setup problem, driving problem, or both?

[Rick Kirchner]

Last couple of races I've had someone who followed me post some videos, and what I saw in the pixels confirmed what I was seeing and feeling in the car. For one, I'm missing many apexes, not all, and not just a few, by feet.

This seems to be a relatively new phenomenon. I haven't had a working camera since my Replay XD was stolen at Roebling nearly 10 years ago. But I went back and looked at old videos and while I occasionally missed one back then, it was nothing like now.

I suppose what I'm seeing and feeling is corner entry understeer. I turn in at what I believe is the right place and right steering angle to get there and yet it doesn't. I don't correct enough because I'm already looking to the exit and I don't perceive the need to turn more until its too late. I rarely feel a lot of understeer on exit though.

Wondering if this is partly a setup issue with the Hoosier spec tires. In my other videos there were sessions on Avons, non-spec Hoosiers, and even American Racers.

Right now I'm running -1.6 deg camber in the front, and shooting for 19-20 psi hot per Hoosier. Last weekend I was consistently getting 19.5. I've heard this tire might want to be stood up at less than -0.5, and a better pressure would be 18.

1994 Van Diemen.

Thoughts? Comments?

[teamwisconsin]

I don’t say this as a way to drum up business for myself, but get a camera back in the car, and send your video to a coach. Most all of us have a video analysis rate. Send a copy of the video (Google drive link, YouTube link, etc) to a coach and see what they say. Sometimes a fresh set of eyes can help you see if it’s car related or driver related. A lot of times when drivers have driven the same car for years (or tracks) they fall into habits. Shortcuts, of a sort, at least in terms of energy and movements inside the cockpits. A coach can help tune you back up and give you clues to look for if it happens again over time.

[DaveW]

Last couple of races I've had someone who followed me post some videos, and what I saw in the pixels confirmed what I was seeing and feeling in the car. For one, I'm missing many apexes, not all, and not just a few, by feet.

This seems to be a relatively new phenomenon. I haven't had a working camera since my Replay XD was stolen at Roebling nearly 10 years ago. But I went back and looked at old videos and while I occasionally missed one back then, it was nothing like now.

I suppose what I'm seeing and feeling is corner entry understeer. I turn in at what I believe is the right place and right steering angle to get there and yet it doesn't. I don't correct enough because I'm already looking to the exit and I don't perceive the need to turn more until its too late. I rarely feel a lot of understeer on exit though.

Wondering if this is partly a setup issue with the Hoosier spec tires. In my other videos there were sessions on Avons, non-spec Hoosiers, and even American Racers.

Right now I'm running -1.6 deg camber in the front, and shooting for 19-20 psi hot per Hoosier. Last weekend I was consistently getting 19.5. I've heard this tire might want to be stood up at less than -0.5, and a better pressure would be 18.

1994 Van Diemen.

Thoughts? Comments?

Without knowing your spring rates or much of anything other than what you said, the Hoosier bias FC spec tires need a very soft, low roll stiffness setup. With a too stiff setup grip suffers.

In my Handling presentation I noted this:
---------------------------------------------------------------
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 excess suspension stiffness, friction and RCH.
---------------------------------------------------------------
The Hoosier tire compound is fairly stiff and high hysteresis, so the above applies to them.

[Rick Kirchner]

I don’t say this as a way to drum up business for myself, but get a camera back in the car, and send your video to a coach. Most all of us have a video analysis rate. Send a copy of the video (Google drive link, YouTube link, etc) to a coach and see what they say. Sometimes a fresh set of eyes can help you see if it’s car related or driver related. A lot of times when drivers have driven the same car for years (or tracks) they fall into habits. Shortcuts, of a sort, at least in terms of energy and movements inside the cockpits. A coach can help tune you back up and give you clues to look for if it happens again over time.

In terms of shortcuts/bad habits, etc, I've considered that - have I been getting just old and lazy?

I have a chinese copy of the XD but it seems to shut off after just a few minutes. If I had to guess its the card vibrating until it loses contact and a bit of electrical tape around it will probably solve that.

[Rick Kirchner]

Without knowing your spring rates or much of anything other than what you said, the Hoosier bias FC spec tires need a very soft, low roll stiffness setup. With a too stiff setup grip suffers.

In my Handling presentation I noted this:
---------------------------------------------------------------
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 excess suspension stiffness, friction and RCH.
---------------------------------------------------------------
The Hoosier tire compound is fairly stiff and high hysteresis, so the above applies to them.

Front springs are 400, rears 1000; front bar is that common stiff "U" shaped VD thing of the era.

[DaveW]

Front springs are 400, rears 1000; front bar is that common stiff "U" shaped VD thing of the era.

I've noticed a similar thing with my Citation, and the softer I go on roll stiffness, the better the car works. I'd try disconnecting the front bar or at least setting it full soft, if that's possible.

If you get oversteer, you can reduce the rear spring rate/roll stiffness or use stiffer front springs..

It took me a LOOOONG time to realize how soft I had to go and I'm not all the way there yet. I just modified my front swaybar motion ratio to cut its stiffness in half. The next experiment will be no front bar at all.

[billtebbutt]

Rick. You have PM

[Rick Kirchner]

I've noticed a similar thing with my Citation, and the softer I go on roll stiffness, the better the car works. I'd try disconnecting the front bar or at least setting it full soft, if that's possible.

If you get oversteer, you can reduce the rear spring rate/roll stiffness.

It took me a LOOOONG time to realize how soft I had to go and I'm not all the way there yet. I just modified my front swaybar motion ratio to cut its stiffness in half. The next experiment will be no front bar at all.

I ran without a rear bar at all for probably 3 seasons, but it was rolling over so much it was nearly picking the inside front off the ground. Started noticing it in the pics photographers take. Unfortunately I think i sold my soft adjustable bar!!

[DaveW]

I ran without a rear bar at all for probably 3 seasons, but it was rolling over so much it was nearly picking the inside front off the ground. Started noticing it in the pics photographers take. Unfortunately I think i sold my soft adjustable bar!!

Did you ever try disconnecting the front swaybar? That's what I was suggesting.

[DaveW]

I ran without a rear bar at all for probably 3 seasons, but it was rolling over so much it was nearly picking the inside front off the ground. Started noticing it in the pics photographers take. Unfortunately I think i sold my soft adjustable bar!!

No rear bar is maybe the root cause of the issue, but the other things I said also apply.

[Rick Kirchner]

No rear bar is maybe the root cause of the issue, but the other things I said also apply.

Oh no, I have one now, since about 2014. I did try a much softer front bar once and scared the crap out of myself. Perhaps I just needed to adapt a bit and get used to it.

[DaveW]

In my experience, 95% of the time serious handling issues (especially like what you described) are setup-related. You may be driving the current setup improperly, but trust your butt first, then work on driving once you fix the obvious issue. Drivers don't usually lose the basics of how to drive, we just lose confidence with age if the car reacts badly. You're 64 and I'm over 82, so you are not, IMO, over the hill yet.

[BeerBudgetRacing]

I have a chinese copy of the XD but it seems to shut off after just a few minutes. If I had to guess its the card vibrating until it loses contact and a bit of electrical tape around it will probably solve that.

Get something like this:

https://www.amazon.com/ZOMFOM-Motorc...dp/B0DQYDGKFB/

The card/components sit separate from the cameras.

[EYERACE]

What the reader notes lacking > you don't mention it, but the reader is to guess your lap times are suffering because of your hitting apex problem.

[John LaRue]

• PSI is in range.
• What are the front and rear tire temps showing? (Pay attention to temps across the face of the tire and what the tire surface looks like.)
• It is a bias tire not a radial so, IMHO, your front camber is excessive but you need to do what the tire temps tell you to do.
• What are your rear camber numbers?
• Your spring spread also is really big compared to what I am used to. (Are you running heavy springs to control roll? Small bar big spring or big spring small bar.)
• Are you debriefing yourself after each session? Go through each corner and document entry/apex/exit.
• The camera is great but you should be able to do this without video.

[DaveW]

• ...Your spring spread also is really big compared to what I am used to. (Are you running heavy springs to control roll? Small bar big spring or big spring small bar.)...

John,

I agree with your comments except for your spring rate comment - his car may have vastly different motion ratios, and that may require those spring rates to get the desired wheel rates.

[Rick Kirchner]

Unfortunately, no crew, no temps. I ran about this degree of camber on the front with the ARs, and as much as 2.5 deg with the Avons, and had good temps. I don't recall where I got the advice on camber though, might have been Hoosier a few years back.

Rear camber is -0.5

Springs are in line with the original Primus setup sheets. Back when I had Steve Lathrop model the suspension I was wondering how good the VDs suggestions were, and he confirmed that they were a decent starting place. Given that the car really didn't change much from 90-95, one would expect the last series of suggestions would be pretty good. So I've made a few tweeks from there. Same thing with the ARBs. VDs of this era tend to run a really stiff front and a soft rear. That said, I could see where the new tire could really change things up.

My note-taking has slipped over the years, but I'm painfully aware of what's going on. The video just confirms it. For the last two weekends though it's been further hampered by new engine issues - some oil leaks - one this last weekend was truly massive - lost about a half-quart. VARA has mostly gone to double weekends now, and as you are all aware, if you have to work on something there's not a lot of time...

[lil_fatboy]

Rick,
I ran a 95 for years and I have to say the setup “window” is huge on that car compared to the later versions. There is a lot more to it than saying the car is pushing on turn in. Is it a high or low speed corner? I surprised no one has talked about wing settings. Any corner you are taking in third or fourth gear the wings are involved.
It’s very hard to figure these things out when you’re alone. Get a track map and after your test session sit down and think about what the car did on corner Entry, apex, and exit. High speed you adjust wings. Low speed you are going to adjust suspension. I ran t bar in front and small fork bar in the rear. I don’t remember the sizes I have to look at my notes. 450’s in the front with about four turns preload 700’s rear no preload. Rake at .05 measured at valve cover with smart tool. Front ride height about 1 inch to 1 1/4 depending on track. Camber with Hoosier 1.5 front .5 to .7 rear. Get the Hoosier tire guy to take temps for you. You want no more than 20* spread across the tire. Tires hot off the track should be at 20-21 psi.
On slow speed corners If the car is pushing on turn in to apex adjust the front suspension. Mid to exit adjust the rear. If your shocks are right you should be able to dial most things with them. Or raise or lower the rear ride height.

[lbermud]

That corner entry understeer and missing apexes by feet really point to front grip not being there when you expect it. That could easily be tire-related, especially if the spec Hoosiers behave differently than what you were used to with Avons or older Hoosiers.

[S Lathrop]

I found that the best tuning trick was to adjust the static rear ride height. Corner entry push can be solved by raising the rear a bit. Play with the rear ride height until you get the best handling you can get with what ever spring combination you are using. Change the rear springs, and then see what you get.

I used a formula to calculate the dynamic ride height. If I changed spring rates at one end of a car or the other, I would calculate the dynamic ride height for the new spring rate and then adjust the static ride height so as to keep the dynamic ride height constant.
If you just change spring rates but do not change the ride height to keep the dynamic ride height constant, you make 2 suspensions at the same time.

The dynamic ride height is the ride height the car will oscillate around when the suspension is displaced. As an example, if you stiffen the spring rate, but keep the same ride height, the car will oscillate around a new dynamic ride height. Now you have made 2 changes at one time. You have changed the spring rate and the ride height the car operates at.

If I want to reduce mid corner to exit push, but I don't want to change the entry balance, I will increase the rear spring rate and lower the rear of the car so that the dynamic ride height stays constant. Then when I apply power the car will be more neutral or even go a bit loose with power. Going with a softer rear spring and a bit more rear ride will have the opposite effect.

Bottom line, I found that rear ride height and rear spring rates were the most effective tuning tool in the box.

[Rick Kirchner]

I want to thank everyone who so thoughtfully replied here.

To fatboy - it's primarily high speed and medium speed corners. So yeah, perhaps wing changes. I've been running the same settings at the same tracks for many years, except for a brief experimentation with more "speedway" (single plane) front wings at Fontana and Willow Springs a few seasons back. I also ran 800 lb rear springs and no rear bar for a few seasons, but found that really produced corner exit understeer as the thing would really squat in medium and slow speed corners.

That said, when I first got the car it was using the anti-dive and anti-squat a-arm locations, and I haven't given those settings much thought since then, as I found the car to be pretty undriveable at my level of experience (push in, loose out). But maybe its time to give those some thought as well. Anybody run The anti-settings with a midyear VD?

The oil issues I had the last two events really compromised my note taking, but I'll improve that and attempt to get some temps taken next time out.

Since I don't have any bar options that will work, I'm going to make a couple simple alignment changes, perhaps a 1/4" more rear ride height and stand the tires up more - 0 camber in the back and -.5 in the front.

Next two events are at places I've not run yet - Laguna and the new Circuit at Buttonwillow, so I really won't have any comparative data until willow Springs in November, other than feel and experience of course. I took most of last year off due to a medical, so some of this was a brain disconnect between the first season I ran the spec tires until now. What my notes from 23/24 said the most was "inconsistency".

[lil_fatboy]

Never ran without a rear bar except in the rain. What wings do you have ??? What degree are they at ??? Front and rear. Always ran anti dive and squat a arm locations.

[S Lathrop]

I want to thank everyone who so thoughtfully replied here.

That said, when I first got the car it was using the anti-dive and anti-squat a-arm locations, and I haven't given those settings much thought since then, as I found the car to be pretty undriveable at my level of experience (push in, loose out). But maybe its time to give those some thought as well. Anybody run The anti-settings with a midyear VD?

Anti dive and anti squat are 2 very undesirable features. As you load the car under braking or acceleration, the reactive force that keeps the car from diving and squatting impacts the tires and causes a momentary loss of grip. With the harder compounds we run today, sudden loading of the tires causes the tires causes them to slip then bite. But remember that the suspension oscillates, so with every down stroke you get a slip then bite. You feel it as push. Softer springs help a bit but there may be more negatives to the setup with softer springs.

The original design of the Zink Z10 had front anti dive and the car was a pusher. But when we eliminated the anti dive geometry the car worked great.

[Rick Kirchner]

Never ran without a rear bar except in the rain. What wings do you have ??? What degree are they at ??? Front and rear. Always ran anti dive and squat a arm locations.

Rear is the ubiquitous "high speed" (spa?) airfoil and if you put a straightedge across both elements it's running at 14.5 deg for Buttonwillow's longer configuration and considerably flatter at Willow Springs. No wicker, and I've never seen any aero data on FC airfoils.

Front is a biplane design that Marc Bahner scaled down from his RT-40 wings. Main plane is 3 deg with no wicker and the flaps are 23 deg with 1/2" wicker.

[lil_fatboy]

Holy **** that’s a lot of wing @ the front. Can you post a picture of the front and rear wings ???
leave the camber where it is. What is the difference in ride height front to rear ???