Question about wheel offset and compatibility - tire and wheel experts please advise.

sand_man · 08-13-2007, 08:59 AM

I'm on the lookout for a particular wheel that is no longer made. They often come up for sale on the used market with the following specs:

Front: 18"X9" 50ET
Rear: 18"x10.5" 40ET

Because they're a 5X100 bolt pattern, I'll need an adapter to fit them to my 5X130 hubs. Other than the bolt pattern issue, which should easily be solved with an adapter, will these fit my car? Should the adapter also be a spacer of any particular thickness to help with offset? I need to know before I get my hopes up: when the wheels become available I'll need to act quickly as they are highly sought after and don't last long on the used market...so I want to be sure my ducks are in line.

Thanks for your help,
Jeff

Akila · 08-13-2007, 09:32 AM

When I called up Fikse, they told me the correct offset for the 930 was 32mm for a 9" front, 19mm for an 11" rear. Don't know if this is with or W/O factory spacers, I am guessing with. If you are using adapters then I think you have to add 1" for the factory spacer that will be removed before the new adaptor/ spacer goes on. Saying your rears were 11" then it would require a 13/16ths spacer add 1" for factory spacer = close to 2" adapter. Fronts @ 9" need an 11/16ths adapter + 1" spacer. Here is some reading.
http://members.rennlist.com/911pcars/WheelWts.html
Anyone correct me if I am mistaken.

sand_man · 08-13-2007, 09:53 AM

Thanks for the info. To be honest, this gets very confusing for me! This is my current setup:

Fronts: 18X8.5, offset: ET 30
Rears: 18X10, offset: ET 24

I'm pretty sure the factory spacers are on.

RarlyL8 · RarlyL8's Garage

9"=228.6mm, /2=114.3mm, +50mm=164.3mm = 6.5" backspacing
10.5"=266.7mm, /2=133.35mm, +40mm=173.26mm = 6.8" backspacing

DougM · 08-13-2007, 01:43 PM

From a visual standpoint, the fronts will be @13mm or 1/2" more under the fender with a narrower look.
The rears would be @9mm.
You would need to add an additional 13mm spacer to the front and 9mm at the rear to have them line up where your current ones do.
The extra 1/2" width of the rim and more due to the offset would all be added in the backspace behind the rotor.
1" = 25.4mm

sand_man · 08-13-2007, 06:12 PM

Thank you all, kindly. I just wanted to be sure I could get them to fit properly, and it looks like I will....just takes an undertsanding of that "new math"!!

Now, I just need to wait patiently for for the wheels...

DougM · 08-13-2007, 06:29 PM

What style wheels are you possibly going to get?

Akila · 08-13-2007, 11:40 PM

I think that is Top Secret until purchased..........

sand_man · 08-14-2007, 02:31 AM

Quote:

Originally Posted by Akila

I think that is Top Secret until purchased..........

As childish and silly as it may sound - yes, I'm keeping it like a secret...for now

NathanUK · NathanUK's Garage

When working out the backspacing on the front you want the centre of the new wheel (when viewed from above) to be exactly where the centre of the stock wheel was. At the back of a 911 it doesn't matter too much except for the wheelbearing.

sand_man · 08-15-2007, 04:59 AM

Many thanks, Nathan. I understand what you're saying, but follow this:

The factory 8X16 Fuchs for the front of my car have an offset of ET11 (we'll round).
So I think that even with my current SSR wheels at 8.5X18 ET30, which were configured by TireRack to be a "suitable fit", I don't see how the fronts are centered, now. There are no after-market spacers installed to adjust offset.

As you mentioned, I'm more concerned with getting the front figured out, as I'm confident the rear will not be a problem.

I've been playing with an on-line wheel offset calculator. I won't purchase any spacers until I actually have the wheels in hand and mounted with tires. Right now, I'm thinking of running a 21mm H&R DRM spacer on the front. Being that the wheels I'm interested in purchasing are 9X18 ET50 (for the fronts), this spacer would bring my offset down to ET29. My only concern is in pushing the outer edge of the wheel (fender side) too far.

I've also learned that this particular wheel was available in a 5X130 bolt pattern. So right now, I'm just looking at spacers (not 5X100 adapters).

sand_man · 08-15-2007, 07:16 AM

Quote:

Originally Posted by sand_man

Many thanks, Nathan. I understand what you're saying, but follow this:

The factory 8X16 Fuchs for the front of my car have an offset of ET11 (we'll round).
So I think that even with my current SSR wheels at 8.5X18 ET30, which were configured by TireRack to be a "suitable fit", I don't see how the fronts are centered, now. There are no after-market spacers installed to adjust offset.

As you mentioned, I'm more concerned with getting the front figured out, as I'm confident the rear will not be a problem.

I've been playing with an on-line wheel offset calculator. I won't purchase any spacers until I actually have the wheels in hand and mounted with tires. Right now, I'm thinking of running a 21mm H&R DRM spacer on the front. Being that the wheels I'm interested in purchasing are 9X18 ET50 (for the fronts), this spacer would bring my offset down to ET29. My only concern is in pushing the outer edge of the wheel (fender side) too far.

I've also learned that this particular wheel was available in a 5X130 bolt pattern. So right now, I'm just looking at spacers (not 5X100 adapters).

Just remembered that stock Fuchs for '87 were 7x16 for the front. So I was mistaken in suggesting 8X16 with ET11. The correct stock offset would be ET23.3...which makes more sense.

NathanUK · NathanUK's Garage

I THINK that means you need a 6mm or 7mm spacer. 23.3mm - 30mm = 6.7mm short to make up with a spacer.

I hope someone who knows will answer for you.

DougM · 08-15-2007, 01:56 PM

A 23mm offset will be pushed out 7mm more than the 30mm. You will push closer to the lip. Lower offset creates a larger "lip" or "dish".

sand_man · 08-15-2007, 02:43 PM

Well what I'm trying to balance is being sure I have enough clearance on the backside (between the tire and suspension/chassis, when I turn lock to lock) without pushing the wheel too far out to the edge of the fender lip. I'm still at U.S. ride height with plans to go to Euro ride height when I get into freshing up the suspension.

And Doug is correct. The stock Fuchs are pushed further out because of their smaller ET than my current SSRs.

NathanUK · NathanUK's Garage

Oops, I got confused. Your new replacements are 50mm et, while your stock Fuchs are 23mm et.

So, 50mm - 23 = 27mm short to make up with a spacer.

This should mean you need a 27mm spacer?

Lukesportsman · 08-15-2007, 05:46 PM

You aware that at one point PCA didn't allow spacers that altered bolt pattern? I do NOT KNOW if this rule still applies and you might not give a darn. Just wanted to put it on the table if you have the choice to spend a few more bucks and get the appropriate pattern.

I don't really understand why Porsche felt it necessary to fun a pattern equal to my F150 with like size studs in the first place. Left over from wide 5 bolt patterns of VW? Anyone know?

DougM · 08-16-2007, 02:58 AM

In the past I had a set of Kinesis and Fikse that were made for a later model Turbo. The fronts were 8.5" with @46mm offset if I recall. Without spacers and 225 tires there were no problems except that they looked funny until I added a 17mm spacer.

sand_man · 08-16-2007, 05:15 AM

Quote:

Originally Posted by DougM

In the past I had a set of Kinesis and Fikse that were made for a later model Turbo. The fronts were 8.5" with @46mm offset if I recall. Without spacers and 225 tires there were no problems except that they looked funny until I added a 17mm spacer.

Thanks Doug and guys! You've all been very insightful! I've been in contact with a company in Germany regarding the wheels. My first email in English went unanswered. So I translated that into German and re-sent it. Hopefully, the on-line translator didn't butcher their language too badly! I'm trying to work out the shipping and customs issues. I once ordered a KW coil-over suspension from Germany for my MIV GTI and was able to get it without too much trouble, so I'm hoping the same for these wheels!