dhza8

I've been looking at determining the appropriate offset in a somewhat analytical manner. I want to evaluate relative to the OEM set up since I can measure the amount it is "inset" (aka tucked) and approximate how much offset is required to make it flush. Hopefully others can follow my logic and comment:

OEM setup (IS350)

F 18 x 8 offset 45
R 18 x 8.5 offset 50

I measured the "inset" of this set up to be approx.

F OEM Inset 19 mm (3/4")
R OEM Inset 28.5mm (1 1/8")

This is measured by dropping a vertical from the wheel opening at the 12 o'clock position to the ground, and measuring in to the top of the rim at the 12 o'clock position.

Now you need to get get an offset calculator. I use:

http://www.1010tires.com/WheelOffsetCalculator.asp

If you input the OEM wheel specs, and a candidate wheel spec, it will tell you how much the candidate wheel will extend from OEM. You can then calculate the new "inset" by subtracting from the OEM inset. Theoretically, the closer to zero inset, the more flush.

Here's an example:

Let's say you are trying to decide between two different wheels for the front:

F 19 x 8.5 offset 43; or
F 19 x 8.5 offset 35

The 43 offset extends out 8 mm from OEM (8" rim w/45 offset vs 8.5" rim w/43 offset) using the calculator.
The 35 offset extends out 16 mm from OEM (8" rim w/45 offset vs 8.5" rim w/35 offset) using the calculator.

The inset for the offset 43 wheel is the OEM inset (19 mm) minus the extension provided by this wheel (8 mm). The new inset is therefore approx. 11 mm.

The inset for the offset 35 wheel is the OEM inset (19mm) minus the extension provided by the new wheel (16 mm). The new inset is therefore approx. 3 mm.

------------------------------

Now for the rear:

R 19 x 9.5 offset 45; or
R 19 x 9.5 offset 36

The 45 offset extends out 18mm from OEM (8.5" rim w/50 offset vs 9.5" rim w/45 offset) using the calculator.
The 36 offset extends out 27mm from OEM (8" rim w/45 offset vs 8.5" rim w/35 offset) using the calculator.

The inset for the offset 45 wheel is the OEM inset (28.5mm) minus the extension provided by this wheel (18mm). The new inset is therefore approx. 10.5mm.

The inset for the offset 36 wheel is the OEM inset (28.5mm) minus the extension provided by the new wheel (27mm). The new inset is therefore approx. 1.5 mm.


Summarizing:

Set 1:
F 19 x 8.5 offset 43 Inset: 11 mm
R 19 x 9.5 offset 45 Inset: 10.5 mm

Set 2:
F 19 x 8.5 offset 35 Inset: 3mm
R 19 x 9.5 offset 36 Inset: 1.5mm


From this example you can see what many on this board already know:

If you want a conservative setup, assuming F 8.5" / R 9.5", go with offsets in the mid 40s.
If you want a flush setup, assuming F 8.5" / R 9.5", go with offsets in the mid 30s.

mikez

Good work, I found out using similar methods, and our results are similar. But its hard to take tires into account, whether or not the tire will touch the fender when the offset shows that it is safe by 1~2mm

IS-SV

This is good info. Based on what's reported here it jives with what people are finding when fitting MRR GT1's in the 19" diameter to their ISx50's.

t0e

iTrader: (1)

The work as only begun, once you complete this step.

Next is figuring tire size and if you have to shave and roll the fender.

radicalrev

iTrader: (2)

i ****** up my fender already!!!

llamaboiz

your forgetting one IMPORTANT detail...

amount of drop, the more you drop the more it cambers in...

IS-SV

Yes, but won't it camber out when rebounding?

eric_r_ho

iTrader: (9)

So do you think 19x9 +25 in the front will fit our cars? And a 19x10 +35 in the rear? Anyone, please help!! The +25 in the front might encounter some serious issues huh..

Slappy_

Both of those^^^^ are conservative setups. You're only talking a 10mm difference. If you want a flush setup try offsets in the low to mid 20's. Or you can just look here.

A 9 with a +25 is fine in the front. I had a 9.5 +30 on my front just for ****s. If I had coilovers I would have dropped it down, but I'm on Eibachs for now. And I had coilovers they would have cambered in....probably right inside the fender.

mikez

Just me though slappy, but I think when the front sticks out it looks kind of ugly, I only like my rears like that.

I've always been a fan of gt racing looks and only the rears are that aggressive, I think the front sticking out is a drifting or jdm thing lol

Slappy_

To each is own Mike and I can agree....there comes a point when its too much. I think everyones definition of flush can be different.

javyLSU

iTrader: (21)

A 9" wide wheel with a +25 offset will not "fit" unless you are willing to modify the fender (assuming you're dropped and plan on running tires on your wheels). Most people are looking for wheels that will fit without having to modify the fenders significantly. Now, if you're willing to go that route, ANY wheel can be made to fit...

Javier

blk250

iTrader: (3)

good info...

llamaboiz

this is both true AND false...

true: if you want to mod the fender then yes ANYTHING is possible.

false: you could run a 215 tire on a 9" rim and it will fit on a slammed car.

javyLSU

iTrader: (21)

^and by "fit" you mean "willing to put up with rubbing," right? If you want to drive over dips and bumps on the freeway, turn the car and not just drive in straight lines, you will have minor issues.

Javier