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      03-15-2012, 08:59 PM   #1
kklin
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kklin's Z4 M Coupe for SCCA BSP (road tire)

I'm documenting what will be mostly handling modifications I am making to my 2008 Z4 M Coupe for SCCA BSP. Our Philadelphia region has a local Road Tire PAX for SP cars, so I will be driving street tires again.

Just like the 1998 M3/4 that I ran in AS, BS, BSP, and STU for about 12 years, it will be set up mainly as a reasonably comfortable daily street car with modest autocross intentions. The main concession to a factory setup for autocross is with going to larger front contact patch with more negative camber.

The BSP modifications planned are:
  • 15.2 - Bodywork
    A. Fenders were lightly rolled, just in case. So far this has proven to been unnecessary. (Done - March)
  • 15.3 - Tires
    Front: Dunlop Z1 Star Specs 265/35 18. (Done - March)
    Rear: Dunlop Z1 Star Specs 275/35 18. (Done - July)
  • 15.4 - Wheels
    A. Apex ARC-8 18x9.5 35 on all 4 corners from the recent group buy. (Done - March)
    B. Vorshlag 75mm wheel studs and bolts. (Done - March)
    C. 5mm H&R spacers in front. (Done - March)
    D. 5mm H&R spacers in rear for upgrade to 275 tires (Done - July). No spacers needed for the rear with 265/35 18 (March)
  • 15.5 - Shock Absorbers
    C. AST 4150s are on order. (ETA - March/April)
  • 15.8 - Suspension
    F. Camber plates will be installed along with the ASTs. (ETA - March/April)
My remaining posts will include pictures and details when I can get to them.

Last edited by kklin; 07-15-2012 at 04:32 PM. Reason: July 15 tire update
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      03-15-2012, 09:54 PM   #2
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Tires & Wheels & Spacers

Tires and wheel fitment seems to be one of the most talked about topics on the forums, so I took some photos along the way. As of right now, the car is on OE suspension and alignment, which is quite nice on the street.

225 Continental, OE wheel
Here's what my front 225 Continental DW looks like now, after I bought the car off lease last fall. The dealer had to install fresh front tires and align it. I tried to convince him to leave the worn tires on and just give me the new ones - nope. I tried to convince him to put on DWS (so I could drive it in light snow) - nope.


225 Continental / 265 Star Spec
Here's what my front 225 Continental DW looks like next to the 265/35 18 Dunlop Z4 Star Specs. Notice that not only is the latter wider, it is also shorter (see tire specs at TireRack).



225 Continental, OE wheel - 48.2lb
My front 225 Continental DW on OE wheels with only maybe 3,000 or so miles of wear weighs 48.2lb on my bathroom scale.


255 Continental, OE wheel - 53.2lb
My rear 255 Continental DW on OE wheels with noticeable wear weighs 53.2lbs.


265 Star Spec, Apex ARC-8 - 46.4lb
The new 265 Star Specs with Apex ARC-8 18x9.5 ET35 weighs in at 46.4lb. I am currently running a square set up, for a total savings of 17.2lbs, mostly from the rear.


Front strut rub, so use 5mm spacer
The initial fitment was as-is with OE bolts. The fronts could manage only 2.5 turns of engagement which is not enough. When driven gingerly down the block, I could hear noise from the front. This turns out to be the Star Spec's rim protector brushing aginst the front strut which you can see in the center of this picture as light horizontal wear. I had longer bolts, but they were too long. This is cured by installing Vorshlag 75mm wheel studs and using 5mm H&R spacers I had lying around. I am guessing 3mm spacers would work as well, but I had 5mm on hand.


Rear liner rub, ignore
The rear inner plastic liner which doesn't quite fit flat against metal gets some rubbing (center of picture), but nothing to worry about.


Front with 5mm spacer, OE struts and alignment
Here's what the right front looks like, with OE struts and alignment. They peek out past the plane of fender a bit. Once the ASTs come in, they should visually "fit" nicely with negative camber and a slight drop in ride height.


This set up has been driven on the street and at an autocross last weekend with no issues. Another test and tune coming up this Sunday - too bad I don't have my suspension yet, which in a way is good since this was only my second autocross outing in the car so I get to feel the car out some more. So far I love the torque and the 265s up front definitely help dial out understeer (the first autocross I drove on those skinny full depth Contis). Traction off and Sport on is lots of fun on an autocross course.

Clean runs all!

Last edited by kklin; 03-16-2012 at 07:04 AM. Reason: Corrected weight savings: 17.2
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      03-15-2012, 11:19 PM   #3
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Love the size difference in front. Looks so mean.

See ya on the 25th! (autox)
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      03-16-2012, 10:30 AM   #4
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Great write up and pics!
I never got the OEM weights, so this is very helpful. I am also hoping to run 265/35-18 up front next time around.
Looking forward to your review of AST
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      03-16-2012, 12:11 PM   #5
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Great!... Thanks for this.
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      03-16-2012, 07:34 PM   #6
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Great write-up. I'm right behind you. Hopefully, I'll be slowly adding mods over the course of the next year, working my way from AS to BSP.

So, there's no rubbing in the front with just max "stock" camber? You pull the pins? What camber are you running, btw?

Oh, yeah, that first autox with traction off is Hella fun!

And one more thing, if all your runs were clean, then you weren't pushing it hard enough.
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      03-16-2012, 10:24 PM   #7
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its not his first autox, believe me

or read the first post of the thread
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      03-17-2012, 10:34 AM   #8
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Quote:
Originally Posted by BaldTyres View Post
Great write-up. I'm right behind you. Hopefully, I'll be slowly adding mods over the course of the next year, working my way from AS to BSP.

So, there's no rubbing in the front with just max "stock" camber? You pull the pins? What camber are you running, btw?

Oh, yeah, that first autox with traction off is Hella fun!

And one more thing, if all your runs were clean, then you weren't pushing it hard enough.
I ran my E36 M3 sedan in stock class starting in 2000. While lack of grip up front makes for a safe street car, it just wasn't much fun on an autocross course. So I just to have more fun, I went to BSP, and later to STU when it formed (after getting tennis elbow from tire changes), with pretty much only suspension and wheel upgrades. Sounds like you may be like me.

No rubbing with the modest setup I described above which I've been running for 2 weeks now. No pins pulled. Don't know what my camber is. My car is currently OE, dealer aligned having just been clean up from coming off lease when I bought it last fall. Again, the rubbing was per those two photos, all that I needed to correct it was 5mm spacers up front. Now, keep in mind the photos of the OE and 265/35-18 tire heights and the side shot of my car. If your car is lowered I imagine you may run into issues with the tops of the front rubbing on the fender lips. But if you've lowered your car, you've probably made other suspension modifications that allow you to have more negative camber to avoid this possible issue. Before my studs came in, I lightly rolled all my fenders.

Again YMMV depending upon what *tires* you're running. No way to really find out unless your setup is very close to what someone else has documented. Hopefully the write up and pictures help.

As a matter of course, at autocross I run with traction off, so I don't have a feel for how much the M Coupe intervenes. I've played with the Sport button a few times on the highway and don't have a good feel for that either, so I keep it pressed in at the autocross.
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      03-17-2012, 10:39 AM   #9
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Quote:
Originally Posted by Roffle Waffle View Post
Love the size difference in front. Looks so mean.

See ya on the 25th! (autox)
Yup that difference makes a marked difference in overcoming the street-safe understeer.

Too bad you won't be at tomorrow's test and tune.
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      04-17-2012, 09:34 AM   #10
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Currently working on fitting real BSP tires on the car. I am very surprised that you need a spacer on the front. I have the exact same wheels with 285 Hoosiers and a 3mm spacer and I have no rubbing on strut in the the front at stock ride height. I suppose the width of the stock strut could be greater than the KONI GC strut. Oddly, the rear is the problem. with 18x10 25mm wheels and 285 Hoosiers the problem area is the point where the rear fender meets the rear bumper. CRFINE has given me the bodyshop solution to this but right now I am trying to make it work without modifying the body. At stock ride height and -1.8 camber it is very close....going to bump it to -2.2 and see if it will slide under. Hoping to get this done soon as I really want to see what the car can do with ultimate grip.....
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      04-17-2012, 09:54 PM   #11
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What camber plates do you plan on running?

I'm still trying to look into a set that will give me the camber I want. I was eyeing up on Vorshlag, but never heard of any success stories with them yet.
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      04-18-2012, 07:01 AM   #12
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OP- Nice square set up. I'm surprised to see you say no rubbing. I don't get how you don't have rubbing up front. I had a 255/45 on a 18x9 et38 wheel that rubbed on the fender liner on stock suspension, OE alignment. Must be the lower profile tire you have, but side wall height is not that much different between a 255/40 and a 265/35. Anyway, if it works, it works, I was just surprised given your wheel and tire specs compared to what I had on it that ended up giving me a lot of rubbing issues.
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      04-18-2012, 08:37 AM   #13
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Quote:
Originally Posted by onebluemcm View Post
OP- Nice square set up. I'm surprised to see you say no rubbing. I don't get how you don't have rubbing up front. I had a 255/45 on a 18x9 et38 wheel that rubbed on the fender liner on stock suspension, OE alignment. Must be the lower profile tire you have, but side wall height is not that much different between a 255/40 and a 265/35. Anyway, if it works, it works, I was just surprised given your wheel and tire specs compared to what I had on it that ended up giving me a lot of rubbing issues.
I might have had very slight rubbing on the front liners.

Here's the math for theoretical sidewall height for your tire and mine ...
25.5 cm * 0.40 = 10.2 cm
26.5 cm * 0.35 = 9.275 cm

So the theoretical sidewall difference is 0.925 cm. To convert cm to inches, divide by 2.54 cm/in yielding a 0.364 inch shorter sidewall height.
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      04-18-2012, 08:56 AM   #14
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Quote:
Originally Posted by Kgolf31 View Post
What camber plates do you plan on running?

I'm still trying to look into a set that will give me the camber I want. I was eyeing up on Vorshlag, but never heard of any success stories with them yet.
I will most likely get Vorshlag plates when they ASTs I am getting through them come in (to the US).

My OE setup/alignment with the slight tire/wheel mods above is surprisingly adequate at autocross. After first run warm up, it's the rear that needs more grip and constant attention (I've been driving with traction off and sport on). Unfortunately the Star Specs do not run wider than 275 which is only 1cm wider (but heavier) than my 265. I would otherwise consider trying a 285 or wider in the rear after my suspension comes in.
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      04-18-2012, 03:38 PM   #15
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I have no idea how you race that with sport mode on man...

btw, I'll be away down south for event #2 in dover, but will attend the novice classes the following week
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      04-18-2012, 07:05 PM   #16
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Quote:
Originally Posted by Roffle Waffle View Post
I have no idea how you race that with sport mode on man...
I've been autocrossing, though just locally, for something like 15 years.
Quote:
Originally Posted by Roffle Waffle View Post
btw, I'll be away down south for event #2 in dover, but will attend the novice classes the following week
I probably won't know until the last moment if I can the event. You will have a great time at the school - great ROI.
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      04-18-2012, 07:15 PM   #17
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Quote:
Originally Posted by kklin View Post
I will most likely get Vorshlag plates when they ASTs I am getting through them come in (to the US).

My OE setup/alignment with the slight tire/wheel mods above is surprisingly adequate at autocross. After first run warm up, it's the rear that needs more grip and constant attention (I've been driving with traction off and sport on). Unfortunately the Star Specs do not run wider than 275 which is only 1cm wider (but heavier) than my 265. I would otherwise consider trying a 285 or wider in the rear after my suspension comes in.
Let me know how you like them and how they work out.

Quote:
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I have no idea how you race that with sport mode on man...
+1

Too sensitive for me. I can't modulate the gas too well.
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      04-18-2012, 09:08 PM   #18
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I have the vorshlag plates with ASTs and I have no complaints. No creaking or weird spring noise like I used to get from my gc plates. I would recommend not going with their spherical rsms though for a street car, those things things rattle like crazy over bumps.....
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      04-18-2012, 09:13 PM   #19
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Quote:
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I have the vorshlag plates with ASTs and I have no complaints. No creaking or weird spring noise like I used to get from my gc plates. I would recommend not going with their spherical rsms though for a street car, those things things rattle like crazy over bumps.....
Easy to install and change settings?

Reason I'm asking, is that I'm running different street tires and track tires. I want to run -3.0 on track but keep OEM specs on street for DD. I figure I would zero my plates out at DD specs and then mark them for -3.0 and change while i change tires.
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      04-19-2012, 05:02 AM   #20
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Quote:
Originally Posted by Kgolf31 View Post
Easy to install and change settings?

Reason I'm asking, is that I'm running different street tires and track tires. I want to run -3.0 on track but keep OEM specs on street for DD. I figure I would zero my plates out at DD specs and then mark them for -3.0 and change while i change tires.
Install was fine, we'll see how they are as far as adjusting and accurately switching between settings. I installed these over the winter and just guessed at around -2 to start so i really havent played with them much. We'll see how things go at the first hpde in two weeks...
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      06-16-2012, 10:55 AM   #21
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Reference photos for 75mm studs

Reference photos for 75mm studs

One of my rear Apex wheels broke last week at an autocross incident, so I currently have a mix of wheels on my car while waiting for the replacement. I took photos of the 75mm studs on the OE rear wheel, and the Apex wheel with a 5mm spacer. Note how the OE wheels are recessed, hiding much of the 75mm while the Apex does not.

75mm stud with rear OE wheel ...


75mm stud with front Apex wheel and 5mm spacer ...


Since the tire on the broken wheel is probably scrap, I am decided to go to 275 Star Specs in the rear and leaving the current 265 up front.

Last edited by kklin; 06-16-2012 at 11:06 AM.
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      06-17-2012, 10:33 AM   #22
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Thanks for the pictures man, much appreciated.

Let me know if you rub in the rear with 275s. I'm running 265 RS3s (stock wheels, no spacers) and I rub on my inner fenders during high G-Turns.

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