Trailing arm reinforcements? And wheel studs Options

[mb911]

I am at the point where I will be sand blasting the suspension and doing the 5 lug conversion. Do the trailing arms flex that much that they need reinforcement for a street car? And what length wheel stud should I use for the 5 lug conversion?

[sled9146]

Good questions, answers are based on your driving style. Yes, the arms do flex or twist and you should check to see how straight they are now and not wait for the alignment shop to say that you have a problem with one or both sides when your done. Also remember that today's tires are probably better than race tires were when our cars were built. I use Michelin Pilot Sports and they are FAR better. So the chances that you will have twisted arms in the future may be greater than you think.

Your wheel studs should be at least 52mm. Original for 356C and early 911 and 912 were 45mm. If you like the old school racer look with wide steel wheels and studs that stick out, and steel lug nuts you can use 66mm or 72mm.

[Bruce Hinds]

Not sure about the trailing arm question, I purchase a set of boxed arms after building my mild v8 street car that I auto crossed some. I never installed the boxed arms. Seems fine for what I've done which has included some wild mountain driving in Colorado.

Studs - that would depend too on what wheels you chose to run. 911 wheels will fit fine with the shorter studs, but when you go to wheels off the boxter and other models you may need spacers since the off sets are different.

[mb911]

Not sure about the trailing arm question, I purchase a set of boxed arms after building my mild v8 street car that I auto crossed some. I never installed the boxed arms. Seems fine for what I've done which has included some wild mountain driving in Colorado.

Studs - that would depend too on what wheels you chose to run. 911 wheels will fit fine with the shorter studs, but when you go to wheels off the boxter and other models you may need spacers since the off sets are different.

I am using 15x7 and 15x8 Fuchs so that clears that up.. I will have to think about boxing the trailing arms

[campbellcj]

To box or not to box. That's an age-old question. Many folks say the added weight isn't worth it as the flexing is not a significant problem to handling. Especially if you still have rubber (or any flexing) bushings in the suspension, you are getting movement all over the place.

The unreinforced arms can bend (permanently) in extreme circumstances but if your car is light, skinny tires and you don't bounce off berms that's a non-issue.

Mine are boxed but came that way, not sure I'd do it again. But also my car has substantial reinforcing on the tub plus a welded 10-point cage. Bearings or semi-solid mounts everywhere. And 10" slicks.

[Mark Henry]

This area it's more an issue with the body mount suspension console area.

[Bruce Hinds]

This area it's more an issue with the body mount suspension console area.

Where did I read that the Teener was designed to be a little flexible and it really helps it hold the road on uneven pavement as found in a lot of mountain roads. Stiffening the chassis only has a significant effect on a track.

Or did I make that up?

[Cracker]

It is my opinion that it would be unnecessary to reinforce the trailing arms for a street car/hot rod. The stock stud length works fine for Fuchs so long as you're not using a spacer longer than 5/8" - all the best!

Tony

[tomrev]

I think the better option is to drill the holes to insert some 1 in. OD steel tube, going diagonally thru the trailing arm, and weld where they go thru. Sort of internal trussing, two per arm, on opposing angles. A search will bring up photos. Much less weight, weld embrittlement, and a stronger finished product.

[TravisNeff]

the stock 45mm studs should be fine, unless you want to run spacers.

Racer Chris did some great investigation about how much a trailing arm can flex. You'll have to do a search to find it.

For the trailing arms, if you smack a curb with an un-reinforced arm, the trailing arm will bend. If you smack a curb with it reinforced, it most likely will bend the tub too. Of course if you hit hard enough in any condition you risk messing up the tub.

I do like how Eric Shea had reinforced his trailing arms by using tubes laterally through the arm vs. a boxed sheet metal reinforcement. Enough welding on those arms can bend them too!

[mgp4591]

the stock 45mm studs should be fine, unless you want to run spacers.

Racer Chris did some great investigation about how much a trailing arm can flex. You'll have to do a search to find it.

For the trailing arms, if you smack a curb with an un-reinforced arm, the trailing arm will bend. If you smack a curb with it reinforced, it most likely will bend the tub too. Of course if you hit hard enough in any condition you risk messing up the tub.

I do like how Eric Shea had reinforced his trailing arms by using tubes laterally through the arm vs. a boxed sheet metal reinforcement. Enough welding on those arms can bend them too!

And when Jamie bent his arm up over a year ago, he was pretty happy that the arm gave way instead of twisting up his console, tub, or worse. Not only how you drive it will determine your choice but what kind of power you are using. Jamie is running the Subie 2.5, over twice the power of a 1.7 stock 4 cyl... Bottom line is, arms are easier to replace than a twisted car.

[JRust]

And when Jamie bent his arm up over a year ago, he was pretty happy that the arm gave way instead of twisting up his console, tub, or worse. Not only how you drive it will determine your choice but what kind of power you are using. Jamie is running the Subie 2.5, over twice the power of a 1.7 stock 4 cyl... Bottom line is, arms are easier to replace than a twisted car.

Absolutely. If I had a boxed arm when I had my wreck. IT would have screwed up a lot more down below. The fact that my trailing arm buckled helped take that pressure off my suspension ear. While my fencer was screwed up good. I literally bolted in a new trailing arm & My alignment wasn't even off (IMG:style_emoticons/default/confused24.gif)

[mgp4591]

And when Jamie bent his arm up over a year ago, he was pretty happy that the arm gave way instead of twisting up his console, tub, or worse. Not only how you drive it will determine your choice but what kind of power you are using. Jamie is running the Subie 2.5, over twice the power of a 1.7 stock 4 cyl... Bottom line is, arms are easier to replace than a twisted car.

Absolutely. If I had a boxed arm when I had my wreck. IT would have screwed up a lot more down below. The fact that my trailing arm buckled helped take that pressure off my suspension ear. While my fencer was screwed up good. I literally bolted in a new trailing arm & My alignment wasn't even off (IMG:style_emoticons/default/confused24.gif)

And then at WCR, Rick and Mark put on a great tutorial of body repair that we all enjoyed! The teamwork here is great and not only online! Jamie, do you think the modest tubing reinforcement that Eric does would have bent your console?

[screenguy914]

What came first, a distorted control arm that leads to loss of control/collision or a collision that leads to a distorted control arm?

I would suggest adding more chassis rigidity whenever adding add'l torque/HP to the drivetrain

It's always better to start with a more rigid chassis so the suspension can do its job and not have a flexy chassis compromise it.

[Cracker]

...the question regarding strengthening the trailing arm HINGES on it being a street driven car - most likely a /6. We all know, a six doesn't have enough beans to harm the arm in a street (tire) application. Consider leaving it alone and turn your attention to the many other things that will be vying for your attention. I *have* run a 15mm spacer with stock wheel studs - with steel lug nuts and all threads engaged (with a little left over).

All the best.

T

[shoguneagle]

There use to be a lot of information concerning this "problem" going back to Brad Robert's and the old 914club.com. It ultimately boils down to the same question unsolved involving whether to "stress strengthen" or to leave the rear trailing arms stock. Same question back then and it is still here today.

It has been mentioned it depends on whether the car is for 'street" or for "track"; what about a combination?

I have built my car over the years for both the track, street, autoX, and the desert. You have to remember I lived in Arizona for a time. The following is what I did to may car to meet the goals of the above:
seam welded planned split lines in front and in the rear; welded the cross sheetmetal to the outer sheetmetal of the fenders as well as tying them to the shock suspension consoles which were also seam welded; outer rear mounting consoles and inner ears reinforced; inner stress kit installed; outer Brad Mayeur stress kit installed; 911 front suspension and brakes with 18mm torque bars/Koni Red adjustable shocks; rear set with 911 brakes, Koni Red Adjustable and Adjustable perches and 150# springs; four corners set on Elephant Racing Brass suspension parts; front 21mm and rear stock sway bars; front tires 205/45-17 and rears 235/35-17, all rims CupII; 3.2 1987 Carrera engine with moronic injection; probably more since I have enjoyed building and finding out answers such as this thread covers.

All the above rhetoric boils down to the car having some flex for give when under heavy load; thus, as Mark Henry says, "this area more of an issue with body mount in the suspension console area" and whether the stock can take it from the modern tire improvements, modifications, purpose, and knowledge. I built from the ideas of others and as they changed over time; I always felt that certain points had to be stress and others did not. One thing I did not seam weld is the car crunch zones since it was to be run on the street. The same reasoning goes into the rear suspension arms where I wanted flex both on the street and on the track; I would much rather have a point of forgiveness at extreme loads rather than have it react differently when reinforced.

I have to agree with the ones who do not stress the rear arms especially for the street because these cars do need some flex but not where it is a "flexie flyer" either on the track or on the street.

These are my thoughts and now I can go back into my "old age dreamworld" working on the car.

[dug]

A wise old IMSA racer said they stopped bending trailing arms when they upped the rear spring rates enough to stop the car from bottoming out. They were running 13" slicks, so you can imagine the grip they had.

The spec miatas run 325lb rear springs, and 700 fronts on 205/50 tires. 911 RSRs get converted to coil overs because they can only get the equivalent of about 400lbs using torsion bars. Fortunately, 914s already have coil overs in back, so it's easy to run higher spring rates.

So if you're gonna use wide sticky tires, definitely up your spring rates before you worry about reinforcing the trailing arms.

[mbseto]

I think the better option is to drill the holes to insert some 1 in. OD steel tube, going diagonally thru the trailing arm, and weld where they go thru. Sort of internal trussing, two per arm, on opposing angles. A search will bring up photos. Much less weight, weld embrittlement, and a stronger finished product.

Here's a set of pics of this process from one of Eric Shea's posts:
http://www.914world.com/bbs2/index.php?showtopic=205604

...and 13 pages of different ideas and even some destructive testing:
http://www.914world.com/bbs2/index.php?showtopic=42873

[Steve]

Track car I would box it. Street car I would not. I hit some black ice once, spun out and hit a curb. It bent the trailing arm and did not hurt the car. Replaced the trailing arm and I was good as new.

[mb911]

Not sure how this got revisited but decided to leave alone and just sand blast and powdercoat..