It's been a while since I've been active on here, but I'll pop in every once in a while to look things up.
Recently, I got an itch to try reducing the body roll, and looked into rear anti-roll bar options. I was considering Daox's setup, since I'm still using the MAF housing he developed, but I'm running a chain and turnbuckle on the spring perches to pull the rear alignment into specs.
After doing some research on some cheap and dirty methods, I've seen people talk about welding or clamping a flat bar onto the open end of the torsion beam to close it off. Naturally, I headed to Home Depot to scout out what materials I could use. I found a length of 3" steel bar, but that's way too much for what I want. Unfortunately, I couldn't find any aluminum flat bars.
I ended up spotting an aluminum saddle-style door threshold measuring 3" by 3'. It had a slight curve to it, which I figured would allow it to self-center inside the torsion beam, and it was thin enough to be able to twist it some by hand. I just wanted a little bit more stiffness, and not go 3-wheeling around corners, so I grabbed that, three C-clamps, and some nylon lock nuts.
I thought installation would be a breeze, but it turned out the C-clamps expanded a bit when I put them onto the torsion beam, and the bottom plate wouldn't fit on. I had to elongate the holes a little bit with a Dremel and grinding bit and grab some washers to better secure it. The door threshold actually fit amazingly well, perfectly seating onto the torsion beam.
I was surprised at how well it works. I took it around the block and threw it back and forth, and the rear end definitely feels stiffer than the front, but it doesn't feel like it's totally solid ekther. I'll see how it changes the feel on the road tomorrow during my work commute.
All in all, it cost just about $20!
Last edited by Cani Lupine; 12-28-2020 at 10:29 PM.
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View my fuel log 2014 Mirage DE 1.2 manual: 49.2 mpg (US) ... 20.9 km/L ... 4.8 L/100 km ... 59.1 mpg (Imp)
My Mirage is a bouncy ride, no steering feel, I don't ever feel rearward sway except driving rear steering trucks at work, but that is a different feeling again.
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View my fuel log 2014 Mirage ES 1.2 manual: 42.2 mpg (US) ... 17.9 km/L ... 5.6 L/100 km ... 50.7 mpg (Imp)
Daox did the math on this technique and decided it put too much strain on the joints where the crossmember connects to the trailing arms. He even fabbed up a prototype.
I believe that. When we built the Festiva "race car" (the dreaded FASTIVA autocross car), we welded a piece of flat steel across the bottom of the beam axle to make it a box. It worked GREAT! But, ultimately, the axle cracked near the welds on both ends. It definitely concentrates a lot of extra stress in that area when you remove the flex from the center section.
In our case, we caught it early, welded the hairline cracks, and continued to "send it". Probably not the best answer for a daily-driven street car.
Keep a close eye on the area around the welds for signs of stress fractures. Especially since you're already introducing "unusual" stresses with the toe-correction kit you have in place. As long as you're just casually street driving it, it will probably be fine. We beat the heck out of that poor Festiva with multiple drivers autocrossing it every other weekend with stick 225-width tires for a year and a half.
Check out this rear bar that Sonic owners are bolting into the torsion beam to stiffen it up...
HERE is a complete installation with images and comments.
I have never mentioned it because I am too lazy tbh, but MKIV VW folks did this often. It was called an O-Bar. It really worked, but it was simply a hollow bar inserted inside of the axle beam.
Resident Tire Engineer
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View my fuel log 2014 Mirage ES 1.2 manual: 44.4 mpg (US) ... 18.9 km/L ... 5.3 L/100 km ... 53.3 mpg (Imp)
I believe that. When we built the Festiva "race car" (the dreaded FASTIVA autocross car), we welded a piece of flat steel across the bottom of the beam axle to make it a box. It worked GREAT! But, ultimately, the axle cracked near the welds on both ends. It definitely concentrates a lot of extra stress in that area when you remove the flex from the center section.
In our case, we caught it early, welded the hairline cracks, and continued to "send it". Probably not the best answer for a daily-driven street car.
Keep a close eye on the area around the welds for signs of stress fractures. Especially since you're already introducing "unusual" stresses with the toe-correction kit you have in place. As long as you're just casually street driving it, it will probably be fine. We beat the heck out of that poor Festiva with multiple drivers autocrossing it every other weekend with stick 225-width tires for a year and a half.
That's one of the reasons I went with aluminum instead of steel. It does have some flex by hand, so hopefully it shouldn't overstress it with street driving. I might cut it shorter to let it flex a bit more, since it did feel a lot stiffer than the front now.
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View my fuel log 2014 Mirage DE 1.2 manual: 49.2 mpg (US) ... 20.9 km/L ... 4.8 L/100 km ... 59.1 mpg (Imp)
On my normal commute to work, which involves about 20 miles of mountain roads each way, it worked amazingly well. Unfortunately, I kept getting stuck behind slow traffic, but the few times I was able to corner at my normal speeds, there's definitely an improvement. It corners near flat now, unless you're really pushing it or warming up your tires. When cornering at my normal speeds, it feels much more stable. It has me like Ken Miles, "She can do more, I can feel it!"
I did notice some rattling, though, so I cut about 7" off that was hanging past the U-bolts, and put some Gorilla tape along the contact points. That cured the noise, and I don't think the length reduction will affect the stiffness since it was outside the clamps anyway.
But I'm still shocked that an aluminum door threshold worked this well.
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View my fuel log 2014 Mirage DE 1.2 manual: 49.2 mpg (US) ... 20.9 km/L ... 4.8 L/100 km ... 59.1 mpg (Imp)