308 wheel offset/backspace...math help

Current situation

80 2V 16x7 Gotti fronts, 16x8 rears

I've measured the wheels the best I can with the tires on and come up with the measurements found in the crude cross sections.

After reading this thread

http://ferrarichat.com/forum/showthread.php?t=8361&highlight=308+wheel+offset

Stock QV 16's are +11.15 Front and +11.45 rear

Given my current wheels can I say that I'm running +8.9 fronts and +10.16 rears? I'm assuming that the measurement is in CM since when I do the metric conversion of 3.5"=8.9 CM/89 MM etc

EDIT

I can't seem to upload the images I did on MS paint so I'll have to try and explain them.

Measuring the front wheel from the back of the wheel hub (where the wheel hub meets the rotor) to the rear lip = 5" or 127MM/12.7 CM And the front lip to the back of the hub =3.5" or 88.9 MM/8.9 CM

Rear wheel is the same (what I would call "backspace") of 5" but the front lip to the rear of wheel hub is 4" or 101.6MM/10.16 CM

So if anyone can make sense of my info, which is the offset number I need to be concerend with when looking for new wheels? The 5"/12.7 cm of the hub to the rear lip or the 3.5"/8.9CM & 4"/10.16CM from the rear of the hub to the front lip?

Sorry for beating this dead horse issue but after 6 years of the Gotti's, they have to go....

Thanks

 

Maybe this helps.
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You are confusing "offset" with "backspace" and "frontspace". Those stock 16" 308QV wheel numbers are the "offsets" (the distance from the wheel CENTERLINE to the wheel mounting surface) in millimeters:

offset = (backspace-frontspace)/2

so, for the data that you give, the front wheel offset is about (127-89)/2 = +19 mm and the rear wheel offset is about (127-101)/2 = +13mm -- both of which are close enough to the stock 308QV values to be OKish; however, you should really try to match the fronts better to make the steering geometry more correct.

 

Why not just work from the original Ferrari info, i.e., the circa 11mm offset.
Some of the things you need to keep in mind when choosing/specifying your new wheels is to maintain your original suspension geometry and keeping your scrub radius to the minimum (bump steer). If you have access to a workshop manual all of the data should be there (castor, kingpin, toe-in, suspension mounting piont angles, etc.)

What type of rims are you after?

Have fun.

 

Confused no doubt =)

Thanks.

The clarification of "offset" is what I was looking for. If I know where I am, I can see where I'm going or need to go.

I kind of like how the current Gotti's fill out the wheel wells, which is why I wanted to see if I could figure out where I was.

 

I had found these, but the 17x7's are +40MM and the 18x8's are +20MM

http://www.discounttire.com/product/wheels/voxmg.sml.xl.jpg

But it's the overall style I'm looking for.

I've also got a set of HRE 505's (288 GTO style) that I'm trying to refinish, but it's been a slow process.

 

Nice, clean, simple 5-spoke rims. You would need spacers to bring the offset back to original specs. (29mm for the 17" and 9.5mm for the 18"). Hill Engineering do these in standard widths that would get you close enough. I believe Daniel at Ricambi America may stock some sizes.