Suggested Mods for autocross

[Bossdog]

My 2006 Z4M will be my 4th car to autocross, a couple of Mustangs and an STi previously.
I am looking for suggestions on hardware upgrades (primarily Suspension). I know this car is pretty good stock and I not looking to burn a bunch of cash nor Compete Nationally.

I will be ordering some Apex Arc 8's 18 x 8.5 / 9.5. to get rid of those heavy stock beasts. I don't want to get into rubbing or rolling fenders. Any other conservative wheel size combinations suggested?

What about front and rear stabilizers bars, Coil overs (that won't break the bank) and/or springs.
If I have to choose between comfort of ride and 1/2 second at AutoX, I'll always choose comfort! (my wife loves driving this car too!)

Thanks for any input

[dc_wright]

Before you make any mods or even any tire/wheel changes, you need to figure out who you're going to autocross with and what class you want to run in. As an example, the SCCA is pretty restrictive on wheels if you're going to stay in Street class, you can change diameter +/- 1" but you can't increase the width at all.

[Bossdog]

Originally Posted by dc_wright

Before you make any mods or even any tire/wheel changes, you need to figure out who you're going to autocross with and what class you want to run in. As an example, the SCCA is pretty restrictive on wheels if you're going to stay in Street class, you can change diameter +/- 1" but you can't increase the width at all.

You are correct! I will be running mostly with SCCA.
However, I'm not really concerned about what class I run in. I intend to mod as I like and run in what ever call I end up in. If a Mod will improve handling with reasonable cost and not degrade the Daily Driver aspect, I'm likely to do the Mod despite its consequences to the class I run in.

[Kgolf31]

I personally suggest you stick within the Street Class, as any other mods will bump you to an competitive class. And whether you say it or not, you will not enjoy it once you see yourself getting beat.

You can get dual adjustable suspension that can adjust rear rebound/compression on OEM Perches, so you won't compromise daily driving.

Exhaust, 17x8 and 17x9 wheels on a 245/275 setup. Exhaust and front swaybar.


Trust me, been here done that. Tried to mod my 128i for STX and make it a daily driver, didn't happen. I have headers and an exhaust that rattles the cabin, springs that makes the car ride rough, Recaro seats...etc etc.

[Bossdog]

Originally Posted by Kgolf31

I personally suggest you stick within the Street Class, as any other mods will bump you to an competitive class. And whether you say it or not, you will not enjoy it once you see yourself getting beat.

Thank you for your input, it is appreciated.

Regarding not enjoying getting beat; it may provide insight knowing my first autocross vehicle was a 2001 V6 Mustang convertible, ( G Stock) possibly the worst AutoX platform to start from of any. When I added a Cold air intake I went into STX. 3200 LBS, 167 hp to the wheels and a live axel with no panhard par and I still had a ton of Fun. There is always a "meathead" in every class with a ton of car and no driving skill that is fun to beat!

I'm looking forward to throwing around the Bimmer, in any classification

Do you have a brand of 2-way Coilover you would recommend?
I'm not inclined to spend $3K on a KW or TC kline set up. Is the H&R set up for $1,200 an improvement over stock? I may be willing to spring for $1200 (Pun intended)

[The HACK]

So...you're looking to mod for mod sake, not for autocross sake.

In that case, it's all about what you want to spend, not what you want to achieve. IF that is the case, you picked a very poor chassis. Because if you don't want to spend a lot, you won't get a lot on this car.

There's nothing you can spend south of $3,000 that will be a significant enough improvement over stock to justify it, IMO. You wanna go have fun and toss the car around? The MZ4 Coupe is far more "toss-able" in bone stock mode than $1,200 worth of coil-overs will give you in return.

[Kgolf31]

Originally Posted by Bossdog

Thank you for your input, it is appreciated.

Regarding not enjoying getting beat; it may provide insight knowing my first autocross vehicle was a 2001 V6 Mustang convertible, ( G Stock) possibly the worst AutoX platform to start from of any. When I added a Cold air intake I went into STX. 3200 LBS, 167 hp to the wheels and a live axel with no panhard par and I still had a ton of Fun. There is always a "meathead" in every class with a ton of car and no driving skill that is fun to beat!

I'm looking forward to throwing around the Bimmer, in any classification

Do you have a brand of 2-way Coilover you would recommend?
I'm not inclined to spend $3K on a KW or TC kline set up. Is the H&R set up for $1,200 an improvement over stock? I may be willing to spring for $1200 (Pun intended)

Lol I'm with you. My first was a E46 325xi with All-Season Tires, a CAI and wider wheels which bumped me into STX as well.


I run TCKline. Honestly a 2-way is going to be pimp money. I don't know if there are any single adjustable shocks that can be used with OE Perches, at least a couple years ago that wasn't the case.

I have no experience with H&R.

[Kgolf31]

Originally Posted by The HACK

So...you're looking to mod for mod sake, not for autocross sake.

In that case, it's all about what you want to spend, not what you want to achieve. IF that is the case, you picked a very poor chassis. Because if you don't want to spend a lot, you won't get a lot on this car.

There's nothing you can spend south of $3,000 that will be a significant enough improvement over stock to justify it, IMO. You wanna go have fun and toss the car around? The MZ4 Coupe is far more "toss-able" in bone stock mode than $1,200 worth of coil-overs will give you in return.

Completely agreed.

Front bar, RE-71Rs and it'll be a hoot.

[Bossdog]

Originally Posted by The HACK

So...you're looking to mod for mod sake, not for autocross sake.

In that case, it's all about what you want to spend, not what you want to achieve. IF that is the case, you picked a very poor chassis. Because if you don't want to spend a lot, you won't get a lot on this car.

There's nothing you can spend south of $3,000 that will be a significant enough improvement over stock to justify it, IMO. You wanna go have fun and toss the car around? The MZ4 Coupe is far more "toss-able" in bone stock mode than $1,200 worth of coil-overs will give you in return.

Based on my research, I kind of thought that was the case. The Z4M is put together pretty well. I'll put some light weigh rims and RE-11's on and go with that. If I get the urge to get really competitive after a season or 2, perhaps I'll pony up the $3K for some coilovers.

Thanks for everyone's input!

[Kgolf31]

Originally Posted by Bossdog

Based on my research, I kind of thought that was the case. The Z4M is put together pretty well. I'll put some light weigh rims and RE-11's on and go with that. If I get the urge to get really competitive after a season or 2, perhaps I'll pony up the $3K for some coilovers.

Thanks for everyone's input!

IMO - Really competitive is building the car for Street Class.

After that there is no Street Touring Classing for the car, as production model is low...and it goes into BSP IIRC to die against the other cars in that class. At that point you're cutting fenders and ripping out AC

Have fun. The new crop of street tires are insane compared to last year

[dc_wright]

Originally Posted by Kgolf31

IMO - Really competitive is building the car for Street Class.

After that there is no Street Touring Classing for the car, as production model is low...and it goes into BSP IIRC to die against the other cars in that class. At that point you're cutting fenders and ripping out AC

Have fun. The new crop of street tires are insane compared to last year

^This^

For some unfathomable reason the SCCA thinks all Z4's are equal in Street class and everything from the 2.5 to the M are all packed into B Street, but for Street Touring they exclude the M so B Street Prepared is the next available class.

Originally Posted by Bossdog

Based on my research, I kind of thought that was the case. The Z4M is put together pretty well. I'll put some light weigh rims and RE-11's on and go with that. If I get the urge to get really competitive after a season or 2, perhaps I'll pony up the $3K for some coilovers.

Thanks for everyone's input!

The Z4M will serve you well in Street class at most local events. At regional or national events the Z4 is at a technical disadvantage to most of the other cars in the class so expect mid pack finishes at best. If as you stated earlier you'll just drop into whatever class you fall into, then get whatever rims you want and tire sizes that go with them, but get the RE71's not the RE11's. The 71's have better grip at lower temps and are a much better auto cross tire. The stock M suspension is pretty good already, but a stiffer front sway will help a bit and you absolutely want to get the Bimmer World camber shim kit and dial in about -2.5 degrees of camber up front. Getting some neg camber in the front will help tame the severe under steer of the Z4 and make a world of difference in how the car handles. Since the Z4M strut mount is the same as the E36 M3 you can use the shims to add neg camber. Can't do that on any of the other Z4's and the shim kit is much less expensive than installing camber plates.

[Bossdog]

Originally Posted by dc_wright

^This^

For some unfathomable reason the SCCA thinks all Z4's are equal in Street class and everything from the 2.5 to the M are all packed into B Street, but for Street Touring they exclude the M so B Street Prepared is the next available class.



The Z4M will serve you well in Street class at most local events. At regional or national events the Z4 is at a technical disadvantage to most of the other cars in the class so expect mid pack finishes at best. If as you stated earlier you'll just drop into whatever class you fall into, then get whatever rims you want and tire sizes that go with them, but get the RE71's not the RE11's. The 71's have better grip at lower temps and are a much better auto cross tire. The stock M suspension is pretty good already, but a stiffer front sway will help a bit and you absolutely want to get the Bimmer World camber shim kit and dial in about -2.5 degrees of camber up front. Getting some neg camber in the front will help tame the severe under steer of the Z4 and make a world of difference in how the car handles. Since the Z4M strut mount is the same as the E36 M3 you can use the shims to add neg camber. Can't do that on any of the other Z4's and the shim kit is much less expensive than installing camber plates.

I will definitely get the camber shims and front bar. As for the 71's, they are more noisy, more harsh, don't last as long and are more expensive than the 11's. For me, the added performance the 71's bring are not worth all the trade-offs.

Thanks for your input though, very helpful!

[Kgolf31]

Originally Posted by Bossdog

I will definitely get the camber shims and front bar. As for the 71's, they are more noisy, more harsh, don't last as long and are more expensive than the 11's. For me, the added performance the 71's bring are not worth all the trade-offs.

Thanks for your input though, very helpful!

What ever you do, do not ride on anyone with RE-71Rs. You'll quickly regret not getting them. They are that much better in every way. The wear is worth it.

[Bossdog]

Originally Posted by Kgolf31

What ever you do, do not ride on anyone with RE-71Rs. You'll quickly regret not getting them. They are that much better in every way. The wear is worth it.

The price difference between the 11's and 71's on the staggered set is only about $35 at the Tire Rack. If I was the only person driving this, I certainly would get the 71's. However, I have to make my wife happy too. What about the noise and harshness? If mama's not happy, I will certainly regret it!

[dc_wright]

Originally Posted by Bossdog

The price difference between the 11's and 71's on the staggered set is only about $35 at the Tire Rack. If I was the only person driving this, I certainly would get the 71's. However, I have to make my wife happy too. What about the noise and harshness? If mama's not happy, I will certainly regret it!

She'll be driving a car with one of the stiffest chassis BMW has ever made (not just one of the stiffest cabrios, this includes sedans and coupes too), with 35 series tires. Regardless of what brand/model tire you buy it will ride like it has Fred Flinstones wood log roller wheels on it compared to her daily driver sedan. I doubt she'll notice the difference between the RE11's and the RE71's.

[Bossdog]

Originally Posted by dc_wright

She'll be driving a car with one of the stiffest chassis BMW has ever made (not just one of the stiffest cabrios, this includes sedans and coupes too), with 35 series tires. Regardless of what brand/model tire you buy it will ride like it has Fred Flinstones wood log roller wheels on it compared to her daily driver sedan. I doubt she'll notice the difference between the RE11's and the RE71's.

dc wright, I suspect your correct, she is not likely to distinguish between the 11's and the 71's tooling around town. She is currently driving it with Goodyear run flats and she's OK with the firmness of the ride so that's what I have to compare to. Most of the driving is around town, not highway. I guess if she doesn't like the autocross tires, I can put the stock wheels with the run flats back on after each event. I was hoping to not do that only because I HATE the run flats, they really suck.
Ahh, First world problems!

[dfjaws]

Camber has been a major issue for me and I think most people who autocross this platform. I would STRONGLY recommend some camber plates and/or camber bolts. -3 degrees seems to be the trick, along with some wider front tires. Next season I plan on running a 265/35/18 up front with around 2.5 to 3 degrees of negative camber.

[Bossdog]

Originally Posted by dfjaws

Camber has been a major issue for me and I think most people who autocross this platform. I would STRONGLY recommend some camber plates and/or camber bolts. -3 degrees seems to be the trick, along with some wider front tires. Next season I plan on running a 265/35/18 up front with around 2.5 to 3 degrees of negative camber.

Yes, More camber on most platforms for autocross seem to be a Plus. My plan is to start with the camber shims and see how that works. Sounds like I won't be able to get to -3 with just the shims. Do you know if camber shims put you our of stock in SCCA?

What size rims are you putting those 265/35's on?

[dfjaws]

Originally Posted by Bossdog

Yes, More camber on most platforms for autocross seem to be a Plus. My plan is to start with the camber shims and see how that works. Sounds like I won't be able to get to -3 with just the shims. Do you know if camber shims put you our of stock in SCCA?

What size rims are you putting those 265/35's on?

Yes, it will bump you out of street class. I would suggest running 245/40/18 and 275/35/18 on stock wheels if you want to stay in a stock class.

[Bossdog]

Originally Posted by dfjaws

Yes, it will bump you out of street class. I would suggest running 245/40/18 and 275/35/18 on stock wheels if you want to stay in a stock class.

I just received a set of Apex Arc 8's from the recent group buy. I think I will use the tire sizes you noted above. I am looking forward to autocrossing this vehicle for the first time in the Spring.

[dc_wright]

You can run 255/35 x 18 up front also without any issues. And yes, the camber shims move you from Street to Street Touring. For the E36M3 which the Z4M front suspension is copied from, BMW offers crash bolts that give about 0.5 degrees camber adjustment and are legal for Street, but I checked and they don't offer them for the Z4M unfortunately.

[F360C]

Originally Posted by Bossdog

I just received a set of Apex Arc 8's from the recent group buy. I think I will use the tire sizes you noted above. I am looking forward to autocrossing in the Spring.

Originally Posted by dc_wright

You can run 255/35 x 18 up front also without any issues. And yes, the camber shims move you from Street to Street Touring. For the E36M3 which the Z4M front suspension is copied from, BMW offers crash bolts that give about 0.5 degrees camber adjustment and are legal for Street, but I checked and they don't offer them for the Z4M unfortunately.

I agree with dc-wright on this... run at least a 255 with that 275 rear. These cars need way more tire up front for autox. 255 is good, 265 even better and square 275 is where the money is at. With that said I also found the 255/35/18 fit better then the 245 due to the height of the sidewall. Our cars can take more tire up front then most people think with out rubbing. The limiting factor I find with the front tire is the diameter of the tire.

Last autox of the season coming up for me this weekend!