Quote:
Originally Posted by pelemay
Please stop me before I say something stupid: unless the alloy wheel were actually wider than the tire, then my only real rub concern is with the rubber tire, right ? So, the result of half the tire width minus the offset would be the parameter we should actually compare, isn't it ? (The width of the wheel has no actual effect, I would think, for a constant offset.)
Let us assume that the original Trail wheel has a +15mm offset (can someone please confirm this, btw ?) and the original tire is 265mm wide. I calculate that the inside face of the tire is (265mm/2) - (+15mm) = 117.5mm "inside" from the mounting pad plane.
The "new" 285mm tire mounted on a +12mm offset wheel would sit at (285mm/2) - (+12mm) = 130.5mm "inside".
The difference between those results tells me where the new tire will end up, on the UCA side: (130.5 - 117.5) = 13mm closer to the UCA. (A shortcut to this result is that the tire is 10mm wider on either side of its middle plane and the new wheel protrudes 3mm less outside.)
I think I can easily get 13mm closer to the stock UCA without hitting/rubbing anything on that side, yes ? (...then the only remaining issue would be with the outer edge of the tire, when turning/reversing/wheeling...)
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Actually, I think all of this is logical and theoretically correct. However, the reality is that it's difficult to compare tires based on the nominal dimensions. As was mentioned, all 285s (or any other nominal width) are not equal. They are roughly equal, but can still vary quite a bit. Some may be taller, some may have a larger tread width, some may have a larger section width, etc.
The other problem is that the shape/size of the tread blocks at or near the shoulder may be the deciding factor for some of the possible rubbing. Generally you won't have any rubbing in the center of the tread pattern, but when turning, it's going to be the shoulder areas that have more potential to hit something when angled one way or the other.
When it comes down to it, you're trying to match a 3D wheel inside of a 3D wheel well, so it's not quite as straight forward. From what I can tell, even sticking with the exact wheel/tire/size/offset combinations, you STILL might not have the exact same experience as another member due to some small variations in suspension (could be driver/cargo weight, sagging due to age or use, etc.). When you go to a different wheel/offset AND a different tire brand/size, that just adds another variable to the matter.
It's really a situation where the most probable fitting is from following others' suggestions. But if you want something different, it MIGHT end up costing a bit more to make it work - or you might come to the conclusion that it just doesn't work and then you have to get new tires.