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Unread 12-29-2012, 07:11 PM
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Fair! Fair! is offline
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Default Re: Vorshlag BRZ Project Build Thread

(continued from above)

Other FT86 Track & Autocross Preparation Work

We have worked on a number of local FT86 owner's cars, getting them ready for track and/or autocross use. Britney's FR-S was already modded with a custom exhaust and some aftermarket 17x7" wheels and 215mm Hankook R-S3 tires when it came to Vorshlag for some front camber help.

Looking at other Subaru modders online, they went with the smaller shank diameter Subaru "crash bolts" at the upper front strut to spindle bolt location. Normally the FT86 (similar to the Impreza which the suspension is based off of) has the "enlarged shank" 16mm bolt in the upper spindle mount holes and the 14mm bolt in the lower holes. This "crash mod" entails swapping out the fatter upper spindle bolt with the slimmer 14mm bolts, so now there is slop in the mounting holes and you can tweak the strut inboard a bit more without slotting any holes. It... is not the ideal way to gain camber, but it is a simple and inexpensive way to gain about a degree.

So Britney's FR-S and it had -.2 and -.4 deg camber up front from the factory. We spent a whopping 30 minutes installing these bolts and got the front camber to -1.7 on both sides. Not bad for the stock ride height, and anything is better than the stock setting for track use. Personally I like to see -2.5 or more for track but hey, for as cheap as these bolts are it isn't half bad.

Next up was Mark's FR-S, which got the first production Swift lowering springs we've installed as well as Whiteline's front and rear camber kits. The front kit is similar to the crash bolt fix, but uses nicer bolts and other specific hardware (see below for further details). The rear kit includes a pair of offset and adjustable elastomer bushings for the upper control arms. Mark already had some 18x8" ET48 "Sparco" wheels, which were pretty and at least an inch wider than stock. However, since the costs were low and they were 18" diameter, they were also fairly heavy. Still, almost anything is an upgrade over the skinny stock 17x7" wheels. For tires he had 225/40/18 Michelin PS2s.

We started by checking his ride height, toe and camber settings at all four corners.

Before and after ride height checks shown on the RF corner (from 14.5" down to 13.5").

Then we pulled his OEM springs and rated them on our digital spring rater. And we rated Matt's OEM BRZ springs as well. Yes, they are indeed different...

Here are the FR-S and BRZ OEM spring rate charts. Kind of big, but they need to be to be legible.

FR-S and BRZ OEM spring rates, as tested by Vorshlag. Click above to enlarge.

As you can see, the stock FR-S rates are pretty soft, but fairly linear both front and rear. The BRZ's OEM springs are stiffer up front (+63 lbs/in) and softer in the rear (-20 lbs/in). In the grand scheme of things that isn't a lot of stiffness, but the balance difference is probably noticeable if you drive the two cars in stock form back to back on track. But who wants to keep these soft stock rates and 4x4 ride heights? Most of you reading this won't.

After rating Mark's FR-S springs, we installed the Swift BRZ lowering springs, p/n 4F912, which we also tested for rate.

Click the Swift spring rate chart above to enlarge.

The overall drop when we installed these Swift springs onto Mark's FR-S was almost exactly 1" at all four corners. We shortened the bump stops as well. We took about 1/3rd of the OEM bump stop off from each corner.

Once the springs were installed, it was onto the Whiteline rear UCA bushings. These were tricky to install, mostly due to the hassle of cutting apart one of the OEM bushings to be able to press it out of the control arm. We figured out some tricks and with our bushing installation rig we were able to get the old ones out and the new Whiteline bushings installed. Kind of a mess, but once the "flange" was cut off the OEM rubber bushings they could be pressed out. This is a job probably best left to "advanced" modders or your local suspension shop.

Now the rear camber can finally be adjusted (which the stock rear suspension is otherwise lacking) and a pair of OEM rubber bushings are gone, so this point will no longer deform under heavy lateral loading (track/autocross use). We like this kit and will be picking up a set for Matt's BRZ as well as some sets to stock and sell.

Whiteline's eccentric camber bolt kit as installed on the front strut of an FT86 @ Vorshlag.

Last up was the installation of the front camber adjustment bolts. Unlike the smaller diameter Subaru crash bolts we installed on Britney's FR-S, Mark went with the eccentric camber bolts from Whiteline. Again, these replaced the big 16mm shank upper strut mount bolts on the front struts and also allow the struts to be tweaked relative to the spindle, for some slight camber adjustment. Again, about a 1 degree change is normal. We sell this kit here at Vorshlag, as well as all of the Whiteline parts for the FT86. This is another cheap and easy way to get some camber adjustment in the fronts of these cars. But ... just like with slotted strut mounting holes, there are downsides.

First, given enough lateral force on the strut mount, the smaller diameter or eccentric bolts could slip, which would knock your camber out of alignment on one corner. This could happen from tapping a curb or heavy pothole, or even aggressive track driving with high enough grip tires. This didn't happen on Britney's FR-S on 215mm RS-3 tires, even with crazy KenO driving it, so that was a good test. Mark's car seems to be holding up with these eccentric bolts as well.

Next, any time you tweak the strut angle relative to the spindle you are removing wheel and tire room inboard at the strut. Now this doesn't pose a problem unless you are pushing the envelope on wheel/tire room inboard - on Matt's car with the 255mm tires, it was a big deal. Even without any strut mounting tweaks the 245's barely fit inboard, and the wider 255mm tires needed a 5mm spacer. If we had done crash bolts instead of camber plates, both situations would have needed to move the wheel outboard more, with more spacer thickness. There is no free lunch - every modification always has pros and cons. Just keep that in mind when using crash bolts or slotted strut mounting holes to gain negative camber. For street use on normal street tires of normal widths it isn't an issue. And keep an eye on your camber; if it slips, get the car re-aligned.

Left: Before with the OEM springs. Right: After the Swift spring and Whiteline bushing installation.

Mark's finished FR-S now sits 1" lower, rides better, and should handle better with a bit more spring rate. The camber is adjustable both front and rear and the rear UCA has Whiteline elastomer bushings. The added negative camber up front will help handling at the limit and save tire wear on the track. I'm still not a huge fan of camber bolts, but on certain set-ups and street tires, they can work. And honestly we sell camber plates, so crash bolts are never going to be high on my list of approved mods.

2013 Scion FR-S on Swift lowering springs + Sparco 18x8 ET48 wheels.

Mark also has our Subaru M12-1.25 long wheel studs installed on the rear hubs of his FR-S. He uses the longer studs to work with a 10mm hub-centric spacer he needed to make the +48 offset 18x8" Sparco wheels sit with a wider rear track out back. He said it fit without the spacer, it just didn't fill out the fender very well.

Mark said the rear studs were easy to install once he figured out how to remove the rear hub assembly (see above left). Off comes the half shaft retaining nut, then you unbolt the hub assembly from the emergency brake bits and you can remove the rear hub. Once removed from the car, you can use a press to push out the rear studs; the new studs go in the same way. With the Vorshlag 65mm studs installed out back, now there is full engagement of the threads on the longer/larger Vorshlag lug nuts even with that 10mm spacer installed (see above, right).

Our 65mm Subaru style Vorshlag wheel studs install into either the front or rear hubs relatively easily. As you can see the installed length is 48mm past the hub face up front, compared to only 25mm of stud protruding with the stock wheel studs. This upgrade gives you a solid 23 mm increase in stud length over stock, but they don't look silly or stick out excessively with the Vorshlag lug nuts. A solid upgrade for any track or autocross car - more lug nut engagement and the ability to run up to a 20mm thick spacer, if needed.

We installed these on the front hubs of Matt's BRZ when he upgraded to 255/40/17 Hankook R-S3 tires. The front wheels needed a 5mm spacer to allow this fat tire to clear the struts. Any spacer use requires longer wheel studs, as the stock studs are very short. This also necessitates new lug nuts since the stock nuts are very short, close ended lug nuts.

For those extra picky folks worried about long wheel studs making their FT86 look like Roman chariot wheel spikes, or the modern equivalent, fear not. As you can see above on the BRZ with our "65mm wheels studs" and a 5mm spacer there isn't a hideous amount of stud protruding past the lug nuts. This is just how a race tech inspector wants to see - full lug nut engagement, plus a little more. Perfect.

(continued below)

Last edited by Fair!; 01-02-2013 at 07:47 PM.
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