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      10-16-2017, 03:30 PM   #1
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Talking B Street final tire selection

(I have subsequently decided on tires, down the thread a bit)

Should I use 265-35-18 or 275-35-8 Rear tire on the stock wheel for autocross? Smallish course with slow corners.

In an RE71R both are a 9.5 measured rim. I was tending toward the 265 for the smaller diameter and faster out of the hole and can lower the car more later.

For front I was headed 245-40-18 as I was looking for the best tire to reduce understeer on the stock suspension

Experiences?

Last edited by Over it; 10-25-2017 at 06:45 PM..
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      10-17-2017, 04:26 AM   #2
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I could really use tire size advice of folks experienced in autocrossing the Z4MC.
I'm super excited to hop in such a light car. The tire will be the RE71R


I have been running my MKIV Supra on 12 year old RA-1s massaged with Formula V.
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      10-17-2017, 05:47 PM   #3
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Not really familiar with your car/tire, but wouldn't you want a square setup if you're trying to reduce understeer?
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      10-17-2017, 06:49 PM   #4
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Quote:
Originally Posted by joelselman View Post
Not really familiar with your car/tire, but wouldn't you want a square setup if you're trying to reduce understeer?
You can eliminate understeer and actually transition to an oversteer condition if you go skinny enough on the rear tires. The problem though is that while you now have over steer you may be significantly slower because you've reduced overall grip.

Quote:
Originally Posted by in2twins View Post
Should I use 265-35-18 or 275-35-8 Rear tire on the stock wheel for autocross? Smallish course with slow corners.

In an RE71R both are a 9.5 measured rim. I was tending toward the 265 for the smaller diameter and faster out of the hole and can lower the car more later.

For front I was headed 245-40-18 as I was looking for the best tire to reduce understeer on the stock suspension

Experiences?
The RE71's have extremely stiff sidewalls and in my experience they don't like much pinch fit. I had 275/35 x 18 on 18 x 8.5 wheels and the pinch fit coupled with the very stiff side walls caused the shoulders of the tire to be very rounded. I dropped down to 265/35 x 18 and actually get about 5 mm more contact patch width.
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      10-18-2017, 04:26 AM   #5
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Wondering if I should have ordered 5mm spacers for the front???

I ended up ordering 18x9.5 ET35 Apex PS-7 with PSS 265-35-18 square.
12mm spacers in the rear
No spacer in the front.
75mm studs
This will be my street set-up.



I am looking for input on the best way to adjust the front camber without plates. I.E. Turner, H&R or?

Thanks,

Last edited by Over it; 11-23-2017 at 07:47 PM..
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      10-18-2017, 04:44 AM   #6
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Quote:
Originally Posted by in2twins View Post
Wondering if I should have ordered 5mm spacers for the front???

I ended up ordering 18x9.5 ET35 Apex PS-7 with PSS 265-35-18 square.
12mm spacers in the rear
No spacer in the front.
75mm studs
This will be my street set-up.



I am looking for input on the best way to adjust the front camber without plates. I.E. Turner, H&R or?

Thanks, Carl
Go with the Turner bolts and shims, or see if the Bimmer World E36 camber shim kit will fit. You'll get much more camber shimming the lower mounting points than you will with the smaller "camber bolts" that go into the upper mount point. They typically only give you about +/- 0.25 degrees adjustment.
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      10-18-2017, 06:13 AM   #7
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Quote:
Originally Posted by dc_wright View Post
Go with the Turner bolts and shims, or see if the Bimmer World E36 camber shim kit will fit. You'll get much more camber shimming the lower mounting points than you will with the smaller "camber bolts" that go into the upper mount point. They typically only give you about +/- 0.25 degrees adjustment.
Thanks, I have some questions:

What is the length and thread pitch for the bolts?
I imagine these are grade 10.9?


So, with pins removed how many washers did you shim by? I realize this is not a substitute for a proper alignment but if I bring it in close the local alignment folks won't struggle so much.

Do I need a spacer in front to clear the stock suspension or is it to move the wheel out the same distance as the rear?

I would just figure it out but I don't have a car yet...I'd like to have the necessary parts on hand as getting stuff to Hawaii can be expensive if I have to rush.

Thanks for your help.

Last edited by Over it; 11-23-2017 at 07:47 PM..
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      10-18-2017, 09:54 PM   #8
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With stock suspension I had to add a 5mm spacer at the front for my 18x9.5 PS7s. It was touching the strut otherwise. Running 255/35 tires.
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      10-19-2017, 02:40 AM   #9
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Quote:
Originally Posted by mtnbkr View Post
With stock suspension I had to add a 5mm spacer at the front for my 18x9.5 PS7s. It was touching the strut otherwise. Running 255/35 tires.
Understood.

I still am looking for best tires sizes on stock wheels and within the limits of stock suspension.

Thanks
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      10-20-2017, 03:46 AM   #10
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Quote:
Originally Posted by in2twins View Post
Understood.

I still am looking for best tires sizes on stock wheels and within the limits of stock suspension.

Thanks
So I have opted for 265-35-18 rear and 235-40-18 front RE71R.
We shall see.

Now on to the suspension.
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      10-20-2017, 05:30 PM   #11
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Quote:
Originally Posted by in2twins View Post
Thanks, I have some questions:

What is the length and thread pitch for the bolts?
I imagine these are grade 10.9?


So, with pins removed how many washers did you shim by? I realize this is not a substitute for a proper alignment but if I bring it in close the local alignment folks won't struggle so much.

Do I need a spacer in front to clear the stock suspension or is it to move the wheel out the same distance as the rear?

I would just figure it out but I don't have a car yet...I'd like to have the necessary parts on hand as getting stuff to Hawaii can be expensive if I have to rush.

Thanks for your help.

Carl
It's a bit of an experimental process. As you add shims it moves the top inside of the tire closer to the spring perch on the strut. Depending on wheel offset, tire size, and lowering, the tire may or may not interfere with the lower spring perch. If you're alignment is pretty good when you start and you use same thickness spacers on each side, then you should be pretty close for the final alignment check.
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      10-20-2017, 09:29 PM   #12
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I figured. I have sheet aluminum 1mm thick that I have fabricated into temporary wheel spacers to get precise figment. I ordered 3 & 5mm spacers for the front and a 12mm for the rear. Once it is dialed I will use a 1 piece spacer.
If anyone is willing to pm me the bolt length for the shim I can get them and various washers locally. Otherwise I'll order from Turner.
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      10-25-2017, 03:33 PM   #13
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Quote:
Originally Posted by in2twins View Post
Wondering if I should have ordered 5mm spacers for the front???

I ended up ordering 18x9.5 ET35 Apex PS-7 with PSS 265-35-18 square.
12mm spacers in the rear
No spacer in the front.
75mm studs
This will be my street set-up.



I am looking for input on the best way to adjust the front camber without plates. I.E. Turner, H&R or?

Thanks, Carl
Just so we are clear... The square fitment you chose with the wheels means you go to BSP not BS. You are only allowed a .5" width change on the wheel width to stay in BS. Moving up an inch in front moves you to B Street Prepared.
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      10-25-2017, 06:37 PM   #14
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Quote:
Originally Posted by Jackal View Post
Just so we are clear... The square fitment you chose with the wheels means you go to BSP not BS. You are only allowed a .5" width change on the wheel width to stay in BS. Moving up an inch in front moves you to B Street Prepared.
There's ZERO width change allowance from OEM for Street classes. You can change diameter +/- 1 inch from OEM, and offset can change within a +/- 7mm range, but that's it.
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      10-25-2017, 06:39 PM   #15
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Quote:
Originally Posted by in2twins View Post
I figured. I have sheet aluminum 1mm thick that I have fabricated into temporary wheel spacers to get precise figment. I ordered 3 & 5mm spacers for the front and a 12mm for the rear. Once it is dialed I will use a 1 piece spacer.
If anyone is willing to pm me the bolt length for the shim I can get them and various washers locally. Otherwise I'll order from Turner.
I have run the stock wheels with 235/265 RE01R/RE11s and you will fit with out any spacer. The 235 is still a bit narrow especially for an AX course. You really need a 245 or larger or front to dial out the natural understeer this chassis seems to have at slow speed. The issue is when you step up to a 245 you start running into fitment issue but not because of width but more overall diameter of the tire. I find out of all the various tires sizes I have run an overall diameter of about 25.5-25.8" is the max you can run up front to be able to fit and not rub too terribly on the corner where the front fender meetings the bumper. My favorite when I was running the stock wheels was the 255/35/18f 275/35/18 set up. Some would argue the front tire is too wide for the rim but on an AX course I don't think it matters. The addition of overall grip is worth the downsides. On a track I would comment differently.

Overall width of the tire for this car completely depends on the suspension you are running and the amount of clearance said suspension gives you on the strut side. On my car with GC coils the max I can run up front is 275 on a 9.5 rim. I would love the 10" rim but it is just a tad too big. A buddy ran a 10" rim on the front of his coupe with Motion Control coilovers but he also did some pulling and rolling to the front fenders

I am currently running 275 square RE71s on
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      10-25-2017, 06:40 PM   #16
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Quote:
Originally Posted by Jackal View Post
Just so we are clear... The square fitment you chose with the wheels means you go to BSP not BS. You are only allowed a .5" width change on the wheel width to stay in BS. Moving up an inch in front moves you to B Street Prepared.
The Apex set-up is for the street (not competition). For competition I will be on stock wheels with RE71Rs 265-35-18/235-35-18. The Turner bolts will not be used in the competition set-up.

I am still mentally putting together my B-Street suspension. To that end, I am working separately with both Ground Control and TC Kline on two different B-Street legal comprehensive solutions.
I would love to here about the experience of others in this endeavor.

Thanks,

Last edited by Over it; 11-23-2017 at 07:48 PM..
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      10-25-2017, 06:42 PM   #17
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Quote:
Originally Posted by dc_wright View Post
There's ZERO width change allowance from OEM for Street classes. You can change diameter +/- 1 inch from OEM, and offset can change within a +/- 7mm range, but that's it.
Yes, ^^^^^
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      10-25-2017, 09:21 PM   #18
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Quote:
Originally Posted by in2twins View Post
The Apex set-up is for the street (not competition). For competition I will be on stock wheels with RE71Rs 265-35-18/235-35-18. The Turner bolts will not be used in the competition set-up.

I am still mentally putting together my B-Street suspension. To that end, I am working separately with both Ground Control and TC Kline on two different B-Street legal comprehensive solutions.
I would love to here about the experience of others in this endeavor.

Thanks, Carl Byck
My car is a 3.0si Roadster that started with the M Sport suspension. Current setup is Koni Sport struts/shocks, H&R front sway with Ground Control adjustable end links. Still running the M Sport springs. Wheels are stock Style 108 at 18x8 front, 18x8.5 rear. I'm currently running Hankook RS-4s, 245/40 x 18 front, 265/35 x 18 rear. I was running same size RE71s and decided to give the Hankook's a try. They're a good choice for a lower cost tire but they're a tick off the RE71s. Just got delivered today a set of Flow One Race Spec F2 wheels. 18x8 ET40 for the front, 18x8.5 ET42 for the rear. Going to run 245/40 RE71s in the front and 265/35 RS4s in the rear since they've done fine there. The new wheels with the 265/35 tires will be my track day fronts so I'll have a square set of 265s for the track.
I won B Street locally last year and again this year with the car, but just barely. At state championships it's taken a 5th and a 3rd. At a national tour event I don't think I could trophy with it in B Street, but I may run a couple events in 2018 since non-M Z4s will likely move to C Street next year. I'll have to see how it fares against ND Miatas which will likely be the majority of the competition in that class.
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