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Old 08-07-2019, 04:31 AM   #8238
Scooby Newbie
Member#: 500326
Join Date: Apr 2019
Chapter/Region: International
Location: Australia
2015 WRX Premium 6MT


Originally Posted by MountainMan10 View Post
Check out to compare different tire sizes. 265/35 is a bit small. 255/40 is closer to stock.

The vendor where you buy the wheels will probably recommend lug nuts.

I have seen You Tubes on +38 being the "perfect" fit where "perfect" means flush with the fenders. However I have seen posts on this forum from people who were surprised at how +38 actually fit when they got them. Personally if "perfect" mean flush look and that's what you are going for I would go with +45. I think you will find that flush enough. If "perfect" means keeping OEM handling stick with +50 or above.

Going below +45 might require rolling the fenders. Fit is going to vary depending on the actual wheel and the actual tire selected. Tire and wheels are a bit like shoes. One brand size 10 is a 10.5 in another brand.
Either we're looking at different measurements or we're thinking of different stock tyre sizes -- the stock wheel size on the 15 WRX is 235/45r17.

That calculator you linked to confirms my statement that 265/35r18 is closest to the diameter of the stock 235/45r17:

Additionally, it has been said time and time again in this very thread that 18x9.5 +38 fits without fender modifications -- no mention of flush fitment, merely that they fit the car without mods. That is of course dependent on tyre size, but from memory the majority of those posts quoted tyre sizes around the 255/40 - 265/35 ballpark.

The same assertion has been made when using coilovers, which, without increasing camber, would exacerbate rubbing issues if that wheel spec didn't fit properly without mods.

Originally Posted by Norm Peterson View Post
Ultimately, steering response is a matter of how quickly/precisely your inputs at the steering wheel become vehicle turning, or yaw. Time is involved here, and stiffer components get to their new-required state more quickly than otherwise identical but softer ones. We're not talking about lots of time here, not even a whole second, but little time lags are something that you can pick up on at least on a near-subliminal level. Think in tens to hundreds of milliseconds terms here.

As for something a little more concrete, I actually have some datalogged comparative data where the only differences in car setup were the wheels & tires. Same stretch of road, similar weather conditions, same make and model tires (MPSS), with the same tread widths (10.2"). One set was mounted on "measuring width" wheels (9.5"), and the other was mounted on "max-recommended width" wheels (11"). There was a small diameter difference, but only about 0.4" (0.2" on sidewall height). The max-width setup turned in a little better, and had a noticeably more stuck-down "feel" at a little over 0.9g than the measuring-width setup had at a little over 0.8g. The "measuring width" setup wasn't bad, just that it felt a little "soft" in comparison to the wider wheel arrangement.

The max-width setup has datalogged beyond 1.3g once fully warmed up in road course track driving.

So in terms of performance I'm better off going with a slight stretch to "stiffen up" the sidewall characteristics? If that's the case I'm curious why meaty fitments are touted as the "more functional" fitments when compared with stretched fitments (barring ridiculous stretches purely for stance).

Originally Posted by MountainMan10 View Post
Doesn't that prove my point that 35 offset is pushing the limit?

With higher than recommended camber you are still getting some rubbing with the rear fenders shaved.
You might be getting confused because in my OP I said I was tossing up between 18x9.5 +38 VS 18x9 +35. Despite the higher offset, the 18x9.5 +38 will actually "poke" out roughly 3.5mm further than the 18x9 +35.

18x9 +35 is a more conservative offset as far as wheel poke is concerned. Remember offset means nothing without width, and vice versa.

Originally Posted by Norm Peterson View Post
Visually, you'd be kind of hard-pressed to see the difference. Measuring width is just that - it's the width that's been established within the tire industry on which the tire is measured. You can probably take from that that it's a "middle of the road" width where neither handling crispness nor softer ride quality is particularly emphasized over the other attribute.

One thing I should have mentioned in the earlier post is that there can be considerable differences in ride quality and handling crispness/turn-in response among tires of the same nominal size. Even when the tires are claimed to be within the same general performance category (i.e. performance all-season). Some years ago, Falken brought out their Ziex ZE-512 tire model, and to say it was a "soft-responding tire" and "disappointing" from a cornering/handling point of view would be putting it mildly. Bridgestone's RE-92 (not a great tire in other respects) was far better in the corners.

For reference I'm gravitating towards mounting Bridgestone RE003s (Firehawk Indy 500s in the USA) or Federal RS-RRs on these wheels if that helps in any way.
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