barchetta1

Im looking at a set of ccw classics.. they are 17", 10" front and 11" wheel. backspace is 7.5" (edited from 7.7") front and 8.5' rear.

By my calculation that is a large offset on the rear which is a good thing I think.. its 63.5mm?? 11" is 279.4" subtract 7.5" which is 215.9 and you get 63.5.

Fronts are the same63.59mm offset 254-190.5mm=63.5.

then.. will my 285,40,17 tires work on a 11" I think they would.. but my 255, 45,17 would be too stretched on the 10" wheel I think..

I edited this... sorry about that.

Advice please??

MatthewMiller

I have 17x11.5" CCW classics for all four corners of my car (they are on it my avatar). They all have 7.96" backspacing (43mm offset) and fit just right both front and rear. I also have two other sets of 11" wheels (one 17" and another 18"), all with the same backspacing (which on the 11" wheels is 50mm offset). These are perfect, with no real poke (the 1/2" less compared to the CCWs is all from the outside edge). So those 10" fronts you are considering will be a good fit - they won't poke out as much as mine, and they should have good clearance on the inside edges. The 11s for the rear may require a 1/2" spacer to clear on the inside. If that's required, it's not a big deal as long as you have enough thread length on the studs. You might need to use the ARP long studs.

On both my 11.5" and 11" wheels I'm running 315 tires, and they are perfect for that width wheel (I'm running Hoosier A7s on the 11.5" CCWs, and they are wide for 315s, so they can use the extra wheel width). Your 285s are going to be a stretch on the 11s, but looking at the specs for the Continental ExtremeContact Sport (one of the only tires you can still get in these sizes), they do spec it for up to 11" wheel width. Their "measured rim width" (the width of the inside edges of the bead when the tire is not mounted) is 10", so it's a 1" stretch. The 255 is only spec'd to a 9.5" max wheel (8.5" measured rim width), so it's a little out of bounds. You can probably make it work, but it may wear a little extra on the edges. For those wheels, ideally I'd think you'd want a 275/40 on the front and 315/35 on the back.

WVZR-1

I'm not changing my math for your typo - you need to learn the math, You should be able to understand the formula the way I presented it.

OP - you measured these wheels yourself for the back-spacing?

Wheel calculations are made from Total Wheel Width and not advertised widths, a 10" wheel would have a 'TWW' of 11" and an 11" a 'TWW' of 12". That's a trade +1" dimension for calculations.

Wheels are closer to 56 offset for the front and 64 for the rear. Fronts would fly as far as fit goes but for the rear you'd need 15mm spacer of some sort. A 15mm pass-through with longer wheel studs would work well. Once you had the wheels in hand you could maybe 'tweak' the rears for a fit.

The math with your #s: 10 + 1 = 11 / 2 = 5.5 (7.7 - 5.5 = 2.2 x 25.4 = 55.88), the 11 + 1 = 12 / 2 = 6 (8.5 - 6.0 = 2.5 x 25.4 = 63.5)

barchetta1

Thanks guys.. Im hoping to work this deal.. its remote.. he measured the backspace for me. So some risk there that he got it right but he seems smart.

Hope this deal goes through Im so excited! these are my dream wheels for my car!

thanks for telling me what I was hoping was the case.. I did not expect the spacers in the rear but I did expect that my brand new continentals in the front would wind up on craigslist.. I may just try and sell them as a set on craigslist or here if I get nice boxes in this deal...

EDIT: Ugh I just realized I typoed the front backspace.. its 7.5" not 7.7.. but the offsets I mentioned are correct.

So hopefully the fronts wouldnt poke out.. that would be a deal breaker... Id end up buying inner barrels and those are not cheap!

barchetta1

In regards to the tires.. yes, my thought is, I cell my c6 replica 17" wheels chromed with the brand new tires and I break even and buy new tires.. otherwise these very expensive wheels have the wrong tires on them.. they dont deserve the wrong tires.

WVZR-1

WRONG!!!

You need to review your math using the formula I laid out. Are these wheels local?

You need to understand the math and the formula!

Using your newer numbers the CCW will be further outboard by nearly 1"

Drop a plumb-bob on a string from the wheel opening edge at axle center and measure from your current sidewall towards the string to determine approximately where the new wheel/tire will sit.

barchetta1

they are not local.

I will head out to the garage,.. your formula just clicked.. offset is from the CENTER of the wheel so I am way off.. recalculating.. ugh..

barchetta1

NOW Im confused.. he is stating 10" and 11".. so now I ned to ask if its advertised or actual. I would think he is stating actual.. these are off a "race car". But now I need to go back and ask him.. ugh..

Im hoping they are actual rim edge to rim edge measurements.

barchetta1

ok if these are actual widths then my calculation was correct.. 63.5 front and 76.2 correct?

WVZR-1

You need snapshots that depict the actual and also the back-spacing.

A tape measure pulled rim edge to rim edge, a straight edge laid across the wheel and a rule from bolt flange to the straight edge. Your assumption of being a 'smart guy' could be in your favor maybe or then again maybe NOT!!!

barchetta1

Ok I asked him and his response was I measured inside where the bead seats the tire.. . UGH.. I dont want to push him too hard as he didnt want to ship..

Think you know what he means?

barchetta1

I see why you say add 1" now... bead plus lip... makes 100% sense now. thanks for being so persistent with me.. this could have been a disaster.

EDIT: ok spoke to him and you were exactly dead on.. edge to edge the wheels are 11" and 12"

the backspace he measured was to the edge.. so that means subtract .5" for the 7.5" and 8.5" correct

so that would mean fronts 38.1" offset and rears 50.8" I believe.. (edited, had them reversed)
10 + 1 = 11 / 2 = 5.5 (7.0 - 5.5 = 1.5 x 25.4 = 38.1), the 11 + 1 = 12 / 2 = 6 (8.0 - 6.0 = 2 x 25.4 = 50.8)

barchetta1

So then if I am right.. will this work.. this is how he measured the inside wheel width.

WVZR-1

I CAN NOT HELP YOU - you've changed wheel dimensions at least 3 times!! You either GET IT or you don't. You post snapshots like I mentioned and I'd be happy to help. You mention he doesn't want to ship so maybe it's all irrelevant!!

barchetta1

I understand.. disregard.. I appreciate your attempt to help.. sorry about all the changes.. have a great weekend!

WVZR-1

Pay the guy for his time to provide you with the snapshots that I mentioned. He deserves some consideration maybe just because you don't quite understand. There's no tires on them - dimensions should be very easy!!!

***He might interpret the offer 'TO PAY' as a serious/interested party and just accommodate you. In the end it would benefit his for sale intentions.

barchetta1

Had a detailed conversation with him. He measured outer to outer 11" and 12".

He measured the backspace to outer edge. which. that means subtract .5" for the flange. if thats means the backspace is really 7" and 8" which.. which means my FINAL calculation is correct.. I just need to know if such a small offset of 38.1 on a 10" wheel (11" edge to edge wheel) will fit..

If the answer is yes I will trouble him and pay him for the photos you mentioned... Otherwise, I think Im wasting your time, and his time due to my excitement.

WVZR-1

^^^^^^^

This is wrong!!!!!!

The wheels are 10 and 11 (advertised width). There's nothing wrong with his 'for sale'.

I'd assume he understands back-spacing and what ever he told initially is maybe correct. You don't seem to understand the math.

One final time - if his back-spacing is 7.5 I'd think his offset is 50 +/- and it would be considered a FIT.

Regarding the rears - if the 8.5 is correct then the 15mm pass-through should work well. You also need to understand how pass-through are fabricated. There are minimums that are required to maintain spacer to car hub-centricity and also create hub-centricity to the wheel.

barchetta1

He said he laid a straight edge over the back of the wheel and measured to the hub face. that is not backspace based on what I am seeing. regardless Im offering $20 for the photos..

thanks for your patience..

MatthewMiller

No, he's measuring backspacing correctly. You measure that from hub face to the absolute inner edge of the wheel. So you should not be subtracting 0.5" from it.* As WVZR-1 says, those fronts have a nominal 10" width (which is 11" from absolute edge to absolute edge) and 51mm offset, and will fit well.

The rears will have 63mm offset, and as we noted they will probably require about 12mm (~1/2") spacer to fit properly on your later C4. I'm not even sure that's required on the rear: I think the big issue is whether they'll clear the trailing arms. I can't help you with that measurement since I have aftermarket arms that aren't the same dimension or placement. The other important clearance is the top inside of the fender liner: they might touch with the inside edge of the tire when the suspension is fully compressed. You could try them without spacers and just see how they clear everything. Then get the spacers if needed. BTW, another way to think of that set of wheels is that they all have the same center and outer barrel half, but the rears have a 1" wider inner barrel half - i.e., all of the extra 1" of width is toward the inside of the hub face.

Here is a chart that does the math for you, and also has a good diagram for how each measurement (width, backspacing, offset) is taken: http://www.wheelspecialists.com/wheel-specs.

Below is a pic of one set of 17x11s with 50mm offset (7.96" backspacing) on my car at all four corners. The 10" fronts you're looking at would be centered on the hub exactly like mine (well, within 1mm), with 1/2" less width to either edge. So compared to mine in the pic, they will sit 1/2" further inboard at the outer edge, and also clear everything on the inner edge by an extra 1/2". In the rear, mine are how your 11" CCWs would fit with a 12mm (1/2") spacer. Without the spacer, they would be 1/2" further inboard, but would also have 1/2" less clearance on the inside edge.



* This is different than how we measure nominal wheel width. Nominal width has more to do with what range of tire widths will fit properly, so that is measured from inner bead surface to inner bead surface. I know this stuff gets a little confusing.