Porsche Brembo 996 BBK conversion

[Tbonem3]

I don't get it mainstreamer. What you're essentially saying is that people with zcp wheels (let alone csl with lower offset) don't even need any spacer at all? Maybe your fronts really are CSL, not zcp?

[mainstreamer00]

I don't get it mainstreamer. What you're essentially saying is that people with zcp wheels (let alone csl with lower offset) don't even need any spacer at all? Maybe your fronts really are CSL, not zcp?

All I'm saying is that from my experience in running this setup, after having asked the question about clearance, many members recommended running MINIMUM 15-18mm spacers in order for the wheels to clear.
I originally purchased 18mm front spacers (huge clearance), down to 12mm (current, still plenty of clearance but this pushes the wheels out to a good offset).
Even with the 12mm current spacers (see previous post), there is a very decent gap left.
I'm not saying that this setup does not need spacers to clear, but my experiences would indicate that the spacer size actually needed is far less than what people have recommended me (and others) in the past.
Wheels are confirmed ZCP as well.

Not to discredit anybody's input or experiences, and I very much value and appreciate the help that you and others have given here. Regardless, I would recommend anybody to take measurements from their personal cars, and to calculate from there. It is recommended to run at least 6mm clearance between spoke/caliper to be conservatively safe. 👍

[sdmcoupe]

Any chance instructions on how to splice the BMW brake wear sensor to the Porsche ones properly?

[Tbonem3]

It's only 2 wires, so should be very simple. Just make a circuit I think. Cut off the white porsche harness, splice together (butt connectors/heat shrink) those two wire to your bmw harness.

[Tbonem3]

Regardless, I would recommend anybody to take measurements from their personal cars, and to calculate from there. It is recommended to run at least 6mm clearance between spoke/caliper to be conservatively safe. 👍

I'll try to measure the space between my 8.5" et22 (32-10mm spacer) wheel so we can reverse calculate what's needed.

EDIT: Ok, just measured with micrometer. The closest part of the spokes to the most outboard part of the caliper. Now, my wheels are reps, so maybe csl and zcp' spokes are slightly different? Probably not by much at all.

Anyway, I got 17mm. That's from et22. So, theoretically, an 8.5" et 38 wheel would have a 1mm gap. CSL wheels are et44, so they would theoretically need 3mm spacer, but that would be very tight, so 5 or 10mm would be better.

I still don't understand how mainstreamer and I can have a very similar gap right now (a finger/ fat finger), when my wheels' offsets are so much lower, and we run a very similar spacer (10mm vs 12mm).

Only thing I can think of is that, in your photo mainstreamer, your finger is on a part of the spokes that comes outward a bit. Your spokes get closer to the calipers as you get closer to the hub.

I know I'm going to be mounting true CSL wheels on a car with 996 brakes in the near-ish future, so we'll know definitively then. I'll take pics.

[repoman89]

Oh, we might have forgotten to calculate for the difference in width between CSL and ZCP. It's not just their difference in offset 47->44, but zcps are 12.5mm narrower, so 6.25mm (from midline) plus the 3mm between csl/zcp = 9.25mm difference. That is, to get the same distance from strut and brakes, a zcp wheel would need a 10mm spacer to match CSL.

I'll try to measure the space between my 8.5" et22 (32-10mm spacer) wheel so we can reverse calculate what's needed.

EDIT: Ok, just measured with micrometer. The closest part of the spokes to the most outboard part of the caliper. Now, my wheels are reps, so maybe csl and zcp' spokes are slightly different? Probably not by much at all.

Anyway, I got 17mm. That's from et22. So, theoretically, an 8.5" et 38 wheel would have a 1mm gap. CSL wheels are et44, so they would theoretically need 3mm spacer, but that would be very tight, so 5 or 10mm would be better.

ZCP has offset of 47, but add in 6.25mm due to being half inch narrower. That means 9.25mm greater than what CSL would need. So if CSL just clears with 5mm spacer, then ZCP would need 15mm spacer (9.25 + 5 = 14.25)

He said he’s running ZCPs though. I got the same 10 mm difference as you between ZCPs and CSLs but if he’s running ZCPs with a 12mm spacer and has 15mm of clearance, CSLs would have 13mm clearance with no spacer at all

[Tbonem3]

You know what, I just realized, we don't need to take the wheels' widths into consideration. That's only for the edge of the wheel kissing the strut or outer fender. We only care about the hub and spokes!

Ok, so while a ZCP wheel would need a 10mm spacer to "look" like a CSL wheel, mounted, it doesn't need 10mm spacer to clear brakes the same as CSL.

Starting over, CSL wheel is 3mm more aggressive than ZCP (at the hub!) So whatever spacer ZCP wheels need, CSL would need 3mm less. I think that's why people say 18mm for ZCP and 15mm for CSL. Makes sense to me.

Now I want to find out if the 15/18 really is that needed. My guess is 12/15 is good. Mainstreamer's input suggests it's not. But his exp and mine don't jive too well, so I still want to do some measurements. My wheels are reps, so maybe we shouldn't take my personal "gap" and apply it to real OE wheels.

Bottom line, right now, if I had zcp/csl wheels doing this conversion, I'd have some 10, 12 and 15mm spacers ready to go! I think 18mm is probably too much.

[repoman89]

My wheels, without spacers, are 12mm more aggressive than CSL wheels. If CSLs had 13mm clearance without spacer, that would mean I'd have 25mm! An inch! No way lol. Now add in my 10mm spacer, and I have 35mm of clearance?

I'm just going by mainstreamer00's 15mm of clearance with a 12mm spacer on ZCPs that are inset 10mm compared to CSLs. Maybe your spokes are different?

[repoman89]

You know what, it's the other way. The 6.25mm from midline doesn't add to the offset, it detracts. So ZCP wheels are actually 3.25mm further away from the calipers than CSL!

This simple math confuses the hell out of me too lol. I put it in a calculator last night and got the same 9mm further away from the calipers result that you got earlier for CSL vs ZCP. https://www.1010tires.com/Tools/Whee...et-Calculator#

[repoman89]

You know what, I just realized, we don't need to take the wheels' widths into consideration. That's only for the edge of the wheel kissing the strut or outer fender. We only care about the hub and spokes!

Ok, so while a ZCP wheel would need a 10mm spacer to "look" like a CSL wheel, mounted, it doesn't need 10mm spacer to clear brakes the same as CSL.

Starting over, CSL wheel is 3mm more aggressive than ZCP (at the hub!) So whatever spacer ZCP wheels need, CSL would need 3mm less. I think that's why people say 18mm for ZCP and 15mm for CSL. Makes sense to me.

Now I want to find out if the 15/18 realy is that needed. Mainstreamer's input suggests it's not. But his exp and mine don't jive too well, so I still want to do some measurements. My wheels are reps, so maybe we shouldn't take my personal "gap" and apply it to real OE wheels.

Quoting the third edit! This makes sense to me, but add in the fact that ZCP/CSL spokes go from the hub to the edge of the wheel and the real equivalent spacer for the purposes of a brake kit will be somewhere in between 3mm (at the hub) and 10mm (at the end of the spokes) since the brakes live in between. Based purely on the fact that the calipers are pretty far from the hub I'd guess somewhere between 6-8mm difference for clearance.

[Tbonem3]

Ya I see what you're saying, but 6-8mm for CSL or ZCP?

[repoman89]

Ya I see what you're saying, but 6-8mm for CSL or ZCP?

What I meant was that if a 12mm spacer gives 15mm clearance for ZCP wheels as mainstreamer00 suggests, then I'm guessing that a 4-6mm spacer (12 minus 6-8mm) would give 15mm of caliper to spoke clearance for CSLs. Really depends on the exact geometry and shape of the spokes at the radial distance from the hub that the calipers live in. It's complicated and now I don't feel too bad for not being able to figure it out.

[bassel_sy]

Yes. csl wheels or zcp though? Fronts are different. Rears are no issue either way (no spacers needed).

ZCP, im literally trying to run the identical setup as mainstreamer. 996 with RR brackets , on ZHP wheels. spacers are 12 in the front at 10 in the rear w/ 75mm race stud. Per mainstreamer hes has clearence no prob. just wanna make sure so i can swap these spacers out before they get here.

[Tbonem3]

If you end up coming to me for the install, I have extra sets of spacers (3, 5, 10, 12, 15) on hand. But it sounds like you're going to be just fine.

[mainstreamer00]

^ that 15mm I quoted was a total guesstimate ;}
My finger could be smaller/fatter

Good discussion either way, as running a spacer on front ZCP/CSL wheels is probably needed as the fender still has room to play.