Car rules and preparation for a "Street" Class car

[Jackal]

Certainly good food for thought there Reijo. In my case though, I'll be looking to step down to 18's from the 19's that are on there currently. I like a little more sidewall and feedback from the tires.

I'm looking at a set that are lighter than what's on there currently, stock widths ( I was looking for an extra .5 inch width, but they aren't available in that size), and only a few mm difference in offset.

[Reijo]

fyi, I used Hawk HP+ pads on the S2000 and they dust but they were vastly superior in initial bite compared to the stock pads ... very worthwhile.  I have stock pads back in and the brakes do not quite feel the same anymore even though the S2000 was noted for having excellent stock brakes.   

Of course, if you use the car for track days as well, then you will have to change set-up etc. etc. if you want to be competitive ... or run some compromise set-up etc.

[Reijo]

Certainly good food for thought there Reijo. In my case though, I'll be looking to step down to 18's from the 19's that are on there currently. I like a little more sidewall and feedback from the tires.

I'm looking at a set that are lighter than what's on there currently, stock widths ( I was looking for an extra .5 inch width, but they aren't available in that size), and only a few mm difference in offset.

Ah, so you are going in a good direction ... and smaller dia. wheels/tires are cheaper too.   

You are allowed up to 1/4" (6.35 mm) leeway for offset as per the rules.

R

[Jackal]

As I interpret the rules, spacers are allowed and counted as part of the wheel to ensure stock offset.

I'd love to go to studs though for ease of wheel changes. I know longer bolts are allowed to allow spacers, but a stud conversion is not a Street allowable mod.

May I just add... get with the times German cars!!  Use studs. Wheel bolts are a pain... especially with spacers!!

[Reijo]

As I interpret the rules, spacers are allowed and counted as part of the wheel to ensure stock offset.

I'd love to go to studs though for ease of wheel changes. I know longer bolts are allowed to allow spacers, but a stud conversion is not a Street allowable mod.

May I just add... get with the times German cars!!  Use studs. Wheel bolts are a pain... especially with spacers!!

Yeah.... sometimes the rules can be a pain and there may be no gain (studs = bolts weight-wise) ... You could actually write a letter to that effect to the BOD and see if are willing to allow that.  I think that would be a reasonable request and you never know.

Reijo

[PedalFaster]

Lots of people giving setup advice here, but I'm going to pull rank since I ran an E46 M3 nationally for a season in 2014. They're obviously different cars, but the Z4M's platform was derived from the E46 M3's and should have similar setup needs.

The M3's Achilles heel is understeer due to its skinny front wheels and a lack of front camber, and I can't imagine the Z4M's any different. Given that, I'd start off with just tires and an alignment. RE-71Rs are a significant improvement on almost any other street tire and should help your times a lot. For the alignment, max out your front camber (making sure that you remove the strut top pins first), set the front toe to around zero, and set the rear toe to zero or a hair of toe-in in.

Struts are probably a good idea since, if you're still on the stock shocks, they're almost definitely worn out by now. Unfortunately, it doesn't look like Koni has an off-the-shelf shock for the Z4M, and I know from firsthand experience that Bilsteins raise the car's ride height significantly due to their gas pressure. Not really any good options there without spending big bucks -- it might be worth your while to research if it's feasible to modify M3 struts to work on your car.

Get wheels if you really want them, but they're not going to make a significant difference in your times.

Last but not least is the sway bar. Everyone I know who ran an E46 M3 (myself included) got a stiffer aftermarket front bar, then ended up running it on full soft because the car would push too much otherwise. Given that, if I were you, after making the changes above I'd run the car with the stock bars and only get a bigger bar if needed to address balance issues. I'd even consider a bigger rear bar.

You are allowed up to 1/4" (6.35 mm) leeway for offset as per the rules.

Actually, last year the allowance was increased to 7 mm.

I'd love to go to studs though for ease of wheel changes. I know longer bolts are allowed to allow spacers, but a stud conversion is not a Street allowable mod.

Stud conversions are actually legal in Street and quite common on German cars. Alternately, you can buy a couple of wheel pin / hanger tools like this one -- they make changing wheels easier, although not as easy as a stud conversion.

Last but not least, check out the E46 setup thread on M3Forum if you haven't already.

[Reijo]

Here's where you can request a rule change:

https://www.crbscca.com/

[Reijo]

I stand corrected.  Thanks Stephen!  Good info.

[PedalFaster]

Here's the wheel offset rule:

13.4 WHEELS
Any type wheel may be used provided it complies with the following:
A. It is the same width as standard and as installed it does not have an offset
more than ±7.00 mm (±0.275”) from a standard wheel for the car. The
resultant change in track dimensions is allowed.

Interestingly, I went looking for the stud conversion rule and didn't find anything relevant. I've personally seen countless cars at national-level events that have done it in Street (nee Stock), so I know it's a commonly accepted modification, but the rule could use clarifying -- as I read the rule book, a strict interpretation could indeed hold that a stud conversion was illegal. I'll write a letter.

[BrianHemming]

Interestingly, I went looking for the stud conversion rule and didn't find anything relevant. I've personally seen countless cars at national-level events that have done it in Street (nee Stock), so I know it's a commonly accepted modification, but the rule could use clarifying -- as I read the rule book, a strict interpretation could indeed hold that a stud conversion was illegal. I'll write a letter.

That is interesting - I had the same recollection as you.

All I can find in the Street rules is this:
13.4 WHEELS
~~~~Wheel studs, lug nuts, valve stems (including pressure-relief types), and/or
bolt length may be changed. ~~~~

That could be interpreted to mean it's ok, but in the Street Prepared rules the conversion is explicitly mentioned.  I would take that to mean it's not "Street" legal .  Looks like the street allowance is only to change wheel nuts or bolts, but not to convert bolts to wheel studs/nuts.

From Street Prepared
15.4 WHEELS
B. ~~~~ Wheel bolts may be replaced with
studs and nuts.~~~~~

As a BMW owner who regularly curses wheel bolts I would say it's definitely a comfort and convenience (and sanity) upgrade.

[Jackal]

13.4 WHEELS
~~~~Wheel studs, lug nuts, valve stems (including pressure-relief types), and/or
bolt length may be changed. ~~~~

That could be interpreted to mean it's ok, but in the Street Prepared rules the conversion is explicitly mentioned.  I would take that to mean it's not "Street" legal .  Looks like the street allowance is only to change wheel nuts or bolts, but not to convert bolts to wheel studs/nuts.

From Street Prepared
15.4 WHEELS
B. ~~~~ Wheel bolts may be replaced with
studs and nuts.~~~~~

As a BMW owner who regularly curses wheel bolts I would say it's definitely a comfort and convenience (and sanity) upgrade.

All of this pointed me to the thought that converting from bolts to studs was not allowed in Street classes.  Although I will say that when using spacers,  there is no better reason to move to BSP.  I almost don't care if no other prep is made for that class.

[PedalFaster]

We're a bit friendlier here, but if I were still in the States, I'd advise you to convert to studs, run in Street anyway, and punch anyone who complained in the nuts. :p

As Brian posted, in a formal protest you could very reasonably argue comfort and convenience, especially since (as I understand it) the reason German automakers use bolts rather than studs is to save weight.

I wrote a letter, but it'll be a few months before a response is printed in Fastrack.

[Jackal]

We're a bit friendlier here, but if I were still in the States, I'd advise you to convert to studs, run in Street anyway, and punch anyone who complained in the nuts. :p

As Brian posted, in a formal protest you could very reasonably argue comfort and convenience, especially since (as I understand it) the reason German automakers use bolts rather than studs is to save weight.

I wrote a letter, but it'll be a few months before a response is printed in Fastrack.

I'd like to stay within the letter of the law, but the bolts are a significant pain. 

By "wrote a letter",  what do you mean?  Are you a contact from us to the powers that be in the SCCA?

[Reijo]

Anyone can write a letter to the Solo Events Board (SEB) ... inquiring about rules, suggestions for rule changes and new rules etc.

Of course it does not mean they will respond favourably to you!      They evaluate every letter that comes in ... btw, see the link I posted somewhere above about writing a letter .... that is how you do it.

R

[PedalFaster]

I'd like to stay within the letter of the law

The point that Brian and I are making is that the letter of the law is ambiguous. I'd be comfortable making this change under the comfort and convenience allowance in 13.1, which reads:

comfort and convenience modifications which have no effect on performance and/or handling and do not materially reduce the weight of the car are permitted.

Do studs affect performance or handling? No. Do they materially reduce the weight of the car? No. I think you can therefore reasonably claim them under comfort and convenience. But hopefully the SAC / SEB clarify the rule anyway.