Lengthening A-arms - by how much?

[cstreit]

I'd like to lengthen my a-arms on the racecar to add more camber to them, I just can't get enought even with offset strut plates and ball-joints. 2 degrees max!

So... I'm going to pull the a-arms this winter and lengthen them in order to put some more camber in.

Question is. How much?

I could do the angle calculation from the pivot to the ball-joint king-pin and the top, but I'm not sure where the "top" is... is it the top of the strut, or some other "theoretical place".?

Anyone done this? If so, how much?

Thanks!

CHris

[J P Stein]

About .300 movement at the top over that distance(inboard) or bottom (outboard) equals -1 deg camber. This assumes a length
of 18 inches (WAG... so ya best check that) top mount to ball joint.

[cstreit]

..Thx... Then WTH can't I get more than -2 degrees with the offset strut plates and ball joints on a '70 chassis?!

[Green 912]

Thats odd as I can get 2.75 on a 69 tub using the weltmeister type mono ball strut top and no other mods. Are you using coil overs?

[gestalt1]

the elephant racing offset ball joints can give about 3/4 deg. extra camber. you coulsd also have some camber added to the spindle, i'm sure you know about these options already. how would you lengthen the a-arm? i've heard of this but not seen and photos of where the addred length is added.

[J P Stein]

Originally posted by cstreit
..Thx... Then WTH can't I get more than -2 degrees with the offset strut plates and ball joints on a '70 chassis?!

Well.....I figure you've mooved the top inboard about .600 all ready....then the fun starts. First, the shock's dust covers hit the inner body work. Then, your trick offset mounts hit the inner body work. I been down this road on my 914. -2 was max I could get.
Then I went to bias ply slicks & had to get back to -.5....it never ends.........

[cstreit]

I'm running coil-overs and have verified that the upper spring-perch doesn't hit the strut tower. There is not dust-boot as a result to interfere. It's the upper strut mount that's contacting the body there.

Lengthening the a-arms is actually an old PCA club racing cheater trick. You cut the a-arm and then weld in a short piece from a donor, grind, paint, looks stock. For me I don't need to worry about looking stock as it's allowed in my group. The other alternative would be to add a rod-end type configuration to it and make it adjustable. DOing this from scratch makes me nervous though as I don't know the forces applied to it, nor how I'd "make" a ball joint. I've see it done before.

[gestalt1]

i always thought the 935 typ front suspension looked like something that could be fabricated. however your right about the ball joint mounting etc.. once you get into the details it is more work than just welding on roomier strut towers. i think the big advantage to lengthening the a arm is to improve the steering geometry with wide tires, not just more camber.

[Green 912]

Can you go with tower boxes? That would cure the camber without making a double track with a wider front track than rear as well s not be a cut/weld and stuck with it type of thing. Too much front track can make for a handful on the straights. Most folks that run with coil overs have to go with the boxes to get good camber numbers. You could also install the Porsche Porn of 935 type front arm$ and save the cutting and welding.

[TimT]

photo courtesy VCI

Ive modded a pair of stock arms with a rod end similar to the pic.

I got the pins to secure the strut from Smart Racing

[cstreit]

Tim,

Wanna sell 'em? Make me a pair and save me the time?

Smart Racing eh? Okay!

Problem with camber boxes is that I'd have to cut out the front cage braces... But that may be the route anyway.. How hard are thsoe bad-boys to align?

[Green 912]

Check the SRP site they have good instructions and pix online. Good metal and basic welding skills, a level body and a good protractor are required. I found that cutting a bit small with a plasma cutter and bring the box cut to size with a 60 grit blending wheel easy to dial them in.

[Jeff Alton]

Chris, you have front coils right? I know they are expensive but have you considered 935 style ERP or TRG front suspension? I have used both and the ERP one is slightly nicer for sure (and lighter) but this would also provide you with some adjustability if you needed it.

Tim, I like that jig, can you provide a measurement from the uprights that hold the arm on the back of that photo to the center of the pin? Or did you do yours with out a jig?


I would make one of those up, looks like a good solution.

Cheers

[RS2]

Chris
We've had the lower control arms lengthened by 10 mm and that works out fine to give us all the negative we want.

[cstreit]

Jeff, Oh I've considered it, I just haven't been able to stomach the price considering it's some tubing and rod-ends, lol.

RS2 - Was that an adjustable 10mm or fixed? I'm looking for -3 to -3.5, will I be able to get around there?

[Jeff Alton]

I know the feeling, everytime the box shows up with that stuff I do roll my eyes.....

Cheers

[safe]

Chris, what did you do?

I'm thinking about lengthening my a-arms.
Around 10mm would have been my guess about how much to add. But I would like to know from somebody how much extra camber 10mm will introduce.

[hesaputz]

Call Steve Cox at Cox Motorsports in KC - he routinely does this mod on his stable of RSR's, and knows exactly where 10mm will get you.

[cstreit]

I ended up welding in cnmber boxes. Wasn't nearly as difficult as assumed. I'll find the article for you.

[cstreit]

Here you are.

Installing front camber boxes - any gotchas?