Can anyone help answer this question:
What is the longest wheel lug bolt that can be used in the rear without hitting anything (like the e-brake)? i.e. Could someone use bolts designed for 15mm spacers on a wheel with 7mm spacers?

all the good quality studs have a shoulder on them so that the stud bottoms out in the hub, so you don't have to worry about what is behind the hub. You can use as long of a stud as you like

You cannot use as long a stud as you like, so I'd recommend ignoring that advice. You have a good question. I'm only answering because it seems no one else has offered any reasonable input yet.

8mm (roughly 5/16") longer is long enough to wonder if it will cause problems, especially if it turns out the 15mm spacer's bolts are already a little long. This may have occurred if the spacer manufacturer decided to use a longer bolt than the minimum required since bolts don't come in every possible mm of length. So what I'm trying to say if that when compared to the OEM bolts and their 28mm shank, these bolts could have a longer shank length than 43mm (28+15) since they would have rounded up to the next available bolt size.

The bottom line for me is I would not recommend it unless someone comes up with what the true limits are. If you do proceed, before moving the car you could put the rear wheels up in the air with the car in neutral (properly chocked of course) and gently turn the wheels after installation to see if there is any sign of them striking something. Of course, that assumes that you didn't hit something and break it when tightening down the bolts in the first place.

It might be worth some peace of mind just to get the recommended bolt length for 7mm spacers (35mm shank or the next size up; or 52mm (45mm + 7mm) for bolts that are measured using the full bolt shaft length. At a quick look, you could get the correct length at some vendors for around $60 for 10 bolts, or you could splurge and get the nice titanium ones all around for around $300 at World Motorsports.

Hi Stormrune, thanks for the warning. Probably just not worth the risk. The trouble is that I can't find any 52mm bolts that match the stock appearance. Some are zinc plated = wrong finish and hard to paint. H&R apparently changed their design, and there's no longer the "dimple" in the center (just a flat bolt head). Looks like I'm going titanium from World Motorsports. Thanks!

you can get any kind of bolts on ebay. you can put wheels w/bolts on and turn the wheels around, see if anything is hitting. Its very distinct. then try it with the handbrake also.

I opted for the titaniums as well, their price made it a reasonable stretch in my mind. You'll find photos of the ones I got for use with 5mm spacers in post 73 here: https://rennlist.com/forums/997-foru...olts-5.html#73

I dare you to find studs that don't have a shoulder.
I had 90 mm studs laying around, and i test fit them without any spacers at all.

how are you supposed to screw these in far enough to interfere with the parking brake?

nvm, you are talking about bolts
I only use studs

Oh, I see! Now your first post makes complete sense. Sorry Dan, I should have noticed you said stud at first too. As soon as you said something about 90mm studs over on 6speed I figured out what you must have meant.

I can't give you a quantitative measurement, but I can tell you that you can go with too long a wheel bolt. It partially depends on the thickness of the wheel mounting flange where the lug bolt attaches, and this is not the same on all wheels, not even all OEM Porsche wheels. My wife has GT3 wheels on her C2S and it had originally come with Sport Design wheels. We swapped the sport designs back to her car temporarily and the new bolts we had bought for her to use on the GT3 wheels were slightly longer than the stock OEM ones. After torquing them down and starting to drive off, there was a distinct clicking noise as the wheel rotated. We found the original bolts that she had run with the SD wheels, put those back in and the noise was gone. So I don't know what the slightly longer bolts we coming in contact with, but it was something.

The GT3 lug bolts (marked with "GT" on the head) were meant to be used with 5mm spacers, hence the extra length. As someone suggested the wheels can be mounted with longer bolts and then the wheels hand turned to see if there is any interference. You wouldn't think 5mm would make a difference but obviously in your case it did. I'd be interested to also know what the bolts were hitting.

I can't recall if the noise was from the front or rear wheels. If the rear I'm guessing something that was part of the parking brake shoe assembly. At the time, I didn't investigate further as to the cause, just that changing the bolts made the noise subside.