STR Class in SCCA Autox

"Wrong Wheel Drive (41%)" (rduncan5678) 04/07/2016 at 08:52 • Filed to: None

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STR or “Street Touring Roadster” is one of many classes available to run in SCCA SOLO (better known as autocross). This class is often referred to as the S2000 class since they seem to dominate anything else run there. Since I decided to put 15x8 wheels and Flyin Miata Coilovers on my car, I am now also running in that class. I have no dreams of winning my class or being super competitive, but I am trying to optimize my build so that I can at least beat some of the other Miatas in STR or have a very fun time trying. Anyways, I have a question for anyone that understands the classing rules a bit better. My question involves fender rolling and what exactly is allowed.

Per the current SCCA Rules: “Fenders may not be cut or flared but the inside lip may be rolled to gain additional tire clearance. The outer fender contour may not be changed”

So, does this mean that using a fender rolling kit (or just a baseball bat as some fellow auto-x people have suggested to me) would be allowed? My issue is that with the wider wheels and coilover suspension, I am getting a bit of rubbing between the tires and fenders. It is actually worse during street driving (potholes, bumps, etc) than on a course, but it is still an issue on the tightest turns or pavement surface changes during an autox. I have driven two events so far with this setup. I am very happy with the performance characteristics but I would like to get rid of the rubbing and potentially go lower in ride height.

Chris_K_F drives an FR-Slow > Wrong Wheel Drive (41%) 04/07/2016 at 09:02

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From my understanding, it as. As long as the rolling only changes that little lip that comes into the wheel well off the fender. The flat outside surface of the fender (that ugly bit where it looks like they just chop off the widest bits of the car for efficiency) needs to remain unchanged though.

Trunk Impaired 318 > Wrong Wheel Drive (41%) 04/07/2016 at 09:09

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Yes, rolling the inside of the fender would be fine.

Wrong Wheel Drive (41%) > Chris_K_F drives an FR-Slow 04/07/2016 at 09:14

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But wouldn’t the act of rolling the fender alter the outside of it?

Wrong Wheel Drive (41%) > Trunk Impaired 318 04/07/2016 at 09:17

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I am trying to figure out what, if anything, rolling the inside of the fender helps. I am a little confused how the inside can differ from the outside.

Chris_K_F drives an FR-Slow > Wrong Wheel Drive (41%) 04/07/2016 at 09:19

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Depends on the amount of pressure applied. It should take more force to actually bend the fender out, than simply turning that little lip back. I’ve personally never rolled fenders, but I’d imagine that should be the case.

fourvalleys > Wrong Wheel Drive (41%) 04/07/2016 at 09:40

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The fender has a little lip that hangs down at a 90-degree angle from the outside of the fender. “Rolling” is when you use a roller to bend that little lip upward so it doesn’t stick out towards the tire anymore. It gives you maybe 1/2" clearance depending on how wide the lip is.

I had the fenders rolled on my NA, and it helped me run 15x8 +45 at a pretty low ride height. It rubbed before the roll, it didn’t rub after. I had good pictures, but they’re long gone. edit: I found one that shows the damage from the rubbing.

It is way harder to find photos than what I expected... but here’s a photo that shows how that lip would look before:

Here’s what it looks like while it’s being rolled:

And here’s how it would look after:

Here’s a video of that guy doing the rolling. Disclaimer: I didn’t watch it, so it may be awful.

JGrabowMSt > Wrong Wheel Drive (41%) 04/07/2016 at 09:52

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If you’re too aggressive, yes. I’m heavily avoiding rolling the fenders on the wagon to fit a 275 tire, I’m trying to play with wheel offset to minimize it, and honestly I’ll raise the rear suspension before I roll the fenders on a unibody...ugh.

I’ve seen lots of rolled fenders, and I’ve watched people do it before. There are actually fender rolling tools that ensure you don’t warp or change the outside of the panel, because what you’re doing is just pinching the inner lip of the fender to meet the inside of the fender instead of having an edge.

Wrong Wheel Drive (41%) > JGrabowMSt 04/07/2016 at 10:13

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Are there disadvantages to wheel offset? My wheels are zero offset so some positive offset might actually be a good idea. I am worried that simply rolling the inside of the fender would not be enough to clear the wheels as they currently are or if I went lower or went with wider tires on the wheels.

Wrong Wheel Drive (41%) > fourvalleys 04/07/2016 at 10:15

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This is a perfect explanation, now I get it! Okay so fender rolling refers specifically to that lip. That makes a ton more sense how a baseball bat could work for that then. So when I see fenders sticking out, those are generally flares and would be an illegal modification in my class. Okay, I definitely want to roll my fender lips and look into some wheel offset then.

JGrabowMSt > Wrong Wheel Drive (41%) 04/07/2016 at 10:18

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The only thing that you can run into as far as offset issues is clearance. I’ll be swapping in some tubular control arms instead of the massive stock ones, which will mean I can stuff a wider wheel on, but if your offset puts the wheel too far back, you can rub on suspension components in hard turns. If the wheels are too far out, they rub on the fenders. Proper offset puts you somewhere in the middle of those two extremes.

In my case, I’m going from a 7.5" wide wheel to a 9" wide wheel, but I want to add .5" of offset to the wheel instead of using a .5" spacer. It’s a lot more complicated than that, because I want the .5" of dish on the outside of the wheel for looks more than the offset gains, but it’s a mixture of making sure I am not throwing a full 1.5" inside the wheel wheel because the tire will be a 50 profile probably, which will be pretty fat (18" diameter wheel).

And of course, all of this because I refuse to move to a larger wheel.

Wrong Wheel Drive (41%) > JGrabowMSt 04/07/2016 at 10:27

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Makes sense, I will definitely be trying to find the right balance. From what I can tell, I definitely have plenty of clearance to the suspension components. I would like to just bring the wheels in slightly closer to car but I need to figure out how adding positive offset would actually work. Is that actually possible?

fourvalleys > Wrong Wheel Drive (41%) 04/07/2016 at 10:52

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Yep! It depends on how much camber you can run (and what STR allows you to do to adjust camber...) but you can get some pretty wide wheels on a Miata. Like I said above, 15x8 +45 fit no problem on my NA with coilovers and a fender roll. It was pretty close to “stupid low” but it worked out pretty well:

Also, screw that hardtop. Ugh.

JGrabowMSt > Wrong Wheel Drive (41%) 04/07/2016 at 10:59

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New wheels. I’m actually having a set of wheels modified, but I wouldn’t suggest it for most. There’s a guy in Burlington that’s going to do it, I think I’m going to try and stop by his place on Saturday to drop them off. Not all wheels will allow for it either. My wheels are tricky business, I have to take a long look at them tomorrow and measure like crazy to be sure.

I’m a little lost by all the different wheel offset measurements because I can’t find a place that can tell me my current offset, I just have a good idea of how the wheel needs to sit and I know that a lot of people run wide as hell wheels on Mopars.