Does a strut tower bar have any useful effect on chassis stiffness for a car with 100K miles?

Question

Aftermarket strut tower bars are generally considered to be decorative on many brand new cars. However, it seems to be a bit more logical that a chassis with 100K miles would have developed some flex and could use a cross-member to stiffen things back up.

Background: the specific car in question is a 2004 Subaru Impreza WRX wagon, daily driver with 110K miles, none of them off road or racing.

So, the specific questions:

1. Does an aftermarket strut tower bar have any measurable effect during an enthusiastic daily commute?

2. If so, how do you measure the effect?

I have to admit, there have been plenty of times when I have wished that there was a bar across the engine bar just to give me something to lean on (as opposed to the intercooler!). That doesn't seem like a sufficient motivator, though.

EDIT to follow-up on some of the points in the answers: the fundamentals of the suspension have already been sorted: Hotchkis sway bars with new bushings, KYB Excel struts (that are effectively OEM replacements) with Kartboy endlinks. This isn't an autocross car but the easy targets have already been addressed. Now we're literally talking about tightening up an aging chassis.

And the answer can be no, there won't be a difference.

Answer 1

From my experience with a number of Subarus (my current oldest one being an MY2000 Impreza turbo with PPP and 130,000 miles on the clock) I can state that a strut brace makes an amazing amount of difference to both my usage (definitely enthusiastic) and my wife's (normal commute plus kids to school etc)

It stiffened the handling up significantly, makes cornering feel much more precise and makes her feel safer when driving. This is an old, well used car - and before adding the strut brace it did feel 'tired' - maybe the wrong word, but everything does get looser with age:-)

For me it just makes some manoevres on the track feel much less likely to upset the balance of the car - essential at 140mph plus!

Answer 2

I would say it depends on the chassis. Since the GG chassis Impreza is relatively stiff to begin with, I'd say any effect would be near-placebo. Improvements would be in steering/cornering feel, rather than something that can be measured quantitatively, like better lap times. Also, they make a LOT of different braces for your particular car - not just the strut tower brace. Look into Cusco.

I've put strut braces on S13/S14 240s where the ride stiffened up noticeably and cornering seemed a tad more responsive. However on higher mileage cars, this effect was almost negated by the next weakest link - worn suspension bushings, worn shocks, inadequate anti-roll bars, worn/misaligned tires/suspension. I've put a strut tower brace on a brand new M3 (brace was an actual M Motorsports part) that wasn't noticeable at all given the quality of the chassis.

Also keep in mind that the design of the brace is important. There are cheap ebay braces that just attach at both strut towers that can flex by stepping on it with your foot. Quality braces will mount on several points - both strut towers and two attachment points on the firewall.

edit to be more aligned with your original question.. years ago we worked on an old datsun. New control arms. new steering bits. new racing coilover setup. new wheels and tires. all new bushings replaced. And when the car was pushed to the limit? The chassis flexed. You can almost hear it in some places.

The sure fire solution? Seam welding and/or a roll cage. Your car may be a daily driver, but nothing looks as awesome as a cage in a street car :) (eclipsed only by contusions suffered from smashing your un-helmeted head against the cage).

More anectdotal "information". I had spoken to a pretty established chassis shop that worked primarily on Evolutions. They had seen cars with all manner of aftermarket bracing - front/rear stbs, front "power" brace, braces in the trunk, braces that went under the fender.. braces underneath the car that tied the frame rails together. While these upgrades enhanced steering feel and overall "stiffness", in practice these cars weren't as fast as cars with well sorted out "dialed in" suspension.

Answer 3

I would say that anything that you can do on the street would be noticeably impacted by a strut tower brace, even during "enthusiastic commuting". The street is no place to be doing "nine tenths" or "ten tenths" driving, and even with spirited driving, on the street you are unlikely to have any noticeable impact.

If you aren't running R compound tires, you probably don't have the traction to make a tower brace do anything, even if you have fairly high performance "street tires".

If you think you're really pushing your car on the street, try going out for an autocross event. You can probably find an "solo" or "autocross" event within an hour or two of where you live pretty much any weekend in the summer. The "solo" events, as the name implies, are doing timed runs against the clock, not other cars, through a course set up with pylons. A properly set up course should have no opportunity for running into any obstacles, and will give you a feel for what sort of environment it takes to need a tower brace.

I've never heard of a car's chassis "getting tired", so putting a brace in would really make no difference.

Answer 4

Depends on the car I suppose.

I've heard a lot of people raving about how much it helped, but my experience is different.

I upgraded my stock front strut tower brace on the MR2 to the TRD model, installed the rear TRD brace, and also did an underbody brace at the same time. No difference detected at all. The car had around 140,000 miles at the time, with many of those miles at autocross, rallycross, and rough dirt/gravel road rallys. I did the upgrades as I was concerned about the car getting beat to death. Figured I should reinforce it. Turns out that I was worried about it for nothing. :-)

My Eclipse has a cage in it and originally had a front brace, but not a rear one. I added a rear one primarily to give me a place to fasten equipment to on long road rallys. It made no difference otherwise. I removed the front brace as it was always threatening to short out the positive battery terminal. No change noted. The car had about 90,000 miles, with many hard autocross, rallycross, road rally, and open track days on it. However, it has also had an 8 point cage since about 30,000 miles or so. Definitely not as well built a car as the MR2, the braces may have helped if it didn't have the cage, maybe.