Street category

Andrew Jonell · **Joined:** Mon Mar 23, 2009 6:43 pm **Posts:** 1350

I think that it's a good idea to get away from a "Stock" car being A6s, 32-way adjustable Ohlins, and a fence post doubling as a FSB. On the other hand, seeing how much grief TIR -> RT has caused just in classing questions, Street is going to be obnoxious at best. That said, maybe Hoosier will release a new tire for the first time in almost a decade seeing how fantastic summer tires have gotten in the past few years.

For sway bar chat, I don't really like the new rules because it's going to become an arms race to get the biggest bars on front and rear and destroy the car from literal band-aids. My nascent understanding of suspension design is that sway bars should be added and tuned last; however, in autocross the sway bars are the first thing you do.

Chuck Branscomb · **Posted:** Thu Mar 21, 2013 9:52 am

JamesShort wrote:

Chuck Branscomb wrote:

The stiffness of a cylindrical bar in torsion changes with the fourth power of the diameter. Hence bar stiffness increases in a hurry with diameter. If a stock bar is say 25mm, and someone can fit a 45mm bar in its place, stiffness goes up ~ a factor of 10. Hence it will be easy to rip off mounting parts pretty quickly with increasing bar diameters in many cars. The standard engineering factors of safety used in the design of the bar mounts, mounting locations, unibody/frame loading, etc, etc, all never expected such potential craziness as massive bar diameters like above. Perhaps it won't be an issue since it won't work from a handling perspective anyway on most cars. I have no idea.

Picture a control arm sway bar end link mount. Now picture said mount with a bar with a 10x stiffness. Now add a pothole or bump to the equation.

While true, most of these humongous bars would be hollow to capitalize on the higher torsional constant (J) per unit mass/density.

Yep, so you subtract out the center missing material which doesn't have much effect to torsional stiffness. Still you get stiffness varying with 4th power of the diameter changes. Some cars (M3) already come with hollow bars too.

The concern about tire grip overstressing bar mounts, chassis locations, etc, pales in comparison to road input issues. Even small bumps now might provide an input far exceeding design limits.

JamesShort · **Posted:** Thu Mar 21, 2013 9:56 am

Andrew Jonell wrote:

seeing how much grief TIR -> RT has caused just in classing questions, Street is going to be obnoxious at best.

Yeah, I thought of this too, RT/TIR might just have to disappear

but this will be discussed (probably for a long time) before a decision is made.

Quote:

For sway bar chat, I don't really like the new rules because it's going to become an arms race to get the biggest bars on front and rear and destroy the car from literal band-aids. My nascent understanding of suspension design is that sway bars should be added and tuned last; however, in autocross the sway bars are the first thing you do.

You are right, it's better to minimally tune with sway bars, but two things 1) Stock/Street allows for sway bars and not springs, so why not? and 2) from a non autox perspective, sway bars are significantly cheaper including parts AND labor relative to springs/coilovers etc so they are a common mod for people who want to modify their car for better handling.

Steven Carter · **Posted:** Thu Mar 21, 2013 10:07 am

James, you've been driving on one of the thickest FSBs on the market from Speedway Engineering (via Gendron). That bar hasn't torn your mounts, has it? While certainly a theoretical risk it hasn't born itself out as a consistent issue (Keith Vail's experience stands out as a cautionary tale, but is not the norm)

At a certain point thicker bars will run into binding/fitment issues as well.

Given the adjustable nature, one could also set it at full soft for DD, then full stiff (or whatever) for competition.

I will say that blade style bars may become much more common than before. Somewhere, Guy Ankeny is smiling broadly.

JamesShort · **Posted:** Thu Mar 21, 2013 10:11 am

You clearly have not seen the ball bearing mounts that we have

. The bracket/mount is monstrous and bracket/bushing binding is impossible given the design. Anyway, we don't run it anywhere close to full stiff because the car pushes like a beast many a times anyway.

That bar did require that I chop the brake line mounts off my brand new Koni DAs though

.

Chuck Branscomb · **Posted:** Thu Mar 21, 2013 10:13 am

That's the ticket Steve. Come up with a sway bar design that allows for a much lower total stiffness for street driving where shock load inputs will destroy chassis mounts, control arm mounts, etc, while allowing for an easy adjustment at an autox. In a blade style bar where you can design the ends to carry the load of a very stiff torsion section, one could conceive of some additional bar that is added to the main section to greatly increase torsional rigidity...something like that. Some way to make it easy to swap out for driving on the street. See...this thing *will* open it up to crazy stuff most likely.

Steven Carter · **Posted:** Thu Mar 21, 2013 10:26 am

JamesShort wrote:

You clearly have not seen the ball bearing mounts that we have

.

Ooooh....ball bearing mounts. {genuflects in respect}

Keith didn't have them, and while they did eventually tear, it remains not a common occurrence.

You make your mods, you take your chances, right? :wink:

It does seem reasonable to allow for a stronger mounting point as it is allowable in ST, and without any significant impact.

JohnByers · **Posted:** Thu Mar 21, 2013 11:02 am

RT goes away with this. Would be redundant.

And I just set my car up, bought new pimp magnets for RTR :lol:

I waited a year to see if it was gonna gain traction. I think it did, but now they did a huge 180 where I think a 90 would have been sufficient.

Remember, this isn't set in stone and is out for SCCA member comment. Letters are going to FLOOD in

JamesMilko · **Posted:** Thu Mar 21, 2013 11:04 am

I think ST needs a good look at now. Should it really be another prep level?

After a quick run through the rules the main differences I spotted are:
Removing trim pieces and other trivial exterior modifications
Strut bars (Is there a modern, competitive car where this is meaningful?)
Subframe connectors (Again, is there a modern car where this is meaningful?)
Larger wheels
Shock absorbers with more than 2 adjustments and remote reservoir
Springs
Drum -> Disk swaps (obsolete on a modern, competitive car)
Brake lines & air ducts (pointless for AX on a modern, competitive car)
Suspension bushings
Battery relocation
Oil pan and oil pickup changes
Air intake
Exhaust manifold change
High flow cat
ECU Tunes
Lightened pulleys

Of those, ones that are meaningful for a modern autocross car:
Larger wheels
Shock absorbers with more than 2 adjustments and remote reservoir
Springs
Suspension bushings (maybe)
Air intake
Exhaust manifold change
High flow cat
ECU Tunes
Lightened pulleys (maybe)

To me it barely seems worth it. Basically bigger wheels, springs and a bit of extra HP. Am I missing something big here? But, then again I have no dog in this fight.

Need to figure out what to do with street tired SP/P/M cars if you kill RT/TIR.

Jordan Normark · **Posted:** Thu Mar 21, 2013 11:11 am

I like where they are going with the new rules. I have always been tempted to buy a car that can play in a stock class and the stree tire rules make this even more alluring. There is something wonderfully simple about driving the car to an autocross, unloading a couple of small items, spending 5 minutes or less checking tire pressure and putting magnetics on, then using the rest of the time helping out, walking the course, chatting etc.

Early miata's were notorious for breaking sway bar mounts with a larger bar and thus beef up kits were made. Most of the failures I saw came from putting a large front bar on an otherwise stock suspension ala stock class. As Steven mentiond, I am sure R-comps add to the stress. As others have said here, in this situation the bar takes most of the load so the mounts get stressed. I have had a large bar on the front of my car with stock mounts for the last 13 years and 100+ autocrosses, but I think running front spring rates from 450-700 lbs has reduced the overall stress that goes into the bar and its mounts. I have yet to have a crack or failure in the front sway bar mount.

JamesShort · **Posted:** Thu Mar 21, 2013 11:12 am

So I just realized the new Street class allowance is +-1" of wheel diameter. Honestly that's worthless other than for cars with 16" stocks wheels (tire selection is infinitely better for 15" or 17" wheels). I think a provision to all to go from staggered stock wheels to square would be reasonable too. Maybe staggered to square with the width being the halfway width rounded to the next lower 1/2"?

Jordan Normark · **Posted:** Thu Mar 21, 2013 11:21 am

JamesShort wrote:

So I just realized the new Street class allowance is +-1" of wheel diameter. Honestly that's worthless other than for cars with 16" stocks wheels (tire selection is infinitely better for 15" or 17" wheels). I think a provision to all to go from staggered stock wheels to square would be reasonable too. Maybe staggered to square with the width being the halfway width rounded to the next lower 1/2"?

Not that they are as competitive, but NA miata's with 14's can open up the door by going 15's

Edit: No mention of allowing an increase in rim width...hmmm.

I know of one club member with an SE NB miata with 16's that will be thrilled if these changes are adopted.

Steven Carter · **Posted:** Thu Mar 21, 2013 11:27 am

Jordan Normark wrote:

I like where they are going with the new rules. I have always been tempted to buy a car that can play in a stock class and the stree tire rules make this even more alluring. There is something wonderfully simple about driving the car to an autocross, unloading a couple of small items, spending 5 minutes or less checking tire pressure and putting magnetics on, then using the rest of the time helping out, walking the course, chatting etc.

This. It is as enjoyable as it sounds, Jordan. I just unload and put on the numbers. I set tire pressures before I leave, check it before going to grid and then adjust as needed during runs. If I was a better driver, the car as it's setup now could be a top PAXer on a regular basis.

The same is also true for when I drove in TIR, so I suspect it will be similar with Street classing, although the need for tire swapping to keep the outside shoulders from wearing out has been limited by the Camber plate allowance. I bet the Mini folks might be even happoer than I am...as well as the Civic Si drivers.

JamesShort · **Posted:** Thu Mar 21, 2013 11:45 am

I wouldn't get *too* excited by camber plates because VERY few chassis' have camber plates that work with stock diameter/size springs. The WRX and BWMs are some of the very few strut based cars that do.

JohnByers · **Posted:** Thu Mar 21, 2013 12:32 pm

the +/- 1" is important to me cause 17" tires are MUCH cheaper than 18" :thumbsup:

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