85 Citation in C-Mod

[captain_pants]

One more event in the books! I tried lowering the rear 1/8" and changed to a softer rear bar (75% of the original stiffness), but I was still chasing the tail of the car on the first run. I disconnected the rear bar and the car was much better! Here's a video of my second run, which was my fastest:
http://www.youtube.com/watch?v=RZ2a01VJqUY

This run was one of those special ones where your conscious mind is just observing what your subconscious is doing, and only doing micro adjustments when the plan wasn't working exactly as expected. At the end of the run I was trying to align two run-time sticky notes but simply couldn't because my hands were shaking from the adrenaline. This is why I do this sport!

I need to separate if I have steady-state oversteer (fix w/ springs/bars) or turn-in oversteer (fix with shocks), but it's quite challenging to determine that on our slalom-heavy courses. I definitely was 'backing it in' to a few large offsets on later runs, which is fun but not the fastest way. I'm going to try adding some front rebound damping as my next step.

The fix for the camera vibration was pretty simple - I tied the GoPro mount to the roll bar with a nylon strap, and positioned the suction cup mount so that the strap was preloading the camera inwards. My hope was that the high-frequency vibration from the engine would be somewhat damped by the suction cup and bodywork, and the nylon strap would stop the mount from oscillating over the bigger stuff. Success!

It's also interesting from the video how long the car was on the rev limiter. I could not hear that given everything else going on, and there's no obvious surging going on. The winter plans installing the MicroDynamics rev limiter I picked up from Pegasus. I'm hoping that it gives a more obvious "dun-dun-dun-dun" staccato rev limiter like I've experienced in other cars.

[S Lathrop]

One more event in the books! I tried lowering the rear 1/8" and changed to a softer rear bar (75% of the original stiffness), but I was still chasing the tail of the car on the first run. I disconnected the rear bar and the car was much better.

Why did you stop at 1/8 inch lower?

You might try going to a rear spring that 50 pounds per inch softer and lower the car 1/4". This should solve the corner entry issue but might make the car more likely to over steer as you apply power in the corners

Disconnecting the rear ARB really only has a big effect on corner entry.

Shocks: Shocks are there to manage the movement of the mass of the car on that corner. Using shocks to change handling is like using trim adjustments to trim an airplane when the plane is not rigged correctly in the first place.

[captain_pants]

Why did you stop at 1/8 inch lower?

You might try going to a rear spring that 50 pounds per inch softer and lower the car 1/4". This should solve the corner entry issue but might make the car more likely to over steer as you apply power in the corners

Time was my prime factor. We have ~6 minutes between laps, including driving to/from grid spot, getting in/out of car, bleeding down pressures, thinking about next run, etc.

My second factor is ground clearance. There has to be some practical limit where you're breaking/wearing parts from dragging them on the ground; what's the next step if you can't lower the rear more? I assume spring/bar changes are that next step for steady-state cornering.

I should figure out something I can stick on the bellhousing to check real ground clearance during an event...

Disconnecting the rear ARB really only has a big effect on corner entry.

I know you were building race cars when I was still playing with toy cars, but that doesn't match up with what I've read anywhere else or experienced personally. Is there something different in the Citations than other cars that I'm missing?

My understanding is that springs and bars affect all phases of a corner, and that shocks only affect the car as it is rolling and/or pitching. I'm very eager to learn, especially when something differs from the status quo!

Shocks: Shocks are there to manage the movement of the mass of the car on that corner. Using shocks to change handling is like using trim adjustments to trim an airplane when the plane is not rigged correctly in the first place.

To be clear, I'm not talking about steady-state handling adjustments - only transient behavior. Autocrossers spend very little time in a steady-state corner (especially compared to oval racers!), so my thought was to add front low-speed rebound to shift a little weight off the inside front and onto the inside rear during corner entry. This lines up with Neil Robert's Phase 2 corner definition here: http://www.ozebiz.com.au/racetech/th...hocktune1.html

Low-speed shock tuning is a huge tuning tools for autocross, and I think that's borne out by the average competitor's willingness to spend $$$$ on shocks. I had a revelation with my previous car (Honda S2000 in STR class) when I decreased the front bar, added rear bar, and increased both compression and rebound damping on the front end. The car now transitioned very predictably, as well as having a nice steady-state balance after some fine-tuning. As a consequence, tire temperatures also equalized after having the fronts being much hotter than the rears.

Here's my thought process on targeting shocks first: If I increase front rebound and it works, then it was the right direction. If not, it's pretty easy to go back quickly with two lunch-box latches, 8 Dzus fasteners, and some shock knob turning. If it understeers terribly in corner entry, and still oversteers in steady-state cornering, then the roll stiffness distribution (springs/bars) was the real cause. Then I change springs and ride height Saturday night in prep for Sunday's race.

If I change the springs over the next few days, I can't undo that at the Saturday event if it wasn't the right choice.

In essence; minimization of parts-swapping (can be read as laziness ) and rapid adjustability during the event are my key drivers. Sound reasonable?

[S Lathrop]

Shocks: the rule I go by is that any amount of damping greater than what is called critical damping actually reduces mechanical grip. Critical damping is that level of damping that allows the mass of the car to return to the static position in the shortest possible time. Another way to say it is critical damping is the least amount of damping that stops the car from over shooting the static position after it had been displaced. We do increase damping in response to track conditions. As the track gets better, it takes more total damping to get the response time down to optimum. But over step that level of damping and you feel the car start to slide when you ask it to do something. But using the shocks to change the handling balance, while it can be done, reduces the mechanical grip potential available in the tires.

One way to keep the car out of the ground is to use bump stops that raise the spring rate over a short distance enough to keep the car from bottoming. We have proven on a 7 post rig that you can enhance mechanical grip with properly setup bump stops.

The main tuning tools are ride height, rake, spring rates and anti roll bars. Ride height changes have 2 very powerful effects when you make a change. You raise or lower the roll center of the car and you change the CG height. The effects are about equal when you model the effect of those changes.

Another way to think about balance is that as you transition into a corner, you are transferring load from the inside tires to the outside tires. Raising the ride height, one end or the other will increase the rate at which that transfer happens and how much that transfer actually is. As you load the tires, they in turn develop a slip angle. There is no cornering without slip angle. Balance is how the slip angles build on the front tires relative to the rear tires. You build the slip angles until you reach the maximum the tire can deliver. Push or loose is nothing more than getting to the limit of the tires at one end or the other.

What makes a Citation unique is that we designed the car to be neutral handling. So when something is out of balance, the car will over-steer or under-steer just as easily. You can balance the car with the shocks but you do that by reducing the mechanical grip of one end of the car to match the other end of the car. VD as an example builds terminal under-steer into their cars, so that when you go over the limit, you don't spin and get to look at what you are going to hit. For most drivers this is much more comfortable situation.

There is a plywood material called Jabrock. It is used for skids on the bottom of cars. Starting in 1994 I built my cars with the bottom of frame stepped up 1 inch from the front bulkhead to the dash. We filled that gap with 1" wood/blocks, the bottom layer being Jabrock. The wood would absorb the impact of the track against the bottom of the car and lift the chassis just enough so the car from the dash back would pass over the track. Even with this, we still use bump stops as a critical part of the suspension setup. And I find that bump stops work very well at the rear and do not cause the car to go loose when you bang into the bump stops.

That is the lesson for the day. Most of the books on handling are not written by people who have designed and built a lot of cars. That is why you probably won't find this approach in any book. I did not learn it from a book.

[captain_pants]

Fascinating stuff. Thanks for laying that all out, Steve!

Note that this car does have bumpstops. But the grounding-out is not when the car is in heave or roll to the point where a bumpstop would be in play. Picture nicely rounded but depressed tire tracks where there's 1" of floorpan clearance when stationary in them. Now imagine that at the apex of a corner, parallel to the direction of travel, and drive into and out of those at speed. I'd need bumpstops that engaged at ride height to prevent contact in that scenario.

[S Lathrop]

Fascinating stuff. Thanks for laying that all out, Steve!

Note that this car does have bumpstops. But the grounding-out is not when the car is in heave or roll to the point where a bumpstop would be in play. Picture nicely rounded but depressed tire tracks where there's 1" of floorpan clearance when stationary in them. Now imagine that at the apex of a corner, parallel to the direction of travel, and drive into and out of those at speed. I'd need bumpstops that engaged at ride height to prevent contact in that scenario.

I know you can get Jabrock in 6mm thick sheets and maybe 4mm thick as well.

The bump stops have a fairly progress spring rate. They only add 40 lbs. per inch for the first mm of compression. Double them up and you get half the spring rate rise. Another solution is adding third spring setup to both ends of the car. I have some experimental systems on the track now.

[captain_pants]

Two more events down! Sadly, that means we're done for the year.

I managed to get one of the fastest drivers in the club (Joe Premecz, 4th in ES this year at Nats) in my car on Saturday as a co-driver. I had added four sweeps/flats of additional rebound in the front end since my recent post. He thought the car was too loose - I thought it was too pushy. Hmm, what to do? I hurriedly took out 2 sweeps of rebound mid-event, and in doing so in bright sunlight I noticed that the two rebound knobs stood out noticeably different lengths from the shock body. That doesn't look right! And here comes the grid worker to send us out, so it's time to slap the bodywork back on and go! He had me by a decent margin and I closed that gap to 0.6 seconds on my last run.

So I dragged the car home Saturday night and got lots of light out into the trailer to better equalize the knobs. The way the shock adjustment pockets are cut, I'm not confident where full stiff is, so I took a measurement from other hard points on the shock body to the knob and did my best to equalize the adjustments. They were about 8 flats different! I know I checked that earlier, so I must have done something wrong. Then, watching the videos closely, it was clear that the car oversteered on turn entry into left turns and understeered on turn entry into right turns. That's embarrassing...

For Sunday's event, the fastest driver in our club (Jeff Janzen, 2nd in ES this year and 1st in SSR previously, SoloPro instructor) hopped in the car. It was about 70F and raining just hard enough to keep the surface continuously wet but there was no standing water. We went out on the R25s, and the car was pretty knife-edged with a tiny sweet spot of slip angle. We paid special attention to handling asymmetries but couldn't notice anything, meaning at least I made things better with the shocks! I ended up beating Jeff in the wet, but not by much.

The rain stopped just after we finished the first run group and the surface dried throughout the second. We got a couple dry laps in during fun runs, where we noticed that the car was handling pretty well now. No noticeably asymmetries.

My over-winter list just grew one item longer: A full shock audit along with finding an easy way to 'zero' the Penske shocks at events to ensure the same right-left adjustment.

[S Lathrop]

You do the adjustments on shocks by going full hard ( be very careful when you do it) for needle valve type adjusters. Then you back the adjusters out an equal number of turns/clicks. For adjusters that change the preload on a shim stack, zero is usually full soft and then add preload to you desired setting. Penske high speed canister adjuster is an example of the preload type adjustment.

Remember that any more rebound than that required to reach critical damping just reduces grip. More rebound will actually hold the tire off the ground over very short time intervals. The inertia of the chassis is such that when the tire passes over a bump, rebound will hold the tire up and thus reduce the contact pressure between the tire and the ground.

Now changing rebound as you did might give you a better balance than you had and thus the car might be faster. But you are likely achieving that balance at a lower level of grip and the tires are giving you less than they are capable of. Time constraints make adjusting shocks an easy choice. But make a note to your self that you need to try changing pitch or spring rates instead.

[captain_pants]

My issue right now is that I can't turn the needle adjuster to full hard as the wire passing through it hits the shock end. See this picture (Not mine, but illustrative): http://shop.penskeshocks.com/images/D/fv%20eye.jpg

The wire bottoms on the eye 'slot' before the adjuster stops turning. It might be 1 sweep away from full rebound, or it might be 10 sweeps away. This appears to be a non-Penske part on my car, so maybe the eye is mislocated slightly? I think I need to open that eye up a bit, but I'll disassemble things first and measure everything to see what's going on first before doing anything non-reversible.

From my Honda S2000 days working with Penske/Stimola/Ankeny, they suggested that any more than 2 turns (12 sweeps/flats) from full stiff was wide open with no change from there. I made spacers to fit my Honda mounts that positively set the distance when assembling the shock eye (really a pin) onto the Penske shaft; this meant that the adjuster only had two turns total of adjustment before positive stops on either end. That was nice for rapid field adjustments! 10 sweeps from stiff = 2 sweeps from soft.

I hear you on the high-speed damping reducing grip if above critical for a given surface, but I understand that low-speed damping has more effect on relative load distribution between the axles while the body is rolling to/from level. As always, I'm eager to learn and will experiment with both over time.

Also note that my car is running very soft springs and dampers to deal with cold tires and non-smooth surfaces. I may well be below critical damping.

[Jim Garry]

The way the shock adjustment pockets are cut, I'm not confident where full stiff is, so I took a measurement from other hard points on the shock body to the knob and did my best to equalize the adjustments. They were about 8 flats different! I know I checked that earlier, so I must have done something wrong.

Two things.

1. Before each event "inventory" your shock settings by counting how many sweeps it takes to get to full hard. Then compare to your event notes. You really need to do this.

2. I found with those shocks that rebound would "self adjust" during events! So I used cotter pins or some such devices (can't recall exactly) to lock the sweep adjusters in place. Were they not there when you acquired the car? These are critical. If not used the rebound settings move on their own.

[captain_pants]

Two things.

1. Before each event "inventory" your shock settings by counting how many sweeps it takes to get to full hard. Then compare to your event notes. You really need to do this.

2. I found with those shocks that rebound would "self adjust" during events! So I used cotter pins or some such devices (can't recall exactly) to lock the sweep adjusters in place. Were they not there when you acquired the car? These are critical. If not used the rebound settings move on their own.

Chalk this one up to user error! I'm not too proud to call myself out on the internet. I had checked a couple of events before, but now I realize my 'zero' point isn't actually zero due to the asymmetry of the lower shock eyes.

I do have the cotter pins in place. I wondered why they were there but just left them in place as they were convenient for adjustments. That's very interesting that they loosened. My Penske 8300s never did on my Honda.

[captain_pants]

A picture someone took at our last event:
http://nrondin98.wixsite.com/roni/au...Item-itbwxo361

A great 60/60 car. 60' away, 60 mph!

(No, the photographer is not really only 60' away. Probably 100' or more in reality.)

[captain_pants]

Trying to put the pictures inline:

513887_017f72054ec44dc8b71325f6382bccc8-mv2_d_4752_3168_s_4_2 by corey_dyck, on Flickr

FB_IMG_1474638921968 by corey_dyck, on Flickr

FB_IMG_1474638928990 by corey_dyck, on Flickr

In the marbles? I'm not lifting!
FB_IMG_1474638935075 by corey_dyck, on Flickr

[S Lathrop]

Your last 2 pictures are the first time I have seen the rocker rear suspension on a 84 Citation.

There is a wind screen available that covers the cockpit tubing above you hands.

[Jim Garry]

That used to be my car Steve. You converted it to push rod using the original rockers. Changed the motion ratio from 0.5 to 0.9!

[S Lathrop]

That used to be my car Steve. You converted it to push rod using the original rockers. Changed the motion ratio from 0.5 to 0.9!

I know.

It is fun to see a picture of my work on the track. That car is something to be proud of. You won a lot with it and so this the previous owner. I think the current owner will carry on in the tradition that you are a part of.

[captain_pants]

The car is definitely a people magnet, specifically the more technical types (read: nerds) that attend autocross. Whenever I pull the body work off the crowd grows quickly. It's a beautiful machine with a definite purpose.

Is there a way to stiffen the tail/duckbill at the back? It looks like it's positioned to give a small amount of down force, but the cutouts to clear the rear rockers have removed the stiffness of the downturned lip. You can see it bowing down even at low speeds.

[S Lathrop]

Is there a way to stiffen the tail/duckbill at the back? It looks like it's positioned to give a small amount of down force, but the cutouts to clear the rear rockers have removed the stiffness of the downturned lip. You can see it bowing down even at low speeds.

The best way would be to support the tail from the rear of the transmission. I would think about a bracket that might be 6 to 8 inches wide and an inch or two front to back. I would pad the mating surface.

When the design was new, the top of the tail was supported by lower body work that enclosed the transmission. Over time that part would sag because we had the tail pipe exiting through the lower body work.

[captain_pants]

Every adjustment I've been making to this car has been to reduce oversteer. Stiffer front bar, softer rear bar, lower rear end, remove rear bar, increase front compression and rebound, etc. Granted, our local site has lower grip so most cars are oversteer-biased there, but this was extreme.

I also noticed asymmetrical handling, where the car was oversteer-biased on turn-in one way and understeer biased on turn-in the other way. I experimented with asymmetric front rebound settings and got that tuned much better. It irked me that I couldn't bottom the Penske adjuster screw (item 19 in this diagram) in the shock eyelet (item 21 in the same diagram) before it stopped turning to get a zero point. The adjusting wire hit the edge of the 'pocket' in the eyelet, so I made a note to enlarge the eyes the next time I had the shocks out. I also planned to send the shocks out for a dyno check over this coming winter. The final adjustment to limp through the summer was nearly full stiff on the right front rebound and about 2 full turns from stiff on the left front rebound. I would prefer more damping on the right front but couldn't get it.

This weekend I pulled the shocks to install some slightly stiffer front springs to reset the balance to my liking. To my surprise, the front right shock eye jam nut was completely loose on the shaft (item 6 on above diagram). It had been unthreading from the shock shaft! The eye had moved substantially out of its normal position, explaining the need for the asymmetric shock adjustment. The left front was still tight. The previous owner had a shop change the springs - they must have missed this one jam nut. It turns out that the previous adjustments I had made had the shocks pretty close to each other, even though they appeared to be asymmetric!

Previous discussions with Penske tuners suggested that anything beyond 2 turns from full stiff was pretty pointless as the needle valve was fully open at that point. I positioned the eyelets so that I easily had access to any position from full stiff to 2+ turns softer. Of course there is more than enough adjustment range built in, so no material needed to be removed.

Moral of the story; I need to check EVERYTHING on the car over the winter. These jam nuts are impossible to check without winding the spring perch off. Once you have the spring tension off, all it takes is a simple wiggle to confirm that they're locked together.

I reassembled everything, corner balanced the car, and checked a few more items off the never-ending to-do list. I'm hoping for a car that handles a little more predictably in 2 weeks when I get back to a track. It was good before, I'm really excited to get back out in it now!

[S Lathrop]

Have you done a complete alignment? Have you scaled the car recently?

The car is designed to be neutral handling. This means that if things are not setup correctly, the car is equal likely to over steer or under steer.

To get the handling issues you describe, you can have something as simple as the caster angle different form one front corner to the other. You could have significant cross weight. Toe settings might not be as close as you need them to be. Ride height being off can cause much of what you are fighting.

Shock adjustments can change car handling but this is not the way to setup a car. You need the right and left side shocks doing the same thing. Shocks need to be serviced every year. Do you know what the gas pressure is in each shock? Low gas pressure will make a shock not function properly and over pressure is like increasing the low speed bump adjustment right off the scale.

The tolerances for setups are very close. Ride height should be set within 1/32 of an inch. 1/32" change in ride height will be noticeable. Camber should be within 0.1 of a degree. The toe has to be set within 1/64 of an inch and the toe should be that same relative to the center line of the car.

If you need help, you can send me a PM.

[captain_pants]

Yes, I've matched everything else side-to-side. What are the expected targets? I've found all kinds of specs for Swifts and other brands, but no starting point for Citations. Corner weights were within 0.5% cross before I started this weekend, and are within 0.3% cross after the spring swap, with both rear tires having the same weight to the pound. All measurements are with me in the car.

Maybe I'm missing something? If you had a 'perfect' setup, but then turned one front shock's rebound full stiff and the other front to full soft, wouldn't you expect problems? That's what I had with the loosening shock eyelet before I experimented with what I thought was shock asymmetry as an experiment. I'm just sharing my revelation over the weekend.

The car was handling fairly well before I made this spring change (with what I thought was an asymmetrical damping setup). Maybe you or someone else can infer something from a video? Here's a recent set of 3 runs on 3 different courses at an out-of-province race: http://www.youtube.com/watch?v=iEqSSdFZe-o
Most 'moments' were driver induced - either being too greedy with trail braking or just plain driver error.

[Jim Garry]

I used to make TONS of driver errors until I set my car up the way I needed it to be.

Also, stop moving your hands all over the steering wheel like it's a Buick. Keep them at 9 & 3 except in the grid.

Don't know why it's so nervous. Especially with your changes. Have you checked bearings? Uprights?

Sent from my SM-G930V using Tapatalk

[S Lathrop]

... but no starting point for Citations. Corner weights were within 0.5% cross before I started this weekend, and are within 0.3% cross after the spring swap, with both rear tires having the same weight to the pound. All measurements are with me in the car.

Maybe I'm missing something? If you had a 'perfect' setup, but then turned one front shock's rebound full stiff and the other front to full soft, wouldn't you expect problems? That's what I had with the loosening shock eyelet before I experimented with what I thought was shock asymmetry as an experiment. I'm just sharing my revelation over the weekend.

The car was handling fairly well before I made this spring change ...

The shock issues could explain the problem you had. Something to remember: any more damping than the minimum amount to achieve critical damping will kill mechanical grip. Critical damping is the minimum amount that stops the shocks right at ride height after a down ward displacement. The car does not redound past the starting ride height. Now you may find that more damping gives a more derivable car and you can drive that car faster but you are driving a car that is slower than what is possible.

First: have you bothered to send me an email requesting a setup sheet for your car? Why not at least ask the person who designed and built your car for help? Your car is unique for that design because I converted the rear end to a push rod / bell crank system from the original rocker system. As such, the motion ratios for your car are radically different form all the other cars you are looking at for setup guidance. This difference will make a huge difference in the setup you need. Also Jim Gary is a great resource. Have you contacted Jim?

Second and way more important, when you changed springs, did you change ride height to compensate for the change in the spring rates? And why did you change springs? What did you want to get from the spring change?