3.2 Carrera track widening

[Yoram]

I have just acquired a "plain vanilla" 87 911 with the OEM 16x6 front and 16x7 rear Fuchs wheels. I do not want to change the OEM tire size, but I want to increase the track width to the extent possible with the standard body (no fender lip rolling).

Would anyone know how much can I move the outer surface of the tire out (e.g. if I were to use hub spacers with the existing wheels, what size spacers would I need), front and rear, without fouling the fenders in full jounce? The car is not lowered and has the OEM springs and anti-roll bars.

I prefer to do this with 16 x 8's in the rear (smaller offset) if I can find any, and small spacers front and rear.

My rough measurements based on curb position are about 10 mm in front (20 mm track increase) and 20-25 mm in rear (40-50 mm track increase), but I have no way of verifying no fouling under jounce.

Thanks!

Yoram

[Wil Ferch]

Look at what I say here---> post #10--->

Should I use spacers with these wheels?

...which embedded refers to another post....I comment there on #18..... should make for some interesting options for you to consider.

Post #18----> Anyone have 928 21mm spacers on a 911?

[Zeke]

If you install 8's on the rear and mover the 7's to the front, you won't need spacers. In fact, I would not use them for a number of reasons in that exact circumstance.

Stiffer steering already due to 7's (6's on spacers will have same effect).
Softer suspension in front due to wider track (spreading load inward and outward with 7's is better).
Either longer studs and spacers or offset type can be used, but offset not as safe.

[Yoram]

Milt and Wil, a belated thank you for your replies (was traveling). Wil, thanks for the great links!

The question still remains: What is the maximum safe spacer width for the rear and the front?...

I have now read about folks using 21mm, 25mm and even 28mm in the rear. Of course with more negative camber and other mods one can get away with wider spacers. I'm wondering what is the maximum safe one to use to avoid rubbing if otherwise everything is kept stock. Sounds like 21mm for sure, possibly 25mm in the rear? How about the front? 10mm? 13mm?

In order to keep the handling balance (with higher limits) as unaffected as possible I want to increase the front track as well, but less than the rear (less room). The resulting slightly softer front suspension is a good thing, as it would reduce understeer to counteract (directionally) the increased understeer due to the wider rear track (minimal change in effective spring rate in the rear with track change due to different geometry).

Milt, going with 7" in the front and 8" in the rear without spacers is not a good option in my view due to the following reasons:
1. Keeping stock tire sizes, the tire face moves out 13 mm both front and rear, which is not enough in the rear and maybe too much in the front.
2. 16 x 8 OEM Fuchs are near impossible to find and very expensive (16 x 6 less desirable so can't recover by selling), and since I need spacers anyway, might as well use the 7" in the rear.


Thanks again, folks!

Yoram

[UrQuattro]

Just so you know, you'd be able to run 8" wheels w/ 225/50 tires in the front and 9" w/ 245/45 in the rear without issue.

You also run the 7/8's with the stock tire sizes and not have any problem at all.

Michael

[aston@ultrasw.c]

FYI

True Design Wheels will convert a 6 or 7 fuchs into a 9.5 with any offset you want (more or less). They do a great job and the price is very reasonable.

[Yoram]

Michael and Aston, thanks for the feedback.

First I need to clarify that for street use I do not want to increase the tire size, I want to stay with 205 fronts and 225 rears, as I think they offer to best size for fun and safe public road use while still being able to feel some slip angles and gentler limits than the wider tires, which while offering higher limits, in my opinion cannot be really safely explored on public roads.

Michael, I am wondering about the 225 and 8" for the front... the 245 and 9" in the rear I can see, as the outer face would move out a nominal 18.3 mm, assuming the stock 7" offset is 23.3 mm, the 9" offset is 15 mm, and the tire grows by 10 mm on each side: 23.3 - 15 +10 =18.3, which is even less than the apparent available room. However, the 225 and 8" in the front would result per my figures in the tire face moving out a nominal 35.4 mm : 36 (6" offset) - 10.6 (8" offset) + 10 = 35.4 mm vs. stock (205 on 6"), which is way too much.
Even 7" in the front with 225 tires sounds like the tires would stick out and rub without flaring or rolling fenders - according to my figures the face would move out a nominal 22.7 mm vs. stock, and I'm measuring not much more than 10 mm available...
Am I figuring something wrong?? Do I have my offsets wrong?

Aston, would True Design convert a 7" to a smaller offset without changing width?

Gentlemen, thanks again and please throw in anything else that comes to mind.

Cheers,

Yoram

[Bill Verburg]

It's easy to lower o/s or ET, just use a spacer, the ET decreases by the width of the spacer.

the concern w/ widening the track w/ spacers in front is that you change the scrub radius, more scrub radius as from adding spacers in front is going to increase the effort and kickback through the steering wheel, this is generally not a good thing.

Increasing the wheel width does so to a much lesser extent and is an acceptable compromise to increase front end grip.

in front the wheels can be made to stick out up[ to ~1" more than w/ 6" ET35 wheels, where the limit is depends on ride height, suspension and how much alteration of the fender lip is acceptable

in back the limit is pretty much the same, ~1" but it depends on the same things as at the front

[Por_sha911]

Someone posted a chart of wheel and tire sizes that will fit your car. You may want to do a search.

[Wil Ferch]

Yoran:

I don't get it. You ask for information. I offer you post #18 which noodles all the possible rear spacer sizes based on what others on the board have said works...and what doesn't work. Based on that...some math noodling on my part in my linked post...I give you the (rear anyway) maximum width spacers for each of the 7", 8" and 9" wheels that are "safe" without interference.

And you say...immediately afterwards... you still want to figure out the max spacers?.

So my question.....Did you read the info you already have?.

Let me post #18 right here again--->
----------------------------------------------------
From all this data ( just from this post and the embedded links alone), we can come up with some pretty interesting "facts"....all dependent however on "specific" tire sizes ( and shoulder shape...square vs round) amount of camber being run, and amount of fender lip rolling done.

Outside edge "vertical plane" locations/equivalents:

7"Fuchs = base
8" Fuchs = 7"Fuchs + 25mm
9" Fuchs = 8"Fuchs + 10 mm
9" Fuchs = 7"Fuchs + 35 mm

Also, from the link:
8"Fuchs + 25mm spacer = "not good"

From Jeremy:
9" Fuchs + 12 mm spacer = "good"

So let's see if we can substitute equivalent values and see if this all hangs together...OK?

8" Fuchs + 25 mm spacer = not good ---> this is the same as saying ( 9"Fuchs-10mm) + 25mm = not good....or..

..9" Fuchs + 15 mm spacer is "not good"
Jeremy says 9" Fuchs + 12 mm spacer = "good".

So HERE we define the very NARROW window of opportunity, somewhere between 12mm and 15mm spacers on a 9" rim. Let's say the practical limit is 12 mm spacer with 9"Fuchs based upon all this.

So....9" Fuchs+12 mm spacer = OK
that means 8" + 22mm spacer = OK ( limit)
that means 7" + 47mm spacer = OK ( limit)

This also implies my spacer of 21mm could be increased by 26mm ( say 1") to get to this limit for my 7" Fuchs case. Frankly, looking at Jeremy's pics and my own car which looks IDENTICAL to Jeremy's pics...I still can't see that although numbers don't lie.....

Hmm......

-Wil
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[Yoram]

Hi Wil,

Sorry for frustrating you - not intentional...
Yes, I read the post carefully, and reached the following key conclusions relevant to my quest:

1. I believe that implied in the statement '8" Fuchs = 7"Fuchs + 25mm' is that the 8" is with 245 tires while the 7" is with 225 tires. This is because per my figures the 7" ET is 23.3 and the 8" ET is 10.6, so that net face outer plane move with the same tires would be only 12.7, not 25.

2. I cannot believe the statement '7" + 47mm spacer = OK ( limit)' because I measure crudely less than 30 mm lateral room between the stock 7" outer plane and the inner lip, and it also contradicts point 1.

So... please bear with me if I'm confused... at this point my hunch is that statement 1 is correct and I can get away with a 22-25 mm spacer keeping my 7" rims and 225 tires, while statement 2 sounds questionable.

I will gladly eat my proverbial hat if I'm wrong...

Cheers,

Yoram

[tcar]

Yoram;

Why don't you just move the 7x16's to the front and put 8x16's (911 offset, not 951) on the rear.

Keep the same exact tires you have now.

This will move the outside face of the tire to almost the inner fender lip. They'll be out as far as they can go.

No spacers needed.

As mentioned twice above by Milt and UrQuattro, at least.

No spacer figuring out stuff.

[Yoram]

TCar!,

Great question!

Two answers:

1. I don't have 8x16's, real Fuchs ones are difficult to find and expensive, and I don't want to use replicas.

2. We cannot get away from figuring offsets... :-)
For the rears, the 7's have an offset of 23.3 mm, and the 911 8's have an offset of 10.6 mm, so the difference is 12. 7 mm, which based on my crude measurements looks like only 1/2 of what is possible there...
For the fronts, the 6's have an offset of 36 mm, which if you put 7's there gives you a difference of 12.7 mm, which for the fronts, as you say, may just work.

I was thinking about your (and the other folks') proposed solution with 1/2" (12.7 mm) spacers in the rear, but once you decide to use spacers (blasphemy!!) you might as well keep the same rims...

This is my twisted logic so far...

Thanks!

Yoram

[GaryR]

Also, if you use spacers without integrated lug bolts you most likely need to install longer lugs. An easy way to see if you need them is to get one open steel lug nut and tighten it on. If the lug nut threads are not completely filled with bolt you need longer lug studs..

[tcar]

Friend has 7x16 Fuchs on the rear of his SC with a 1" (25 +/- mm) spacer, looks virtually the same as my 8x16 without a spacer. Fits perfectly.

You can do, barely, a 1/2" spacer in the front with 6x16 Fuchs.

[Yoram]

Gary and TCar,

Thanks. What each of you is saying makes perfect sense to me.

TCar, your numbers fully support my speculation for the fronts, and for the rears if the 8's carry 245 tires and the 7's carry 225.

I think I know now what fits. What makes the most sense is another story...

Thanks again,

Yoram