Cal Club Autocross Forums

I'm sure you guys have been reading up on this (sccaforums, miata.net, s2ki.com) and just wondering your thoughts. My opinions on items 1 and 2:

1. Factory differentials only.

2. MX-5 could prove to be an overdog given the same wheel/tire width (8.5"/245) combo over an S2000. I wouldn't be inclined to exclude the MX-5 but perhaps affording the S2000 wider wheels and/or tires would make this more of a fair fight? Here you have a class that S2000 guys have been clamoring for and now you have the MX-5 (or even MR Spyder perhaps) as the car to beat.

Just trying to gather more food for thought.




TOPEKA, Kan. (My 7, 2009) – Sports Car Club of America’s Solo Events Board has approved a new supplemental class—Street Touring® R (Roadster), for competition in 2010.

The approval comes after considerable member support to expand the ST category to include a class for modern roadsters. While many cars are eligible, member feedback helped establish the Honda S2000 and Mazda Miata as the class’ performance targets. Allowances will be tailored for eligible vehicles to establish performance parity.

The class will have the following requirements and restrictions:
- Two seat sports cars
- Engine displacements up to 2.8-liters
- No forced induction

Eligible vehicles will include, but is not limited to:
- All STS eligible vehicles per the requirements and restrictions, plus
- Honda S2000
- Mazda Miata
- Mazda MX-5 Miata
- Toyota MR2
- Toyota MR2 – Spyder
- BMW Z3 (non M)
- BMW Z4 (non M)
- Mazda RX-7 (non-turbo)
- Porsche Boxster
- Porsche 968
- Porsche 944 (non-turbo)
- Pontiac Solstice
- Saturn Sky

Excluded vehicles due to performance potential:
- Lotus cars

Additional class notes include:

- Tire Allowances:
o AWD – 225mm
o 2WD – 245mm

- Wheel Allowances:
o AWD – 7.5”
o 2WD – 8.5”

- Catalytic Converters:
o Same as ST, STS allowance.

- Limited Slip Differentials:
o STR: Only standard LSDs allowed OR Allowance same as STX, STU

The class will run with supplemental status in 2010, meaning that no National Champion will be crowned. Should the class show considerable interest, and meet participation requirements, it may be approved for full National status in future years.

The SEB is seeking input on the following items. Members should send any input on these items to seb@scca.com.
1. OE LSD vs. Aftermarket LSD: All of the target vehicles are available with Limited Slip Differentials (or electronic equivalents) as standard equipment in some optional configuration. Restricting all cars to OE limited slips would reduce costs. That said, not all factory LSDs are equal and an argument can be made that, for reasons of parity, aftermarket parts should be allowed.
2. Inclusion of 2006-present Mazda MX-5: Is this car appropriate given the desired performance level of the class?

I think I'd probably build a Cayman, especially if non-OEM diffs are allowed...

I'm surprised the the MX-5 is seen as such a threat, I understand the weight difference, but with ST mods can't you get the S2K to have a much more usable powerband to help make up for it's extra weight? I thought S2000s were a bunch more powerful than MX-5s.

Is everyone scared because Brian did so well in CSP?

;)

The weight is the fear, the MX5 will have similar enough thrust to the S2k that it appears, on paper at least, that it will be faster... I'm also not so sure the Spyder won't be as fast if not faster than an S2k.

And yes, there are lots of older cars that are sleepers. The old P-cars are just the beginning, they really should put in an age limit IMHO.

Robert,

If that's a 73 RS, forget about it.

Seb,

It's not so much a game of power to weight ratio as it is tire to weight ratio. In this case, the S2000 loses.

I hate the idea of yet another ST class with a different set of rules. :unimpressed: SP rules have been forced to change in the last year (brakes ect) to help progression from ST to SP, yet within ST you have different rules from one class to another.

I am OK with a combination of ST and STX/U rules, but for gods sake not a brand new set rules with a new wheel size.

I say give STR the ST cat rules, but the rest should be STX, right down to wheel size.

Does anyone know if a 265 will fit an NC? I recall hearing rub issues with the 245 on the CS cars, and that the CSP guys were going well past an ST fender roll to fit the fat boys. If the NC could not fit the 265 the S2K picks up an advantage right there.

Robert Puertas wrote:;)

479938862_8f8d65affb_m.jpg

Gawd I love that car...but it ain't a roadster unless you want to take a sawzall to it. And then you would deserve to be waterboarded.

Jason Uyeda wrote:I think I'd probably build a Cayman, especially if non-OEM diffs are allowed...

And that's why I don't think they should be allowed. :ibrightdea:

Ken Motonishi wrote: Seb,

It's not so much a game of power to weight ratio as it is tire to weight ratio. In this case, the S2000 loses.

I'd be leaning toward the Miata. As Ken points out, the tire limitations are a problem. I'd also be concerned about the increased difficulty of managing the S2000's vtec compared to the linear power band of the Miata......especially on tires of the same size.

I'd like to hear the arguments on the differentials. I'm inclined to agree with the OEM limitation, but could be swayed with a convincing argument.

What does the s2000 weigh? Our MX-5 tipped at 2500, but there's probably 100lbs of options that don't need to be there for STR.

Jay W

I like Jason's take on it, we don't need another new set of rules. Can the MX-5 fit 265 tires?

}:)

Yeah....agree the tire/weight ratio is an issue......hp is not so much of a factor in autox.....except when the S2k is out of VTEC. Advantage to Miata.

On the other hand, if you can change springs, the S2k has a lot to gain there (compared to the Miata which is much more balanced to begin with) - e.g. keeping that inside rear wheel down and enabling more throttle/acceleration out of corners. I wonder if that is why the Miata seems to have better suspension geometry (etc.) than the S2k.....e.g. mostly spring rate variation F/R?

Could be pretty close times between all of them.....but an NC Miata with tires/springs/shocks and little else can run pretty fast (CSP).

Reijo

Jayson Woodruff wrote:What does the s2000 weigh? Our MX-5 tipped at 2500, but there's probably 100lbs of options that don't need to be there for STR.

Jay W

Around 2780-2840 lbs stock, full tank of fuel, spare tire depending on MY. Figure whatever an MX-5 weighs and add 300 lbs- or roughly the weight of Paul Whitehead riding in the passenger seat all the time if that helps. :gpower:

In AS trim, the lightest cars at Nat's are reported to weight in the high 26xx range.

Although I hear Paul is on a diet. Yesterday for lunch, he went to a Buffet. I thought you're only supposed to go to Buffets if you're in Vegas...But when you got a stomachs that's twice the size of mine, it makes more economic sense I suppose.
:mrt:

Sebastian Rios wrote:I like Jason's take on it, we don't need another new set of rules. Can the MX-5 fit 265 tires?

Yes, if allowed an aggressive fender roll: 245's fit in stock fenders, or with a light roll in back if you're running anything below a +40 offset rim.

What does a race-ready S2K weigh? I find a published curb weight of 2864 std. / 2756 for the CR. What kind of rear wheel horsepower numbers would you expect for a prepared car?

For comparison, a modified '06 MX MX-5 weighs 2500 lbs and puts out 160 rwhp with no cats (header and race midpipe.) In pure stock form, my '06 put out 140 rwhp.

That gives us an lb/hp ratio of about 15.6 lbs/rwhp for the modded MX-5, and, using the stock honda crank number, 11.8 for the S2K. From experience, the Honda cleans the Mazda's clock in a straight line. If you can keep the S2k out of the powerband, it would be a fair fight... given the variety of courses we see, I think both cars would end up a fairly even match.

Also, throw our the wheel restriction: there's no benefit to a much wider wheel with a 245 (unless you like the mad-tyte do-rift-o look) and it saves costs by not having to run a hard-to-find wheel (like the 7.5's used to be when STS started). Regulate tire size only.

I'm all for this class. I like having a dual-purpose car, and the allowable mods make it an even better street car. I'm having a great time this year running SST, and I can comfortably drive the car to&from the track on the same tires, so don't have the hassle of a tow rig or tire trailer. To stay in CSP, I had to cut up the fenders for 275+ tires, go way up on spring rates, and develop an alternative intake system/engine management... there goes any hope of being a street car.

To get more intrest in Solo, we need to focus on classes where folks can run their street-legal cars... this is a step in the right direction.

Steve,

How many cats come stock with an MX-5? Is it two? Isn't there one integrated into the exhaust manifold? How much of a difference does eliminating this single cat make? Probably more significant than the second one. At this point I'm assuming there's two cats? Who makes the most efficient exhaust manifolds (how much power gain?) for the MX-5s and do they all do away with the integrated cat? With the 2009 MZR engine I'm surprised the Mazda engineers could only eke out one HP (167 over 166) out of the improvements they made to the crankshaft and rods and 500 more rpm before fuel cut.

Ken

Steve L.: I was wondering if the MX-5 could fit 265 tires, I just assumed they could fit 245s.
So can they fit 265 tires?

S2k people: Can you effectively make the powerband more usable for autocross given the allowances in ST? If so, I wonder what the curve would look like in comparison to an MX-5.

Sebastian Rios wrote:Steve L.: I was wondering if the MX-5 could fit 265 tires, I just assumed they could fit 245s.
So can they fit 265 tires?

S2k people: Can you effectively make the powerband more usable for autocross given the allowances in ST? If so, I wonder what the curve would look like in comparison to an MX-5.

Not apples to apples but a 245 A6 on a 9" wheel is ~1.16" narrower than a 285 A6 on the same wheel. I don't think Brian's car was flared 1.1" on each side I always hear you, "can't" fit this or that, but quite often it's not nearly as difficult as most make it out to be... I'm not sure what the limiting factors are on an NC (other than the fenders) but don't forget you also don't need full lock on an autox course.

The S2000 will def. gain from ST allowances. You should be good for at least a 1000rpm (~7mph) VTEC drop (AP2). Stock for stock the AP2 has ~2% trust advantage 25-43 and ~10% 43-redline over a 6spd NC. It's difficult to compare (on paper) because the cars respond to mods so differently and the gearing possibilities/intricacies do make a big difference.

Jason, Goodwin would have some accurate info on fitment, but I think 255 might be the limit for an NC given the proposed fender allowances. To be honest, I don't think I'd want to go any bigger than that regardless.

Some additional data: my CSP car weighed 2370 at Nationals and aside from wheels/tires, fit the STR allowances minus the flywheel, header, clutch diff and steering wheel. Given what I had left to do in the car, you could probably get a 6spd STR NC down to about 2325 (don't recall the weight diff with the 5spd). I ended up at a little under 170whp, so take away the header (cat-delete) and you're looking at about 155-160whp tops.

I don't have extensive experience in S2k's however I know they lack area under the curve when it comes to power on most solo courses. I'd personally go with the 6spd NC (seem to be in the minority) as I'd expect it to maintain an average acceleration advantage over the S2k. I'm curious how the S2k responds to throwing more wheel and tire under it though. My gut would be that it could hit diminishing returns quicker than the NC just from a gearing standpoint. What's the general consensus in AS, stuff as much Hoosier under as possible, or are there some running more conservative widths to maintain acceleration and gearing?

I did a road trip and a couple runs with Jay's STU wheels/tires (5Zigen 17x9 w 245 Neovas) on the car and while they were only 5lbs/corner more than the CSP setup, acceleration suffered quite a bit. As I posted on Miata.net, there's no way I'd want to be lugging around heavy STR shoes with a 5spd.

At first I was pretty confident that the MX5 would be a clear favorite, but now I'm beginning to think it'll be a fair fight. On a faster transitional course, the S2k should do just fine.

(I just posted a nice, detailed response, and the web hamsters ate it.)

Ken: yes, there are two cats, but only the front one is monitored. There are no good headers as they are all too short in order to mate with the stock midpipe. I still run the stock front cat and am able to make good power: any of the off-the shelf headers would be another 4-5 hp, but a good one would be as much as 10 with a good torque gain across the range.
There's a lot of potential in the MZR if it had a bigger throttle body and a good header/exhaust. Could use bigger cams, too (if that was legal anywhere.)

Sebastian: yes, 265's fit with the right offest wheel and a good fender roll. They will rub the inner liner by the front bumper, but those will rapidly self-clearance.

What ruleset would most benefit my (Shauna's) 99 10AE Miata , and could it be competitive?

Edit: The one thing I do feel strongly about is wheels...9" width should be allowed screw those .5 sizes, there are a million *x9" wheels out there.

Sebastian Rios wrote:What ruleset would most benefit my (Shauna's) 99 10AE Miata , and could it be competitive?

CSP... Yes...

Brian, I run a 6-speed NC: I find myself using 3rd gear a lot, so you've got to be comfortable with a lot of shifting.