Suspension design is one of the main things that got me into building my own cars. When I started on my latest design the C5 stuff was fairly new. I agonized a long time between using C5 and the circle track race equipment. At the time there was a lot of complaining on the vette racers forums about spindle flex, pad knockback, and bearings wearing out. THis was before the upgraded SKF and ZR1 bearings were available. I had visions of a super car that could be run on banked race tracks and I'd had pad knockback before and it sucked. Plus I wanted the design freedom to put my pickups and such wherever I wanted and create longer controls and such. I could already see a future where the majority of hot rods would be using the vette stuff too and I wanted something different. Nowadays I'm a litle more inspired by pro-touring and hot rods, at the time I was much more inspired by true racing cars so that also aided my decision. PIctures like this made it more stark - just compare the C5 hub to a real aluminum racing hub (slightly different than the one I used).
The downsides were
1) Big hub means big wheel offset to get a good scrub radius, which means I am limited on my wheel choices and have no recourse to buy/sell used wheels.
2) no parts compatibily, all the brakes and steering are custom
3) the biggest downside is weight, a C5 hub is ~8.5 lbs, but the spindle and brake bracket are only 6 lbs with UBJ. My hub is ~6 lbs, but my upright and brake bracket is 13.5 lbs for a 25% increase in weight.
However, it also looks way more hardcore and of course quite different from another me-too vette front end. Also my LCA's are about 1" longer (always good) and my spindle pin is very high, ie my CA mounts are very low allowing me to retain a very low RC without compromising other geometry. I also can use mammoth brakes as I have no issue with wheel clearance, and I use a direct mount hat which is stronger with less deflection than an offset hat. My crappy photography doesn't do it justice but the latest package looks truly awesome when you pull the wheel off. For some reason I don't have that picture.
The first upright you see in the photos is a Coleman modular asphalt spindle with custom dimensions. It is the same basic spindle used on the Agent47 front end and the Schwartz chassis. As you can see I added some further boxing and pin reinforcement at the expense of 1 lb.
Some of things I was striving for in my design were low scrub, low scrub radius, mild camber gain under bump and aggressive caster gain for extra camber gain in turns. In the end I actually copied the layout of the C5 pretty closely (I had a geometry file for the vette). The difference is my design ended up with less RC movement and less scrub and less bumpsteer, with longer IC's and slightly lower RC, while maintaing similar figures for trail, caster gain, and camber gain.
I wanted a high performance suspension, but I also wanted something that felt very stable going down the freeway, my sports cars have always felt darty to me with their big tires. I also tried to set the coilover as upright as possible for maxium motion ratio. Note also the high mounted swaybar, based on the standard circle track splined hollow bar and bendable aluminum arms.
I am running a 450 lb spring and I think it works out to about a 275 lb/in wheel rate. Pretty stiff on the street but then again my daily is a '92 Cadillac.
One regret was not setting the UCA up with a shim style alignment system. THe adjustable length UCA is actually pretty easy to setup and adjust, but not as easy, fast as a shim setup, plus with a shim setup you can instantly go back to previous settings.
The bushings are Currie "JOnny joints' which are basically an articulating polyurethane rode end. They are hard to keep greased and honestly the NVH level doesn't feel that different from when I used QA1 teflon rod ends. And they definitely have more stiction, so that's some thing I might change abck to using rod ends at some point. All of the coilovers also have a poly bushing at one end. I'll be honest though, the NVH in this car is pretty high, despite all my efforts I cannot really say it feels as streetable as I would like.
My street wheel is a 18*10.5" with 9" backspacing and my track wheel is a 18*12 with 9.375" backspacing. In the rear I use 18*13 wheels for both street and track.
Just last year I built my own uprights out of box steel re-using the Coleman aluminum steering arm/BJ mount. My overall design saved about 2lbs from the modified coleman. You can see the new spindle being built below, although I really didn't take enough pictures. Note the double shear mounting bracket for the caliper adapter, with enough room to shim it side to side to make up for welding distortion and tolerances. That system worked pretty well. With machining and fastidiousness you could probably shave another lb out of the whole design, but by the time you are done with everything its like "eh".
These are the original modified and gussetted Coleman spindles based on a Grand National pin.
Here are some of the parts of the one I built
Note the custom built trigger wheel from eMachineShop that will eventually be connected to a Racelogic traction control system.
You also may note the change in steering rack- I originally had a circle track rack that I had modified to support my wide track that never worked well. My suggestion is if you need any kind of custom steering - go directly to Woodward. This would have saved me a lot of headaches if I had done that originally. This new rack works great, and looks very pretty as well, and was setup with custom width for me. Tony Woodward got the assist just right on the first try too based on my input.
here are some pictures of the rack
The new uprights helped support an eBay purchase I made of some SERIOUS PFC Endurance racing calipers. These things retail in the Hoerr catalog for $3k apiece. Needless to say I paid no where near that. THey were a lightly used spares package from a Ferrari challenge team that was based in England. NIckel plated mono-block goodness !! Only downside is pads are hard to get, very expensive, and since they are race pads my wheels are permanently dusty. But man do they look cool LOL. I have not even had them on track yet. Remember how I mentioned lots of brake clearance ? I am using a 15" rotor in a 18" wheel with a ~8+" wide caliper that uses 1.25" thick brake pads. Makes all the Baer/Wilwood/Stoptech street based stuff look pretty wimpy (and looks are what we care bout on lateral-g right ?)
The hat is direct mount and uses Brembo floating hardware with anti-rattle clips (as developed for the McLaren F1 !). THe rotors are custom made from Coleman.
I'll have to look on the camera for some other photos, I can't believe I don't have a photo of the mounted caliper on the 15" rotor. The rears are 14" Coleman rotors with the same floating hardware. I am using a racing style dual M/C system driven by a hydraboost. I built the custom adapter to do this i'll show that some other time.
The shocks are nothing to be proud of however, some rebuilt obsolete Bilsteins in the back and some AFCO adjustabl circle track shocks up front. Someday I would like to upgrade those pieces, but I really don't feel like my driving is sophisticated enough to pursue that right now. Mostly I think they could be a little softer for street driving.
Anyway I hope you enjoyed the photos and seeing a suspension design that is quite a bit different from an upgraded '60's era GM or another plain jane vette front end.
Brian Hobaugh SCCA National Tour June 2014
First Hemi 'Cuda Convertible Ever Built
Short clips: Goodguys Pleasanton autocross and pit videos
Hybrid Mode
