16 x 9" fuchs backspace?

[Scooter]

Just another point of reference. I have also been going through this with the backspace issue, since I too am buying Minilites for my car. I was provided a backspacing chart by Minilite to determine what I needed: see Minilite,Minilite wheels,historic and classic car wheel replacement,competition and Classic Car Enthusiast,mini lite wheels. I then measured the backspace on my deep 6 Fuchs, which turned out to be 112mm as calculated by PET, not 121mm, as indicated on some other sites.

[Joe Bob]

Scooter it's a gentlemanly discussion.....

Terms on wheels are often used incorrectly and people use different terms for the same item.

For example, I am using a 15x6 on my travel/tent trailer. The guy building the adapters from 4 lug, 4inch to 5 lug, 130mm asked what the "hub diameter" was. Thinking the hub was the mounting surface, I gave him that measurement. What he wanted was the diameter of the bearing housing. Which is called the "Pilot Diameter" in this thread, Wheels fitments, all are 17" unless other wise specified

The purpose for that measurement is make a hub centric adapter to go over over the bearing housing/hub/pilot to be snug.


Then, there is the definition of negative and positive offset...

Some people confuse offset and backspace...the following is from Tire Rack....

The offset of a wheel is the distance from its hub mounting surface to the centerline of the wheel. The offset can be one of three types (measured in millimeters).*
Zero Offset

The hub mounting surface is even with the centerline of the wheel.
Positive

The hub mounting surface is toward the front or wheel side of the wheel. Positive offset wheels are generally found on front wheel drive cars and newer rear drive cars.
Negative

The hub mounting surface is toward the back or brake side of the wheels centerline. "Deep dish" wheels are typically a negative offset.

If the offset of the wheel is not correct for the car, the handling can be adversely affected. When the width of the wheel changes, the offset also changes numerically. If the offset were to stay the same while you added width, the additional width would be split evenly between the inside and outside. For most cars, this won't work correctly. We have test fitted thousands of different vehicles for proper fitment. Our extensive database allows our sales staff to offer you the perfect fit for your vehicle.

*Backspacing, similar to offset, is the distance from the hub mounting surface to the inside lip of the wheel (measured in inches).

As mentioned, offset is part of backspace....not an interchangeable term.

[foxpaws]

So, I don't really want to hi-jack, but, it is a backspacing question...

Backspacing eludes me…

I am looking to put 17x9s on the rear of the puppy (’87 Targa) – and save the pristine fuchs…

Plus, I like a bit bigger wheel than the 16s – and of course, finding tires should be a bit easier.

I have seen that I probably need backspacing of 5.63 (????)

So, the 2 Piece Porsche factory wheels I am looking at have a backspacing of 6.85

Can I make them work with a spacer - or is that too much difference?

Thanks!!!!

[Joe Bob]

A one inch spacer isn't much.....turbos had more than that. I assume you will be using longer studs? Stock SC fenders or modded?

IMHO, Stock fenders won't allow much bigger than a 245 tire on a 9 with a spacer.


Why don't you have 17xXX built by Lindsey with the offset to fit inside the fenders you have?

[foxpaws]

Ah joe bob - Welpe is bone stock -

So, I think the 245s would be a bit narrow on 9s - don't they usually use like 285?

I can get 2 piece factory wheels for dirt cheap... I mean dirt... with pretty decent rubber.

But, it sounds like maybe I should wait for some different wheels...

[Joe Bob]

Your limitation is the fender width, outboard. Since you are spacing the non stock wheel out an inch to match the stock offset......245s are about as big as you can use on an 8 or a 9.

If you can bring the wheel INBOARD, by using less spacer you can add more tire. Your problem THEN is rubbing against the oil lines on the passenger side if you have a front oil cooler. It's a balance...

[foxpaws]

So, don't '87s have front oil coolers - stock? I haven't had the car that long to really look - it has spent 80% of the time I have owned it on wheel dollies shoved over to one side of my garage (a product of buying it in fall in Colorado).

Hummmm... much thought involved here. I suppose it might be some trial and error involved.

thanks Joe bob! I at least know a lot more about backspacing than I did 1/2 hour ago!

[Joe Bob]

Typically 87s do have front coolers with oil lines under the passenger rockers....you just never assume what people have done over the years.

[Bill Verburg]

Originally Posted by Scooter

Just another point of reference. I have also been going through this with the backspace issue, since I too am buying Minilites for my car. I was provided a backspacing chart by Minilite to determine what I needed: see Minilite,Minilite wheels,historic and classic car wheel replacement,competition and Classic Car Enthusiast,mini lite wheels. I then measured the backspace on my deep 6 Fuchs, which turned out to be 112mm as calculated by PET, not 121mm, as indicated on some other sites.

for some reason they separate the flange width from the bead width and also use some jargon that is not common

they are calling backspace 'jack drop', that is not industry standard

it complicates the ET calculation by involving a separate term(flange width) that is included in the calcs that I posted above

for some reason you persist in believing that backspace is calculated in or by PET, it is not, in PET they have the part #s and ET that is all

[Bill Verburg]

Originally Posted by foxpaws

So, I don't really want to hi-jack, but, it is a backspacing question...

Backspacing eludes me…

I am looking to put 17x9s on the rear of the puppy (’87 Targa) – and save the pristine fuchs…

Plus, I like a bit bigger wheel than the 16s – and of course, finding tires should be a bit easier.

I have seen that I probably need backspacing of 5.63 (????)

So, the 2 Piece Porsche factory wheels I am looking at have a backspacing of 6.85

Can I make them work with a spacer - or is that too much difference?

Thanks!!!!

Backspace only becomes important when you are tryng to fit the absolute max possible width wheel.

For fitting 7, 8 or 9 on the back of an SC it is not at all important, for fitting 9.5 or 10 it is.

All you need to know is the bead width and ET, in this case 9" I don't know what wheels you are looking at but just for the sake of discussion suppose that it is a typical late ET55

so f you want to fit a 9" ET 55 on the back of an SC and have it fit like Fuchs 9 ET15 then you need to use a spacer, the spacer reduces ET by the thickness of the spacer. So since 55 - 15 = 40, you will need a 40mm spacer, if you want the wheel to sit more outboard then you use a thicker spacer, ie a 45mm spacer will have the outer face sit 5mm further outboard, a thinner spacer moves it further inboard

[Bill Verburg]

Originally Posted by foxpaws

Ah joe bob - Welpe is bone stock -

So, I think the 245s would be a bit narrow on 9s - don't they usually use like 285?

I can get 2 piece factory wheels for dirt cheap... I mean dirt... with pretty decent rubber.

But, it sounds like maybe I should wait for some different wheels...

to determine the tire to use on a given wheel you need to know the design range of the tire, this info is available at Tirerack and the various tire manufacturers web sites

it will vary by tire and wheel diameter

for 16" wheels 245/45 is among the best fitments but are getting to be rare birds
Fuzion Zri is on of the available 245/45 x16 tires it has a design wheel width of from 7.5 " -9 ", for best performance you want the 9" for best comfort you want the 7.5"


A 285 is going to be an extremely difficult fit on an SC, a lot of racers do use them on 10" wheels for ex a Hoosier R6 285/30 x18 has a design wheel width of 10 -11" these are not casual fitments on SCs The widest I felt comfortable w/ was a 275/40 on 9.5. w/ these wheel/tires the trailing arm bolts, oil lines and fender contours all had to be modified.

if you are not a racer and are going to use a 9x17 or 9x18, you will likely want to shoot for an installed ET of 15 and a 255 or at most 265 tire, I'd stick w/ a 255 unless you are experienced fitting big tires.

The other concern is the effect of the tires on gearing, most people will be very unhappy if the OD of the tire is too much bigger than stock

stock SC rear is a 225/50 x16 w/ an OD of ~24.9" a typical 245/45 x16 is slightly shorter and most people enjoy the extra acceleration ability that comes from shorter gearing

if you go to a 9x17 w/ say a typical 255/40x17 the OD is ~25", there is some idiosyncratic variation but most 255/40x17 will be a tad taller than most 225/50x16 and will thus have slightly taller gearing .1" isn't a big deal but a 275/40 x17 @ ~25.7" really hurts low end acceleration at one time there was a great 265/35x17 available form Bridgestone but they haven't been available for years

[Bill Verburg]

Originally Posted by foxpaws

So, don't '87s have front oil coolers - stock? I haven't had the car that long to really look - it has spent 80% of the time I have owned it on wheel dollies shoved over to one side of my garage (a product of buying it in fall in Colorado).

Hummmm... much thought involved here. I suppose it might be some trial and error involved.

thanks Joe bob! I at least know a lot more about backspacing than I did 1/2 hour ago!

a stock '87 would have a cooler in the front passenger side fender, that would only become an issue if a really over sized tire is fitted
In front of an SC the typical fitments are 7 - 8" w/ 205 -245 tires again you don't want a larger OD and the wider and taller the more involved the fitment is.

A typical 8 will want ET25 - 31, the lower ET will be closer to the lip, the higher to the struts and inner wall. if you use say a 225/40 x17 on an 8ET27 that will be a pretty safe fitment, the smaller the tire the more leeway you have to go in or out

[GaryR]

Originally Posted by Bill Verburg

Backspace only becomes important when you are tryng to fit the absolute max possible width wheel.

For fitting 7, 8 or 9 on the back of an SC it is not at all important, for fitting 9.5 or 10 it is.

Bill!

After all I went through I have to say in the case of fitting a 9" wheel (+/- a few mm a 9" wheel is 10" overall width) backspace is everything! A 5" backspace, as the max offered by Minilite, will put the wheels too far outboard and they will rub a standard "SC Flare". You need a 5.5" backspace (+/- a couple mm) depending on the overall wheel width.

7", 8", not nearly as critical and the Minilite's available offsets will put the wheels out, filling the wheel wells nicely.

I NEVER would think of correcting you Bill, but when it comes to those 9" wheels and an SC I have gone through the pain!

[Bill Verburg]

Originally Posted by GaryR

Bill!

After all I went through I have to say in the case of fitting a 9" wheel (+/- a few mm a 9" wheel is 10" overall width) backspace is everything! A 5" backspace, as the max offered by Minilite, will put the wheels too far outboard and they will rub a standard "SC Flare". You need a 5.5" backspace (+/- a couple mm) depending on the overall wheel width.

7", 8", not nearly as critical and the Minilite's available offsets will put the wheels out, filling the wheel wells nicely.

I NEVER would think of correcting you Bill, but when it comes to those 9" wheels and an SC I have gone through the pain!

It was only a PIA because you made it that way,

truly for a 9 all you need to know is ET, sure you can worry about other stuff but it just obscures the issue. Fuchs use the narrowest flanges of any wheel i've ever seen, most after markets have .5" flanges but all I've seen are between the Fuchs .35" and .5", so the widest a 9 can be overall is 10", the flange only becomes an issue at max width, the tire is the most important to situate w/ clearance and the tire moves in or out w/ ET

As we discussed when you were doing research a stock Fuchs 9 ET w/ backspace ~138mm fits fine w/ plenty of backspace clearance and plenty of front-space clearance, I've seen 10s fitted on SCs but off the top of my head I don't recall the ET that was used, I know that they wee Fikse and believe that the ET may have been 18.6 w/ a~158mm backspace, I do recall that often different width spacers were used to juggle things a bit.

The widest I've ever fitted on my '76 Carrera is 9.5(10.5" overall) ET19.05 Kinessis w/ backspace ~152.5mm, w/ the 275 tires there is only a few mm gap to the cut-down trailing arm bolts. I think I sent you some pics, your 275s must have fit something like that but probably w/ a tad more clearance because your 9s don't stretch the width as much as a 9.5, mine at the lip have only enough clearance to not hit on bumps there is nothing left and that involved shaving the lips and re-contouring the whole area above the lip.

any way unless fitting to a race can most owners will be satisfied w/ a more comfortable fit which is a 9(10" overall) which has to have proper clearance if the ET is reasonable. It just can not be otherwise. Yes, you can worry about backspace but then it complicates other issues such what to do if you need a spacer, which is an issue that is there everytime someone wants to fit a high ET late wheel on a relatively low ET speced 911 chassis.

There is just no 9x18 or smaller wheel w/ ET15 that won't fit the rear of a straight SC/Carrera and there is room to go a little inboard or a little outboard

As I mentioned previously if you think width and Et then the spacer just falls out of the woodwork so to speak.

I agree that for the max fitments of 9.5 or 10 you do need to start worrying about backspace,

An example is on my 993 10 ET65 fits perfectly no issues in or out, but to try to fit a 10.5 or 11 then the backspace limits you. as there is only .25" clearance inside w/ 10 ET65

from the Minilite page referenced above they make 9" ET -30 to +4 none of these wheels can possibly fit an SC Carrera unless 930 fenders are used, they all stick out too far, We don't need to know backspace to know that

they also make 5.5, 6, 6.5, 6, 7 & 8 for 911 use but they do not specify the ET that they make them with, If I was shopping for Minilites I would want to know the width and ET then I know how it will fit, a stock 6" Fuchs is ET36 w/ front space ~48.5mm & backspace ~120.5mm w/ some room to be moved in or out, if their wheel is ET30 and the flange is .35" then I know that it sits 6mm more inboard if its ET40 then I know it sits 4mm more outboard, if the flange is the max .5" that does not affect where the tires sits which is the important thing, ie the tire moves in or out w/ the ET

You are certainly free to fret about it in any ways that you choose but for normal wheel fitments why not think the easy way

[Scooter]

Originally Posted by Bill Verburg

for some reason they separate the flange width from the bead width and also use some jargon that is not common

they are calling backspace 'jack drop', that is not industry standard

it complicates the ET calculation by involving a separate term(flange width) that is included in the calcs that I posted above

for some reason you persist in believing that backspace is calculated in or by PET, it is not, in PET they have the part #s and ET that is all

I acknowledge that I am incorrect in stating that the backspace measurement is provided in PET, however, I am correct in my measurements.

Porsche provides 112mm, not 121mm, as the backspace for deep 6 wheels. I confirmed this measurement by taking the measurement myself, along with a shop professional, from the back of the hub to the wheel lip, which is also the measurement used by Minilite. I really don't care if the jargon is industry standard or not, or if it is not proper to measure a certain way. What I do care about is getting the right wheel for my application. The best way to do that is to compare apples to apples; using my measurements in the same manner as Minilite, which is what I did to get the right wheel for my car.

Good luck to the OP. I hope you are very happy with your Minilites. I am sure they will look great.

[Bill Verburg]

Originally Posted by Scooter

I acknowledge that I am incorrect in stating that the backspace measurement is provided in PET, however, I am correct in my measurements.

Porsche provides 112mm, not 121mm, as the backspace for deep 6 wheels. I confirmed this measurement by taking the measurement myself, along with a shop professional, from the back of the hub to the wheel lip, which is also the measurement used by Minilite. I really don't care if the jargon is industry standard or not, or if it is not proper to measure a certain way. What I do care about is getting the right wheel for my application. The best way to do that is to compare apples to apples; using my measurements in the same manner as Minilite, which is what I did to get the right wheel for my car.

Good luck to the OP. I hope you are very happy with your Minilites. I am sure they will look great.

Well good for you!

Just for my own edification could you tell me where Porsche provides the backspace information

[GaryR]

Originally Posted by Bill Verburg

It was only a PIA because you made it that way

Actually it became a PITA when the guy from Minilite assured me (and Dan Jacobs, who actually ordered a set to try) that their 8" front and 9" rears would be fine with stock SC flares. Everything I new said "uh-uh" and sho-nuff they didn't fit.

Thanks as always for your expertise, look forward to seeing you at Limerock on 4/1!

[Bill Verburg]

Originally Posted by GaryR

Actually it became a PITA when the guy from Minilite assured me (and Dan Jacobs, who actually ordered a set to try) that their 8" front and 9" rears would be fine with stock SC flares. Everything I new said "uh-uh" and sho-nuff they didn't fit.

Thanks as always for your expertise, look forward to seeing you at Limerock on 4/1!

It's been my experience that vendors have a tendency to be , ummm.... optimistic. I'm shocked that Dan went along w/ it he certainly knows better

Part of it is the desire to make a sale, part of it is unfamiliarity w/ the edges of the envelope on our cars, and part of it is the general publics demand for very aggressive fitments that at least appear to fill the wheel well.

Looking forward to the season too, The way things are going it'll be snowmobile racing on Apr1

[Wil Ferch]

The final piece of the puzzle that most people ignore is the tire used itself. I have run Fuchs 7" in the front of my 85 Carrera ...and the various tires ( all 205/55/16) all ended up fitting differently. Some were close to giving me rubbing problems....some didn't.

Go back to the Bill V drawing. Look at "tread width" and "section width". Throw-in if the tire in question is square-shouldered , or round shouldered....and it then should come as no surprise that some people say "this fits"..and some say "no". For the rear, I have run "wide" 225's that were almost as wide as some "Skinny" 245's. You *need* to look at the tire specs.

IMHO...as to wheels, I think you need overall width, ET and for "good measure".... backspace to take into account rim bead material thickness. Maybe even front-space if fender lips are a concern. If nothing else, as Bill V says....it will help "triangulate" all the numbers to see if they all match to themselves.

BTW...from the posted pictures of some of the Minilites fitted, it does seem they will rub the rear fender lip...awfully close.

The amount of camber you run makes a difference too...as well as ride-height.

I keep endorsing that we quote as many variable as we can when we post "this fits" or "this doesn't"....but it's not catching on. People keep on asking if tire size "X" can be run...and leave it at that. Need also brand name, model of tire, ride height, camber, wheel specs, etc, etc....to make a fair comparison.

[Joe Bob]

That's why they make spacers......