the offset is -.5"?

Difficult to say. Sometimes a rim design can make it hard to measure. When you are talking rim width, you are actually talking about the distance between the the inside rim flange, and not the outside of the rim. In many cases, a 7" rim is more like 7½" from lip to lip and a 6½" is 7". Is the offset stamped inside the rim anywhere? In many cases they are. It will either read "Offset" or "ET". I is often written in the same place as the rim size, if it is there.
If the inside lip and the outside lip are the same thickness/width and shape, you can just find the middle of the rim, and then measure how far the hub flange is set on either the outside or inside portion of the rim. If it is recessed, as you say, you have a positive ET/offset of about +½" or +12,7(+13mm.) millimeters. If possible, measure this in millimeters, since that is the standard for ET numbers.

I have put in a drawing here so you can see what I'm on about.

If you have a rim that is 6½x14", your 205/70-14 tires section width (outside to outside) is about 8,5" with a diameter of 25,4" depending on the brand and model. The 16" size will be either 205/60-16 that has a section width of 8,7" with a diameter of 25,7" on a 7x16" rim. or a 215/55-16 that has a section width of 8,9" and a diameter of 25,3".

If you opt for 7x17 inch wheels the section with is the same, only the diameter is a little different. 205/55-17 will be 25,5" and 215/50-17 will be 25,2. For a trailer, I would not put more than 16" wheels on with the standard diameter, the tire profile gets too low on the 17"s. If you have room and want to, you can always step the entire thing up 1" and go for 205/60-17 or 215/55-17, but that will increase the section width about 0,1"-0,2" and step your dimeter up 1". This will of course lift your entire rig a ½", but sometimes it's an option - and it does look cool to get the fender gaps filled out a little

Man, that was a long one

Ive Looked into doing this numerous times and the problem for the Mastercraft trailers lies in the centerbore. Mastercraft had KMC specially design a Hoss that had a larger centerbore. The trailer specific part number is no longer in production for a 5on4.5" pattern. The only option would have been to buy a set of polished wheels and have the centerbore opened up...

Moral to the story would be to make sure to measure the centerbore on the wheels to make sure they will fit over the trailer bearing.

Just another thing to think about...

No spinners. That was a short lived fad. No class, all ghetto.

So true, so true. Ugly as phuck!!!