Relationship between offset and rim size

[SpyderGuard]

I'm going from a 17x7 to a 17x7.5.

Time and time again, I've read on this forum that the acceptable range for Solara is +35 to +45, with the ideal range being +38 to +42, but is this the same regardless of your rim width?

My intuition is that offset should increase with rim width, but I want to know for sure.

If you increase rim width from 7 to 7.5, but keep the same offset (say, +40), your rims will protrude outwards by an extra 1/4 inch or 6.35mm. To maintain original geometry, doesn't your offset need to be increased by about 6mm, to +46 or so?

I currently have 17x7 +40. As I increase the rim width 17x7.5, I'm wondering if it's best to stay at +40 or go up to +45.

[WTF??]

hmmm... So you have an option to get a different offset with the rims that you want???

I remember for my rims they just had a set offset and didnt have a choice unless I changed the whole rim size

But I think youll be finewith your options without rubbing

[Fletch]

I am 80% sure that offset does not increase with wheel width. www.tirerack.com has a decent info / tutorial about questions like that. I'm not exactly where it is on their site but it shouldn't be too hard to find.

[Mole]

with a positive offset for ie: +38 offset.

you are moving away from the hub, hence having the wheel pushed out further.

if you want wider wheels and worried about the wheel protruding, you would need a higher offset, for ie: +40.

you cant really tell that much of a difference b/w the two offsets.

[Mole]

I am 80% sure that offset does not increase with wheel width. www.tirerack.com has a decent info / tutorial about questions like that. I'm not exactly where it is on their site but it shouldn't be too hard to find.

correct. offset does not increase width. offset is simply where the wheel is positioned.

[SpyderGuard]

I am 80% sure that offset does not increase with wheel width. www.tirerack.com has a decent info / tutorial about questions like that. I'm not exactly where it is on their site but it shouldn't be too hard to find.

correct. offset does not increase width. offset is simply where the wheel is positioned.

Thanks all!

Actually my question was not whether offset automatically increases with width - I know it doesn't.

The question was: Am I supposed to use a higher offset when I use a wider rim? That is, if I am currently using 17x7 +40, should I go to a 17x7.5 +40 or a 17x7.5 +45, or does it matter at all?

Also, TRDMole, are you sure about the protruding issue? I thought the opposite: lower offset = wheel pushed out further. A lower offset makes the hub attach to the wheel closer to the inside of the wheel, thus making the wheel protrude. A higher offset makes the hub attach to the wheel closer to the outside of the wheel, thus tucking the wheel into the car. It's a little complicated for me to visualize, but I think I'm right.

Anyway, I guess the long and short of my question is that I currently have a 17x7 +40 (with 225/45/17) and want to know what will happen if I go to a 17x7.5 +45 (also with 225/45/17). I think I originally expressed the question more complicated than it really is.

To thicken the plot a bit, my car has been lowered by about an inch all around (Tokico/Vogtland).

[Mole]

wait a tic.

omg. sorry for the incorrect info. the lower the offset (+20) the further it will pop out vs (+40)

gee.

stick with 40. if you go in too far, you might rub against the strut housing.

its real easy to get things mixed up. i like to base offset on how far away the wheel is from the strut housing.
Lower offset- +38= away from strut
Higher offset- +45= closer to strut