Wide wheel setup: Please confirm my fitment calculation

[hexagone]

Howdy.

I’m planning to put in the order for my dream wheels this Monday. Dream car with dream wheels yada yada yada.

Before I put a big irresponsible and illogical dent on my credit card - I wanted to confirm my calculated dimensions with everyone on here that is knowledgeable. Jonesmechanical I’m looking at you sir!

Suspension spec (in case it matters):

Front: Stock struts with Koni sport shocks / GC threaded sleeves / eibach 550lb/in springs.
Rear: Koni sport shocks / GC threaded sleeves, eibach shorty 650lb/in springs

The centers I am using to build wheels from the ground up were 17x8, et40, with 1” lips and 6.5” barrels originally; the center adds .5” of thickness. This also equates to 155mm of backspacing. They have a very thin backpad, so like the pictures show below- the bolts are painfully close to the calipers (awesome, because I am able to squeeze out every millimeter for lip size).

Taking into consideration my front roadstars being 17x7.5 et41, with 150mm backspacing, and about a finger’s width of space left between the strut and inside lip, that means the estimated maximum front backspacing would be ~ 160mm (150mm + width of finger).

And with all of that- here is a spreadsheet of what I would be able to put together. The green highlighted rows are based off of the original 17x8 et40 dimension that I started out with- and then increasing the lip and barrel size accordingly.

As things stand- the maximum ‘safe’ dimensions I can put together are 17x8.5 et33.65 front and 17x11 et14.6 back, is this correct? Can I squeeze out anything more from the list below? And will 245/35/18 & 295/30/18 Hankook Ventus’s suffice?

I should also note- these will be 18’s, not 17s.

K thx.

[Sky1Z3]

I think Greg recommends a max of 11" rears with an et of 19. But I'm in to see what the wheel guru says, and to see what the resident wheel whore comes up with. :d

[jonesmechanical]

So how do the rim shells mount on this rim style. Both on the face side, both on the back, or one of the back on the front sandwich.

To make things easier for me, and not give me a headache and keep it simple, set the wheel back side down (so the hub surface is on the surface) on a flat surface and measure from the surface to the flange where the wheels halves will bolt to. I assume that they are the same front and rear, if not, tell me what each of them is. I will figure out the best orientation of the wheel center offsets (which ones would be best for front/rear). Let me know if any of the centers don't work on one of the axels because of brake clearance or something else.

[hexagone]

So how do the rim shells mount on this rim style. Both on the face side, both on the back, or one of the back on the front sandwich.

To make things easier for me, and not give me a headache and keep it simple, set the wheel back side down (so the hub surface is on the surface) on a flat surface and measure from the surface to the flange where the wheels halves will bolt to. I assume that they are the same front and rear, if not, tell me what each of them is. I will figure out the best orientation of the wheel center offsets (which ones would be best for front/rear). Let me know if any of the centers don't work on one of the axels.

The center is sandwiched in between both shells. One shell on the front, one shell on the back.

Unfortunately I'm about 900 miles away from my centers and the car, and won't be back for a few weeks. The turn around time for new shells is also 5 weeks... and well, I'm trying to avoid taking the wheel build into fall. So I can't do any in person measurements now (or drive le car)

[edit] I'm gonna go order my little brother to measure the centers for me and get you this number. Once again- really appreciate the help!

[jonesmechanical]

Wow, that changes everything, especially since there is considerable thickness to that center. If there is 3/8" of material there you are going to have rims that are a weird size (not necessarily a bad thing). You won't be 11" wide unless the center happens to be 1/2 wide, but then you would actually get shells that would normally net 10.5" wide, but because of the sandwich style (which I have never seen before) it get you to the 11. But if it's 3/8 thick, the wheel will be 10 7/8" wide!

There has to be someone close to the wheels that can get these dimensions. Until you get these specs, you are stuck. A picture is worth a thousand words, in this case, likely a thousand dollars. Your welcome!

[hexagone]

Wow, that changes everything, especially since there is considerable thickness to that center. If there is 3/8" of material there you are going to have rims that are a weird size (not necessarily a bad thing). You won't be 11" wide unless the center happens to be 1/2 wide, but then you would actually get shells that would normally net 10.5" wide, but because of the sandwich style (which I have never seen before) it get you to the 11. But if it's 3/8 thick, the wheel will be 10 7/8" wide!

There has to be someone close to the wheels that can get these dimensions. Until you get these specs, you are stuck. A picture is worth a thousand words, in this case, likely a thousand dollars. Your welcome!

I think the flanges of the centers, to which the shells mount up against, + the 10mm pad for the bolts approximately add up to half an inch. But it looks like it won't be until the end of the day when I'll get dimensions of the centers.

And I've decided against gold. They look strangely dated in gold vs. a dark silver.

[Grauc]

Are you worried ab the wide rear 17" tire having the 'bubble' look to it as it will have some more profile vs. A 18" wheel?

[hexagone]

Are you worried ab the wide rear 17" tire having the 'bubble' look to it as it will have some more profile vs. A 18" wheel?

No, I just wanted 18s since the beginning of time and they'll be the only set in the world like it in this spec.

There has to be someone close to the wheels that can get these dimensions. Until you get these specs, you are stuck. A picture is worth a thousand words, in this case, likely a thousand dollars. Your welcome!

update:

[jonesmechanical]

Wow, perfect. And them are some freaky looking fingers. Guy or girl? hard to tell.

[hexagone]

Wow, perfect. And them are some freaky looking fingers. Guy or girl? hard to tell.

My 16 year old brother

BTW, how are you getting away with your 19x9 et38?

I'd like to avoid a half size up front and wouldn't even mind a paper thin spacer up front to clear the strut and use the 18x9 et40 front- so the tire sizes stay proportionate.

[edit]

Just ordered a powdercoat close to BBS's DBK LMs and about to order red caps.

Am I revealing too much?

[jonesmechanical]

BBS 3 piece M coupe wheel build
Wheel center: 25mm offset, 12.5mm thick center
Front wheel, max front spacing 3.5"
25+12.5mm = 37.5mm or 1.48" do a 1.5" front
shell, and it will net 2" wide, and net 3.5" f.space
now, add a 7" back half, and net this:
7+.48+1.5=just under 9"

wheel width: 8.98"
actual width: 9.98"
offset (mm) +38.5mm
backspacing (in):6.507"
front spacing(in):3.473"

Rears, max back spacing is 7" front spacing 5.5"
so 7.5" back halves, and 3.5" front halves.
7.5+.48+3.5=11.48" wide, net 12.48" wide.

wheel width: 11.48""
actual width: 12.48"
offset (mm) : +19.7mm
backspacing (in):7.016"
front spacing(in):5.464"

[hexagone]

Rears, max back spacing is 7" front spacing 5.5"
so 7.5" back halves, and 4" front halves.
7.5+.48+3.5=11.48" wide, net 12.48" wide.

wheel width: 11.48""
actual width: 12.48"
offset (mm) : +19.7mm
backspacing (in):7.016"
front spacing(in):5.464"

you mean 3.5" outside halves and 7.5" insides, correct?

Because if I could squeeze out 4" outsides I'd be in heaven. Hell, I could even machine the backpad and flange 2mm each to make space.

[jonesmechanical]

So, this build is 9" front and 11.5" rear. You could go to 2" front wheel halves and go 9.5" wide in front, but I don't have much experience with that.

You could also go with 11" rears, but then spacers would be involved.

I would definately recommend these back half wheel hoops. They are going to uber close to the strut, and to the inner wheel well/trailing arm, but will either need no spacer, or likely a 2-4mm shim. Going to less wide back halves will just compromise your setup offset and make tire fitment more challenging. The way the centers sit, its almost perfection for building the wheel for max back spacing, which is where you want to be.

If you want a conservative setup, keep the back halves the same, and reduce the front halves (which you may not be able to get 1" front halves) to 1" and 3.5" in the back, so you net 11" rear and 8.5" front and then space it out, but will likely take anywhere from 12-20mil spacers to dial it in just right.

The real questions here is whether to run 11.5 rears with close to no spacer, or run 11" rears with 15+ mm spacers.

you mean 3.5" outside halves and 7.5" insides, correct?

Because if I could squeeze out 4" outsides I'd be in heaven. Hell, I could even machine the backpad and flange 2mm each to make space.

Yes, correct, I just edited that. I was typing and doing math at the same time. You fortunately I was clear towards the end, but now edited.

4" Heaven would be fitment hell. You could talk to the guy that just fit 12" rears with 285's (you could likely to 285 35 18's), he ran 285 30 19's on a 12. It would be possible, but committing to the most extreme fitment ever attempted. Also, 19" wheel have the ability to run a bit more backspacing, unless your willing to do a touch of grinding on the swing arm to make that happen, so 18"x12" may be death without making it happen with modification.

My 16 year old brother

BTW, how are you getting away with your 19x9 et38?

I'd like to avoid a half size up front and wouldn't even mind a paper thin spacer up front to clear the strut and use the 18x9 et40 front- so the tire sizes stay proportionate.

9" front on a 38 offset set works on 18" and 19" on every stock strut and coil over I have had experience with. That is what I am recommending, you will just need a slight shim. So thin that you will still maintain the hub centric contact of the wheel on the stock hub. The key on the coil over is if you go really low, get "shorty" springs so that the spring nut and spring sit high enough to not interfere with your wheel/tire backspacing. If not, it really limits wheel sizing a ton on the front.

[hexagone]

9" front on a 38 offset set works on 18" and 19" on every stock strut and coil over I have had experience with. The key on the coil over is if you go really low, get "shorty" springs so that the spring nut and spring sit high enough to not interfere with your wheel/tire backspacing. If not, it really limits wheel sizing a ton on the front.

I think I got this covered. The Eibach springs GC sent me are tiny, so I think I can safely assume these are the shorty ones. Will be reusing the stock strut so I'm good there too.

4" Heaven would be fitment hell. You could talk to the guy that just fit 12" rears with 285's (you could likely to 285 35 18's), he ran 298 30 19's on a 12. It would be possible, but committing to the most extreme fitment ever attempted. Also, 19" wheel have the ability to run a bit more backspacing, unless your willing to do a touch of grinding on the swing arm to make that happen, so 18"x12" may be death without making it happen with modification.

I would love to attempt the extreme, but will settle and not take a big risk with an investment that is far from logical to begin with. And while I could easily take a bit of stretch, or even poke and dial everything in- those days of 'improper' fitment are over- and it's not on any of my previous "budget" sub-10k cars.

So it is settled.

18x9 +38.5 - 245/35/18 Hankook Ventus V12 Evo
18x11.5 +19.7 - 295/30/18 Hankook Ventus V12 Evo

Oh boy.

[jonesmechanical]

Its going to be epic. Nothing short of that. I wonder even if the dimensions in the picture are actually 25.4mm and 12.7mm respectively, because they are soo close to an even 1/2" and full 1". If they are, it will only help you out with less backspacing and a bit more width, which won't hurt.

[hexagone]

Its going to be epic. Nothing short of that.

Thanks again for the help.

I'm planning on driving the car with a friend from Chicago to H2Oi show in maryland in September. Having them next to a car with the same 15x6.5" setup and rubberband tires wheels will be ridiculous.

[Grauc]

[QUOTE=hexagone;22318368]No, I just wanted 18s since the beginning of time and they'll be the only set in the world like it in this spec.



Oh okay, i misread and thought they'd be 17''

[felonious monk]

Am I revealing too much?

Wild guess... BBS Motorsport Magnesium.

[hexagone]

Wild guess... BBS Motorsport Magnesium.

like all of these 5x120 e26s I had?



nope.

[felonious monk]

Where and how are you finding these things?

[hexagone]

Where and how are you finding these things?

During college I had lots of spare time where I'd scavenge the internet between class, during class, after class for rarities. Over 3 years and probably close to 100 sets of rare wheels coming in and out things came to a slow end where I'm employed now and can just build what I want, rather than spend copious amounts of time searching the highly obscure market of used wheels.

Looking back- I sold a lot of stuff for a lot less than it's worth, unfortunately. But having the memory of only spending $1100 for a big truck delivering a pallet of 15 airmailed BBS e26s to my garage.... is simply priceless. In fact, I don't remember what his username is- but the guy on here with an estoril roady with 17" motorsport wheels has 4 of those in the picture above

[Mscire2]

For what its worth 9.5" can be done in the front, albeit I am running 17's below is my build I did on my Fikse's. I have completely un touched rear fenders and with a 10mm spacer in the back it only just touches the tire on very hard 1st to second shifts when I threw one it to see how it would look and if it would work. Obviously with them rolled flat it would be no problem.

17x9.5" front with 3" lips and 6.5" inner barrels Final offset of ET24
17x11" Rear with 4" lips and 7" inner barrels Final offset of ET18

Im also on Ground Controls with swapped strut hats since I am lazy and haven't put my plates in yet and have zero rubbing . Ill see if I still have the pictures of the fitment on it.

[hexagone]

For what its worth 9.5" can be done in the front, albeit im running 17's below is my build I did on the Fikse's im running. I have completely un touched rear fenders and with a 10mm spacer in the back it only just touches the tire on very hard 1st to second shifts when I threw one it to see how it would look and if it would work. Obviously with them rolled flat it would be no problem.

17x9.5" front with 3" lips and 6.5" inner barrels Final offset of ET24
17x11" Rear with 4" lips and 7" inner barrels Final offset of ET18

The shape of the face has a lot to do with lip size. Mine has pretty much no convexity at all.

Close up pics of your fronts?

[Mscire2]

The shape of the face has a lot to do with lip size. Mine has pretty much no convexity at all.

Close up pics of your fronts?

You are correct on that. Also the Fikse's mount with the face on the outside and the lip and barrel behind so you loose about ~3/4" of lip.
Here is the actual formula for calculating the offsets for my wheels.
(Total Width in mm / 2) - Lip Width in mm - 20mm

Click on the pictures to view them larger.

[jonesmechanical]

Yes, 9.5's are an option, and he would be safer than the above fikse's because you could keep the offset with a small shim to about a 32 offset. Swapping the hats would get you there with 2.5 or so degrees of camber.

Mscire is only running a 235 up front, but its also a rather tall tire. I am so tempted to go 9.5's on my 19" forgelines, because I already have the polished 2.5" lips to get me there, but I really don't want to go to the trouble and then have to deal with fitment. Of course, I'm running 265 30's right now, but with 255's I think it would be a go. No one has really done a 9.5 with a 255 or 265 that I can remember.

More than anything, I think the decision needs to be based on how the 245 35 18 fits a 9" and a 295 30 18 fits a 11.5". It would be a close to perfect match in stretch proportion running a 9.5 and a 11.5 with 245 35's and 295 30's.

Hex, I would almost go for the gold and hit that front end with 2.0 lips up front and go to the 9.5" wide front. At this point, you have all the info. Even on that e28 bbs coupe thats running 12" rears, its running 9's up front. 9's is agressive, but 9.5's can work with minimal camber and a bit of stretch.