Thread: Narrowed control arms

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I bought a 1935 Chevy with a Mustang 11 rack, the tires are to close to the outside fenders. I am thinking of getting narrowed upper and lower control arms. Do they just bolt on or will I run into some clearance problems? Thanks Jim

I built narrowed control arms (1") for a MII setup in my 30 A-bone. It still drove like it was on rails - at least up to 125 . . .

Thanks for the info Richard. Now to save on cost I wonder if I could have the stock arms cut and welded like Jack did? Would there be enough adjustment on the tie rods to makeup the difference Jim

Richard,

The suspension was based on a Progressive Automotive crossmember and stock MII parts. I didn't cut either the upper A-arm or the lower spring support.

I got the 1" on the lower spring support by moving the mounting holes inboard and adjusting the strut rods accordingly. The uppers were scratch-built, as there was no way to move the pivot point inboard. I thought the slight change in relative length upper to lower might cause a problem, and I was prepared to remake the lowers, but it worked out fine.

I've attached a photo, which isn't very good. For the uppers, I bent a couple of pieces of heavy-wall DOM tubing and slotted the ends to accept a plate for the ball joint mount. The other end had 4-bar bushings. The crossbar was steel barstock with milled flats for the bolts on top and the mounting pads on bottom.

There was enough adjustment in the tie-rods that I didn't have to make any changes.

Cousin Richard is correct, the rack tie rods need to be shortened, but they have plenty of thread to allow that. I've got the Heidt's on my '36 Roadster.

I found some better photos of my narrowed MII front suspension. Note the new holes 1" inbord of the originals. That took the lower arms in. I fabricated the uppers myself, and made them an inch narrower than the stock ones to keep everything pretty much even. I'm sure it changed the geometry somewhat, but the car ran like it was on rails . . . at least up to 125 or so.

Another photo.

I myself really wouldn't look at this very lightly as changing those pivot points to gain clearance is very serious. You may luck out as it seems Henry did but shortening the control arms does a lot more than just move the wheel in. This will change roll center height, camber characteristics and curve, likely some caster change, length of side view swing arm and front view swing arm would change, scrub radius, bumpsteer and other serious issues could come up so just make sure you know what you are getting when you go to buy. That being said, I'm assuming you are just going to cruise in this car so it might not be too serious for you. It could wear your tires more quickly and make your car twitchy and shaky at speed or in corners. You could just get different rims and tires with more backspacing (if possible) or a narrower tire.

. . . it was engineering and careful fabrication.

Roll center: I located the static roll center before I changed the A-arms, plotted it on my AutoCad, then fabricated the upper control arms to make sure it did not change. I also tracked (AutoCad again) the movement of the roll center under a range of body rolls - both with the original and the modified A-arms. I didn't consider the minor differences I saw to be significant.

Scrub radius: Again, I measured it, and kept the relative position of the upper and lower ball joints constant. Scrub radius stayed slightly positive both before and after the modification.

Caster: No change. There was plenty of adjustment.

Static Camber was set at ride height the same with the modified arms as it was with the stock arms. Granted, camber changes as the arms swing, but I plotted that on Autocad also, and found that the difference wasn't significant over the limited travel of a high-performance hot rod suspension setup. The old adage that steering geometry becomes less critical with less motion is still true.

Finally, here's something to consider. In putting something like a MII suspension under a street rod with a different ride height, weight, center of gravity, instant center, power level, weight distribution, and just about any other specification we care to consider, it's kind of a crapshoot to start with unless either the builder or the supplier engineer the application. The relatively minor mods I made caused no difference.

I could take my hands off the wheel at 120, and it cornered like a dream. No shake, no tire wear, no problem.

But I do agree with you that someone buying off the shelf should be careful.

By the way, changing the backspacing WILL change scrub radius - and not in the direction you want to go with a rear wheel drive car.

Sorry Henry, I wasn't fulling thinking when I posted. I thought about how I said you 'lucked' out later and figured how bad that musta sounded. I didn't intend to make it sound like you were just lucky but rather that yours worked quite well when it could have been much worse. If an uninformed guy goes out and buys something and bolts it on it can change much more than they intended it to and I just wanted to make sure that was known. I also agree that changing the backspacing on the front will change scrub radius but when compared to changing arms I figured it was the lesser of two evils. And I did say that with his intended purpose it might not be a very serious deal, but I think the truth about doing uninformed bolt-on swaps should be realized. It might not work all that well or it could be just downright dangerous.

No biggie. My reply probably sounded a little more terse than intended also. The reason for my detailed post was to make it very clear that changing suspension without thinking it through probably wasn't a good idea.

When I put my 38 together with MII stuff , I upgraded to the large chevell type rotor (I purchased the caliper bracket from FatMan.) Uppon fender instalation I had the same interferance problem. I solved this by using a S10 rotor that moved the bolt face of the rotor inboard 1" per side.

paul

Are you saying the S 10 rotor sits 1 in. inboard of the mustang rotor? Jim

No, when I up graded to the larger 11" brakes using the chevell type calipers, your also supose to use the rotor as well, (It is a chevy car) but the tire-fender problem arose. I tried the S10 that is 1" smaller between the wheel bolt face and the outer disc face.

paul