KJS

iTrader: (5)

Offsets and wheel fitments is one of the few things that I just can't comprehend, I've tried googling and searching but i still have some questions, so I'm here to have someone spoon feed me the information so I can try and understand it. Here's what I know:

Lower Offsets (+15's, +18's etc), stick out more (away from the rotor), Higher offsets (+38's etc) are set back towards the inside of the fender more.

I understand that a lot of these wheel offset decisions are around clearing the brembos. Here's what I don't understand,

Lets take RPF1's as an example:

18x9.5 +15 are considered very "aggressive" (stock fenders), they clear both brembos without spacers, but tend to poke out passed the fender so negative camber and fender rolling is need with coilovers. Could a lower offset rim run a wider rim, like 18x10 +15 because the wheel is so far out that there is room on the inside of the fender?

18x9.5 +38 aren't as aggressive, but will not clear the front brembos without spacers, so you would have to run spacers (i'm not sure how big or anything), effectively pushing the wheel out to a lower offset. If you run a 10mm spacer does it basically make the +38 into a +28, furthermore this means the +15 rims are clearing the brembos with almost 13mm of extra space? I don't understand how "Stance" guys tend to run these rims and spacers yet get to tuck the rim almost inside the fender.


Furthermore, what are the appearance difference between the different offsets? Are the +15's more concave and the +38s less concave? Or do they look identical but the width of the rim is just in a different place?

Raptord

iTrader: (10)

In response to one of your questions; Yes, using a 10mm spacer with a +38 offset wheel gives a "final" offset of +28.

KJS

iTrader: (5)

Which is useful when a wheel isn't offered in a +28 offset

evoDON

iTrader: (11)

the reason people will run a higher offset, such as a +38 is because the rear wheels are your problem with fitment mostly. there is less space in the back then in the front. people will buy higher offset wheels and use spacers to clear the brembos up front so that the wheels actually fit (18x9.5 +38 with a 20mm spacer upfront making it a 18x9.5 +18). You could also buy 2 wheels with a low offset and two wheels with a high offset in order to clear the brembos with out spacers, such as a 18x9.5 +15 rpf1 for the front and an 18x9.5 +38 rpf1 for the rear.

You are correct about concave with most wheels. An offset such as a +15 will normally be more concaved then the same wheel with a +38. except for flat faced rims which always look the same and the center area of the wheel where the lugs come through are thicker or thinner to either push the wheel out towards the fender, or tuck them into a wheel well.

To answer this question, "Could a lower offset rim run a wider rim, like 18x10 +15 because the wheel is so far out that there is room on the inside of the fender?"
- Just because you are running a higher offset doesnt mean that you can run a wider wheel, it all depends on room, width of wheel and offset. if you have two wheels. and 18x8 +20 and an 18x10 +20. the 18x10 will be an inch wider on each side of the wheel, the size difference in wheel width is split between the front of the rim and the back, not just to one side of the wheel.

Wheels are pretty confusing at first but once you understand them, or have someone actually show you first hand they are simple. Hope i helped out a little bit

llDemonll

iTrader: (21)

Clearing the brakes has not a lot to do with the offset, but more to do with the spoke design

take xxr 521's for example:
both the 10.5" an 9" widths (and whatever else) had a flat spoke design in the rear, so no matter what the offset, this particular model of rim (xxr 521's only is what i'm referring to) will clear the front brakes with a 25mm spacer. width does not play into effect

the rpf-1's you're talking about, the spokes will "bend inward" as the offset increases because the point at which the spoke mounts to the rim remains the same, but the hub changes locations based on the offset. as the offset increases, the top of the spokes are closer and closer to the face of the hub (where the hub rests on the brake disc), thus decreasing the distance between the spokes and the brake caliper

KJS

iTrader: (5)

I guess I would need to see a +15 and a +38 side by side to see the differences. For RPF1's I cant tell by looking online.

Would running a +15 in the front and a +38 in the back, look weird, cause alignment issues and such?

KJS

iTrader: (5)

Light bulb just clicked. On the 9 is +15, the 10 has +38. I'm assuming for other rims its different, but you can see on the +15 the area where the lugs go is much deeper than the +38, which im assuming is how enkei got the +38's to look pretty close to the +15s, without giving up the dish look. Interesting.

GTijoejoe

iTrader: (25)

To fully understand you should know what the measurements actually are.

The offset is measured from the center of the wheel, so taking in account the actual wheel width will dictate how far in our out from the fender the wheel will sit. I can take a +0 offset on a 6" wide wheel and it will sit inboard from the fender compared to your stock wheel.

If you really want to guess how a wheel will look, understand what your stock wheel width/offsets are as a gauge. (Offset difference +/-) plus (1/2 * difference of the wheel width) = your delta