Wheels / Offset question

[GaryR]

I've started work again on my wide-bodied SC hot rod chassis and it's come time to think about wheels again. I'm considering 15" Minilites in 8" and 10" but am really in a quandary about offsets as this car has standard SC trailing arms and 930 flares. Any idea on approximate sizes (offsets/backspacing)? The car currently has Boxster front brakes mounted on Bilstein RSR struts but I am putting stock SC calipers back on and selling the Boxster setup with the adapters.

Minilite offsets are listed as -
15x8 MA1580B ET3-ET[-]16
15x10 MA1510B ET(-)13 – ET5

An issue may be tires a I will need at least 245's up front and 295's in the rear, what's out there for a road tire?

If Rota makes Fuch replicas 8"&10" in 17's (or anyone else for that matter) please point me to them.. or I suppose I can wait a year for another set of Zuffenhaus Fuchs!

[Bill Verburg]

Originally Posted by GaryR

I've started work again on my wide-bodied SC hot rod chassis and it's come time to think about wheels again. I'm considering 15" Minilites in 8" and 10" but am really in a quandary about offsets as this car has standard SC trailing arms and 930 flares. Any idea on approximate sizes (offsets/backspacing)? The car currently has Boxster front brakes mounted on Bilstein RSR struts but I am putting stock SC calipers back on and selling the Boxster setup with the adapters.

Minilite offsets are listed as -
15x8 MA1580B ET3-ET[-]16
15x10 MA1510B ET(-)13 – ET5

An issue may be tires a I will need at least 245's up front and 295's in the rear, what's out there for a road tire?

If Rota makes Fuch replicas 8"&10" in 17's (or anyone else for that matter) please point me to them.. or I suppose I can wait a year for another set of Zuffenhaus Fuchs!

To avoid lots of work for naught, I'd suggest that you might want to find the tires that you want to use first. Everything else will follow from there.

From what I've seen the selection of street 15 & 16" tires is limited

the typical SC wide body fitment(SC hubs and suspension and no spacers) is 9ET~12 & 11ET~ -8

in front to use an 8 you will also want the original 930 21mm spacer. Then use an 8 ET ~30 for a little more aggressive fit than was seen on the original 930s or w/o the spacer you will want ET~20, If the highest ET you can get is 16 that places the outer face of the wheel 1mm further inboard from the lip than the oe 7ET23.3 + 21mm spacer, most fitments are more aggressive wrt the lip rather than less.

In back w/o spacers 10 ET~13 places the outer face of the wheel a little more inboard than is usual.

[GaryR]

Thanks Bill, what I really want is the Minilites in 17" but they just don't exist AFAIK. Tire selection is a lot better once you go 17" so I may just have to compromise. The Group4 wheels are growing on me....

[GaryR]

I hate spacers, so for a custom fit on the Group 4's what would I order for offsets/backspace for an 8" front and a 10" rear to have them just "fit", with tires right to the lips of the flares? Sounds like front 8" would be about ET~25 and rear 10" about ET~25 also? For 9" front, as you state, an ET~12..

All in my head right now so the numbers may be whacked..

Originally Posted by Bill Verburg

the typical SC wide body fitment(SC hubs and suspension and no spacers) is 9ET~12 & 11ET~ -8

in front to use an 8 you will also want the original 930 21mm spacer. Then use an 8 ET ~30 for a little more aggressive fit than was seen on the original 930s or w/o the spacer you will want ET~20, If the highest ET you can get is 16 that places the outer face of the wheel 1mm further inboard from the lip than the oe 7ET23.3 + 21mm spacer, most fitments are more aggressive wrt the lip rather than less.

In back w/o spacers 10 ET~13 places the outer face of the wheel a little more inboard than is usual.

[Bill Verburg]

Originally Posted by GaryR

I hate spacers, so for a custom fit on the Group 4's what would I order for offsets/backspace for an 8" front and a 10" rear to have them just "fit", with tires right to the lips of the flares? Sounds like front 8" would be about ET~25 and rear 10" about ET~25 also? For 9" front, as you state, an ET~12..

All in my head right now so the numbers may be whacked..

Lets start w/ what the factory used on 930s
front w/ the early 911(SC) hubs
7ET23.3 w/ 21mm spacer, we only need to worry about the proximity to the lips, lets call this the base fitment.
8ET15 will place the outer wheel face exactly where the base fitment places it, each additional +1 mm moves the face 1 mm inboard and each -1mm moves it 1mm outboard, so 8ET20 sits 5mm more outboard than the base fitment, ie 5mm less lip clearance, this is called a more aggressive fitment but should work fine

for a 9" front ET27.7 places the outer face of the wheel exactly where the base fit does 9ET22.7 moves the wheel 5mm outboard ie you have 5mm less clearance at the lip.

back
the factory never used 911 trailing arms except perhaps on the 2.8 RSRs, but a common fit for 11s is ET-8, lets call that the base fitment here
a 10 that places the outer place where the 11 does would have to have ET-20.7

If the wheels you want don't allow those ETs then the only way to further reduce ET is by the use of spacers, 1mm of spacer reduces ET by 1

[KTL]

Those group4 10's look fantastico.

For reference purposes, my '79 SC with 930 flares wears:

17x8 ET+18.6 with 1/4 in. front spacers and also sectioned A-arms (~3/4 in. longer). Tires are fairly close to the fender lips with 245/40 tires. So my front wheels are effectively approx. an ET(-)7mm

17x10 ET+5.9 with 930 rear spacers, which makes them effectively an ET( -)22mm wheel.

You also can go with Superlite GTR wheels if you decide to go with 15 in. I'm leaning toward getting away from the larger diameter wheels. The wheel/tire combo is much heavier as you go larger. I have a set of BBS Motorsport wheels I got a deal on from cstreit. So i'm going to rebuild those to my desired widths and likely run 16s with them. Probably go with Goodyear Eagle RS DOT or radial slicks. I know your project is a street car, but it seems it has some race-inspired features going into it?

[GaryR]

Thanks guys. It took me a bit to tear my mind away from the "Fuch and Minilite" box but I can picture my hotrod with the Group 4 wheels now. Signal green, 70's classic race wheels, what could be better (and different!).. Waiting for an answer on available offsets but maybe I will be the 1st on my block to show these beauties off!

[JeremyD]

For reference -

My wide body on SC Suspension uses zuffenhaus fuchs - 9 x 11 (17's)

in the rear - I can run 315's rear offset is (-8)

on the front I can easily run 255's - can probably get away with 275's

with the 255's I run a 4mm spacer on 17mm offset -

I had my True Design 17" weld up wheels made to the same offsets.

[GaryR]

Would these fit, available right here on Pelican! Braid USA Fuch replicas in 15", would use the new Pirelli P7 Corsas.. they look fantastic (and retro!).

Front - PEL-SBZ9X15-RSR (what offset would I specify with no spacers, 22?)
Rear - PEL-BZ11X15-RSR (what offset would I specify with no spacers, -8?)

I will be selling my Boxster (S?) front calipers w/pads and adapters to fit Bilstien struts soon also, going to use stock SC calipers. $650 takes the whole setup, ready to bolt on..

[Bill Verburg]

Originally Posted by GaryR

Would these fit, available right here on Pelican! Braid USA Fuch replicas in 15", would use the new Pirelli P7 Corsas.. they look fantastic (and retro!).

Front - PEL-SBZ9X15-RSR (what offset would I specify with no spacers, 22?)
Rear - PEL-BZ11X15-RSR (what offset would I specify with no spacers, -8?)

I will be selling my Boxster (S?) front calipers w/pads and adapters to fit Bilstien struts soon also, going to use stock SC calipers. $650 takes the whole setup, ready to bolt on..

To match Jeremy's setup 9ET 17 w/ 4mm spacer
you use 9ET21

To match Jeremy's setup 11ET-8
use 11ET-8

Did you use the app I sent you?

[GaryR]

Originally Posted by Bill Verburg

To match Jeremy's setup 9ET 17 w/ 4mm spacer
you use 9ET21

To match Jeremy's setup 11ET-8
use 11ET-8

Did you use the app I sent you?

I will once I actually get ready to order Bill, right now i'm using the "Pelican/Bill Verburg" application...

Not using a spacer, so add 4mm to that to get 9ET25, correct? You guys are better than Siri!

[otto in norway]

I can't get these numbers to add up... Maybe it's just me, but I tried to do the wheel offset calculations on this calculator, and from what I can understand, I will need a offset of -38mm in order to fit replacements for my RUF speedlines. (Replacements without spacers) The RUF's are 17x10 ET 5. I'm using a 43mm spacer.

Is this not right? (wheel offset - spacer distance = total offset to the hub)

Calculator:
http://www.jonathanrowny.com/page/offset-calculator

[Bill Verburg]

Originally Posted by GaryR

I will once I actually get ready to order Bill, right now i'm using the "Pelican/Bill Verburg" application...

Not using a spacer, so add 4mm to that to get 9ET25, correct? You guys are better than Siri!

No, No, No

I believe Jeremy has the same setup you want, except that you will use 15s instead of 17's but that makes little to no difference.

SC chassis and suspension/hubs w/ 930 sheet metal added

the caveat is that any add on sheet metal is subject to idiosyncratic differences due to installation differences

but if Jeremy is using a 9ET 17 w/ 4mm spacer for the same fit you want to use 9E13. My previous post was in error, too early in the AM or just old fashioned "Old Timers disease'

Jeremy's 4mm spacer changes the wheel o/s from 17 to 13(a spacer reduces the ET by it's thickness)

As far as I can see the Braid BZ's only come in a few fixed o/s's, perhaps I am wrong, you should definitely contact them for their recommendation.

The 9ET15 looks to be close enough for you purposes but the 11ET-27 sticks out 19mm(.75") more than Jeremy's and that's hard to cover, a spacer only makes it stick out more.

[Bill Verburg]

Originally Posted by otto in norway

I can't get these numbers to add up... Maybe it's just me, but I tried to do the wheel offset calculations on this calculator, and from what I can understand, I will need a offset of -38mm in order to fit replacements for my RUF speedlines. (Replacements without spacers) The RUF's are 17x10 ET 5. I'm using a 43mm spacer.

Is this not right? (wheel offset - spacer distance = total offset to the hub)

Calculator:
Wheel Offset Calculator - The Ultimate Stance Calculator | Jonathan Rowny

I'm not sure what you want but
10ET5 w/ a 43mm spacer is the same as a 10 ET-38

[GaryR]

Well, I have heard back from two Canadian Pirelli dealers and from Pirelli Tire North America. One dealer said "end of summer", the other asked how many I want, and PTNA said: "We thank you for your recent inquiry. We are currently working on importing the Pirelli P7 Corsa Classic into the United States but as of yet there is no confirmed date of arrival. Please indicate what size you are looking for.

Pirelli Tire North America
Consumer Affairs"

I swear there were a lot more sizes listed when I first went to the site, this is what there is now:
P7 CORSA Classic, Motorsport tyres - PIRELLI INTERNATIONAL

15''
235/45R15 80H
235/45R15 80W
285/40R15 82H
285/40R15 82W
305/35R15 87H
305/35R15 87W

16''
255/50R16 89H
255/50R16 89W
315/40R16 90H
315/40R16 90W

TYRE SIZE FITMENT RIM SIZE
225/595-15 (235/45R15 80W) 7.5 > 9
265/40VR15 (285/40R15 82W) 9.5 > 11
305/35VR15 (305/35R15 87W) 10 > 12
290/660-16 (315/40R16 90W) 10.5 > 12.5
230/660-16 (255/50R16 89W) 7 > 9

Looks like it's either 235+305 15's or 255+315 16's... if they ever come out.

I run a 245 on 8" wheels so 8"and 10" would be fine for 15's, while 9" and 11" would be right for the 16's..

Bill - Braid does custom offsets but i'm not too thrilled with the 15 and 16" tire selection for wider widths and the promise of those Pirelli's isn't enough for my $4K...

[Bill Verburg]

They don't supply tire diameters or revs/mi which is info that I would want to know when evaluating fitment.

[GaryR]

How about the chart on this page -
CR6ZZ | Avon Motorsport

I can run 245's in front on an 8" wheel, 295's on the rear on a 10"..

[Bill Verburg]

Originally Posted by GaryR

How about the chart on this page -
CR6ZZ | Avon Motorsport

I can run 245's in front on an 8" wheel, 295's on the rear on a 10"..

Do you really wqnt to run a 26.9" rear tire?

Think about the difference when you went form your 18s to 15s on the race car.

Your target rear tire is ~25", shorter is better but a trade off where a taller tire is acceptable to get a desired width is often necessary, The more torque your engine has the taller the tire is acceptable.

When I had the stock 3 liter in my '76 a 245/45 x16 was a much nicer tire than the slightly taller 225/50(I should have stayed w/ 225/50x15 but I was young and naive). When I installed my first 3.6 the 245/45x16 was too short, but the 275/40 x17 that replaced it was a little tall overall but was very nice for long interstate drives , 255/40 x17 is a much, much nicer compromise.

You wants/needs may be at variance w/ mine

[GaryR]

Bill - remember this is for a retro look long-nose Hot rod, will have approx. 250-275 HP once I get the EFI installed (selling the 46mm PMO's and all manifolds, linkage, etc. too!)... The race car is for the track and fast driving, this is for show and fun.. will even have a stereo!

I think the big 50/60 series tires will look the bomb on those little wheels!

[Bill Verburg]

Originally Posted by GaryR

Bill - remember this is for a retro look long-nose Hot rod, will have approx. 250-275 HP once I get the EFI installed (selling the 46mm PMO's and all manifolds, linkage, etc. too!)... The race car is for the track and fast driving, this is for show and fun.. will even have a stereo!

I think the big 50/60 series tires will look the bomb on those little wheels!

It's not hp it's torque that is King, especially on the street were revs and gearing are somewhat more limited.

I think understand what you are aiming for and my comments were in that regard.

w/ stock gearing, the taller the tire and smaller the engine the less 'fun' your car will be