need some help tuning the suspension on my daily driver

[Electroman]

good enough for me.

thanks for the help everyone, I think I have a good idea about what I need to do now. If I run into any issues I know who to ask

[Bruce2]

... as I understand it all else being equal the longer the bar the softer it is.

That is true.
However, the diameter has a much greater effect on the spring rate than the length.

If you increase a bar's length by 10%, you reduce it's spring rate by 10%. It is a linear function.

But if you increase a bar's diameter, it's spring rate increases by the power of 4. That is, a bar that's double the diameter is 16 times stiffer. Or in the case you brought up, comparing a 21 to a 22mm bar (of equal length), the 22mm bar will be 20% stiffer.

Now, if you combine the effect of the bar's length to the diameter, comparing the 67 and later swing axle bars (552mm long, 21mm dia) to the 68 and later IRS bars (676mm long, 22mm dia), the come out within 2% of each other.
In other words, they have exactly the same spring rate!

[Electroman]

so its been three months since my last post and I thought i should do an update. I also have a few questions.

I have the rear suspension and brakes finished and along the way a few things changed mostly for the better. I did end up doing the IRS conversion, I weighed both options and cost wise I could do the IRS conversion for like $50 more than trying to fix the swing axle so I made the obvious choice. I also welded the frame horns up, I stitch welded them with 2 inch stitches spaced about 2 inches apart. one thing I added that I don't remember if it was ever mentioned before was a mid mount for my trans, I figured the more secure I can get the engine mounted to the body the better. I ended up using my 67' spring plates and torsion bars, modifying the spring plates as necessary. then replaces all the rear suspension bushings with urethane. I also fabbed up a Kafer bar, smiler to piledrivers home made one. I used 1/2" grade 8 threaded rod for the links and some 1/4" plate to make all the connecting brackets. The grade 8 bar was probably a bit over kill but at least I know it wont stretch. I do have one concern with my design though, using 1/2" rod for the cross bar between the shock towers seems to have resulted in a bar that is slightly flexible. what I mean is if I grab the bar in the middle and try and wiggle it it moves some, I tried to compensate for it by putting the bar under some tension but I don't know if that will be enough. how rigid should that bar be? also I replaced my shocks. when I took the old ones off I noticed it took almost no force to compress or extend them and they seemed really old, so they went in the trash. I picked up a set of low pressure Gabrial shocks for really cheap. I have heard good things about their shocks and since they were so cheap and are so easy to change I thought I would give them a shot. about my wheels, I said before that I got a set of 4 bolt rims cheap and I was planning on I believe I sad a 175 tire. well once I got around to getting some tires I discovered that I could get a set of 185/65R15 for a better price than the 175's. so I went with the 185's I was recommended before. with the brakes I went with 69' and later rear drums, as far as I know they are the same size as a 67's front drums so hopefully they will be enough rear brake. so thats what I ended up doing on the rear end. all I have left to do back there is install the cv's and axles and fab up an engine mount for even more rigidity.

so now I'm moving on the the front end. I already ordered a bunch of parts that should be here in the next few days. I got the caster shims, camber adjusters, and all the disc brake parts. so It turns out that the front shocks on my car are already GR-2's so I think I'm going to leave those alone for the time being. now for some questions. A few post back someone mentioned welding up the front shock towers for added rigidity, I don't see how this could hurt but is it worth the time? what I mean is there really enough load on them to make a difference if they are welded or not? since I will be doing a wheel alignment in the next few weeks I figured I should get some opinions on the specs I'm thinking about. first on the front I will either install a 3/4" sway bar or at minimum add two more mounting points to the middle of the stock one. as far as the front alignment specs: caster I figure it will end up around 5 or 6 degrees with the one set of shims, I'm thinking around 1.5/2 degrees of negative camber, and 2mm toe out. on the rear I'm debating a 3/4" sway bar but not sure if I want or even need it. wheel specs I'm thinking of are: the same 1.5/2 degrees negative camber, and 2-3mm of toe in. remember this is primarily a street driven car but I do plan on getting out and doing some auto crossing with it. that being said are those specs good or should I do something different?

sorry for the book

[helowrench]

G2 shocks on the front of my bug were a little too stiff.

Rob

[Jadewombat]

I wouldn't worry about the truss bar being too flexible, just run it for a while and see how it feels. The cars didn't come with one so anything you add will help. Is the car back on the road or are you still upgrading?

[Electroman]

unfortunately I still have many upgrades to do. in the next week I'm tearing the front suspension apart to upgrade it, and I still have fuel lines to run and I have to rewire the whole car. not to mention I still have to actually build my engine seeing as its still in boxes. did I mention that I'm also in the process of painting the car? lol lots to do but its getting there slowly.

thanks for the comment though, I do plan on running the kafer bar as it is right now, just wanted to know if anyone had some experience on how stiff that link should be. about the GR-2's I have driven with them before and they do seem a bit stiff but I'm also changing tires and a few other things so I'm hoping that will help tame them a bit.

I guess what I'm really trying to figure out right now is my wheel alignment specs. also I'm assuming that to adjust the rear alignment I should have the car weighted down like it would be driving down the road.

[Ol'fogasaurus]

http://www.shoptalkforums.com/viewtopic ... 1&t=137970

DaleM made a couple of posts on the suspension and handling forum that contains a lot of information, this being one of them. Although this is more towards racing there is a lot of general good advice that can be derived from it for a daily driver.

Lee

[Ian Godfrey]

I would seam weld the tops of the front shock towers, particularly as it may be necessary to trim the tops of the towers to get good turning circle with 2 deg neg camber. This will all depend on the offset of your wheels. The rest of your alignment settings are a good start for handling but will probably result in some inside tyre wear. Sway bars are more 'fine' tuning and will depend a lot on the choice of shocks and torsion bar stiffness. I'd try the 19mm on the front and see what the rear needs to balance that.
If you add 944 rear sway bar brackets, there are 924/944 bars in a variety of diameters 14mm, 18 and 20. (can be cheap at the wreckers)
enjoy