Suspension setup debacle

I've been lurking in on these forums for a quite a while now and finally decided to just go ahead and make an account. So Alright, I'm new here to the forums and have a barrage of questions regarding suspension, and how it affects the dynamics of a cars character that I think may be able to be answered on here.

I am in the midst of designing my own square tube, mild steel chassis and will soon be building it on Cad to test for structural rigidity, crash safety, and most of all weight. My issue comes in with the suspension, my design calls for an independent double wishbone design, and I was wondering if it would be possible to use the wheel knuckles from a front wheel drive car on all four corners? Could the extra mounting points be used to make a Multiple linkage rear setup? Has anyone done this before? I have tried using the search bar to avoid being the guy that double posts. But I just can not seem to find an answer to this question.

The wheel knuckle I am thinking of using is from the Ford fiesta Just for more information.

Thank you for reading

The only limitation is what the geometry is that you can work around, you can physically make it work.

The other question is in regards to wheel offsets and scrub, but you can resolve that.

The lower ball joint will basically drive your suspension (and to an extent chassis) design if using an off the shelf upright. It's a good way to save a bunch of time and really I enjoy having some suspension decision made for me rather than having EVERYTHING be clean slate so you can reach analysis paralysis easily.

I used RX7 strut type front knuckles on my build. I made a sheet metal adapter that allows me to run the stock lower ball joint and an off the shelf rod end as an upper ball joint.

If you are clever you can adjust mechanical trail, King Pin inclination, Spindle offset, and caster. Start with a good model of the upright/brakes lower ball joint and then select a tire size F&R that works with your weight distribution. Since the location of your LBJ with relation to the hub face is fixed you need to be careful to design around a purchaseable ofset of wheel to give you good scrub Radius for your selected KPI. Once you've fixed the lower ball joint relative to the contact patch and selected a KPI th suspension basically designs itself.

Also go over to http://www.locostusa.com to search and post. It seems that's just about all we do over there.

In consideration of what percentage of the total project cost and time the hubs consume, and how cheaply used car hubs or uprights can be obtained, I wouldn't pick that part first.

I'd decide what configuration of suspension will work best for the application, then see what existing parts are closest.

If it's a small rear-wheel drive car, Miata/RX7 can be hard to beat...

In reply to Apexcarver:

I'm still on the learning curve for suspensions, so please excuse my ignorance .

What do you mean I'm limited by the geometry? Am I not limited by the mounting points on the Wheel knuckle since those are the areas that the triangulation of the arms will all eventually end?

In reply to dragoon119:

I think that's what Apexcarver meant, you're limited by the geometry that the mounting points will allow for - FWD uprights typically don't allow for much droop of the lower arm.

The other thing to watch out for is the number and strength of mounting points on the rear uprights. The car you're designing is presumably RWD and will need much beefier rear suspension than FWD cars have.

In reply to GameboyRMH:

True, the car I'm designing is rwd, but I thought the fwd wheel knuckles would be stronger due to the fact that they have to deal with the compounded stresses of the engine's torque, weight, and steering. If placed in the rear, the knuckles will only have to deal with the weight of the diff, and other suspension, and drive line attachments, etc. I am trying to keep the weight inboard of the both front and rear wheel centerlines so both sides won't have to deal with as much. Also, since the worlds automakers are so attached to the relative cheapness of Fwd production. They are more prevalent in the junkyards around my area. So parts are relatively inexpensive to source. Depending on the vehicle of course.

In reply to motomoron:

I am trying to design a lightweight, rear wheel drive sports car with very little frills to get in the way of driving. I am also trying to steer clear of the suspension of the established light weight RWD cars, namely the Rx7-8, Miata, and S2000. I am trying to go about another route in suspension building without breaking the bank while still being different.

Oh didn't realize you were using the front uprights on all four corners, that will work assuming the upper part of the upright that would have been attached to the strut can handle the forces involved in keeping the wheels pointed straight at all times when attached to a wishbone. Normally that part of the load is on the tie rod mountpouint, and any kind of dummy tie rod setup will cause some kind of bump steer.

Before you dive right into custom fabbing you might want to see what kits are on the market that might fulfill your needs, there's a lot of new cheap kits that might fit your requirements. The Exocet is a sevenesque that uses Miata parts but you said you want different...the Smyth G3F is an MR-layout car that uses VW Jetta parts. And there's the FFR 818 that uses Impreza parts but that's a very finished streetable car that sounds like it might be over your budget ($10k kit + est. $5k parts).

You should be able to adapt a FWD spindle to work in a RWD setup without too much problem. I am using the front spindles from a Suzuki Swift in my design (see below).

But for the front spindles, it might be a little more difficult. Usually, FWD front suspension will have a pretty big kingpin inclination to achieve a negative scrub radius. You can restore a neutral or positive scrub radius by using low offset wheels.

You will have do fabricate an upper ball-joint adapter (like the ones used on the front suspension of FFR cars, like the one below). You can reduce the kingpin inclination by making that bracket as close to the wheel as possible.

The KPI will probably still be on the high side, so you'll have to run a high caster angle to compensate. But higher steering effort will result.

Finally, you'll need to pay close attention to how you attach the spring to the suspension. MacPherson spindles are not meant to support the weight from the bottom ball-joint. Either you attach the spring to the upper ball-joint, or you run a bunch of washers like the FFR guys do and hope for the best.

After looking at all these compromises, I chose to make some custom front spindles for my design, but you could simply find a good RWD front spindles and design from there.

C5 Corvette front and rear spindles are the same. I have looked at building a all wheel drive hot rod with them as the drive hubs will simply bolt into the front.

Probably larger than what you want but they are a good part.

What about using a s13 240sx rear subframe setup?