Wheel offset has me confused.

[IXMandalorianXI]

My '96 r33 Skyline has Rota GTR, 18 x 9.5 inch, ET30 on the front and Rota GTR-D, 18 x 9.5 inch, ET12 on the rear. (Put on by previous owner)

The 12mm offset is throwing me for a loop. Is it due to the "deep dish" design of the wheel that the offset it so low? Or is it actually that low on the rear normally?

If I were buying a set of new wheels, could I put 30mm offsets on the rear and reasonably expect them to fit?

I have GTR Brembos and 370Z rotors (355mm/350mm) if it matters.

Thank you.

Edited July 8, 2024 by IXMandalorianXI

[Kinkstaah]

The offset doesn't really have anything to do with dish directly. I mean it kind of does but it also doesn't, it's only tangenial.

The offset is purely how much offset (get it) the mounting face is from the CENTER of the width of the rim.

I.e, the mounting face would be directly in the middle of the 9.5inches if it was a 18x9.5 ET0 rim.

Given it is a +12 rim, the mounting face is 12mm further away from the center (to the outside of the car).
Your fronts are +30, so the mounting face is 30mm further away from the center (to the outside of the car).

I would wager this doesn't look right, because most skylines generally have the same with guards front to back. So I'd think your fronts look significantly more sunken in than your rears. I'd wager by about 18mm, or so.

[IXMandalorianXI]

11 minutes ago, Kinkstaah said:

I would wager this doesn't look right, because most skylines generally have the same with guards front to back. So I'd think your fronts look significantly more sunken in than your rears. I'd wager by about 18mm, or so.

I should clarify that the previous owner put the wheels on, so Im not entirely sure what he bought. I was searching the Rota page and found these two as the only matches. It did not occur to me that perhaps they sell these wheels with different offsets.

I guess the best way to solve this is to take the wheels off and measure them from the inside to be sure.

[GTSBoy]

Check for spacers on the front, in case they've been pushed out a little to try to match he rears better.

[IXMandalorianXI]

Ok, maybe I'm approaching this the wrong way. I'm trying to buy new wheels, and I was having trouble finding the exact offset needed for my r33 GTST Spec 2. I figured trying to reverse engineer the wheels already on the car was a good method, but maybe I'm over complicating tings.

I tried using this thread, but I was unsure how to translate what others had and their set-ups versus my own. I know the wheels I have right now are 18 x 9.5, front and rear, so it's just the offset that's really throwing me for a loop. I'm not sure if stock GTST offset would be the correct answer because again, I have GTR calipers and 370Z rotors. I've replaced the rotors recently and taken the wheels on and off enough times to know I don't have any spacers.

Edited July 8, 2024 by IXMandalorianXI

[Duncan]

You are right, there are 2 ways to approach it, you can go for wheels known to fit well on the car, or measure from what you have.

If you jack up the car and check the distance from the inner side of the tyre to the first obstruction (generally the control arm, or a shock) and then do the same from the outside of the tyre to the guard, that tells you how much wider you can go or what offset you can use.

I'd note that 9.5 is huge on the front of a 33 gtst, if they are not scrubbing anywhere including fuil lock then don't change anything about the front width and offset.

[IXMandalorianXI]

1 minute ago, Duncan said:

I'd note that 9.5 is huge on the front of a 33 gtst, if they are not scrubbing anywhere including fuil lock then don't change anything about the front width and offset.

It's very possible my measurements are wrong as I did measure with the wheel and tire still on the car. It's possible I didn't judge inner gap correctly and ended up adding width. I'm eager to buy new wheels, but I think I might be putting the cart before the horse. The best thing to do this right. I can take off the wheels off, I might even just have the tires taken off and do some proper measurements. It won't cost me much, if anything, and will save me a whole bunch of headache in the long run.

[hardsteppa]

The offset of the wheel is usually stamped on the inside of the rim. So just pull the wheel off and see if it's marked as such.

[IXMandalorianXI]

36 minutes ago, hardsteppa said:

The offset of the wheel is usually stamped on the inside of the rim. So just pull the wheel off and see if it's marked as such.

Thank you for the heads up! Will definitely take a look!

[Kinkstaah]

When the going gets weird... measure!

[Murray_Calavera]

11 hours ago, IXMandalorianXI said:

I have right now are 18 x 9.5, front

I am amazed that you have 9.5 inch wide rims on the front! What size tyres are they paired with? How much negative camber do you run? What has been done to the guards? 

Edited July 9, 2024 by Murray_Calavera

[Kinkstaah]

TBF, I had 9.5 +27 on the front (and rear) of a 34 which most consider to be much the same as a R33.

It fits exactly where a 18x9+30 otherwise would, if you run the same size tyre on either rim. I had a 265 on the front of mine and the tyre sidewall on the inner is the limiting factor. 

I ran like -1.5 camber.

I am putting 9.5 +30 into the 'feasible' camp.
Will still be 18mm inset from the 18x9.5 +12 on the back though.

I suspect one of these wheels is not the sizes in the original post, or it looks wonky. Pictures plz, OP, I must know lol

[Murray_Calavera]

I can't remember the offset of the wheels, but my street rims are 17 x 7.5 front 8.5 rear. My track rims are 17 x 8 front 9 rear. 

This seems like madness to me as my 17x8 rims rub with 235/45 tyres on them. The street rims however are perfect. 

I do run 19mm steering rack spacers which makes things a little trickier, but yeah I just can't picture fitting another 1.5 inches of rim in there lol. 

[Duncan]

The tyre makes a massive difference. A 245 semi will be wider than a 255 road tyre

[niZmO_Man]

Even the same size tyres but different brand/tread pattern makes a difference.

[IXMandalorianXI]

7 hours ago, Murray_Calavera said:

I am amazed that you have 9.5 inch wide rims on the front! What size tyres are they paired with? How much negative camber do you run? What has been done to the guards? 

You all are making me think I incorrectly measured the wheels lol. Will definitely remeasure everything once they are off the car later this week.

[IXMandalorianXI]

6 hours ago, Kinkstaah said:

I suspect one of these wheels is not the sizes in the original post, or it looks wonky. Pictures plz, OP, I must know lol

Highly likely I'm just incompetent lol.

 

[Kinkstaah]

Hey OP, wheels look good, previous owner had the right idea, drive and enjoy car 

[IXMandalorianXI]

3 hours ago, Kinkstaah said:

Hey OP, wheels look good, previous owner had the right idea, drive and enjoy car 

Oh they look great...they roll...less great haha, front driver-side is minorly bent. Not dangerously, but enough to be really annoying. Hence, this adventure to buying new wheels (or rather at least one new wheel). Possibly to buy four new wheels if the right ones jump out at me, but definitely keeping them white no matter what.

Edited July 10, 2024 by IXMandalorianXI

[R3N3]

The tyre fitment will be important here. You may be able to fit a super wide low offset wheel in but then you will be limited to stretch tyres..

I personally run a 18x9.5 +11 (rear) and 18x9 +18 (front) on my R33 and the tyres are only slightly stretched (check my build for pics). However, mine is definitely on the more snug fitting side..

IMO a 9.5" rim size (all round) id say a +20 to +25 on the rear and +25 to +30 on the front would be a reasonable fit with some room for decent tyres..