Bill Verburg

google "wheel offset"

David in LA

I've always thought that Porsche offsets were negative...so that adding a spacer meant making it less negative (i.e. a negative plus a positive equals a smaller negative) vs. say American muscle cars which have a positive offset so the center of the rim is outside the hub flange and adding a spacer resulted in more positive offset

Garth S

Precisely! That is why the spacer thickness value is added to the correct value of the offset, be it negative or positive.
Offset, like caster, camber, or toe are essentially vector components - each having magnitude and direction.

Bill Verburg

Please do this, you may learn something

Wilder

I did this morning and I also looked up the offset of various aftermarket Porsche wheels. An educational exercise...thanks for the suggestion.

In summary, I've confirmed everything that you guys have said in relation to possible detrimental outcomes of increasing the scrub radius. The question still outstanding is, to what degree?

The information that I found does point to the fact that straying too far from the original offset can result in excessive loading of the front wheel bearings and excess strain on wheel bolts or studs. As far as how far is too far, one page I found suggested that, as a general rule, no more than 12mm.

I also found that various aftermarket wheels with 8x10 measurement had offsets ranging from ET49 to ET61, varying by as much as 9mm from the OEM 8x18 with ET52.

I plan to call Wheel Enhancement on Monday and ask them what they think. Another alternative someone else suggested is widening the rims to 9x18 and using spacers, which would extend the wheel out without changing the steering axis. This sounds like the right way to achieve the goal, I just don't know if it's worth the expense and hassle.

If anyone has experience using spacers on 8x18 fronts or is running aftermarket wheels with an offset other than ET52, could you please provide some feedback?

By the way, I had always wondered what ET stands for and found the answer: ET stands for Einpresstiefe which means "insertion depth" in German.

KOAN

I have 5 mm spacers that I have to use on my Kinesis 8x17 fronts to get them to not rub on my Big Reds. I find that the spacers cause no steering problems. I haven't had them long enough to know if they will hasten the wear on my front bearings. I did put on longer studs, though, to make sure I had adequate thread engagement.
When I put on my 8x18 Turbo twists, I found that I had plenty of room in the wheel well for the 5mm spacer, and used them, front and back ( 10x18 rear)).. No problem with fitment, and no noticable change in handling. FWIW, I am at RS height and have loads of neg. camber. My rear wheel wells are rolled. The tires I am using with the 18s are Hoosiers 245 and 285.

Wilder

Thanks for the feedback Chuck. I spoke to Wheel Enhancement today and from their standpoint, rubbing on the wheel wells is the only issue to be concerned about. I raised concerns regarding changes in steering axis and possible component wear and they did mention that using spacers always increases the rate at which the bearings will wear out but that using spacers in the front would only help neutralize the understeer inherent in our cars.

David in LA

Using spacers would not increase the wear on the bearings or other components any more than if you were to use rims that were not the factory offset, and in many cases the manufacturer made more than one offset available for different optional rims so there is some flexibility to deviate from the norm. My own personal concern w/spacers is whether the additional stress on the wheel (and perhaps spacer) studs are a concern, but since Porsche uses spacer with certain offered rims, it is probably not an issue as long as you use high quality spacers.

My $0.02....

Wilder

My understanding is that your concern is mittigated by installing spacers with longer studs rather than using hubcentric adapters.

David in LA

But doesn't that still result in increased stressed on the studs in the original hubs? If you move the wheels out by using wheels with less offset rather using spacers, the studs have more direct contact whereas with spacers you are introducing one more component and we know that all components move a bit under weight or pressure. Not that I am saying this is unsafe, just that it is possibly less safe than using wheels with less offset.

Bill Verburg

Stock 993 has a srrub radius of -10mm, small variations from this won't be an issue, but a 14mm spacer in the front changes it to +4mm, that will not be good

jimbo3

At what thickness of spacer does one need to use longer studs?

Bill Verburg

When you can't get at least 9 full turns.

14mm bolt x1.5 thread pitch

rkass

LJ, give wheel enhancement a call. They are pretty good with this stuff. That being said, everything discussed above is on point. They won't contradict the guru advice above, just provide some real life data to your setup (hopefully). For me with my offset of 50 using an 8x18 wheel and BBS LMs, a spacer of no more than 6mm would cause no problems based on their running cars with similar wheels. Understand concept of offset, but not enought to do the math, so not sure if this would apply to your 52 ET. Guess my point is 7 may be outside of comfort factor, so be sure you won't upset front end as others above are concerned with.

RallyJon

Really? What's the rationale for that? Is the issue how many threads are needed to support 90 ft-lbs of torque without stripping.

H&R says for M14 x 1.50 you need 7.5 turns for safety. Tirerack says the same thing.