My Handling issues , figured it out after Summit Point

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.

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Originally Posted by DaveW

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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:

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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.

Quote:

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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.