This post didn't get a lot of response over in the Track/Autox forum so I'll try it here:

I'm thinking of getting back into autocrossing with my Z4 coupe. I'd like to stay legal for SCCA A-Stock, which means minimal mods (shocks, front sway bar, tires, alignment) but does allow option package conversions. In other words I can run with either the stock configuration (softer/taller springs, 18mm rear bar, 17" parallel rims) or the sport package (0.6" lower springs, 19mm rear bar, 18" staggered rims). While it might seem obvious that the sport package set up is the way to go for Autox, I'm not too sure about this and wanted to ask some folks more knowledgeable than I before deciding.

It seems to me that while the lower/stiffer springs of the sport package are a clear advantage, this is negated somewhat by the larger rims. I could run 235/40/17's with the standard set up where I'd need to go with 255-275/35/18's with sport and also have more wheel weight and taller effective gearing.

Also I'm not sure if the slightly bigger rear bar of the sport pack is an advantage (I already have a [stock legal] 27mm adjustable bar up front). While the car might push a bit on entry I think that suppressing the tendency to spin the inside rear tire on exit is just as important, and I think this would be helped by a stiff front / weak rear bar set up. But I'd particularly like input from suspension experts and those who've spent time Autocrossing the Z4 on this point.

Finally, while I've autocrossed a lot in other vehicles years ago I know my skills are rusty and I would gain a lot by just by racing and losing while I dial in to my car for a season before making any changes. Still, even if I run my car as it stands for a while first, I would like to hear opinions on what the optimal stock class autox set up for a Z4 would be.

Thanks.

I definitely see your concern about wheel weight. To put it frankly, no one will say anything until you try nationals, but if you really want to be legal at the local events... I'd say go with the sport package. My z-roadster has the sport package. I feel that the car handles very well for autox. It pushes in the slow speed corners, tends to oversteer on some of the faster corners, which i really like. It's pretty easy to get the back end to rotate on my car when I need it to.

So, I'm not really an AutoX or suspension expert, but i think you'd notice a gain going to the sport package.

First of all you best tire setup would be a Kumho V710 in 285/30/18's. You won't be competitive unless you run a street tire...especially in A stock with STI's, Boxtsers, C4 vettes etc.

If you don't want to run R comps right now...

Get some Hawk HP+ pads, stock pads SUCK. And play with the alignment. This is VERY important. Try alittle toe out in the front...maybe 1/16th or so. And a little toe in in the rear, maybe a 1/16th also. And try and get some negative camber in the car. I don't know how much you can get stock on a Z4.

It is ironic that you bring up the weight of wheels. This month's issue of Sport Car magazine (the SCCA magazine) they have a shootout about tires and wheel weights. Long story short....they found a .2 second gain with lighter wheels. Which is enough when you start to get serious. In autocross you essentially want all the tire you can get. And depending on how big the course you run, you may want a taller tire to keep off the rev-limiter and shifting into third.

I didn't know that a Z4 ran a 235/40/17 in the rear, and the option of a 275/35/18. Wow that is a big difference. About an inch taller for the 275.

But like I said, try and get as much tire on the car as the rules will allow. Not sure about all the options for the Z4.

As far as the rear bar. It is a give and take kinda thing. With no rear bar (a no no in stock) or a smaller rear bar, you MAY be able to get on the gas sooner, BUT you lose it in the quick transtion areas....slaloms.

Hope this helps.
Jason Becker

Vachss,
If you drive a sport package Z4 that comes with 18" stock, can you still run 17s in SCCA and stay in stock?
Either way, running V710's is probably the best single upgrade you can do. Camber and extra widths just make them better. Just a glance at the list of winners in each class shows that they all have either Kumhos or Hoosiers. If you can't get more width in the front, more negative camber will help stick them. Wheel weights can shave tenths of a second, sticky tires shave seconds! http://www.ncr-pca.org/autocross/r-tires.htm
As an experienced autocrosser, you probably already know this stuff though.

My experience on my last Z4 ('03 3.0i sport pkg) was that running 17" V710's on the stock suspension worked surprisingly good.

You have to do a complete coversion form package to package for the car to be legal in stock scca. This means that if you want to run the sport package suspension setup, you have to run the sport package wheel size and offset.

and to be honest, stock Z4's have a ton of rear camber, and not a lot in the front, which is pretty opposite of what you want. On my first event on v710's, I had an inch on the outside should of my rears that wasn't even touched at 28lbs hot, which is VERY low for those kumho's. The fronts had about 1/2" on the inside shoulder not touched, but rolled right off to the outside shoulder, so i think i need a bit more camber and a tad less air in them.

Glad to see that we're getting some autox talk going though. it's helpful!

You have to do a complete coversion form package to package for the car to be legal in stock scca. This means that if you want to run the sport package suspension setup, you have to run the sport package wheel size and offset.

That was the main reason for my question: Is sport suspension w/18" rims better or worse than non-sport w/ 17's (assuming same tires)? Folks in this thread seem to think Sport is the way to go...

and to be honest, stock Z4's have a ton of rear camber, and not a lot in the front, which is pretty opposite of what you want.

I've heard that we can dial in extra negative camber up front by removing pins on the shock towers. I would imagine that this would be stock class legal since it's within the range of adjustment with original equipment (while camber plates would not). I haven't looked into messing around with the front camber and the pin removal, but if anyone has more details on this I'd love to hear about it.

On a different note, what kind of lifetime are folks getting out of V710's? The last time I had dedicated Autox tires it was a set of Hoosiers that just melted away in half a season (of course my driving to and from events in them had something to do with it).

I remove the pins and adjust as much as possible with the slots that are there. It isn't much, but every bit helps. The pins are soft aluminum and get damaged easily! Both the hex key and the thread will strip. My hex key stripped just trying to remove them on mine. Unfortunately, they are not sold separately either.

You can compare the slot length (adjustment) to pictures of adjustable camber plates like TC Kline's or Turner's and get a guess as to how much angle you get.

I doubt the SCCA would care about it.