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

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.

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.

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.

Man, I have just the opposite experience as above.cThree cars of mine have strut tower braces. A 2002 Toyota Avalon, 2004 BMW 325ci and a 1995 M3. All 3 braces were "hingeless", and all 3 cars are unibody contstruction.

All 3 braces made a difference but not all the same. The Toyota Avalon (Solara) brace made the biggest difference. The M3 brace made the least.

No quantitative testing was performed but qualitatively, the "turn in" response times are perceptible on all. I would expect a small increase in handling times as well. Ride quality suffers but minimally.

These, when made specifically for the car, are very easy to install and add minimum weight.

Some vehicles are reinforced better than others. I would suspect the most dramatic effects from Front engine, FWD vehicles.

I hope this helps.

abfisch

It made a noticeable difference on my old Legacy, but I was racing that car. You might not notice it with normal driving. If you are noticing frame flex in your car though, you have problems that a stabilizer bar won't help. If this is bothering you, have the frame checked.

If so, how do you measure the effect?

tl;dr: by measuring the tension between the unbraced mount points.

Today, I installed a Whiteline rear strut bar on my 2004 WRX wagon. The car has 162K miles on the odometer and has always seemed in need of a little more stiffness in the area of the rear seats. There's a large volume back there without any sort of cross bracing (unlike a sedan) and the brace certainly seemed worth a try.

In the spirit of my original question, however, I wanted to see if I could measure the effect on the chassis in a static scenario. I tried two situations: flat on four wheels and with the driver's side rear wheel on four stacked 2x10 boards (which puts the wheel about six inches above the ground). I installed the circular fittings on the car and attempted to collect some reference imagery along with a little qualitative data.

NOTE: yes, in an optimal world, I would have used steel wire and a tension gauge. In the spirit of run what you brung, though....

First, leaving the wheel flat on the garage floor:

What you see there are the connecting holes on the braces with a double line of fairly hefty paracord running between them and tightened with a trucker's hitch. I added the sticky pads for some visual reference at the time. I later added the green line from the bottom of both connecting holes using Paint.net. If you've used a trucker's hitch, you know that you can get the line pretty taught: it made a solid "bwong" when I flicked it.

Here is the equivalent image when one wheel is pretty high up, balanced on some quite sketchy lumber:

This picture is both disappointing and satisfying at the same time. The car clearly isn't made of rubber and tin foil (that's good) but it's also not showing an obvious flex that I could use to say "see? this was clearly money well spent and I am a genius!" Sadly, if you zoom way in, you can see that the front line looks largely the same as in the first image.

What is less obvious is what's going on in the rear line (the part where the knots are). That line is showing some droop (a bit but it's there). What you can't see at all is the change in tension in the line. Whereas before I had a nice "bwong," at this point it was definitely mushy.

At the end of all this, I think I can conclude that, yes, for this specific car, I can measure a definite opportunity for improvement in chassis rigidity that this part will address.

Later, when it's not the snowiest goddamn winter that the world has ever seen, I'll see if I can find a way to measure differences in handling that don't involve me being a huge donkey on public roads.

I know this will be a necropost but i want to put the correct information out there for everyone. Strut tower bars actually lower the lateral Gs a car can achieve. However they do improve handling by reducing body roll. This makes the car more stable, and predictable. As mentioned earlier you may also notice the car is more responsive to steering input do to quicker "turn in". Honestly unless the specific model car you have has poor handling I'd skip it or it would be one of the last things I'd do to fine tune a cars handling. As mentioned earlier, your better off replacing/upgrading all your existing suspension, steering, and related bushings. You really shouldn't noticed the difference strut tower bars make on the street. If you do you're driving in a manner that will get pulled from your vehicle at gunpoint instead of a ticket. Now to answer the question that no one has been able to, and the reason I'm necroposting. If you want to measure the difference it makes. 1. Get a camera and a friend to operate it. 2. Find a tight corner or make one in a big, empty parking lot using cones. Or better yet, do the deer avoidance/emergency lane change manoeuvre. 3. Record the car negotiating the corner as quickly as your skill level will allow. 4. Install the bar and repeat. Watch the footage back to back and you should notice the car is "flatter" in the 2nd pass. The body roll can be measured in degrees off of a still from the video. The main benefit of strut tower bars is the predictability, and added stability, which instills driver confidence, and makes the car easier to drive. While attempting the 2nd pass you should notice it was easier, less dramatic, and you should feel like you had more control of the vehicle. I own a 07 Impreza with coilovers and strut bars.

Yeah dude put the Jack under the left front control arm. Jack car up see how far the left front tire gets before the right front tire comes off the ground. Then add a strut brace and repeat the process. If there is any difference in Heights subtract 1 from the other and you'll have your answer.

This is an interesting topic i have stumbled upon. My point dont or none in put to above but i feel car with staggard wheels and rear wheel drive have greater scope. I drive rear wheel mercedes SLK with 34000 miles from new and is model year 2008/09 Face Lift. With above set up you will technically experience understeer when going into fast curves and corners in wintery or wet conditions but is easily corrected with driver input via 1 steering or 2 more power ( speaking from experience) My car is factory fitted sports suspension and no added bars so far. I have uprated entire front suspension wiith Bilstein B6 parts and work carried out professionally.Unfortunately UK road are not the best in world and suspension is very firm, unless you get a chance to drive very quick to smooth out Rump/Thrump. Front wheel drive cars have built in overstear and its opposite to rear wheel drive. To gain anykind of benefits you have to take this into account. Tha law of physics,"a moving body will stay on its path provided it stays within the circle of traction". What ever you do to your car think of Circle of Traction.