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PostPosted: November 1, 2016, 9:20 am 
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OK, so i have been helping my buddy redesign his suspension but I am hitting a few snags.

Basically, I upgraded his front brakes so that the car actually stops now (one tire locks up under hard breaking and i have no clue why except for the bad suspension design) but on the test drive, the front tires toe out pretty bad (you can see it). I don't see this in my car at all but my car is much different in design. I have solid bearings, its lighter, a bit higher frequency springs and its front steer (steering rack in front of the upright).

His car:
Rear steer (steering rack behind the upright)
Rubber bushings

Since I will be changing his suspension anyway, is there a way to prevent this without using stiffer springs and keeping the rubber bushings? I assume the only really thing to do is to design in anti-dive or compression adjustable shocks (which i know will change other things). thoughts?

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PostPosted: November 1, 2016, 12:31 pm 
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mjalaly wrote:
(one tire locks up under hard breaking and i have no clue why except for the bad suspension design)
Is it capable of locking all four but one just does it prematurely, or is it only able to lock one at all?

mjalaly wrote:
...the front tires toe out pretty bad (you can see it)...
Have you investigated whether it's coming from geometry, bushings, or some combination of both? Things like articulating the suspension in the garage to see how much of what you observed is occurring with unloaded bushings, also a laser point taped to the tire and projected on a wall would let you more visibly see an exaggeration of the bump steer arc. Also you could take measurements (ideally both sides to see how close they are to identical) as it sits on the ground, and run the current geometry through a suspension analysis program?

mjalaly wrote:
...is there a way to prevent this without using stiffer springs and keeping the rubber bushings? I assume the only really thing to do is to design in anti-dive or compression adjustable shocks...
If it's coming from the bushings, urethane bushings or spherical joints? If it's coming from the geometry, adjust the steering rack and/or tie rod end positions to minimize bump steer?

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PostPosted: November 1, 2016, 12:52 pm 
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yeah i was just thinking out loud since i was going off him saying there was no bump steer. I will need to toss my fancy gage on there and see. If its not bump steer then i will dig deeper. I will let you know what i find.

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PostPosted: November 3, 2016, 8:40 am 
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I checked the bumpsteer... yup that's the issue (.062" toe out @ .5in travel). the hard part is going to be fixing it. If you look at the drawing below everything is just way off. Both pivots for the steering arm are completely in the wrong spots. Also, my best guess, is that where the the outer pivot needs to sit wont work beuase it hits the upright. I also cannot move the rack up or down because of how it is mounted :BH:


Attachments:
bumpsteer issue.JPG
bumpsteer issue.JPG [ 38.32 KiB | Viewed 3424 times ]

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PostPosted: November 3, 2016, 10:06 am 
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Can you put a travel bar on the rack like Wilwood has for the mid 50's Chev?


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PostPosted: November 3, 2016, 10:33 am 
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Bobber wrote:
Can you put a travel bar on the rack like Wilwood has for the mid 50's Chev?


a waaaaattt?

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PostPosted: November 3, 2016, 11:26 am 
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Sorry, that should have been Flaming River. Basically it's a bar that mounts externally between the end steering pivot joints of your rack and you can place your inner steering arm joints anywhere along the bar. The bar needs an external support, usually a nylon bushing.


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PostPosted: November 3, 2016, 11:58 am 
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yeah that is if you need pivot locations shorter than the rack. His need to be longer with a sorter tire rod. Not sure he wants to do that or not.

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PostPosted: November 3, 2016, 1:01 pm 
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You can extend the bar beyond the rack but things can get tricky.


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PostPosted: November 3, 2016, 1:11 pm 
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yeah i would rather just add an extension to the rack and shorten the arm to get everything in the right spot.

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PostPosted: November 3, 2016, 3:06 pm 
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In your drawing above you need to account for the length of the steering arm at the outboard end too. So draw a line thru the outer pivots and note the offset of the steering arm and take that into account too.

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PostPosted: November 3, 2016, 3:10 pm 
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horizenjob wrote:
In your drawing above you need to account for the length of the steering arm at the outboard end too. So draw a line thru the outer pivots and note the offset of the steering arm and take that into account too.


oh i know. that drawing is literally what is on his car. pretty much everything needs to change to make it right

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PostPosted: November 3, 2016, 3:30 pm 
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mjalaly wrote:
Also, my best guess, is that where the the outer pivot needs to sit wont work beuase it hits the upright.
Upright, or wheel? You may be able to see at least some improvement by spacing the outer tie rod end up.


mjalaly wrote:
I also cannot move the rack up or down because of how it is mounted
You have a sawzall and a welder, right?


Alternatively...
Dr. Strangesteer, or: How I learned to stop worrying and love the bumpsteer.

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PostPosted: November 3, 2016, 3:44 pm 
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Driven5 wrote:
Upright, or wheel? You may be able to see at least some improvement by spacing the outer tie rod end up.

I flipped the ball joint upside down and it got worse. It looks like it needs to be right where it presses in. Its not going to happen without using a new upright since its cast which means i cant even make a new bracket or weld to it and fell good that it wont brake. its in a very bad location. I might be able to use the old brake mount screw holes but I'm not sure if it is worth it to him to change a bunch of stuff.


Driven5 wrote:
You have a sawzall and a welder, right?
not that simple. the chassis is powder coated and moving the rack looks like it will screw up the steering shaft alignment.

Driven5 wrote:
Alternatively...
Dr. Strangesteer, or: How I learned to stop worrying and love the bumpsteer.
this is more on the dangerous not intolerable side of things atleast in my opinion.


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20161019_052202.jpg
20161019_052202.jpg [ 135.93 KiB | Viewed 3389 times ]

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PostPosted: November 5, 2016, 9:12 am 
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Tell him everything needs to change, and let him say no.

Give him another year to drive an ill designed car.
Meanwhile teach him what makes a car work well.

In that time he will soften up or sell the car.

Rattle cans fix grind and weld marks in powder.
Nothing needs to fix the feeling of driving a well sorted car.

I would start by changing the uprights, the ball joints are way too close together (if that one in the picture is in use)
Those uprights will not make a long travel (supple) suspension without horrific camber change.

"Any suspension can be made to work, if you don't let it."
A stiff short travel suspension is hard on the driver and the chassis (cracks).
I liken that kind of handling to a shopping cart or roller skate.
If you are in the northern hemisphere winter is upon us and its time to strike the iron.

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