17x9 wheel off set

[gofast]

I'm considering Klutch ML7 wheels in 17x9 for my turbo Goblin. My OEM wheels are 18x7.5 with an ET (off set) of 42mm. If I'm figuring correctly, I need to move the wheel center line out 3/4" (19.05mm) (9"-7.5"/2) to retain the same backspace. 42mm - 19mm leaves me with a off set of 23mm to provide the same factory backspace. Is this correct? Stock ETs for this wheel are 25mm and 15mm. Custom ETs are 20-30mm and 0-15mm. I thought I go with an ET of 15mm for a little extra clearance.

My questions are these:
Are my calculations correct?
Does the Goblin require the same backspace as the stock Cobalt SS. I'm using the DF coilovers. Which leads to this question...
For those using 17x9 wheels, does anyone have an opinion as to the ideal off-set? Is it the same for front and back? Is an ET of 15mm a good choice?

 

[Tinkles]

IMO, since there is no bodywork to try to keep the wheels under go with the lowest offset you can. Fenders can be easily bent/shimmed to cover the tire and the added track width should help.

 

[OptimizePrime]

Maybe this will help? You'll need to factor in the tire sidewall as well

https://tiresize.com/wheel-offset-calculator/

 

[gofast]

Thanks, The calculator works great! My 23mm calculation was correct, but using the calculator is the way to go. Easier and more usable information. I'd still appreciate getting feedback from anyone with 17x9 wheels about their offsets.

 

[OptimizePrime]

Sorry! forgot to add I'm going 17x9 +40 with 255/40/17 and a 1.25" spacer up front (5x110 > 5x114 conversion)

 

[gofast]

Have you had them on the car yet? How did that work out for you?

 

[ccannx]

I’m running a 15x10 with a 25 offset on all four with the BC coilovers rears are very close but work with narrow tires. A 9 inch wide wheel should provide another half inch from the strut in the rear at a et25. The stock struts in the rear are much wider but I believe the stock tire was designed to tuck under the spring perch. These pictures are 23’ tall tires I now have 25.3’ tires that touched the spring collar so I put a 1 inch spacer in the rear.

 

[JBINTX]

Klutch ML7 brushed silver wheels 17x9 with 20 mm offset.
Proxes R1R 275/40.
no spacers.
all four corners.
There is a slight rub on upper A-arm at full turn.

 

[Zoom Zoom]

Klutch ML7 brushed silver wheels 17x9 with 20 mm offset.
Proxes R1R 275/40.
no spacers.
all four corners.
There is a slight rub on upper A-arm at full turn.

View attachment 13698View attachment 13699View attachment 13700

That’s a nice set up

 

[JeffsGoblin]

Klutch ML7 brushed silver wheels 17x9 with 20 mm offset.
Proxes R1R 275/40.
no spacers.
all four corners.
There is a slight rub on upper A-arm at full turn.

View attachment 13698View attachment 13699View attachment 13700

JBINTX, Do you know the backspace on your wheels? They look great!

 

[JBINTX]

Thanks! I copied some others on the size. Big meaty rubber on the corners.
Sorry for such a slow reply. Been out of town visiting the daughter.
Mounting surface of the wheel to inner most edge of tire is 6.75".

 

[Mayor West]

I have 17x9 all around, 1.25" adapter/spacers and 42mm offset.

285s in the rear, 245s in the front.

I haven't mounted the rear suspension yet but the calculator says I'll have plenty of room.

Edit: pics