Optimizing 4-link ride comfort

[Chris Edwards]

How much improvement in suspension compliance and ride comfort can be obtained by lengthening the bars as long as possible on a parallel 4-link setup? Any difference in compliance with watts link vs panhard bar? Has anyone used the rubber rod ends at all junction points versus the heim joint rod ends? I planned to use a ridetech coilover with their 5” travel shock and a 12” 175 in/lb spring. ridetech has told me there is no difference in ride quality between an air spring and a coilover if the ride height remains static. Is this true? I have a bad back and I’m trying to make my C10 ride like a 70s Cadillac, with the option of fine tuning the shock stiffness to dial in front/rear road manners.

[stab6902]

A couple of comments that might be helpful:

- If you really want your truck to "ride like a 70's Cadillac" you're going to need way less spring rate and way more suspension travel than the coil-overs you're looking at (unless you have some kind of cantilever system in mind). As a point of reference, 90's Caprices used 103 lb/in springs in the back, and the shocks had 9" of travel.
- Lengthening the arms will have little effect on ride comfort, but it will lessen the amount the wheelbase changes as the suspension moves up and down. This is why longer travel vehicles have longer control arms.
- The type of lateral locating link (panhard vs watts) won't make a difference in ride quality if you're using the same type of bushings.
- Using "soft" bushings is a good idea since they will improve secondary ride (impact harshness and NVH). All comfy cars use rubber bushings from the factory for a reason.

[Chris Edwards]

All excellent points and insight I appreciate it it sounds like you really know what you’re talking about. One thing I’m wondering is how much benefit would it be for me to add about 250 pounds behind the rear axle? If I relocate the fuel tank and battery back there I could really distribute the weight a lot better and this could contribute to a better ride since everyone knows that a loaded bed in a pick up truck always rides better.

[stab6902]

Loaded pickups ride better because they have relatively stiff rear springs from the factory (when compared to the front end). If you set up your spring rates for unloaded ride comfort from the beginning, adding weight won't help. Of course you'll be riding on bumpstops if you ever do load up the bed, but you can't have everything with regular coil springs.

It's best to keep weight as low and as close to the middle of the chassis as practical to keep your polar moment of inertia low.

[Chris Edwards]

Loaded pickups ride better because they have relatively stiff rear springs from the factory (when compared to the front end). If you set up your spring rates for unloaded ride comfort from the beginning, adding weight won't help. Of course you'll be riding on bumpstops if you ever do load up the bed, but you can't have everything with regular coil springs.

It's best to keep weight as low and as close to the middle of the chassis as practical to keep your polar moment of inertia low.

That makes sense. So in terms of polar moment of interia, it would behoove me to run saddle tanks and mount the battery on the frame mid way between front and rear (like the dual saddle tank setup on a 73-87 GM truck)? But from a handling standpoint, everyone always puts so much emphasis on putting as much weight as possible on the rear of a rear wheel drive car. I know the advantages of rear weight bias on handling, but there must also be an advantage from a ride quality standpoint. Countering the engine up front by placing the fuel tank and battery all the way in the rear must contribute in some way to a "balanced" dynamic moreso than placing those items in the middle of the vehicle, or am I missing the key point here?

[stab6902]

Ideally you're trying to get close to a 50/50 weight balance, but I wouldn't be willing to hang a bunch of weight behind the rear axle to get it if you have other options.

[Chris Edwards]

Ideally you're trying to get close to a 50/50 weight balance, but I wouldn't be willing to hang a bunch of weight behind the rear axle to get it if you have other options.

Maybe I'm not envisioning this clearly, but is there any validity to the notion that using a slightly heavier spring rate combined with more weight behind the rear axle (in the form of a rear mounted battery and rear mounted fuel tank) would yield a superior ride quality versus running a light spring rate and little to no weight behind the rear axle.

[Sbeck09]

Not at all. Stiffer is stiffer. Adding a bunch of weight isn't going to really be a fix. That's a band-aid. Softer spring rates with appropriate valving will always right smoother. The add weight thing is relevant when you, for example, build a vehicle around a stock autox class and need to alter the balance but can't remove parts. In your case where you can do whatever you want, get the longest travel shock you reasonably can with a light spring rate. You'll love it.

[Chris Edwards]

Not at all. Stiffer is stiffer. Adding a bunch of weight isn't going to really be a fix. That's a band-aid. Softer spring rates with appropriate valving will always right smoother. The add weight thing is relevant when you, for example, build a vehicle around a stock autox class and need to alter the balance but can't remove parts. In your case where you can do whatever you want, get the longest travel shock you reasonably can with a light spring rate. You'll love it.

You guys have been a great help! I will abandon the rear mount fuel tank, since that would require an expensive Boyd Welding tank anyways. I will use new factory replacement saddle tanks, and will likely keep the battery mounted in the front since due to the saddle tank locations, I would have to mount the battery behind the rear axle. I do have a somewhat lightweight Odyssey battery (~25lbs vs ~35lbs for a conventional group 75 battery to fit the stock battery tray) but I don't think that will be worth the hassle of having the battery mounted in the rear. When I need to put the charger on it, it's yet another strain on my already bad back lol.