My Handling issues , figured it out after Summit Point

As some of you have seen, I've been struggling with my Citation's handling since we modified the suspension after my Watkins Glen wreck in 2018, especially since we switched to the SCCA FC-spec Hoosier bias tires. We've been continually trying different spring rates, ride heights, damper settings, swaybar motion ratios in the rear, etc., etc., and some things got better, but others got worse.

At Summit Point, which I usually like, I threw a lot of changes at the car, none of which helped much, and some (before race 2) that made it worse. My times and race results throughout the weekend sucked.

I pride myself on getting my car working properly, but have been getting VERY frustrated with the lack of improvement. The situation was very confusing, and it was getting so bad that I, for the 1st time on the drive home, thought maybe it was my driving that was the issue and considered no longer driving in competition.

Monday, the day after Summit Point, I began seriously looking for design or mechanical causes and I finally identified the issue. There is an error in the front suspension geometry that hit me like a ton of bricks. It was so obvious that we (Steve Lathrop and I) should have never let it happen.

Luckily, it should be pretty easy to correct. So, again, we are looking forward to next season with FRP !!

What'd you find?

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Originally Posted by 2BWise

What'd you find?

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The swaybar link attachment points to the bellcranks made the swaybar increasing MR (rate) in bump. The result is similar to the effect (understeer) of front increasing-MR-in-bump geometry. New bellcranks will correct it.

The old (RH bellcrank photo) and new (opposite side drawing) are attached below.

Dave says, "There is an error in the front suspension geometry that hit me like a ton of bricks. It was so obvious that we (Steve Lathrop and I) should have never let it happen."

OMG Dave, the rest of on the forum recognized the solution as so obvious that we didn't make the suggestion knowing that you would figure it out before to long.

Of course, that is my attempt at humor. You are illustrating the difference between the pros and the rest of us wankers. I am looking forward to your next driving impression after the change. Thanks for sharing.

Sorry to try to educate myself at your expense....

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Originally Posted by DaveW

The swaybar link attachment points to the bellcranks made the swaybar increasing MR (rate) in bump. The result is similar to the effect (understeer) of front increasing-MR-in-bump geometry. New bellcranks will correct it.

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Quote:

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Originally Posted by DaveW

The old and new are attached below - the new one will be similar to the RH photo

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It looks to me that this is the right bellcrank, dampers are behind (left in picture) and ARB is forward (right in picture).
So the swaybar attachment on the new one is the circled point.

On the old one, the attachment point starts moving both laterally and rearward and the further in moves the less lateral and more rearward movement - thus increasing the MR.

On the new one exactly the opposite happens because is starts with maximum rearward motion and decreases rearward movement and increases lateral movement thereby decreasing MR.

Am I understanding this correctly?

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Originally Posted by jtaphorn

Dave says, "There is an error in the front suspension geometry that hit me like a ton of bricks. It was so obvious that we (Steve Lathrop and I) should have never let it happen."

OMG Dave, the rest of on the forum recognized the solution as so obvious that we didn't make the suggestion knowing that you would figure it out before to long.

Of course, that is my attempt at humor. You are illustrating the difference between the pros and the rest of us wankers. I am looking forward to your next driving impression after the change. Thanks for sharing.

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Having the front swaybar working properly will require some more setup changes, but at least, I hope, I won't be chasing my tail.

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Originally Posted by BeerBudgetRacing

Sorry to try to educate myself at your expense....

It looks to me that this is the right bellcrank, dampers are behind (left in picture) and ARB is forward (right in picture).
So the swaybar attachment on the new one is the circled point.

On the old one, the attachment point starts moving both laterally and rearward and the further in moves the less lateral and more rearward movement - thus increasing the MR.

On the new one exactly the opposite happens because is starts with maximum rearward motion and decreases rearward movement and increases lateral movement thereby decreasing MR.

Am I understanding this correctly?

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I'm having trouble understanding what you are saying. Let me say it differently.

In both bellcranks, shown in full rebound, the radius to the pushrod is at a greater angle to the pushrod than the radius to the shock. So as the BC rotates under load, the pushrod angle to its BC radius has more rotation to bring it to 90-deg to its radius than does the shock. This means that the lever length of the shock force increases slower than the lever length of the PR, by definition this is decreasing MR.

The shock and the swaybar link are essentially parallel to each other.

So, in the revised BC, the shock pivot is on the same radius line as the swaybar, so they behave similarly.

In the original BC, the swaybar is on a radius line ~31-deg clockwise, so BC rotation CCW under load increases its lever length faster than that of the PR, making it increasing MR compared to the shock or PR.

So as the car rolls or goes into bump, the swaybar geometry acts like an increasing MR suspension geometry, and understeer results, especially under bump travel and gets worse with increasing roll angle.

This results in swaybar stiffness increase that under certain conditions, decreases understeer, because it decreases roll. It also means that softer front springs might be counterproductive, because they allow more roll and the swaybar MR on the more-loaded side increases. That's what makes it a confusing setup.

Clear as mud, right?

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Originally Posted by DaveW

Clear as mud, right?

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I believe I'm understanding.

Looking at the VD Bellcrank the connections of the shock and sway links are at the same radius but at slightly different angles compared to yours at the same angle but different radii .

So the VD bellcrank will have the (although very slight) same condition you experienced
but you setup will require a stiffer ARB.

I think that is the definition of "compromise" in building/packaging these car.

One has to look at all link angles vs the pivot on both the pushrod side as well as the ARB side. The pushrod side linear bump motion has decreasing angular rotation of the bellcrank - The 90-degree radius (not the simple straight line point a to point b radius) to the pivot from the pushrod becomes longer which slows the belcrank rotation. So, to determine net change in ARB MR from the pushrod, one needs to look at both input and input rod angles and how they change vs the pivot in bump.

Another aspect of this geometry error:
Front roll stiffness generally seems more effective in tuning the car's overall roll stiffness, and the rear is more effective in tuning understeer-oversteer balance.

So:

In most of my race weekends since the 2018-19 repair/upgrade incorporating the new swaybar setup, I've suffered from a lack of overall grip. Correcting this error means that the front swaybar will now be much more effective in "hitting the sweet spot" in roll stiffness since the rising rate (MR) swaybar issue will be gone, and the car's overall roll stiffness will no longer be rising rate.

I have some experience with the VD front bell crank setup.

The big difference and why this showed up to be a problem is the motion ratio that I came up with worked fine, until I made the chassis way stiffer in torsion. If the motion ratio had been below .5 for the shocks, this would not have been an issue that bothered anyone. But as you approach 1 to 1 shock motion to wheel motion, things become exaugurated. This applies not only to the sway bars and springs but the shocks as well. A stiff chassis, say over 2000 ft pounds per degree will show issues

Shocks have what is sometimes called nose pressure. That is the force it takes to move the shock. If one shows the dyno curve of a shock without zeroing out the nose pressure, you will see that the force to move the shock might be as high as 30 pounds or so. That is the point on the graph where the shock goes from negative to positive pressure. Guaranteed it is never zero but it can be very close to zero. But most of shocks we run. it takes some amount of force to move the shock shaft. 30 pounds is not uncommon for a lot of the shocks we use today. There are "thru shaft" shocks that have very low numbers but, again, 30 pounds is not uncommon for most shocks.

The reason all this is important is that if you have a high front motion ratio, the load on the suspension has to exceed 30 pounds before the shock moves. But if you car is only 1000 foot pound per degree in torsional stiffness, you don't have much of a worry because the chassis twists to accommodate the loading. But if your car is 4000 or above ft. lbs. per degree, and the motion ratio is above .5, this can be an issue. The car will slide a bit before the suspension moves and the car grips up. Shocks that work well with a stiff chassis and high motion ratio are expensive.

Sorry if this explanation is as clear as mud. Poor Dave has been the person who has had to work through all this.

I differ a bit from Steve in my understanding of what "nose pressure force" actually does.

While high internal pressure in a (non-thru-shaft) damper creates seal friction (not good) and a relatively small, but measurable damper spring rate, the pressure-related force itself (Steve mentioned 30-lb) acts exactly like slightly preloading the spring perches. I.e., it raises the ride height a small amount that is compensated for when one sets weight balance and ride height during an alignment.

However, having said all that, too much roll stiffness from ANY source (springs, swaybars, dampers, tire pressure, suspension friction, roll-center height, etc.) can, especially when the track is not abrasive, cause a serious reduction of grip, sometimes referred to as "skating" where the tires slip across the surface and don't properly engage with the track surface.

Several (~5) decades ago, before the effects of stiff dampers and excess friction were totally understood, the chassis was often referred to as the "5th spring". This chassis flex allowed too stiff, high-friction suspension and dampers to be used w/o killing grip.

I had an instance (1999 Runoffs) where stiffening the chassis by tying the Pinto cylinder head to the roll hoop with an aluminum plate caused a (at that time) mysterious loss of grip. Removing the plate restored grip to its previous level.

Edit - Effects of excess stiffness, friction, etc. from my 2015 handling presentation, linked here:
https://www.apexspeed.com/forums/att...3&d=1539115694
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...reductions in grip are mainly due to the interaction of load transfer rate with tire and tread-rubber characteristics, some of which are noted below:
•Rubber coefficient of friction depends in part on the time rate of load variation –i.e., too fast, and the tread rubber cannot fully conform to and interact with the road surface, and grip will be reduced. Higher-hysteresis compounds are inherently, due to their greater damping coefficient, slower to conform to the road surface, and thus are more affected by friction and RCH.
•Both suspension friction (load increases before motion can occur) and too-high roll center (always-present geometric roll stiffness) will result in almost immediate transfer of load from inside to outside tire as soon as cornering force begins.
•Conversely, load transfer due to spring rates plus swaybar stiffness develops only as the chassis roll angle begins to increase, i.e., more slowly.
•Therefore, limiting chassis roll-angle by increasing friction or roll center height may result in lower grip compared to similar roll-angle and response-time control achieved with swaybars, dampers, and springs.

It was a resounding success. The pervasive understeer, heavy steering, and overall low grip issues are totally gone.

We now have to bring the rear handling up to match the front. It's nice to be working on a different issue.

More to come as the season progresses.

Maybe I should say nothing… but as an outsider if it’s not comfortable, you can’t possibly go like what we all know you’re capable of.

I’ve wondered since the crash if eventually you’d ask if “that time” had come. Any of us would.

But in your case, with your history, I honestly believe it has not. And I never BS about this.

Here’s to carrying on, you and Sherrie both have inspired me since 1972. You still got it.

:D

When I can no longer drive, analyze and/or work on the car to my standards, I will hang it up. I did that with racquetball when my body would no longer take the beating from playing 3 or more times a week (necessary to keep me sharp) any more.

But I still enjoy the challenge in all three aspects of racing, and as I get older, there's even more satisfaction in doing it.

BTW, Eric, I like your signature: "Once we think we’ve mastered something, it’s over"

It seems like I learn (or re-learn) something new almost every day.

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Originally Posted by DaveW

:D

When I can no longer drive, analyze and/or work on the car to my standards, I will hang it up. I did that with racquetball when my body would no longer take the beating that playing 3 or more times a week (necessary to keep me sharp) was possible.

But I still enjoy the challenge in all three aspects of racing, and as I get older, there's even more satisfaction in doing it.

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Not sure I follow much of what you speak but am impressed and thankful you share with the rest of us mortals! Can’t imagine what you would think of driving my FF but I am sure it would be helpful.
Keep up the passion and sharing wisdom with your racing pals.
brian

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Originally Posted by DaveW

:D

When I can no longer drive, analyze and/or work on the car to my standards, I will hang it up. I did that with racquetball when my body would no longer take the beating that playing 3 or more times a week (necessary to keep me sharp) was possible.

But I still enjoy the challenge in all three aspects of racing, and as I get older, there's even more satisfaction in doing it.

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Thanks for taking my comments as intended.

Your last sentence is just the same for our mountain trekking. We absolutely dread our last hike — real, live *dread* — and hope we get bored with it and find something else before that decision is a forced one.

Doubt it’ll work out that way, but seeing drivers like you and Harvey Templeton and Dan Carmichael throughout my life may give a clue as to a proper rebound after we can’t backpack to 13,000 feet any more. Figuring on 2040 for that. :-)

All our best to you both.

FYI:
https://www.apexspeed.com/forums/att...3&d=1539115694

Race results, etc., were not good because I thought I could use the Rd Atlanta tires for a 2nd weekend. That was a bad decision. With the new, extremely smooth, non-abrasive, M-O pavement these tires didn't work well past the 1st race, which was pretty good, finishing 6th and lopping ~2.5 seconds off my qualifying time.

So, in the 2nd race, which was the 6th or 7th heat cycle on these tires, I had VERY little grip which resulted in falling off the pace. Others' opinions were that new vs used tires was worth 2+ seconds per lap.

However, over all, the car worked well with a new larger new rear master cylinder and the revised front bellcranks. A few tweaks on the rear brought the car into a good performance window that, IMO, only needs a tiny bit of fine tuning.

I'm looking forward to the rest of the season, and hope to improve our qualifying and race results.

OTOH, the 50-YO Chevy Van tow vehicle now needs a new water pump, because the current one (~180 K miles on it) developed a leak at the seal during the drive down to M-O. So using the van for long trips is out until that is repaired. That makes attending the Lime Rock race weekend questionable.

Replacing that water pump should not be that difficult. On vehicles of that era, one could actually get at things rather easily.

Now not being difficult assumes
1. A replacement can be found
2. The bolts are not permanently stuck and can reasonably be removed.

Just MHO from 20+ years of owning a 1973 version of that van

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Originally Posted by Steve Demeter

Replacing that water pump should not be that difficult. On vehicles of that era, one could actually get at things rather easily.

Now not being difficult assumes
1. A replacement can be found
2. The bolts are not permanently stuck and can reasonably be removed.

Just MHO from 20+ years of owning a 1973 version of that van

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Not so easy in my somewhat modified '74 G30 Chevy Van. Trying to get at it is where I am now. With a thicker radiator than stock and a clutch fan, getting the fan shroud off is impossible w/o removing the fan or pulling everything off the front of the van (grille, radiator, hoses, etc.) And I can't get at the fan bolts with the shroud in place. So right now it's a "catch 22" situation. I may have to cut the shroud in half (vertically to make it 2-piece) to remove it. Then I'll make some tabs to bolt it back together for reassembly.

Out to the shop I go for the next step.

Dave,
Your van sounds very tight in that area compared to my 1973.

As far as cutting the shroud in half, I had to do that with my 1990 Chevy van for exactly the same r reason. It bolted back together just fine with te addition of a couple pair of aluminum tabs,.

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Originally Posted by Steve Demeter

Dave,
Your van sounds very tight in that area compared to my 1973.

As far as cutting the shroud in half, I had to do that with my 1990 Chevy van for exactly the same reason. It bolted back together just fine with the addition of a couple pair of aluminum tabs.

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I also have a larger heavy-duty alternator (different custom bracketry), an add-on aftermarket AC system/brackets and a cruise control module that are also in the way. I managed to get the shroud out after removing the fan (a huge PITA) by moving a bunch of stuff, but it was a struggle. But I don't want it in the way when I install the new WP and reinstall all the mechanical stuff, so I'll figure out later how to do that. I may trim it in the rear a bit, or if that doesn't look like a good solution, I'll cut it in half like you did.

The old WP's seal failed because its bearing(s) had too much play - good thing they didn't fail completely because we'd have been stuck out on the road. NAPA had an "exact-fit" new (not reman) WP with limited lifetime warranty that I installed w/o issues.

I cut the fan shroud in half vertically, made aluminum tabs to tie it back together, and it goes in OK with some fiddling. Everything should be done tomorrow, and then I'll check things out to assure no leaks, etc.

Water pump has been replaced and that all seems OK. But while checking everything out after the WP replacement with the engine running, I saw that the fuel pump was dripping slightly (apparently leaking from the vent holes), so its diaphragm is on its way out. New FP (also limited lifetime warranty) will be in at NAPA tomorrow. The current one may also have been in there for 180 K miles since the engine was rebuilt. Guess it's a good thing the WP repair made me inspect stuff underneath.

Luckily, compared to the WP replacement, this "should" be a relatively easy job.

Dave,

I've been talking with Steve and put my name in for a set of the front bellcranks. Is there anything else changed out for the installation? Seems like the anti-roll bar pushrods *might* need to be modified, but not certain. Any changes to pushrod length?

Quote:

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Originally Posted by jcolley

Dave,

I've been talking with Steve and put my name in for a set of the front bellcranks. Is there anything else changed out for the installation? Seems like the anti-roll bar pushrods *might* need to be modified, but not certain. Any changes to pushrod length?

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The swaybar links will need to be ~1 " longer to compensate for the new location. I used the original links and threaded on a through-threaded extension using a 1" threaded stud (red Loctite) to hold them together. Pushrod and damper mounting should remain the same.

Quote:

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Originally Posted by DaveW

...I saw that the fuel pump was dripping slightly (apparently leaking from the vent holes), so its diaphragm is on its way out....Luckily, compared to the WP replacement, this will be a relatively easy job.

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Or so I thought...:(

Being able to see and get at the FP fasteners (on the upper side of the FP) required removing right half of the (sectioned) fan shroud and the alternator. The next issue will be holding the FP pushrod up in place while the FP goes in. I tried the G30 shop manual's suggestion of "heavy grease", but that didn't work at all. So I will attempt to hold it up with a "retrieval-claw tool" (the manual's alternate suggestion) when I get back at it tomorrow.

I am sure you already know this Dave, but when I was just a young guy, the fuel pump on our 57 Chevy went out on the highway. My dad fought with it for an hour before I saw that he was having to compress the spring to get it anywhere near close to bolting up. When I suggested bumping the engine over to get the low spot of the cam next to the pushrod things very quickly fell into pl;ace.

I had to change the fp in my 73 in a rest area and remembering that came in very much help.

Quote:

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Originally Posted by Steve Demeter

I am sure you already know this Dave, but when I was just a young guy, the fuel pump on our 57 Chevy went out on the highway. My dad fought with it for an hour before I saw that he was having to compress the spring to get it anywhere near close to bolting up. When I suggested bumping the engine over to get the low spot of the cam next to the pushrod things very quickly fell into pl;ace.

I had to change the fp in my 73 in a rest area and remembering that helped a lot.

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When I pulled the old FP, there was very little apparent force on the bolts - I was able to unscrew them by fingers once they were slightly loosened. So I think I'm lucky with the cam position in that regard. If it isn't, it'll be a real PITA to get it to a better position - I can't see inside the opening w/o an inspection mirror on a stick. I was able to reach in there and push the rod up pretty far, so that seems to correlate with being at or very near the cam low spot.

I improvise a lot because I'm almost always working on stuff by myself. Not that people haven't volunteered to help, I just really like working alone. Always have.

The FP is in - I modified a long-tail throttle tension spring to put side load on the FP rod to hold it up while I bolted the FP in. But now the HD radiator (installed in 1993) appears to also be leaking somewhere in the middle of the core. So that's the next item on the worklist. I'll also do the hoses when I replace that.

See post 36 below - rad is OK. Apparently this was spilled coolant while disassembling things.

Whomever coined the phrase “It’s always something” clearly hasn’t read this thread!

Suggest changing the term to “It’s always at least five things.”

Best of Luck and Goodonya for your perseverance!

Murphy continues to strike!!

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Originally Posted by Steve Demeter

Murphy continues to strike!!

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Actually, it's good fortune - much better to find these issues at home than out on the road!

Quote:

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Originally Posted by DaveW

The FP is in - I modified a long-tail throttle tension spring to put side load on the FP rod to hold it up while I bolted the FP in. But now the HD radiator (installed in 1993) appears to also be leaking somewhere in the middle of the core. So that's the next item on the worklist. I'll also do the hoses when I replace that.

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I pulled the radiator and leak-checked it (brushed soapy water on it everywhere with ~5 psi internal pressure) and there are absolutely no leaks in the radiator. So the only way coolant could have gotten there (seemed improbable anyway to have a leak there) is that I slopped some while removing hoses, etc, prior to replacing the WP. Apparently, the reason running the engine after reassembly didn't pull that coolant out of the fins was that the RH half of the sectioned fan shroud was not yet installed, so there was little air velocity through the rad.

As in my mantra, 'never assume anything because it'll come back to bite me in the butt,' now I know the rad is OK. And I got to clean out debris from the fins from ~180K miles of driving.

So the van will likely be back together today, and I didn't have to buy a $500+ radiator.

Quote:

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Originally Posted by jcolley

Dave,

I've been talking with Steve and put my name in for a set of the front bellcranks. Is there anything else changed out for the installation? Seems like the anti-roll bar pushrods *might* need to be modified, but not certain. Any changes to pushrod length?

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Quote:

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Originally Posted by DaveW

The swaybar links will need to be ~1 " longer to compensate for the new location. I used the original links and threaded on a through-threaded extension using a 1" threaded stud (red Loctite) to hold them together. Pushrod and damper mounting should remain the same.

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I installed the "new" correct geometry (swaybar motion ratio in tune with the rest of the suspension) front bellcranks today in place of the ones I had modified, which were much closer to the proper configuration than originally, but not completely correct. It'll be interesting to see if these make a noticeable improvement over the modified ones.

Our next outing will be at PIRC the weekend of June 6-9.

Quote:

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Originally Posted by DaveW

I installed the "new" correct geometry (swaybar motion ratio in tune with the rest of the suspension) bellcranks today in place of the ones I had modified, which were much closer to the proper configuration than originally, but not completely correct. I'll be interesting to see if these make a noticeable improvement over the modified ones.

Our next outing will be at PIRC the weekend of June 6-9.

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Thanks Dave. Any pics?

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Originally Posted by jcolley

Thanks Dave. Any pics?

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See below:

Quote:

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Originally Posted by DaveW

I installed the "new" correct geometry (swaybar motion ratio in tune with the rest of the suspension) front bellcranks today in place of the ones I had modified, which were much closer to the proper configuration than originally, but not completely correct. It'll be interesting to see if these make a noticeable improvement over the modified ones.

Our next outing will be at PIRC the weekend of June 6-9.

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The correct geometry bellcranks were a slight but noticeable improvement over the ones I modified.

The PIRC race weekend was cut short during the 1st qualifying session because the car quit running. Before that, we were looking pretty good - we were 3rd fastest in the 1st practice. In the second practice we just scrubbed in the race tires.

We initially thought it was a fuel pump issue which would have meant pulling the engine/trans assembly to get at the pump, but later after we got home I discovered the real cause.

It appears to be a T2 ECU connector (ground?) problem (apparently fairly common) because everything is working again. There were a couple of clues we missed at the track (zero oil pressure reading was off along with absolutely zero fuel pressure reading even though we were able to get fuel flow from the sample port.

Once we got home, while pumping fuel out because I thought I was going to have to split the car to replace the fuel pump, I heard fuel running through the pressure regulator. After resetting the fuel pressure regulator (set very low because we had it apart during the diagnosis at the track) I was able to start and run the engine and everything including fuel pressure was OK. So it was obviously not a fuel pump issue. To hopefully prevent a recurrence, I disconnected, cleaned, and reconnected the ECU connector (usually fixes the issue) and I believe we will be OK.

Next race is at Rd America 6/26 - 6/30.

Rd Am was another mixed bag of results, but for the 1st time in several years I was feeling comfortable and confident in the car. The car was so good we twice lowered the rear wing setting down to 5.6-deg (the lowest I've ever run) with respect to the chassis. We also lowered the front wing. As a result, the car was a rocket on the straights, but still had excellent grip in the turns.

Lap times were getting better each session, and I finished 6th in the 1st race. In another lap, I would have passed another car to finish 5th. I was a bit annoyed because the race was shortened by 2 laps even though we finished well within our time limit.

We were looking good in Q2, but after a stop to measure tire pressures and temperatures, the car would not restart because the starter pinion was slipping out of engagement with the ring gear (see next post for the root cause). We could have bump-started for the race, but during Q2, the car also developed a vibration, so we packed up and went home to avert any further damage.

I'll correct this issue, and our next (and last) race of the season will be at Summit Point since we're skipping NJMP. Summit will be a good test of the setup because it's a low-grip track where I was really frustrated last year, leading to my discovery of the front swaybar MR issue.

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Originally Posted by DaveW

...I'll correct this issue, and our next (and last) race of the season will be at Summit Point since we're skipping NJMP. Summit will be a good test of the setup because it's a low-grip track where I was really frustrated last year, leading to my discovery of the front swaybar MR issue.

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I found the cause of the starter issue - one of the starter-bracket mounting bolts fell out (I'll Loctite it this time since it's not accessible when everything is together), allowing the starter to move away from the flywheel. The skipping teeth also caused the starter bolts to its bracket to loosen, exacerbating the issue. Next step will be to pull the trans off the engine and assess how much damage this did. I have a spare flywheel, which I'll install if necessary.

UPDATE 7/6/24:

I got lucky. No apparent damage to the ring gear, and the starter pinion is apparently in good shape (teeth look good and gear OD is the same as a new one). I got the trans on and the starter bolted into place.

I red-Loctited a stud into the hole where the bolt came out and used jet-nuts on both fasteners to hold the starter on. This should prevent a repeat of this issue. Before I totally reassembled the car and while I could get at everything I checked the clearances and cranked the engine to make sure everything relative to the starter worked as designed. The engine cranked perfectly.

There was no obvious cause for the vibration I felt, but it may have been the loose starter vibrating in harmony with the engine.

Now I just have to finish putting the car back together.

We went to Summit Point with the same setup we had successfully used at Rd America, i.e., low wing settings, etc. I wanted to see how the excellent grip and feel from RA would carry over to SP.

We started off well, but I was still looking for more grip on the low-grip SP track, so over the weekend we at various points tried softening the damping, lowering the front and rear ride height, lower tire pressures, softer springs, less stiffness in the swaybars, etc.

Some of these changes initially seemed to help, but in race 2, handling went off midway through the race and we wound up with rubber pickup on the tires, plus lap times suffered. So apparently we went too soft and there was not enough stiffness to scrub off the pickup. In addition, the car seemed a bit too sluggish in its response to inputs.

So, in retrospect, lowering rates, damping, ride height, etc. from the Rd America setup was the wrong way to go. Apparently, I need to stiffen the car a bit to enable predictable use of higher slip angles.

Next time out (next year at Rd Atlanta), we will experiment with slightly stiffer springs and damper settings based on the Rd America setup.

So the saga continues...stay tuned for next season.

Edit: The one thing I didn't do is make any significant change to downforce - see posts # 44 & 46.

Quote:

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Originally Posted by DaveW

...

Next time out (next year at Rd Atlanta), we will experiment with slightly stiffer springs and damper settings based on the Rd America setup.

So the saga continues...stay tuned for next season.

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From some information I recently became aware of, apparently I'm still using too much downforce and overloading the tires such that they don't want to slide, making breakaway unpredictable. That also accounts for not being able to scrub off rubber pickup, as I noted in the last post. :greenflag:

Quote:

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Originally Posted by DaveW

From some data I recently became aware of, apparently I'm still using too much downforce and overloading the tires such that they don't want to slide, making breakaway unpredictable. That also accounts for not being able to scrub off rubber pickup, as I noted in the last post. :greenflag:

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Would love to understand what data you're referring to. Off the top of my head there's only 2 scenarios I can think of that would cause this kind of behavior. 1) Tire load sensitivity absolutely falls off the cliff above a certain load or 2) Frequency response of the tire doesn't support super the high ride frequencies required to support the added DF putting the tire out of its window. The 2nd one seems the more likely of the two scenarios but would be interested to hear your findings.

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Originally Posted by DaveW

From some information I recently became aware of, apparently I'm still using too much downforce and overloading the tires such that they don't want to slide, making breakaway unpredictable. That also accounts for not being able to scrub off rubber pickup, as I noted in the last post. :greenflag:

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Originally Posted by 2BWise

Would love to understand what data you're referring to. Off the top of my head there's only 2 scenarios I can think of that would cause this kind of behavior. 1) Tire load sensitivity absolutely falls off the cliff above a certain load or 2) Frequency response of the tire doesn't support super the high ride frequencies required to support the added DF putting the tire out of its window. The 2nd one seems the more likely of the two scenarios but would be interested to hear your findings.

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A bit of a preface: Last spring I finally resolved the front swaybar MR issue, so the incurable understeer that I previously discussed is gone. When it was present, more downforce seemed to help. So I'm still learning what the car wants with that issue resolved.

This latest conclusion is based on empirical knowledge that at least 2 very fast Citation FC drivers have reduced their front wing size (and overall downforce) and gone faster, even on slow tracks. I had been using a front wing that I've used forever that has a 14" chord. Over the past season I've been reducing both front and rear downforce almost every weekend I've raced, and each time the car has gotten easier to drive and faster, but, IMO, I haven't gone far enough. So the next time I drive the car it'll be with a 10.5" chord front wing and less rear downforce to match.

My thinking on this is closer to your #1 than #2. Bias tires have always wanted more slip angle than radials, and if one can't get to the higher slip angle w/o overloading/over-deflecting the tire it becomes unpredictable. In addition, at Summit Point I had pickup on the tires and very low grip at the end of the last race, so that confirms that I had not gotten to the slip angles required.

I know I am running tire pressures that fast drivers/cars have been running successfully, so too low tire pressure is not my issue.