[jlangholzj]

We'll see if/when shaun comes in but agreed, I get the impression that he's put a lot of work into them. Additionally, its more than just "a dropped spindle", there's geometry differences too.

View attachment 877424

We can see that pretty clearly here. Moving the upper ball joint down is going to extend out what's called the "front view swing arm" which basically just means you get less camber variation in travel. Additionally, the lower ball joint is effectively staying in the same spot while the tire is moving "up". This is going to effectively flatten the angle of the "n-line" or the line from the instant-center to the contact patch approximate center. Flatter n-line means the point at which your force acts on the chassis is going to migrate less vertically as the chassis moves/rolls, which leads to more stability in the corner. The tradeoff to this is that you might need more anti-roll bar because you're also taking "anti" geometry out of the car, or there's less "jacking forces".

Suspension geometry is a ~8-headed snake eating itself. Just changing one thing on its own without considering smaller other changes doesn't lead to anything.

MM's point about tire contact patch flex has truth to it, however its independent from the effectiveness of a drop-spindle design; as-is his point about the "effectiveness" of a given design at street speeds. The whole setup, no matter the design, is a tradeoff on where and how those compromises have been made and the expectation and use case at the end of the day. Back to the tire analogy, the faster times due to the smaller section width may have implications that have nothing do to with the front geometry of the car, but rather how that geometry is balanced across the car. Additionally, a wider cross section for a given offset results in a higher scrub radius or sometimes even changing the direction of the scrub radius, which affects how the car feels under braking, etc. I'm sure this is all stuff that MM has put thought into and tried to distill down for the video and as he says, is just an explanation of "here's why we're doing it differently now".

 

[jlangholzj]

Shaun's effort is an indication of the lengths you need to go to in order to get to the answer of "better."
We worked on a taller spindle design for the 67-69 Camaro when there was about zero design and modeling
software available.

Every few times I open up RCVD, its always amazing to me how "old" the principles are. There's been some additional insight but the base ideas and concepts are nothing new. Any time I look at the information compiled by Doug Milliken or any of his contemporaries, its mind boggling how much extra work had to be done prior to widespread availability of CAD. You guys were nuts and we've got it easy now, especially with something as complex as suspension geometry.

 

[jlangholzj]

My take on what’s being said is not so much relocating the pin to make the car sit lower but actual height of the spindle itself. My understanding of short and tall spindle is in it’s relationship to the upper control arm mounting location. In a performance situation you want the ball joint pivot location to be higher than the mounting point of the control arm. As the suspension compresses it pulls the top of the wheel in following the arc of the control arm for negative camber gain. In the case of the Mustang it’s not so when stock. To get the negative camber gain you can put a taller spindle or lower the mounting location. It comes down to that relationship of the ball joint to shaft location.

In the case of MM, I see it that he’s using a taller spindle to make the ball joint higher in relationship to the shaft while Shaun has shortened the spindle but has also changed the shaft location to accomplish the same basic idea. To me Shaun has taken it to the next level in engineering. That’s my impression of what’s going on.

Kind of. I should have put the disclaimer in my first comment too but I'm not a suspension whiz by any means. Wiring, engine tuning, and tire kinematics i've got down pretty well but chassis and suspension stuff I'm still catching up with. That being said, there's a few things going on from my limited understanding:

Its not just the upper control arm (UCA) that's dictating camber change but also the lower control arm (LCA) or LCA + strut rod in our design. You're correct in that the arcs of these are going to dictate kinematic (moving) camber change but its the difference in them that's the important part. As an example, with the stock-height springs and the LCA in an "OE" configuration, it's pointing down. With the LCA pointing down, the amount of lateral change in the lower ball joint (LBJ) was less than the lateral change than the upper ball joint (UBJ), mainly because of their length difference. That's why moving the UCA inboard points down slightly via the "shelby drop" were able to improve the camber curve for a mostly-stock geometry. Instead of an initial outward movement in the UBJ, it's now an inward movement, so the overall camber change is improved. It's possible to have the UBJ point lower than the inboard point, and still have negative camber curve through travel from static.

The spindle location itself isn't going to have a whole lot to do with any of the above, nor the bump-steer qualities. That's all dictated by the inboard and outboard points of the control arms. It will however change how the forces act on those points which the driver is likely to feel. Additionally, changing the tire centerline via wider tires will affect the scrub radius, which will change how the car feels driving and mainly under braking. Also there are advantages and disadvantages to moving the outboard points closer together. How much of the disadvantages are quantifiable, i don't know, I've not played around with that aspect as much.

Also as an aside as an interesting conversation point, all of the designs discussed up until now are "short spindles", their points all land within the inner wheel diameter. There are designs however like the 350z and 370z that have a "long spindle" where the UBJ lands outside of the tire. Totally irrelevant to the conversation at hand but just an interesting tidbit I thought of when yous tarted talking about long vs short spindles!

350z front geometry:

 

[jlangholzj]

A lot of terminology being thrown around! SAI is steering axis inclination. The angle between the upper and lower ball joints with the steering wheel straight. Does this angle change with camber, or is it a fixed angle of the spindle? The drawing below suggest to me that it might change with camber? I'm just curious and it has nothing to do with your average VMF member buying a few basic tools and aligning their car themselves. People throwing fancy terms around might confuse the rest of us and back in the day I aligned hundreds of cars without knowing most of this stuff. All I can say is that I am thankful for CAD and modeling programs but always curious. I could do rise run and diagonal calculations on multi pitched roofs before they had fancy calculators but arbitrary points I have trouble wrapping my head around.
I found a site with simple definitions! Definitions and Explanations of Suspension Alignment Terms

Care must be exercised for this particular angle. If i remember correctly, the way SAI is measured is from the kingpin axis (steering axis) to the tire centerline, so it it always a fixed value even if camber dynamically changes. SAI can sometimes be used interchangeably with Kingpin Inclination angle (KPI) but I think there's a difference there, just having a hard time with specifically what at the moment or rather clearly conveying why they're different.

Also, that's not a bad site for the basic terminologies. I'll have to dig around because I've got another somehwere too. Regardless of the source, they should all be derived from "SAE J670 – Vehicle Dynamics Terminology". That's the document that establishes the common definitions so everyone's on the same page. It gets more complex, and if someone's interested in reading it, you'll have to....ahem....search around for a copy that's not behind the SAE paper paywall, but they're out there.

It's still boggling the amount of work to do all of this w/o CAD accurately, but it's possible. It'll take so many more checks/steps drawing everything in 2D since it's really a 3D problem but even just using the FVSA (front view swing arm) and SVSA (side view swing arm) you can get some approximations, which is normally "good enough" for napkin math. There's so much variance in compliance and other factors that having an estimate within ~10% is usually fine. Having a grasp on the above gets to be important when you start talking to the guy designing the suspension and doing all the n-line analysis (line from the contact patch to the IC), etc. etc. to get some rough numbers on "whats happening".

This might get a little too far into the weeds...but....Here's a good illustration on what's all going on in a corner, and shows those "n-lines" i keep talking about. One of the nice things about n-lines is that as the illustration shows, the roll center (RC) migrates as soon as you get any suspension travel, or in the case of some cars like circle-track cars that are non-symmetrical the RC is never on the car center line. Because of that, thinking about the RC as the "point around which everything acts" makes it a bit more difficult to start doing some basic hand-calcs on what's going on. In contrast, working with the n-line approach, the acting forces can be slid along the n-line to the car centerline and then used to calculate roughly how that's impacting the car dynamics.

The FSAE forums could be....interesting at times....and there were some personalities (as we all have them) but this post by one of it's more notable members is a good discussion on using n-lines and a FAP vs focusing on the RC: RC vs FAP

The basic part just boils down to "don't loose the forest for the trees" and then also "there's always 18 ways to solve a problem".

I'm no engineer, butt I've read in a couple of places that for a road race car you want around the same degree for the caster and SAI.

I love this thread.

Also w.r.t. kingpin angles (SAI) moto-iq has a good article on the subject: MotoIQ - Kingpin and Scrub

 

[jlangholzj]

The drivers side outer tie rod on 65-66 power steering cars is bent to clear the control valve. That has to jack up the steering geometry. With my longer "Shelby" idler and pitman arms and the significantly shorter SoT steering arms I hope to not need the goofy outer tie rod?

It still is just two points connected in space, you can curve, twist, and bend everything between and the geometry won't care. It'll affect if that link will buckle under force, for sure lolol. In terms of the effectiveness of the geometry however, it doesn't matter. It's pretty common to see "bent" or non-straight links for OE geometry to provide chassis or axle clearance. Here's one from an e60 (mid/late 00's BMW) looks like (the one w/o the arrow):

I find this kind of stuff fascinating, but in the end we are dealing with a quick and dirty suspension designed for the cheapest car Ford offered, the Falcon. The fact that Street or Track and others have been able to make improvements to where I can beat Corvettes on an autocross course is amazing! I don't want to cut up my car to where it is noticeable and yet still be competitive. There are only a few venders seriously into that option.

Going into it, I thought the same thing but the geometry really isn't that bad. After plumb-bob measuring and then re-confirming with some simple 3d scans I was surprised to see the end result. There are some tradeoffs that were made but I'd chaulk that up to 60's era tech. Things were designed with narrower, bias ply tires in mind as well as safety. As an example, toe-in bumpsteer while cornering will give the car a tendency to steer-in, not wash-out. Also, again as I've mentioned, this was all done pre-CAD so it was all done in 2D perspectives and still is damn close.

RE: general design, people might be inclined to say the more "trailing arm" design (it you could call it that) of the front suspension in early mustangs is inferior to a "true double a-arm" style. Or that for newer cars, a McPhearson strut design is inferior to a "double a-arm" style suspension. The BMW e36 and porsche 911 from the G-body through the 964 used BOTH and they're heralded as some of the best handling cars in history.

 

[jlangholzj]

What year mustang did those wheels come off of? Did you have to use wheel spacers? They are different than the American muscle ones pictured on your website with the 315's on them. I like the rims in this photo better. Thanks.

I'm interested too, they're similar to these guys, but if there's an OE equivalent I'd rather use that. I've been shopping around for 18s for takeoffs and something this style would work well. CJ pony Parts VOXX