Boxing in control arms, what's stronger?

Hey all,

I'm notching the trailing arms on my Civic to fit big tires.

The arms are double layered on the upper and lower sides. Would it be stronger to put the plate on top of the arm and weld it from the front and back side, like so

Or cut the plate smaller and sink it in between the two sides?

Can we get a pic of the arm like the third one, but without the plate?

Also, that's mighty close to the rubber, deflection might still have it hitting if this is for corners.

Not sure about that, but what I am sure of is that your boxing plate should not be flat, it should have bent sides so that it welds onto all of the shiny newly exposed surfaces, not just the flat middle part. And +1 on cutting deeper to give yourself more room, not just for deflection but for slightly different tire models.

Edit: I'm leaning towards the first welding approach for clearance reasons.

I'd cut the plate so it's edge is on the middle seam (between inside and outside), then weld it so that the three pieces are welded together...

But yeah, more clearance.  You'd be surprised how much tires deflect.   Are you going to run spacers?

Yeah I'm planning on going deeper if putting the plate on top. Both for tire deflection and if I need to go to a different tire. Still roughing it up. No spacers are planned, I'm doing this to try and fit a 245 inside the stock quarter panels. One side has a lot of filler so I don't want to open that can of worms, plus this is an autox car so the narrower the rear the better to slip through slaloms.

here's more pics I have on hand:

I also have some plates on the way to box in the back side

I'd probably do a C-channel inside that last picture, kind of like the pic below.  Try and tie in all the other cut surfaces, of course, but something along these lines.

2-1 for going sunk inside the rails then.

I can't completely plate off the inside of the arm as the ebrake cable runs inside there.

Should be simple enough.  Hole in each side of the C channel, left and right to pass through, middle to help fish it through.

Tires are squishy, but so is steel.  The metal will move a lot, too.  At least most of the side load is going through the other two arms.

To reduce the stress riser, make the angle cuts more gentle, and close them up, too.  Boxing in the back will definitely help.

How much clearance do you have top and bottom (shown and far side in first pic) to add some rectangular tube or C-channel if it all ends up iffy?

Arms are notched, fully welded on both sides, stich welded all the factory layers together, and added plates along the top and bottom of the arms. All in 1/8" steel.

Should I also add an x-brace on the back side as shown in carboard in the 3rd pic, or just put the dimple-die plates on the back and call it good?

I don't think the x-brace is needed.  Looks like you tied in a lot more material top and bottom.

In reply to Run_Away [FS] :

I think that is good once the back side it welded on. No need for the X in my opinion.

Paint it red.

Red is faster.

Looks good!

I'd skip the X brace, myself.  I'm guessing the area you have the X is already stronger than the rest of the arm with less layers and welds?

Yup.  Skip the X.  It's so small that it really isn't adding anything but weight.

Nice work.

I say paint it blue.  Blue looks slow, so you'll trick people into thinking it isn't fast when it really is.  Sleeper fake out.

I think eric kutil showed on his instagram something similar for his RTA. 

https://www.instagram.com/eric_kutil_racing/?hl=en

I think the post is from around May 30th. 

Cool, thanks for the reassurances guys.

In reply to aw614 :

I saw that! That's what made me pull the trigger on the Honed plates.

Going to be priming and painting the inside of the arms this afternoon, might get one side boxed.

I'll post up when they're done, I took weights beforehand so I'm curious to see how much I added.

Finshed them last week.

Gained about 2lb per arm

Installed with PCI spherical trailing arm bearings in place of the stock bushings.

Really pleased with the fitment of the wheels, specs are bang on. 17x8.5 +58, which is an S2000 specific fitment. Tires are 245/40 RE71. 2.2 deg of camber.

Should balance well with the 255s up front

Bit wider than the 215s it had.

Looks solid - I bet it feels much more precise.