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Old 09-05-2020, 01:55 AM   #1
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Rear 'tuning fork' swap

Hi folks,

My boxster has been a bit 'twitchy' and doesn't feel terribly planted while cornering. A stock Honda Fit (granted, it was on a 71R) beat me up in the hills today and my ego is a bit bruised.

I came across a post on a Facebook 986 group that advocated heavily for swapping out the rear aluminum 'tuning forks' for some eBay counterparts.



Interestingly, I know that my rear wheels push inward a bit since there is damage to the rear wheel lip, and it makes contact with the strut as a result under heavy cornering.

Any thoughts on if this is a valid solution to cure this deflection? Do you think it'll remove some twitchiness or should I be shooting for some sway bars?

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Old 09-05-2020, 04:44 AM   #2
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If the wheels are rubbing against the strut, the Tuning Forks aren't the cause. Actually, with the way the strut mounts into the wheel carrier, I don't think any faulty suspension part would cause the wheel to rub on the strut because it'll move as one solid assembly. The only thing I can think may be causing that kind of movement is if the hole in the wheel housing where the struts slides into (Item 1 in the pic) is not true anymore, or the bolt that clamps it down is not torqued down all the way. That could make cause it to camber in and out, but even that going bad is a long shot.

The other cause may be excessive flex in the wheel. Are you using OE wheels or aftermarket?

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Old 09-05-2020, 05:06 AM   #3
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Stock width and offset wheels? If the tire is getting into the trailing link, something is seriously wrong.......and I doubt it’s the link.

Last edited by jcp; 09-05-2020 at 05:11 AM.
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Old 09-05-2020, 06:23 AM   #4
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Ms. Jolie's post doesn't make sense.

The tuning fork arms aren't the cause of your woes, you probably need an alignment and some HPDE time.

How many miles on the car (suspension worn out?), what kind of tires, what tire pressures, etc.?
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Old 09-05-2020, 09:49 AM   #5
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Hi Everyone,

Thanks for chiming in.

165k on the ODO. I'm running Carerra iii OEM staggered wheels. The rear is 18x10 +65, the fronts are 18x8, unsure of the offset. Front tires are RE71Rs, rears are some Continental Sports (all I could find in 275 when I took two flats on a roadtrip).

I have a little over a decade of time attack/hpde/instructing, but admittedly that was mostly fwd cars.

Definitely need to swap back to 71rs on the rear, but the deflection should be independent of the **************** tire. The offset and spacer alone puts the wheels damn close to the strut to begin with, so it's not deflecting much (maybe a few mm?), but it is happening.

This may or may not be correlated to twitchy feeling.

Unknown on tire pressures. I generally don't dial them in when playing on the street, and the temperature of the road changes by +20F from top to bottom, but I'll try to dial it in when warmed up and see where we're at.

piper, that's a pretty great breakout
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Old 09-05-2020, 11:16 AM   #6
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Those new tuning fork struts in that pic have serious design flaws. Aka, junk.
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Old 09-05-2020, 11:27 AM   #7
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I'm with racer-boy on this. That rear "tuning fork" (what a stupid thing to call a trailing link) is not on the list of things frequently replaced by the fast guys. (And there's a hint: if you're looking for mods to help you go fast, don't copy mods from someone who is all about stance and pose). The ONLY thing that link positively locates is the front / rear distance. The exception here, is when adjustable LCA's ("coffin arms", to the "tuning fork" crowd) are fitted with enough spacer (to gain camber) that they need an adjustable trailing link to correct caster.

I'm also wondering how someone who says they taught hpde for a decade gets to a point where they post the following:
1) I'm racing on the streets and got schooled.
2) I'm blaming the car, but can't really describe the problem, just a vague term like "twitchy".
3) I don't understand how the suspension works in my car.
4) I'm running on mismatched tires.
5) I don't have a clue what my tire pressures are. Nor my wheel-offset.
6) I know I have a suspension or wheel-offset issue because the wheel rubs on the strut (But it hasn't kept me from racing on the street)

I mean, ALL of this sounds like something we'd hear from someone brand new to cars, and especially to high performance driving.

If you can help us more, we can help you more. What exactly IS the driving problem you're experiencing?

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Last edited by maytag; 09-05-2020 at 11:32 AM.
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Old 09-05-2020, 11:28 AM   #8
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Quote:
Originally Posted by beater986 View Post
... The offset and spacer alone puts the wheels damn close to the strut to begin with, so it's not deflecting much (maybe a few mm?), but it is happening. ...
I have some wide 20" wheels on the back of one of my Boxsters. It came that way. The installer made a small dent in each of the struts to give the wheel clearance. Not optimal, but it works.
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Old 09-14-2020, 02:12 AM   #9
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I'm going to ignore the bit of snark since I understand how the post may come off and I see you've actually contributed some decent information here.

The initial post lacked some information because I was just attempting to see if deflection is a known issue and happen to come across that post below speaking about it and swapping the trailing arm.

From my previous experience with 90s Hondas, the trailing arm bushing disintegrating over time would cause the trailing arm to deflect in a similar manner.

The cause of the contact was actually a horribly bent wheel. Visually it looked only slightly damaged and held air, but when we put it on the balancing machine it was drastic.

While this explains the strut contact, it likely does not an explanation for the feeling. Specifically, there is quite a bit of body roll coupled with some under-steer in the front; though the under-steer does not seem to come about consistently.
When I was on a square setup, the car was definitely a bit tail-happy, but in a very predictable and controllable way.

I plan on logging more seat time in the car, freshening up the tired old suspension itself which I am sure is shot, and then attempting to further dial in anything else by adding a rear bar.

At this point, I'm attempting to research what shock/spring combos everyone seems to be going with. The PSS9s look like your standard choice, but given this is a daily driver and canyon car, I am unsure if they will be streetable enough. The ROW 030 seems like an option, but for the price maybe Koni FSD? Not sure how those compare.


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If you can help us more, we can help you more. What exactly IS the driving problem you're experiencing?

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Last edited by beater986; 09-14-2020 at 02:17 AM.
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Old 09-14-2020, 12:38 PM   #10
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Quote:
Originally Posted by beater986 View Post
I'm going to ignore the bit of snark since I understand how the post may come off and I see you've actually contributed some decent information here.
I'm humbled. Truly.

Quote:
Originally Posted by beater986 View Post
Specifically, there is quite a bit of body roll coupled with some under-steer in the front; though the under-steer does not seem to come about consistently.
When I was on a square setup, the car was definitely a bit tail-happy, but in a very predictable and controllable way.
Was that in this car? Are you getting the body roll and under-steer in the same places at the same speed all the time? (you see where I'm going here)

Quote:
Originally Posted by beater986 View Post
I plan on logging more seat time in the car, freshening up the tired old suspension itself which I am sure is shot, and then attempting to further dial in anything else by adding a rear bar.

At this point, I'm attempting to research what shock/spring combos everyone seems to be going with. The PSS9s look like your standard choice, but given this is a daily driver and canyon car, I am unsure if they will be streetable enough. The ROW 030 seems like an option, but for the price maybe Koni FSD? Not sure how those compare.
There are TONS of people on this forum who have MUCH more knowledge and 986-specific experience than I do. (In fact; search just a little bit and you'll find my admission to several major gaffs along the way, haha.) But one thing I've learned to be the absolute BEST advice is the same thing my golf-pro tells me: Until you can repeatable results, don't change ANYTHING. In the driving world, that equates to "make sure your equipment is all working as it should so you have a consistently reliable platform, and learn to drive THAT first. Then address the issues as needed.

Were I you, I'd do exactly as you've said above: freshen-up what you've already got, and get it working correctly first. And, even being the boy-racer around here (notice, I'm not "racer-boy", that's somebody else here, haha) I'd still tell you that the stock 986 components in good working condition will allow just about ANY shenanigans on the street. In my opinion, it's pretty tough to find weaknesses in the 986 (other than hp) until you hit the track. And I'm not one of the slow guys.

NOW: if you're like me, you look at replacing parts as an opportunity to upgrade. I get that, and I'm the same way. You mention coil-overs (PSS9's). again; imho that doesn't make sense unless you're building a focused-on-the-track car.
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Old 09-14-2020, 01:57 PM   #11
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A trailing arm has no effect on the distance from the inside rim of the wheel/tire assembly to the strut.

A twitchy feeling or unstableness could be caused by a bad wheel bearing, bent wheel or just flat out terrible alignment.

Terrible alignment could stem from a bad wheel bearing (most shops don't shake down the rear wheels when doing an alignment; I don't unless I feel something off during the test drive). OR you could have a bent spindle.
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Old 09-14-2020, 03:04 PM   #12
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As others have mentioned, the trailing arms on these cars won't cause your problems. Honda trailing arms have big squishy rubber bushings in them, the Boxster have a hard nylon bushings, so there is very little deflection. When worn, the Boxster trailing arm bushings make a lot of noise, but they typically don't affect the alignment to suffer.

I'd say rebuild your suspension before trying something like a rear sway bar. Maytag is right, until you get repeatable results, you will just end up wasting time and money.
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Old 09-15-2020, 04:27 AM   #13
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Twitchy lack of stability is usually caused by toe-out. Can be either front or rear. Start with an alignment!

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