Front Coil Over Mounting

[1bad68cat]

Hi everyone. It's been a while since I posted. Life threw me some curveballs, so the cougar went on the back burner. I will be working on it again soon. I have a couple questions with the suspension. I installed an Art Morrison Sport IFS kit awhile ago and want to redo the front coilover mounting situation.



Most coilovers are installed on the lower control arm and a bracket welded to the frame. What are the down sides if I mount the coilover to the upper control arm instead of the lower control arm? Think first gen mustang (cougar) and nova bolt-bolt-in coilover kits. I plan to weld tabs to the upper control arm near the upper ball joint.
For the upper coilover mounts, I want to use jacking screws to adjust ride height rather than using the coilover, so I am not adjusting spring load. Are jacking screws a good/bad idea for a mostly street driven car with an occasional track day?


I appreciate any information you can give.

[dontlifttoshift]

I have been thinking about this lately for another dumb project I dreamt up. Here are some of the down sides that I keep landing on.

A. The motion ratio gets relatively bad quickly as the upper control arm is significantly shorter. This is a problem if you want to run a lot of backspacing on your wheels.

B. Ball joint loading. Most upper ball joints are not engineering for the compression load.

C. Packaging can be an issue on some cars and getting enough travel out of a shock that is short enough to fit in the space may be a problem.


On the jack screws. You are doing the same thing when you adjust those as adjusting the collar on a coil over. Its a good idea to have an adjustable mount to allow for shock changes down the road and will certainly make corner balancing and ride height adjustments much easier. I think if you keep the jam nuts tight on the jack screw, it would likely live a long time.


That said, with the coil over already well packaged in your IFS, why would you want to move it?

[1bad68cat]

I have been thinking about this lately for another dumb project I dreamt up. Here are some of the down sides that I keep landing on.

A. The motion ratio gets relatively bad quickly as the upper control arm is significantly shorter. This is a problem if you want to run a lot of backspacing on your wheels.

B. Ball joint loading. Most upper ball joints are not engineering for the compression load.

C. Packaging can be an issue on some cars and getting enough travel out of a shock that is short enough to fit in the space may be a problem.


On the jack screws. You are doing the same thing when you adjust those as adjusting the collar on a coil over. Its a good idea to have an adjustable mount to allow for shock changes down the road and will certainly make corner balancing and ride height adjustments much easier. I think if you keep the jam nuts tight on the jack screw, it would likely live a long time.


That said, with the coil over already well packaged in your IFS, why would you want to move it?

Thanks Donny for the insight.


I was wondering, would the motion ratio be calculated based on the upper control dimensions or an imaginary line going to the lower control arm extending from the shock pivot if it was mounted on the upper control arm?
I'm curious if the Chrysler/Dodge style ball joint on the control arms are this variety.
In my case, I have much room above the upper control arm to install a longer coilover.
I was looking at the jacking screws as a way to eliminate ride harshness. Rather than adjust coilover preload to achieve the ride height I want , I could adjust the jacking screw instead.


As to why I'm considering repackaging, I am looking to install a longer coilover to improve ride quality on the street. When I take the car to the track, I can add a little more preload, then redjust ride height with the jacking screw.

[dontlifttoshift]

My understanding is that M/R is calculated the same as it would be on the lower control arm, just on the upper control arm.

Spring preload does not change spring rate and can not change ride quality. A discussion could be had about the amount of stored energy in a heavily preloaded spring and the shock not being able to keep up with it, I guess. That's certainly above my paygrade but really comes down to shock valving more than spring preload.

Longer coilovers will not improve ride quality unless you are currently travel limited by the coil over itself.

[1bad68cat]

My understanding is that M/R is calculated the same as it would be on the lower control arm, just on the upper control arm.

Spring preload does not change spring rate and can not change ride quality. A discussion could be had about the amount of stored energy in a heavily preloaded spring and the shock not being able to keep up with it, I guess. That's certainly above my paygrade but really comes down to shock valving more than spring preload.

Longer coilovers will not improve ride quality unless you are currently travel limited by the coil over itself.

I'll calculate what my motion ratio will be and see if a change will help or not.

It's actually the stored energy in a heavily preloaded spring as you mentioned that has me concerned. My brother is having ride harshness issues on his setup which is similar to what I have currently. We've tried adjusting the shock valving but didn't see much improvement.

I thought longer coilovers provided better shock control therefore improving ride quality especially on rough roads.

[dontlifttoshift]

With all else being the same, how would longer coilovers provide better shock control?

[1bad68cat]

With all else being the same, how would longer coilovers provide better shock control?

I was looking at it from the POV, if coilover travel is limited then you don't have as much control because the wheel may lose contact with the ground and the shock does nothing for you until the tire touches down again. This may be due to a shock to reacting fast enough, but I would need to research further.

As an extreme case example trophy trucks with the long travel suspension. They benefit from longer travel suspension to absorb the whoops while going at high rates of speed. Also, when I look at OEM applications today, you don't see short travel suspension that I am aware of. I believe there is a happy medium between the trophy truck and my short travel coilover which would be something closer to OEM manufacture travel lengths.

[mikedc]

Hey. Interesting topic.

Suspension height & wheel travel -

The more you lower the car's ride height, the stiffer the corner springs need to be just to keep it off the bumpstops. Basics of lowering a car. That's because there is less suspension travel to work with before it gets into the bumpstops. Stiff cars skitter all over the place on rough surfaces because those suspensions need stiff springs + stiff shocks to control the springs.

Got that?
Okay, now imagine running that concept in the other direction.

Make the suspension even taller than stock . . . and the corner springs can be even softer than stock. Soft suspensions handle rough surfaces better (and ride better). Trophy trucks have very long travel but they are also pretty soft (at least when their complex shock valving allows it).



Spring/shock/coilover motion ratios -

A more direct ratio (the lower end of the spring/shock is mounted out closer to the tire) gives the spring/shock more leverage to control the wheel. But since you can pick whatever spring & shock rates you want, that's not actually doing you any big favors. However it does make the suspension's rubber bushings less detrimental to the functioning of the spring/shock. (Notice that old Mustangs, with that funky spring-over-the-UCA, were built with solid metal pivots on both ends of the UCA.)

On the other hand, a 'worse" motion ratio does have one advantage for shocks - it slows down the internal piston speed. That makes it easier for the (speed sensitive) valving to be set up right and work reliably on bumps. The overall stiffness of the shock would also need to be higher but that's nothing to worry about.



The spring above the LCA design -

I don't see how it does anything better than a lower-mounted coilover, to be honest.
Some cars are done that way to make room for a front driveshaft on a FWD/AWD setup. That's a legit purpose but I don't see any other upside.


The Chrysler upper ball joint and spring loads -

I don't know if you would even need this for a Mustang-type setup with a coil on top. That's mainly a compression load. But here goes:

A version of the popular Chrysler upper BJ already exists that is made for spring loads (at least in tension). It's the LOWER ball joint on 1973-up midsize B-body Mopars. (Charger/Satellite/RoadRunner.). These were the cars with the K-frames mounted on rubber body bushings.

IIRC this lower joint is built like the popular Chrysler upper BJ with the big screw-threaded top. The difference is that the metal 'cup' part is slightly bigger to enclose the ball more, so it's harder for the car's body weight to pull the BJ apart when it's in the lower location.