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Old 01-02-2010, 06:15 AM   #1
Back Road Runner
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Default Long term chassis wear and damage of the GC8 chassis? Weak points?

Well I bring this up because I'm curious if there have been any experiences by any motorsports folks here where there have been fatigue and damage through long term use of the car at an elevated level.

Accelerated wear is the norm of course, but I'm kind of curious if there are any specific weak points to the chassis.

I do drive a Forester, different vehicle, but it uses the GC8 chassis as the base and is essentially a wagon form of that chassis.

I've been doing auto-x and rally-x for 3 years now, and the Forester has transitioned from bone stock to a pretty competent tool. It is of course in a continuous evolution. The suspension has become decently firm at around 30% above STI rates. This stiffness level very blatantly shows off the natural flex in the chassis. I have been running a 4-point rear strut tower brace for a while now that has quite significantly stiffened up the back end. Fender cowl bracing on the front is a future addition. I'm contemplating some additional bracing where needed, but these two areas seem to be the most significant with most other parts a bit more subtle.

My main concern is that I may eventually cause real damage to the chassis and actually get cracking and tearing somewhere. I'm curious if any key areas have shown up for anyone else running setups beyond mine, key things I should be looking for, key bracing I should be using. By key, I mean bracing that actually does something useful. I don't want to toss something on and not have any perceivable difference. Even something as common as the front strut tower brace is questionable as a large number of people have said it has a pretty minimal effect. Under chassis bracing is another big one where people really don't state real perceivable differences. An internal cage would be an obvious suggestion, but this is a daily driver too, so it's not something I ever intend to do. It is neither a track car so I will never partake in any motorsports that require a cage in the first place.

I just want to end up with something durable enough to where I don't have to care. I'm not really stressing the chassis greatly. It's not like I'm doing stage rallies with it and jumping the thing, but at the same time, even just driving around on rough roads, doing rally-x, and going over rough terrain in the winter does work the chassis a bit, at least above anything it would experience at stock trim.
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Old 01-03-2010, 12:20 AM   #2
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if you don't wanna do a cage, you can always stitch weld the unibody and then put all of the interior back in. That will strengthen your chassis a ton. And caging a dailly driver isn't that bad at all. I drive my rally car daily, it just takes an extra minute to get in and out. You can also build a cage to fit all of your interior back in as well. But definitely look into stitch welding the chassis if you are set at not putting in a cage.
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Old 01-03-2010, 09:38 AM   #3
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Quote:
Originally Posted by recce02 View Post
if you don't wanna do a cage, you can always stitch weld the unibody and then put all of the interior back in. That will strengthen your chassis a ton. And caging a dailly driver isn't that bad at all. I drive my rally car daily, it just takes an extra minute to get in and out. You can also build a cage to fit all of your interior back in as well. But definitely look into stitch welding the chassis if you are set at not putting in a cage.
The issue with a cage is not ease of entrance or exit...it's smashing your non helmeted head against a big ass metal tube.
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Old 01-03-2010, 02:54 PM   #4
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Does stitch welding require the cleaning of the insulation along every seam?
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Old 01-03-2010, 03:23 PM   #5
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Originally Posted by Daishi00 View Post
The issue with a cage is not ease of entrance or exit...it's smashing your non helmeted head against a big ass metal tube.
what about the b-pillar or roof? wouldnt those still be there if a cage werent? wouldnt the cage be less likely to collapse in on you and hit you in the head? and arent the chassis less likely to have a 1/2" of padding on them that cage tubes near you are required to have?
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Old 01-03-2010, 11:08 PM   #6
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Can we get a Sticky in this forum to explain why smacking your head on well designed collapsible plastics is safer than thin solid tubing?
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Old 01-03-2010, 11:17 PM   #7
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To the OP... Your car will be fine - for sure!

I own a shell that was used to close performance rally stages. It's a '97 4-door GC. It has jumped and bumped its way through thousands of kilometers of abuse. Some of the stage closing times were compeditive course times... It survived just fine. I used it as a track car for a couple year after I bought it. Sure it flexed a bit when I put it on jack stands, it had faigued, but it is fine - it is safe.

They are tough shells, if something goes wrong you'll know. The issue with stage rally cars - as you mentioned - is the jumping and bumping at very high speeds. That and the fact that most drivers don't slow down when they have a "minor" problem.
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Old 01-04-2010, 03:28 AM   #8
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I'm just concerned because chassis flex is a noticeable aspect, and the creaking and twisting has me wondering if there may be future issues if I don't make an effort to address them.

It's good to hear that you've had positive experiences with your sedan despite heavy abuse.
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Old 01-04-2010, 08:58 AM   #9
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Quote:
Originally Posted by urabus555 View Post
Can we get a Sticky in this forum to explain why smacking your head on well designed collapsible plastics is safer than thin solid tubing?
This.

A good friend of mine made a funny statement when he was discouraging a fellow enthusiast about caging his daily and why the padding wouldn't be any more helpful:

Get a steel tube from home depot, wrap it with the padding, and have someone whack you over the head with it really hard. Tell me how it feels if you wake up.
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Old 01-04-2010, 05:43 PM   #10
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Quote:
Get a steel tube from home depot, wrap it with the padding,
The same could be said if you smack someone in the head with an a-pillar with the factory plastic on it. Honestly, we can all be pussies and never do anything that's not 100% safe or we can take some calculated risks and enjoy our lives. I DD'd a fully caged car for a couple years (with harnesses). It was probably more dangerous than driving a stock car but, I'm still here today and I didn't die from it. If I'd had a bad wreck, I might have died from the cage, then again I might not. I think REAL rollbar padding is better then the thin plastic you find over most car sheetmetal. I'm not talking about pipe insulation that's worth nothing.

http://www.summitracing.com/parts/KI...1/?image=large

I used padding like this on any bar I might come into contact with.

So more dangerous? probably. Is that reason enough not to do it? Depends on how lucky you feel.

If driving at the track wasn't dangerous, I probably wouldn't be doing it.

Last edited by MasterKwan; 01-04-2010 at 05:50 PM.
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Old 01-04-2010, 06:15 PM   #11
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Don't let this turn into another thread about how driving with a cage is super sketchy without a helmet bla bla bla ... lets talk about ways to improce the GC chassis besides a full blown cage.

I was thinking about welding a X brace in the rear of my GC to support the rear strut towers. What are the other major weak points that could be addressed.

I know the fenders are one, and I did notice a significant difference after I install my braces in that area. Especially mid turn at high speeds (sweepers), the car felt much more planted under sustained cornering loads and less floaty.
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Old 01-04-2010, 06:49 PM   #12
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The problem with stitch welding is that it's hard to do without totally disassembling the car, stripping off the undercoating and working on a rotisserie. Another issue is that you completely compromise the rust proofing when you stitch weld because anything you weld on, the sheet metal behind the weld (in the sills for instance) the paint is blown off. When I had the cage installed in my civic, all the metal behind the welds started rusting almost instantly. The stuff I could get at wasn't a problem. The sheet metal inside box sections though, there wasn't much I could do.

How about a weld in 4-6pt in the back? Tied into the sills and the strut towers with a harness bar? Re-enforce the rear chassis, still safe on the street but, will protect you if you have a harness and roll the car over?
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Old 01-05-2010, 12:14 AM   #13
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I understand tearing down the car to the bone. You could also either Rhino line the inside and bottom of the chassis, or use the roll on Herculiner for protection.
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Old 01-05-2010, 09:11 AM   #14
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You understand that there are sections of the car you can't get at right? Like inside the sills? Those box sections under the doors? I ended up filling my sills with 2-part polyurethane foam to stop it from rusting. Stiffened the chassis too.

Most of the time when you stitch weld, they recommend getting the cage in place first because enough welding can actually tweek the alignment of the chassis.

I like the idea of stitch welding. In practice, it just hasn't been that easy to do.
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Old 01-07-2010, 01:39 PM   #15
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^^ yea I've heard a lot about how stich welding before putting a roll cage into a car can potentially warp the chassis. Is this just a myth or is it a sevear issue, if its not too much of a problem I would definitley consider doing some limited seam welding on my chassis, has anyone do any seam welding without a roll cage?
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Old 01-07-2010, 03:40 PM   #16
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I don't know how warped stitch welding can cause on the chassis. But when i have seen it done, it was done in sections and each stitch was spaced 3 to 4 inches apart. Sections I talk about would be like the right rear then the left front then some on the floor board then the right front then the left rear quarter and so on and so on. Same therory as welding different parts of the cage to prevent warping. So if done right there should be very little warping if any. And you could always take the car to a frame shop to see if it has moved, and if it has you can bring it back to specs.
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Old 01-07-2010, 03:51 PM   #17
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Stitch welding is evil devil's spawn! Warped my shell like a drunken bannana! Just kidding.

Seriously, if it's a DD vehicle and you don't want to repaint everywhere that you've stitched, don't stich weld.

Frame horns and wheelwells forward of the firewall are easy enough to do, but IMO, not worth it.

Just think of chassis flex as an active part of your suspension. If you stiffen one area too much, the other areas will suffer. Like upgrading just your swaybars - go too stiff and it's of no benefit.
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Old 01-07-2010, 04:33 PM   #18
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verging on Analysis Paralysis here....

for a DD or rallyx vehicle, stitch welding is overkill, the tradeoffs (esp rust issues) are just not worth the price. our old GC rally car rusted like sheet around the stitch welds, and no amount of galvanizing spray or undercoating ever slowed down the evil oxidation much.

so beat the crap out of your car as is, enjoy it to the max, and when it's too creaky or you keep breaking windshields, sell it on craigslist to somebody out of state

this is why they say NEVER buy a used car from a rally guy
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