Oversteer or Rotation?

Norm Peterson

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Snipped from Koni's Shock Tuning Guide (emphasis mine). Does this sound like what you're noticing?

Adjusting The COMPRESSION (Bump) Damping Control
(Very Important to do this FIRST!)


Bump damping controls the unsprung weight of the vehicle (wheels, axles, etc.). It controls the upward movement of the suspension as when hitting a bump in the track. It should not be used to control the downward movement of the vehicle when it encounters dips. Also, it should not be used to control roll or bottoming.

Depending on the vehicle, the ideal bump setting can occur at any point within the adjustment range. This setting will be reached when "side-hop" or "walking" in a bumpy turn is minimal and the ride is not uncomfortably harsh. At any point other than this ideal setting, the "side-hopping" condition will be more pronounced and the ride may be too harsh.

STEP 1: Set all four dampers on minimum bump and minimum rebound settings.

STEP 2: Drive one or two laps to get the feel of the car. Note: When driving the car during the bump adjustment phase, disregard body lean or roll and concentrate solely on how the car feels over bumps. Also, try to notice if the car "walks" or "side-hops" on a rough turn.

STEP 3:
Increase bump adjustment clockwise 3 clicks on all four dampers. Drive the car one or two laps. Repeat Step 3 until a point is reached where the car starts to feel hard over bumpy surfaces.

STEP 4: Back off the bump adjustment two clicks. The bump control is now set. Note: The back off point will probably be reached sooner on one end of the vehicle than the other. If this occurs, keep increasing the bump on the soft end until it, too, feels hard. Then back it off 2 clicks. The bump control is now set.

Norm





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Thanks,...I'l try messing with shocks. I'm on vorschlags pretty big rates I think 600F/800R iirc but stock PP1bars but front bar deboned and free to rotate so less rate there like stock front bar. When at 8-9/10ths my car cuts like a knife. When I lean on the car the best I can describe is the skipping rock on water and that is really costing me laptime.
Way too much rear spring, unless you have a lot of rear downforce, IMO. Try bumping the compression damping down.
 

fatbillybob

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Way too much rear spring, unless you have a lot of rear downforce, IMO. Try bumping the compression damping down.
Too much spring...That's what my brain tells me. But vorschlag says I'm in the sweet spot for my class description which is non Aero almost stock car. They go 1100 on coil in the rear with aero! I'll play with shock settings first then dink with springs. Development is such a pain. You might be on to something. Flyhal likes his setup at almost same rates on cortex jri shocks and lots of Aero.
 

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Too much spring...That's what my brain tells me. But vorschlag says I'm in the sweet spot for my class description which is non Aero almost stock car. They go 1100 on coil in the rear with aero! I'll play with shock settings first then dink with springs. Development is such a pain. You might be on to something. Flyhalf likes his setup at almost same rates on cortex jri shocks and lots of Aero.
That he does :) @Flyhalf
 

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Sliding isn't fast, that's correct. Controlled yaw/rotation is very different from true oversteer, as it's keeping more of the "static-esque" friction between tires and the road surface, which has a higher coefficient of friction. Oversteer and understeer is asking the front or rear tires to do too much at one time. If you are seeing oversteer on the entry phase of the corner, you are probably upsetting the car via inputs (timing of brakes or lift-throttle). If it's at the exit of the corner, you're probably using too much throttle too early.

Lots of the "popular" or mainstream setups feel playful and balanced at 6-7 tenths but are far too lively near the limit to be driven quickly. People often throw too much rear bar at these cars, as an example.
I would add too much trail braking as a likely cause of entry oversteer. The right amount gives you nice rotation. Sideways is definitely slower, whether slightly loose is faster than slightly tight depends on the driver. Slightly tight is certainly easier to drive and safer.

With the Ford Track bars (& springs), I have been running stiff front, medium rear with if anything too much understeer (with a square wheel & tire setup). So next track day I am going stiff/stiff. Now maybe on an autocross course, where you have a lot more acceleration out of the slow corners, less rear bar might work better. But al lower speeds, more oversteer is easier to tolerate, and maybe even faster if you are good. The other aftermarket bars seem to be similar in size, so I would expect similar results. Now maybe some of the aftermarket springs have a lot more rear spring rate (remember effective roll rates are a combination of spring and anti-roll bar rates). Or maybe Brian has a lot more power than my stock engined GT, or one of those Pedal Commanders that gives you 90% throttle with only 10% pedal travel.
 

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Also remember, using this tire , your car would need to yaw (be sideways) 6.5 degres to get max grip. I have seen a lot of novices stop pushing the car as soon as they generate any significant slip angle, which means they are running at well under the limits. So one guys oversteer might actually be just driving at, or close to the limit. Or "neutral" for a skilled driver.
 

fatbillybob

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Snipped from Koni's Shock Tuning Guide (emphasis mine). Does this sound like what you're noticing?




Norm
Yes Norm it could be. I call it skipping but sidewalk or hoping could describe it. Thanks!! I have raced for years but not on adjustable shocks with meaningful adjustments. Most of my fast years were on the C5 corvette a very forgiving chassis that I could set it and forget it and just drive. The S550 is a much harder chassis to get speed out of. I swear my S550 is an italian car it just does not like me some days. Last Friday at Buttonwillow I was getting delayed upshifts and smoked out in the cabin on the hairpin before the Esses clockwise. I actually could not finish that qualy session. I put the car up on jackstands and for the life of me I could not find a problem. No leaks, No oil, No oil out the tailpipe, no smoking rubber on brake rotors, nothing on fire or burnt, exhaust not touching anything, trans can't really be inspected on stands or see much. The smoke smells like clutch but I'm racing A10 like flyhalf. So I put a new set of tires on and just raced it Saturday and the car was fine and the upshifts fine for the whole race. I swear my Mustang S550 thinks it is a Ferrari 550M.
 

TopJimmyCooks

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SteveW

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fatbillybob, [email protected], Norm Peterson,

Been following along but haven't said anything. Lots of good comments by many experienced people already. Although, I was really confused by the comment that at 8-9/10ths the car is great but at the limit it starts skipping or hopping slideways like a rock across water. After that the focus has been on shock settings for the most part.

Knowing you run on Hoosiers got me thinking tire pressure issue since for me, it has always been easier to feel a shock setting mismatch at less than the limit driving. If the car is handling bumps well, not riding harsh and reactive, but not overly so, to driver inputs you are likely in the ballpark with the settings.

Definitely, dial rebound and compression way back and starting with compression follow the tuning guide Norm posted to make sure that's where it needs to be. That is all free to try. My guts are telling me though that the car feeling great at 8-9/10ths but changing dramatically at the limit makes me think a tire pressure issue, like too high or too low especially with real race tires.
 

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Also remember, using this tire , your car would need to yaw (be sideways) 6.5 degres to get max grip. I have seen a lot of novices stop pushing the car as soon as they generate any significant slip angle, which means they are running at well under the limits. So one guys oversteer might actually be just driving at, or close to the limit. Or "neutral" for a skilled driver.
Yaw angle =/= slip angle. Related, yes.

Your point is valid.

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I'm not going to get into the technical stuff because a) I don't know it as well as most of you and 2) it's difficult to communicate this way, sometimes. Word communication difficult can be. ;)

So, I'll suggest that the way to get faster, more consistent lap times is to improve the person behind the wheel. Do more events. And if you can, do events with clubs like BMW, Audi, Mustang, Porsche, who have in-car instruction. Both in-car and classroom instruction, optimally. (Note that some clubs are limiting instruction d/t Covid currently)

Now natch, the level of instruction varies. You could have Norm. Or you could have me. Hope for the former, settle for the latter. You may still learn something.

One of my favorite anecdotes is from years ago, when I was doing lots of HPDE and just starting to instruct. A buddy was tracking his E36 M3, at the time, a very fast and capable car. His wife hit the wall with it at Atlanta, and so since he had already signed-up for an event and the car was in the body shop, he took his rental car. It was a 3-speed automatic Dodge Neon. For you too young to know this car, it was a POS. A slow POS. A SPOS. LOL. No ABS, no traction control, no horsepower.

Later on, he said that he learned more that weekend driving that car, than in 10 weekends of driving his M3. The M3 (or in our cases, an S550 Mustang) will cover up a lot of bad driving with the car's capabilities.

So, before you spend thousands on suspension and superchargers and K-braces, do about 10,000 miles on the race track, with instruction, on street tires. You'll be plenty fast.
 

Norm Peterson

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Now natch, the level of instruction varies. You could have Norm. Or you could have me. Hope for the former, settle for the latter. You may still learn something.
Better they get you sitting right seat then me. I'm just an engineer.

Excellent anecdote.


Norm
 

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