Front Suspension Crutch 84-87

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Front Suspension Crutch 84-87

Post by neophile_17 »

Hello!

I'd like to improve the front suspension (dynamic camber specifically) on our LeMons car without completely redoing everything (too much time) or buying new control arms (too much money). My thought is to lower the mounting of the upper control arm by welding in new brackets? Inspiration for this idea was the solstice setup as seen below. Has anybody tried this? Anything pop out that would make this a terrible idea? Thanks for your input!

Image

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Re: Front Suspension Crutch 84-87

Post by ericjon262 »

I don't see why this wouldn't work, it'll take some ingenuity though, as there aren't many easy flat spots to make a mounting point there.
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Re: Front Suspension Crutch 84-87

Post by neophile_17 »

Thanks! Good to know I'm not way off base as I've just started to look into the finer details of suspension design. My Summer has also filled up alarmingly fast so this will end up being a fall project. At least I have an answer for my buddies tongue in cheek "Why don't you let me cut all this out and weld a miata suspension in?" I kinda hate miatas, partly because I don't fit, and partly because of how infatuated everyone else is with them.

I had another quick idea to make a smaller improvement but I'm already starting to have reservations about it. If I bolt the upper ball joint to the bottom of the upper control arm instead of the top I would get slightly better geometry. However I would loose the safety factor of the ball joint pin keeping things roughly together if bolts get sheared off. On the other hand they haven't sheared yet (despite a couple wall taps) and I'd definitely step up to 12.9 rated bolts instead of whatever came with the ball joint. Thoughts?

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Re: Front Suspension Crutch 84-87

Post by The Dark Side of Will »

Modifying the crossmember to lower the UCA inner pivot is probably a better bet... It may just be a matter of running a hole-saw through everything, then welding in a new piece of pipe or tubing to take the stock pivot bolt.
There's a droop limiting feature built into the stock crossmember. Lowering the UCA pivot will result in that droop limiting feature not allowing the suspension to extend very far. In the LeMons use case, the correct solution is just to cut that feature off.

I'm not sure how lowering the UCA inner pivot will affect bump steer, but probably not very much since the steering rack is fairly low and the outer tie rods are close to the same elevation as the lower ball joints.
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Re: Front Suspension Crutch 84-87

Post by The Dark Side of Will »

Also: Have you done testing and know you need more dynamic camber? Do you have data based on tread wear or tire temperature measurements?
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Re: Front Suspension Crutch 84-87

Post by neophile_17 »

Thanks for the insight! My initial thought was to do exactly like you suggested. I was a little concerned that the spring would occupy the space that the tube would need to be but I don't have the parts right in front me. That may be the best bet.

I appreciate the warning on the droop limiting feature!

We definitely wear the outside edges of the tires fast. That was with tires too wide for our old wheels as well. That fact combined with the "popular knowledge" that the 84-87 front gains positive camber as it compresses sparked the interest. I will be taking a closer look at the resting control arm angles to see if the rumor holds up before proceeding. I've tried to get tire temperature readings but a more important task always seems to pop up.
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Re: Front Suspension Crutch 84-87

Post by The Dark Side of Will »

neophile_17 wrote: I had another quick idea to make a smaller improvement but I'm already starting to have reservations about it. If I bolt the upper ball joint to the bottom of the upper control arm instead of the top I would get slightly better geometry... Thoughts?

Sam
That won't change a thing with regard to geometry.
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Re: Front Suspension Crutch 84-87

Post by neophile_17 »

You're absolutely right! I was thinking it would make the knuckle taller but the pivot is in the same place.

I did take a look at my other car and without getting a shorter spring and adding that variable the spring interferes with moving the mount tube down. I actually like the anti-droop feature and will trim it to length after moving the upper arm.

I see what Eric was talking about in regards to the frame contour. That will make things a little more challenging but not terribly so.

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Re: Front Suspension Crutch 84-87

Post by The Dark Side of Will »

What static camber are you running? Have you maxed out the potential to mod that adjustment?
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Re: Front Suspension Crutch 84-87

Post by Series8217 »

^^^^^^


Modifying the suspension geometry without fixing the rest of the car first is not the right way to do this.

Please share your tire size, tire compound, wheel size, static alignment (camber AND caster), static ride height, spring rate, swaybar stiffness, control arm and swaybar bushing material, and front corner weights.
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Re: Front Suspension Crutch 84-87

Post by neophile_17 »

We will be changing tire/wheel sizes from last year.

Last year:
225-50R16 on 6.5" wheels 200TW as required by rule pamphlet
Front Camber -0.9/-1.0 (Maxed out)
Caster I forgot
Front Springs Stock with 1 coil cut maybe 220lb/in.
Front sway-bar stock, solid bushings
Rear Camber -0.5" (Maxed out)
Rear Springs Stock 250lb/in.
Rear sway-bar same as front, rubber bushings
All suspension bushings are Polyurethane

This year:
205-50R16 on 7" wheels
We now have smaller diameter springs in the rear so rear camber is open. I bought/cut these to be stock spring rate but they feel slightly softer.

Any advice is appreciated!
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Re: Front Suspension Crutch 84-87

Post by Series8217 »

neophile_17 wrote:We will be changing tire/wheel sizes from last year.

Last year:
225-50R16 on 6.5" wheels 200TW as required by rule pamphlet
Front Camber -0.9/-1.0 (Maxed out)
Caster I forgot
Front Springs Stock with 1 coil cut maybe 220lb/in.
Front sway-bar stock, solid bushings
Rear Camber -0.5" (Maxed out)
Rear Springs Stock 250lb/in.
Rear sway-bar same as front, rubber bushings
All suspension bushings are Polyurethane

This year:
205-50R16 on 7" wheels
We now have smaller diameter springs in the rear so rear camber is open. I bought/cut these to be stock spring rate but they feel slightly softer.

Any advice is appreciated!
Ok those are pretty narrow tires but you're running the same size front and rear. Not much need to adjust brake balance then. You won't brake hard enough to transfer too much weight forward and you don't have wider tires in the rear to make up for the extra weight back there.

You can (and should) run higher static camber in the front and rear. Slot/file/grind whatever you need to in order to get more adjustment. Make sure caster is maxed out. Steering effort will increase from the caster but the feel will be better too.

Because your springs are so soft, you'll need to run quite a bit of static camber to keep everything in check --- possibly -3* or more. Check tire wear and tire temps (3 points -- inside, middle, and outside) after a hot lap.

I'm not sure what the 84-87 front motion ratio is but I suspect your front spring rate is not sufficient to balance the car. The rear struts operate at ~0.95 motion ratio which gets you ~225 lb/in (0.95^2 * 250 lb/in) at the rear wheel. On the other hand, the front motion ratio may be something like 0.7 (this is a guess; you should measure), which gets you 108 lb/in at the front wheel (0.7^2 * 220 lb/in). You need a bit more wheel rate in the rear because you have a rear weight bias (probably 45% front 55% rear but that's just a guess), and also a bit more in the rear so it can "catch up" with the front after hitting a bump.... but double the rate is not reasonable. Some 400 lb/in front springs from WCF will get you close depending on what your actual front motion ratio is. Then bump up the rear a bit more. This is about the limit of what Koni reds can handle.
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Re: Front Suspension Crutch 84-87

Post by neophile_17 »

We do have an adjustable brake bias to the rear and we're plumbed directly to the front calipers. This was put in place when we went to 11.5" discs with Camaro calipers. This is coupled with the Blazer MC. This system works well unless you hit the brakes hard and fast in which case the fronts lock immediately. I've been OK with that as this generally only happens when you need to scrub off a little speed because someone has done something dumb in front of you and this behavior doesn't risk a spin. But if I knew the cause, I'd cure it.

I will definitely consider adding more caster if possible. I am concerned about adding effort as a 2 hour stint on track is already pretty exhausting.

I'll see what I can do to get more front camber. Adding more spring to the front definitely feels like it would help. If possible, I'd prefer to fix the geometry rather than try to compensate for it with a giant spring rate.

I'd like to think the car is a little better balanced because the 3400 is lighter than the 2.8L, the 4-speed is the lightest trans, and we've got the battery up front but most of the insulation/HVAC stuff that was taken out biased weight reduction forward. I guess it's time to actually measure it.

I have a lot to look at and I'll be back mid August with more information after the next race.

Thanks!

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Re: Front Suspension Crutch 84-87

Post by The Dark Side of Will »

You should definitely do this: phpBB/viewtopic.php?p=145235#p145235

Almost complete elimination of brake dive.
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Re: Front Suspension Crutch 84-87

Post by neophile_17 »

That's definitely on my homework list along with tire width stagger. I don't usually get to that list until December but hopefully this year will be different!

I've also got a project that I'm pretty excited about that involves a wheel bolt pattern switch to 4.75" but that's still in the oven...
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Re: Front Suspension Crutch 84-87

Post by Series8217 »

neophile_17 wrote:We do have an adjustable brake bias to the rear and we're plumbed directly to the front calipers. This was put in place when we went to 11.5" discs with Camaro calipers. This is coupled with the Blazer MC. This system works well unless you hit the brakes hard and fast in which case the fronts lock immediately. I've been OK with that as this generally only happens when you need to scrub off a little speed because someone has done something dumb in front of you and this behavior doesn't risk a spin. But if I knew the cause, I'd cure it.

I will definitely consider adding more caster if possible. I am concerned about adding effort as a 2 hour stint on track is already pretty exhausting.

I'll see what I can do to get more front camber. Adding more spring to the front definitely feels like it would help. If possible, I'd prefer to fix the geometry rather than try to compensate for it with a giant spring rate.
Your springrate is way too low. The bandaid for geometry is static camber, not springrate. The car will handle better with the higher springrate even if it has good geometry. A "too high" springrate on the front of a Fiero would be something well over 1000 lbs/in...
I'd like to think the car is a little better balanced because the 3400 is lighter than the 2.8L, the 4-speed is the lightest trans, and we've got the battery up front but most of the insulation/HVAC stuff that was taken out biased weight reduction forward. I guess it's time to actually measure it.
Should be easy to find someone with corner scales at the track. That would be a very useful measurement to have so you can pick the right tire sizes and spring rates.
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Re: Front Suspension Crutch 84-87

Post by neophile_17 »

The bandaid for geometry is static camber, not springrate.
While that will help, a higher spring rate will cause less compression and thus less unwanted camber change. This is the explanation I got from the e30 guys as to why they run such heavy springs in the back. Hence "The best way to make it work is not to let it".

My goal when I started this thread was change the geometry so I don't have to add a ton of camber just so I can have the right amount after the spring compresses in a turn. Too much camber reduces straight line braking. Or that's my thought anyway.

I have an idea how to accomplish this but other things need to come first. Corner weights is definitely one of them.
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Re: Front Suspension Crutch 84-87

Post by neophile_17 »

There was an 85 Corvette (C4) in the junk yard when I was looking for parts this last weekend. I grabbed the front calipers/brackets but I noticed that the knuckle was almost exactly what I was looking for. Has anyone mocked one of these up on an 84-87 Fiero?
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Re: Front Suspension Crutch 84-87

Post by The Dark Side of Will »

neophile_17 wrote:This is the explanation I got from the e30 guys as to why they run such heavy springs in the back. Hence "The best way to make it work is not to let it".
The E30 semi-trailing arm rear has large toe change through its range of motion. Thus the car can isn't terribly stable during dynamic maneuvers. It has tremendous camber gain, though... it's sort of the opposite of what you wanted to accomplish with high spring rates in the Fiero.
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Re: Front Suspension Crutch 84-87

Post by The Dark Side of Will »

neophile_17 wrote:There was an 85 Corvette (C4) in the junk yard when I was looking for parts this last weekend. I grabbed the front calipers/brackets but I noticed that the knuckle was almost exactly what I was looking for. Has anyone mocked one of these up on an 84-87 Fiero?
Have you raced the car yet?
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