Boy howdy is your timing impeccable. I just did all this to fit the 21” Type S Wheels on my A-Spec
Let me go type this up. The stock wheels are +55 offset, so this actually plays to your favor regarding clearances. The trick is not having the wheels extend beyond the fender wells unless that’s what your going for. For the sake of this exercise, I can confirm that a 21x9.5” with a +55 offset will make things flush with the fenders.
Your stock wheels are 20”x 9 with a +55 offset. Those are slightly tucked, but not by much. For every half inch increase in wheel width, the outer part of the wheel extends about 6.3mm outward, but also 6.3mm inward too if you’re shrinking Wheel width. The biggest hurdle I came up against was making sure the tire would not be rubbing on the upper control arm. With the 255/50R20 tire mounted, I had roughly 25mm of clearance on the stock setup on the upper control arm. I mounted a 285/40R21 rubber on the 21” Type S wheels and this left me roughly 12mm of clearance between the upper control arm - I would have been unable to fit 295s on this as the tire would have rubbed. The important factor in this example is both wheels are a +55 offset.
We know a 9.5” with a +55 offset will sit flush with the fender well. Now to understand offset, if you want a 9.5” wheel, but want a +40 offset, that will move your wheel about 15mm beyond the fender well, so it will stick out about 15mm. For every amount you decrease the offset, it sends the wheel further outward.
9.5” with a +55 offset looks like this:
Now for your wheels you’re looking at. The first is 20x8.5” with a +25 offset:
So let’s first pretend this was a stock type S wheel at 9.5”, BUT with a +25 offset. That wheel is going to protrude outward from the fender well 30mm (yikes!) because we know with a stock +55 offset, a 9.5” wheel sits flush as shown above. So your first choice wheel of 20x8.5” with a +25 offset has a couple things going on that I don’t think you’re gonna like.
1) it’s sending the wheel outward +30mm
2) Up above, I said every additional 0.5” in wheel width will push the wheel out 6.3mm. In this case, you’re actually subtracting 0.5”, so you’re bringing the wheel back in another 6.3mm.
So overall, this wheel will stick out beyond your wheel well about 28.7mm. Unless that’s the look You’re going for, I don’t think you’re going to like it.
Let’s move to your next wheel, 20x10” with a +40 offset:
So lets go back to our example of that Type S wheel; 9.5” with a +55 offset gives us that flush fit. Now we look at that +40 offset, you’re now sending that wheel outward of the fender well 15mm. Then we have to factor in the ADDED 0.5” to wheel width and that will send the wheel out an added 6.3mm.
So overall, this wheel will fit, but protrude out of the fender well about 21.3mm. Again, if that’s the look you’re going for, you should be ok.
An item of note on the brake caliper clearance: This is something to take into consideration, but is absolutely dependent on the wheel design. Some spokes have that “spider leg” design more than others. Other spokes are thinner, so it’s difficult to say if you’ll have enough brake caliper clearance, but in all honesty, I don’t think brake caliper clearance is a primary concern because the stock offset is +55. Normally the lower the offset, the more “spider leg“ effect a spoke has. So a lower offset typically creates more caliper clearance, but this is absolutely a general rule of thumb.
So I’m sure at this point, you’re probably like, “ok, what rim width/offset combo should I get so it’ll still fit until the wheel well, and look stock?” So by my calculations, I’d say a 20x8 with a +40 offset should be pretty conservative:
our 9.5” example with +55 offset. Now change the offset to +40 and we know we just pushed that wheel outwards 15mm. But now we only have an 8” wheel width, so that’s 1.5” thinner than our 9.5” wheel. At 6.3mm per 0.5” we’ll be bringing the wheel inward a total of 18.9mm. So now the wheel is actually 3.9mm tucked into the fender vs our 9.5” Type S wheel. I also believe you can still fit the stock 255/50R20 tires on an 8” wheel too.
Another wheel size:
20x8.5 wheel might be easier to find, along with a +45 offset. So step one, take our 9.5” with +55 offset example. We’re going to push the wheel out 10mm with the offset difference. But the wheel is also a full inch less than our 9.5” example. So that’s 12.6mm we’re bringing back in. So in comparison to our Type S wheels, the 20x8.5 at a +45 offset will actually sit inward 2.6mm (negligible) from where the Type S wheel sits in the pictures.
That’s a whirlwind to type and some moderate complication to determining if wheel size will work, but hopefully that helps.
In relation to you dealership indicating you’d need spacers, I’m not sure why that would be unless they know something about specific measurements and caliper clearances vs. the wheels you’re looking at. But with those calculations and pushing the wheels out that far in the examples you have, I don’t see you needing spacers.
