zoasis

I'm going with Circle racing 16X9.5 Front and rear. What is the correct BACKSPACE that I should go with?? I told them 22offset for the fronts and 17 offset for the rears, what would this equate to for the backspace? I don't know how to properly convert this and Circle racing doesn't know for sure either.

I have an idea but I know one of you guys will know for sure, please help so I can complete the order and get on the track, I'll post results as soon as I get them.

2003z

iTrader: (7)

just figured in my head, well on paper, then I looked at my wheels and realized I got it backwards. Mine are 9" +35, and have about 6" backspace (5.877 actually), so the + offset increases the backspace.

Here goes:
9.5" = 241.3 mm

0 offset would be 120.65 back space (half the wheel width)

+17 offset would be 137.65mm backspace or 5.419 inches

+ 22 offset is 142mm or 5.5905"

zoasis

Circle Racing is going to send me a test fitment wheel.

2003Z,
You nailed it right on, I was able to find a conversion table on Yahoo and the 9.5 22 offset is about 6 1/8" backspace and the 9.5 17 offset is about 6" backspace.


I did some measuring and I'm a little leary that the fronts might not clear some of the suspension with the smaller diameter since some of the suspension parts taper down towards the hub at 16" as opposed to 10" diameter. I'm thinking I'll have to go with a smaller width or I'll have to go with a lower offset to clear the suspension parts.

Even if it did stick out of the wheel well a bit, since the diameter is so much smaller, it wouldn't rub anyway would it??

2003z

iTrader: (7)

looking at the car, I see what you mean about it tapering down. What overall tire size are you using. With 255/40-17s, the height is sufficient to not rub if they stuck out of the wheelwell. They have a 25" diameter.

zoasis

I'd be going with 265/45/16 all around. On the fronts and rears, I wonder if I should just go with a 5-10 offset in the rear and 10-15 in the front or something? The only other factor is that I'll be lowering 1" or so with the JIC's, but I think it still would fit OK. What do you think?

zoasis

Screw it, I think I'll just go with 5.5" backspace front and 5
" for the rears.

I'll post pics later.

Craig

HREWheelMaker

2003z... you're almost right! Most people forget to include the "rim flange thickness" when calculating offset/backspace.

Remember, a 9.5" wheel is really 10.5" wide overall- the 9.5" industry-standard width measurement is "bead seat to bead seat," and does not include the rim flange thickness.

We have 'built' a proprietary calculator specifically for making these conversions. Here goes:

17x9.5 +22 = 6.12" backspacing, 4.38" frontspacing
17x9.5 +17 = 5.92" backspacing, 4.58" frontspacing

zoasis' new specs:

17x9.5 w/ 5.5" backspacing = +6.4 ET
17x9.5 w/ 5.0" backspacing = -6.4 ET (yes, a negative offset)

Craig... are you sure you want offsets that low? Very aggressive!!

zoasis

To be honest, on my backspace, I have no clue what I'm doing. Do you know what offset would work in a 16" wheel? My main concern is not rubbing on the suspension because the 16" radius when your inside the wheel well might hit the suspension. My tires are 265/45's

thanks for any expert input you may have. I think if the wheel sticks out a bit, it won't affect handling and since the overall diameter is smaller, it shouldn't rub.

zoasis

OK, I just did a tire height conversion and Kumho Victoracers 265/45/16 comes up to

25.4 inches

The ONLY other R-compound option is Hoosier 275/45/16 which is worse.

The bottom line is, thats not going to cut it.

If they stick out at all, it will rub when lowered and the weight savings I was wanting will not be there with the crappy fat sidewall.

I should have done a height conversion before I decided to order 16's.

So I'm now asking myslef, why in the hell didn't I stay with the 17's since they would be the same height and I could easily fit a 17X9 and 17X9.5

I guess I'm going to **** some people off in about 8 hours when I cancel my orders, I'm sure I'll have to pay circle racing for the centers they already cut.

Unfreakinbelievable!

2003z

iTrader: (7)

I feel your pain, I've bought 3 sets of wheels for mine already.

HREWheelMaker

I've got to be honest, I was asking myself the same question!! (LOL). It seems to me there are even better R-compound tire choices in the 17" diameter...

Anyway, the 16s could have other issues- brake clearance for one. My meusurements of the 'standard' 350z indicate that the small brake calipers have a radius of:
Front = 6.89"
Rear = 7.28" (at bleed screw)

The Brembos are worse, of couse:
Front = 7.51"

This might cause a problem with the wheels' 'drop center'.
If you do the quick math on the Brembo calipers, you'll see that 15.02" diameter is required to clear the O.D. of the brake caliper. Typically, 16" wheels will have only about 15" diameter of clearance in the center portion of the wheel- this is necessary to create the drop-center, which facilitates tire mounting.

Yeah, get the 17s...

zoasis

I ended up going with Enkei RP-2j's 17X9 all around. Hopefully the 35mm offset won't affect handling too much.

zoasis

I ended up going with Enkei RPO-2j's 17X9 all around. Hopefully the 35mm offset won't affect handling too much.