How much shorter of a rear spring can be installed with stock T/A's? Right now I have 10" wide rims with 275/50/15 tires and have about 1/2" clearance between the spring/bolt and wheel/tire. I am getting ready to install a new spring and tires, and would like to have a little taller tire but don't want to lose any tread width so an extra 1/2"-3/4" clearance would be nice (to allow for the extra section width while keeping same tread width). Anyway the point/question I have is how much shorter of a spring can be installed using the stock T/A locations without causing a geometry issue. I know about the offset T/A's offered but before I went this route I think in my situation I would move my spring mounts inboard on the T/A's I already have. This is a "straight-line" oriented car that will be driven on the weekends to cruise nights and such but no autocrossing or anything like that. As always any input and lessons learned from experience is appreciated.

ltlevil

 

Got this 7 leaf from Guldstrand...1 1/2" shorter than stock..you can get composites shorter as well...no geometry issue...

 

Thanks Rich. I just wasn't sure how the spring would act with the bolt on an angle like that. I'm going to go with a composite spring probably 2" shorter. Thanks for the pic that cleared things up pretty well.

ltlevil

 

Your welcome...
Rich

 

ltlevil,

i just installed a custom VBP 360 composite spring that is 1" shorter then stock on each side. running 275-40-18 in the back with stock ta's. so far no issues. i had a modified stock steel 9 leaf spring which i mod the last spring myself. that worked out great but wanted to match the rear with the front 550's.

 

Cool, that's what I'm planning on-1" shorter each side composite. How long did it take for them to make/ship it to you? Looking @ their catalog it seems the prices are the same for different lengths and ratings, you just can't send back a custom ordered spring. Am I correct in thinking this or do you know?

ltlevil

 

it took about two week from the time i placed the order over the phone to receiving it @ my door. cost was the same as non custom springs ($269.95) yes, you own it when it's custom made.

 

Looks like I'll be placing an order shortly. Willie/Rich I have to say- the stance your cars have is just sweet, makes you wonder why they didn't come from the factory that way.

ltlevil

 

I was at VB last week and ordered my spring that was 1 inch shorter on each side. He said it would take about a week to 10 days to get it. I was concerned about the angle but that does not seam to be an issue.

 

I ran a shorter spring but don't know exactly how much shorter. I cut a stock spring on one side only just past the hole and the hanger bolts were at a bind angle when the car was jacked up and the wheels hanging down but as soon as the weight was put on the angle straightened up so there was no bind.

 

I added some steel ears to my trailing arms to bring the bolts back to their verticle orientation. I too was concerned about the spring trying to pull the trailing arms inboard. I know the struts keep them in place, but thought that there was no use in adding another stress factor if it could be avoided.

 

shafrs3

did you do this mod on a stock ta (offsetting spring mount location)? hummm, what a great idea. Can you provide more details of how this was done? i also noticed in your picture that the swaybar mount has been relocated. can you fill me in on that too. are you using a stock swaybar, aftermarket or one you modified yourself? looking forward to your input.....thanks

 

I too would like a little more info, especially on the sway-bar set-up. As always pics are appreciated!

ltlevil

 

The problem with moving the mounting bolt hole location inboard is you are introducing and bending moment on the trailing arm.
Stock the spring load is straight down, no bending moment on the arm. By moving the mounting hole in you are twisting the arm. while this might not show now it is still putting more twist in the front bushing and at the same time the strut sees an increased load.
Old law; For ever action there is an equal and opposite reaction...

 

What keeps the arm from twisting is the lower strut rod and the half shaft link. By moving the bolt spring inboard, there is some decrease in bearing load between the diff and the wheel bearings, keeping the spring from pulling the trailing arm inboard.

 

That is what I thought also. It is moved in just a slight amount I can't imagine this putting tha tmuch more stress on the assembly. You have to post some more pictures on the sway bar setup also. This looks like a good mod and a fairly easy one to do. I'm right at this point now and would like some more info on this.
What size rear rubber are you running?

 

I really think 2" shorter springs and resultant angle of bolts is not a problem as the angle change on bolt is not severe over it's length......
I'd be reluctant to reposition bolt mounting inboard for fear of inducing a concentric load on the bracket...ie,extending calculated moment arm....just my opinion...

 

Gordonm, I'm using BFG 265-50/16 rubber mounted on a 9.5" '87 corvette wheel, with spacers of course. I'll have to remove the rear wheel a take some additional pics and post them.

rihwoods, I not a mechanical engineer, but it appears to me that there is already a concentric load in the stock configuration with the car at rest. If you removed the half shaft and attempted to rest the car's weight on the ground without it, the wheel would twist inwards at the top. The half shafts are already absorbing lateral cornering loads, I'm hoping they can live with this added stress. I don't think it's that much, but time will tell.

 

To me the 1/2 shafts are very poor at resisting twisting motion on your trailing arms. Like a teter toter?? they act only as a support around which forces are applied.
It is the lower stud rods that take all the load. Everything just revolves around the 1/2 shafts.
Years ago I added a upper strut rod or 6 link to share these twising forces about the 1/2 shaft. At that time I removed the 1/2 shafts from a supsension component by removing the clip and at the same time shortening the yoke so it didn't strick the pin.

Get rediculous and move the inner spring mount 2 feet or 3 feet inboard and you can see the massive amount of INCREASED bending moment around the 1/2 shaft.
Sure a inch of so won't hurt but it certainly doesn't reduce the twisting moment about the 1/2 shaft.
Pretent to take a huge pipe wrech, clamp it over the trailing arm and push down hard on the end of the handle. What does it do??? It tries to rotate the trailing arm. It puts the increased load on the strut rod and front trailing arm bushing.
If you put this same load directly on the end of the trialing arm it would simply put load directly up or down on the trialing arm. NO twist at all on the strut rod, non.
Moving the spring mount inboard does introduce a bending twisting moment into the arm.
Not a big one but one none the less.

 

To me they're one link of a 3 link configuration. If you forget the half shaft's function as a drive axle and imagined it as simply another strut rod, with the u-joints being bushings, you could see that upper link (half shaft) is necessary to keep the trailing arm perpendicular to the road, and its absorbing half the load in doing so.