John Parson's II MUCH Suspension Thread Hijack

[Steve Chryssos]

I sure wish we could move this hijack over to the suspension topic where we can go into greater depth.

So basically we have two narrow track cars: an early Mustang and a 67 Chevy II. Neither car offers a lot of room for modern suspension. MUSTANG: One builder, Preston, worked around his packaging issues by pushing the wheels out and covering them with flares (which look totally hot by the way). Unencumbered by the limits of stock fenders, Preston was able to use Coleman spindles.
CHEVY II: II Much is restricted by the fenders. These packaging restraints led to the desing of custom uprights (among other things). If II Much were a Chevelle, you may have been able to incorporate off the shelf spindles into your design.



Is that the case? Or did you guys just whip up a pair of uprights because the mood struck you upside the head?

[derekf]

I sure wish we could move this hijack over to the suspension topic where we can go into greater depth.

Trying something spiffy with the "Split Thread" option. If this works, the hijack will be properly moved per your request.

[Salt Racer]

...If II Much were a Chevelle, you may have been able to incorporate off the shelf spindles into your design.

Is that the case? Or did you guys just whip up a pair of uprights because the mood struck you upside the head?

We did it just b/c we could. No, actually, most off the shelf uprights could be made to work depending on ride height and whatnot. This wasn't the case with II Much, and OE uprights probably won't give you as good a geometry as custom uprights.

...I was torn for a long time on the material for the uprights. I wanted the security of stainless steel, but the performance of the aluminum. As Brian mentioned, the difference is over 10 lbs unsprung weight. The aluminum version needs to be considered a one-off (or two-off) part, and I think a manufacturer would used the cast stainless steel version. More analysis and engineering effort can cut the weight difference down some, I would expect...

The uprights were designed as aluminum from the beginning, so they are a little overkill (strength and weight) when you make them in steel. When you use late model bolt-on hubs as opposed to press-in or forged pins, uprights tend to become big and bulky. Fabricated uprights would be a better way to go since they can be made hollow. Uprights are mostly subjected to bending and torsional stress, so hollow cross section makes more sense.

...Another downside to the "deep rotor hat" style of design is you lose room for ackermann on the steering arm, I have some but not as much as I would like but hey everyone disagrees on what proper ackermann is anyway.

One note on track width - The main reason I went wide was because lateral weight transfer is a product of CG and track width, wider is better. I'm still 4" narrower than a TransAm car or Ferrari Enzo but the flares would have looked ridiculous at that point and it barely fits on the trailer as it is. The secondary reason was long control arms for a very stable RC. Packaging really didn't have anything to do with it although it turned out later that it was a huge advantage when trying to fit all the turbo stuff in etc. I actually started out dreaming of keeping it inside a Maier fender flare envelope but the radical lowering of the car body made that impossible....
Probably another couple years before II Much hits the streets though ?

Ackermann is defined by the relative location of tie rod center to SAI and a couple of other things, so hat depth won't change it. JP's IFS has less than 100% Ackermann (shallow SAI pushed out as close to the rotors).

You're absolutely right about lateral weight transfer. It's a difference between build styles from your car to JP's. Your Mustang is more like a racecar with mufflers and license plate, while II Much is a street car modified for track duties. Speaking of mufflers, have you checked race mufflers from Coast Fabrication? They are extremely light. With a pair of turbos, you really don't need big mufflers to quiet down the exhaust. I'm thinking about running four of them on my car, 2 per side. I think that would make the car quiet enough, and they're still lighter than a pair of 50-series Flowmasters. Of course, it's only a matter of money...

JP is trying to get it running by early fall, and at least conduct skidpad testing at VIR(?) before SEMA. It won't come close to what your car is capable of, but based on my previous work (0.94G on a tall, narrow car with very mild geometry and unshaved KDs), I'd say 1.0G will be easy with much better geometry and R-compound Pirellis.

..It'll be fun to compare notes when I (we) do the front of my 69...but it will be worth it in the end...

Yes, "we". And yes, it'll be worth it.


Steve,
I'll ignore you per your request ;-)