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Coilover choice: Ohlins vs ??

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77
56
Exp. Type
HPDE
Exp. Level
Under 3 Years
TX
I did put a link in my post. If you look at the closeup of the strut, what appears to be a Cortex logo on the mounting ears is pretty clear. As a good number of the Shelby parts seem to be products from other manufacturers (Moroso oil pans, Maximum Motorports S197 camber plates, etc.) with CS logos on them, I wouldn't be surprised if they contracted with Cortex to build the strut housings.

From the Shelby page:

4-post vs 7-post means they couldn't simulate aero load & dynamic roll/pitch/squat, but they were probably targeting street/HPDE non-wing cars so it doesn't much matter. But it gives you a much better starting point for revalving for stiffer springs needed for big aero than starting from scratch and some educated guesses.

My approach to this would give Penske a call to see if they have access to the shaker data, and that thse use "standard" Penske parts. They (or your local Penske shock tuner) could use that to come up with valving for the spring rates needed for the aero you're running - but you need to know the actual downforce you're making (from suspension travel data logs). Buy the Shelby kit, replace the springs with stiffer for the aero load, and have the dampers revalved to match (if the stiffer springs are outside the range of stock adjustment). Figure a few hundred bucks in springs and the same for revalving - still way cheaper than TTX or inverted Penske. And it gives you the chance to try the Penske digressive valving.
Called shelby, the guy I talked to doesn't know anything about these shocks. I called Penske, the sales manager for shelby used to work at Penske and if you get him he does know. Penske did answer all my questions. These shocks are take apart // self serviceable, you can buy their pistons and shims and re-valve yourself or you can give Penske your target damper curve and they will make it. For instance Penske recommended using their VDP piston which is a dual digressive piston but has additional flow ports close to the center of the piston which allows you to pre-load the shim stack but also tune the high speed to give yourself more force if you decided a very flat blow off (Knee) is to little high speed to start with. That said the ONLY thing I'd change with these is the amount of bleed since I'd want a 3 inch per second knee (giving me a softer ride).

The kit comes with brackets to adapt the rear shocks to fit the OEM control arm however Shelby nor Penske sell anything to defeat the magnaride system. You'd have to source an aftermarket item to deal with that. This kit looks like a great place to start
 
531
364
sfo
Aren
Called shelby, the guy I talked to doesn't know anything about these shocks. I called Penske, the sales manager for shelby used to work at Penske and if you get him he does know. Penske did answer all my questions. These shocks are take apart // self serviceable, you can buy their pistons and shims and re-valve yourself or you can give Penske your target damper curve and they will make it. For instance Penske recommended using their VDP piston which is a dual digressive piston but has additional flow ports close to the center of the piston which allows you to pre-load the shim stack but also tune the high speed to give yourself more force if you decided a very flat blow off (Knee) is to little high speed to start with. That said the ONLY thing I'd change with these is the amount of bleed since I'd want a 3 inch per second knee (giving me a softer ride).

The kit comes with brackets to adapt the rear shocks to fit the OEM control arm however Shelby nor Penske sell anything to defeat the magnaride system. You'd have to source an aftermarket item to deal with that. This kit looks like a great place to start
aren't those shocks like $10k? The MCS units are the cheapest of the real shocks and Lex Carson is the real deal from Moton.
 
77
56
Exp. Type
HPDE
Exp. Level
Under 3 Years
TX
Aren

aren't those shocks like $10k? The MCS units are the cheapest of the real shocks and Lex Carson is the real deal from Moton.

Shelby has them listed @ $5200

Penske confirmed the rear shocks are 7500 series shocks. However the fronts are not exactly standard. They use a larger 7/8" diameter shaft and are kind of a one off strut insert. Still take apart and tunable but I am not sure with what parts exactly since the 7500 series uses Penske's standard 5/8" shaft. Either way the 7500 series complete kit starts at $7,000 from Penske proper.
 
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Shelby used to havr it higher than penske but pen told me to order via Shelby. Go figure??? I will believe it when someone actually buys them. Shelb said blah blah blah design on shaker rig. Ok that does not tell me anything.

Springs 1st once geometry is doing what it is supposed to do. Vorschlag mcs co rates I'm not convinced. Ale proved speed (with big HP and aero) at very close to the Vorschlag middle rates 600/750 but I'm not finding all i want yet. I'm wondering if the s197 dynamics should apply to s550 chassis where 3 wheeling is proven fast.
 
77
56
Exp. Type
HPDE
Exp. Level
Under 3 Years
TX
Shelby used to havr it higher than penske but pen told me to order via Shelby. Go figure??? I will believe it when someone actually buys them. Shelb said blah blah blah design on shaker rig. Ok that does not tell me anything.

Springs 1st once geometry is doing what it is supposed to do. Vorschlag mcs co rates I'm not convinced. Ale proved speed (with big HP and aero) at very close to the Vorschlag middle rates 600/750 but I'm not finding all i want yet. I'm wondering if the s197 dynamics should apply to s550 chassis where 3 wheeling is proven fast.
Not sure what you want? It doesn't matter if Penske developed it on a shaker rig or not in MOST cases. They did do it though for the shelby kit because not all shelby owners mess with valving. Based on the damper curves supplied with them I do think they are the best I have seen other than Multimatic DSSV's. I have yet to see any good feed back (engineering wise) regarding the likes of MCS and JRZ.
 
323
318
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
Color me very skeptical on the shaker development as well. That would be one of the least efficient ways of getting a package on a car like this. Shakers are for fine tuning, not rough cuts.
 
I would ask how important is racing to you? Are you running for fun or bucks? Do you have some pressure to perform well? Like for sponsors who are doling out significant money? Or are you just racing for fun and camaraderie with people of like mind? Can you write the costs off against personal or business income without fear of the tax man auditing you and having it all disallowed? You have to be able prove potential for profit or at some point in time they will audit you and suck it all back.

I spent tens of thousands of dollars every year racing for trophies and even when I got into "pro" series the payouts were paltry. Even the championships I won were largely meaningless, it was exciting until you got home and put the trophy on the wall shelf of the dealership that picked up parts cost, then the other bills came in and that prize money didn't go far. And last year's championship trophy meant very little in the hunt for this year's money guy.

If you're just having fun, then keeping costs down should be a priority. But in funding racing activity, as I well know, common sense mostly has no place in the thought process.

But.....the real bottom line is if you can afford the top end parts cost and it's worthwhile to you then do it.
This post nails it. Full stop. We have Penske shocks on one car (Boss) and they are great. $10k.



The other car (Shelby GT) has H&R race springs and Koni Yellows and the car works great. $2k. In fact, car was driven at Watkins Glen this month by my driving coach (Pro driver) and he said the car works great and he posted a 2:09 in traffic.

Yes, Penkes or Ohlins would be a step up but I’m not racing for $. Just fun. I posted a 2:13 as a best with coaching and using data to learn where I was making mistakes got my time down from a 2:17.

Driver is 80% of the equation. Get a Pro to drive your car and set a baseline. When you can equal that base line go for upgrades.

Honestly, a 2:13 at the Glen is about as fast as I want to go there. I’m good now. 🤪

3F13DF7D-5912-4477-9AE0-E5457386815C.png

6BA8DCC5-D4E0-4508-95EB-7B4A8C77E666.png
 
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323
318
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
Well, everybody seems like they agree on damper valving, so I'm going to go ahead and be the turd in the punchbowl...as usual.

---------------------------------------------------------------------------------------------------------------------------------------

First, my philosophy has been developed through trial & error and I’ve now wrapped a mathematical justification around it (which I’m going to leave in the background for simplicity). Usually, it’s done the other way around. This approach has evolved mostly through trial and error. Keep in mind, I’ve been in the position to make a lot of errors. I’m not making my argument from authority, I’m just being honest that I can’t provide a book and page number to support my approach. That may or may not be a good thing.

My opening given statements:

  • Rebound damping controls the unsprung mass while compression damping is more useful in controlling the sprung mass.
  • I’m perfectly comfortable with a damping ratio higher than 1 (mathematically ‘overdamped’) in the low speed ranges of the curve.
  • I can justify just about any damping curve shape (linear, progressive, digressive, etc.) depending on the road inputs. It just so happens that most tracks are similar in terms of the spectrum of road inputs (within relatively small ranges).
  • I tend to run relatively soft springs (which improves mechanical grip, bump/curb riding and tire life) and provide handling response with low-speed damping forces.

My first statement is probably my most controversial. It’s opposite of the Koni tuning advice sheet (which they’ve handed out for about 40 years, same sheet) and most experts. I arrived a justification through these thought experiments.

Thought experiment A: If a car is driving on a bridge and we somehow secure the body of the car and pull away the bridge, what will happen? The wheels and tires will move in the droop direction and the rebound forces will oppose the spring load and the inertia of the unsprung mass. In this we’re scenario, we’d be calling the car chassis the ‘ground’ of our spring/mass/damper system, which I think is valid in most cases because the sprung mass is usually ~7-10:1 greater than the unsprung.

Thought experiment B: If a car is driving down the road and hits some sort of protrusion bump (ordinary speed bump) at speed, it’s the compression side of the damper than will initially be active. In this scenario, we need to provide enough damping to reduce unsprung mass over-shoot, but not so much as to disturb the sprung mass. The difference here is we have the entire sprung mass inertia resisting the road input (as opposed to the much smaller unsprung mass in T.e._A). We have the spring, damper and unsprung inertial forces to absorb the input kinetic energy produced by the road. The forces of interest are on the compression side of the damper.

To extend these thoughts just a bit, on the back side of the bump, we’re back to experiment A. If we assume the tire will momentarily leave the pavement in this scenario (due to overshoot). The more rebound damping we have, the longer the tire will be disconnected from the road. That’s bad. So, given that I favor this view of the motion, it’s really no surprise why I end up with the compression forces being several times higher than the rebound side.

It’s fairly common to calculate forces using a ‘damping ratio’ from a quarter car mathematical model. This is a ratio of the force used compared to the force necessary to limit the system motion to exactly 1 up/down cycle when excited. Several books (RCVD and The Shock Handbook among others) have graphs which leads us to keep this damping ratio in the range of 0.7 (70% of critical damping) for performance applications and closer to 0.3 (30% critical) for ride comfort. The problem with these recommendations is that they seem to emerge from thin air. For me, they never adequately explain how these numbers are derived.

I see damping as a way to control inputs. Broadly speaking, cars see 2 types of suspension input. The first is low frequency, which is the type of input which we want the body of the car to follow. Think CA freeway roller bumps or anything resulting from driver inputs. The other type is high frequency bumps. A pavement transition, pothole or brake zone chatter bumps are all good examples. With these, we want the tire be able to follow the road perfectly (so as not to disturb the contact patch), but we don’t want any of the road input to influence the chassis. A well set up baja truck busting across the desert is a great visual example of this with wheels bouncing everywhere, but the chassis stable.

Generally speaking, at racetracks, we find that low frequency inputs correspond to low damper shaft speeds and high frequency inputs correspond to high damper shaft speeds. It’s *very* important to understand that these are not the same things, just that we often find this correlation. If a track were to have a large, long duration undulation, then we could easily see high shaft speeds from a low-frequency input. When tuning with driver feedback, I refer to low-frequency as “Roller bumps” and high-frequency as “Impact bumps”. That seems to be terminology to which most people can relate.

I don’t want to get too deep into the weeds, but it turns out that low frequency inputs are better controlled by increasing damping and high frequency inputs are better controlled by decreasing damping. What we want is a damper which provides both. When developing a damper valving package, I’ll pick a transition (or knee) point, 3 in/sec damper velocity gives a good first cut. In the 0-3 range, which is predominately low frequency, I have forces in excess of critical damping. It will depend on many factors, but anywhere from 110% to 175% critical is within reason. At the knee point, I dump force and by the time the damper is moving 10 in/sec the damping ratio is much closer to that ‘ride comfort’ number of 30-50% critical. It depends on the damper design/valving as to how easily this is accomplished, but it can usually be done to some extent. Keep in mind, this is painting with a very wide brush.

There are plenty of outlier racetracks which give different road inputs and require different damping curves. The relative importance of the low/high shaft speed vs. low/high frequency inputs is really the determining factor concerning the shape of the curve. This is why I say I can justify about any curve shape. I don’t believe there is a ‘perfect’ curve shape generically or even any perfect curve shape for a given car. It’s all the factors including car, tire and road input.

I tend to run springs on the soft side to gain mechanical grip. The downside to reducing spring rates is that the car will gain compliance, but lose response to the driver. When the driver reports a lack of response and vague car feedback, that’s a pretty good clue you’re too soft. However, if you run higher damping forces in the range of inputs which relate to driver feedback, you find the spring rate floor become lower. It’s a trade which is usually beneficial to make.

Lastly, I want to calm concerns about too much compression. I’ve often been told that too much compression will cause the tire to skip and lose grip. I think this has been found by people who are already running excessive rebound. What they’re bumping up against is too much damping overall. It’s not that compression per say is too high, it’s that it’s too high for the existing amount of rebound. By reducing the rebound, I’ve found compression forces can be safely increased without causing compliance problems.

I don’t particularly want anyone to believe what I’m saying. I’m not writing a gospel or trying to convince everyone I’m ‘right’. I’m simply explaining my process and providing some food for thought. I’m interested to see its reception.
 
77
56
Exp. Type
HPDE
Exp. Level
Under 3 Years
TX
Well, everybody seems like they agree on damper valving, so I'm going to go ahead and be the turd in the punchbowl...as usual.

---------------------------------------------------------------------------------------------------------------------------------------

First, my philosophy has been developed through trial & error and I’ve now wrapped a mathematical justification around it (which I’m going to leave in the background for simplicity). Usually, it’s done the other way around. This approach has evolved mostly through trial and error. Keep in mind, I’ve been in the position to make a lot of errors. I’m not making my argument from authority, I’m just being honest that I can’t provide a book and page number to support my approach. That may or may not be a good thing.

My opening given statements:

  • Rebound damping controls the unsprung mass while compression damping is more useful in controlling the sprung mass.
  • I’m perfectly comfortable with a damping ratio higher than 1 (mathematically ‘overdamped’) in the low speed ranges of the curve.
  • I can justify just about any damping curve shape (linear, progressive, digressive, etc.) depending on the road inputs. It just so happens that most tracks are similar in terms of the spectrum of road inputs (within relatively small ranges).
  • I tend to run relatively soft springs (which improves mechanical grip, bump/curb riding and tire life) and provide handling response with low-speed damping forces.

My first statement is probably my most controversial. It’s opposite of the Koni tuning advice sheet (which they’ve handed out for about 40 years, same sheet) and most experts. I arrived a justification through these thought experiments.

Thought experiment A: If a car is driving on a bridge and we somehow secure the body of the car and pull away the bridge, what will happen? The wheels and tires will move in the droop direction and the rebound forces will oppose the spring load and the inertia of the unsprung mass. In this we’re scenario, we’d be calling the car chassis the ‘ground’ of our spring/mass/damper system, which I think is valid in most cases because the sprung mass is usually ~7-10:1 greater than the unsprung.

Thought experiment B: If a car is driving down the road and hits some sort of protrusion bump (ordinary speed bump) at speed, it’s the compression side of the damper than will initially be active. In this scenario, we need to provide enough damping to reduce unsprung mass over-shoot, but not so much as to disturb the sprung mass. The difference here is we have the entire sprung mass inertia resisting the road input (as opposed to the much smaller unsprung mass in T.e._A). We have the spring, damper and unsprung inertial forces to absorb the input kinetic energy produced by the road. The forces of interest are on the compression side of the damper.

To extend these thoughts just a bit, on the back side of the bump, we’re back to experiment A. If we assume the tire will momentarily leave the pavement in this scenario (due to overshoot). The more rebound damping we have, the longer the tire will be disconnected from the road. That’s bad. So, given that I favor this view of the motion, it’s really no surprise why I end up with the compression forces being several times higher than the rebound side.

It’s fairly common to calculate forces using a ‘damping ratio’ from a quarter car mathematical model. This is a ratio of the force used compared to the force necessary to limit the system motion to exactly 1 up/down cycle when excited. Several books (RCVD and The Shock Handbook among others) have graphs which leads us to keep this damping ratio in the range of 0.7 (70% of critical damping) for performance applications and closer to 0.3 (30% critical) for ride comfort. The problem with these recommendations is that they seem to emerge from thin air. For me, they never adequately explain how these numbers are derived.

I see damping as a way to control inputs. Broadly speaking, cars see 2 types of suspension input. The first is low frequency, which is the type of input which we want the body of the car to follow. Think CA freeway roller bumps or anything resulting from driver inputs. The other type is high frequency bumps. A pavement transition, pothole or brake zone chatter bumps are all good examples. With these, we want the tire be able to follow the road perfectly (so as not to disturb the contact patch), but we don’t want any of the road input to influence the chassis. A well set up baja truck busting across the desert is a great visual example of this with wheels bouncing everywhere, but the chassis stable.

Generally speaking, at racetracks, we find that low frequency inputs correspond to low damper shaft speeds and high frequency inputs correspond to high damper shaft speeds. It’s *very* important to understand that these are not the same things, just that we often find this correlation. If a track were to have a large, long duration undulation, then we could easily see high shaft speeds from a low-frequency input. When tuning with driver feedback, I refer to low-frequency as “Roller bumps” and high-frequency as “Impact bumps”. That seems to be terminology to which most people can relate.

I don’t want to get too deep into the weeds, but it turns out that low frequency inputs are better controlled by increasing damping and high frequency inputs are better controlled by decreasing damping. What we want is a damper which provides both. When developing a damper valving package, I’ll pick a transition (or knee) point, 3 in/sec damper velocity gives a good first cut. In the 0-3 range, which is predominately low frequency, I have forces in excess of critical damping. It will depend on many factors, but anywhere from 110% to 175% critical is within reason. At the knee point, I dump force and by the time the damper is moving 10 in/sec the damping ratio is much closer to that ‘ride comfort’ number of 30-50% critical. It depends on the damper design/valving as to how easily this is accomplished, but it can usually be done to some extent. Keep in mind, this is painting with a very wide brush.

There are plenty of outlier racetracks which give different road inputs and require different damping curves. The relative importance of the low/high shaft speed vs. low/high frequency inputs is really the determining factor concerning the shape of the curve. This is why I say I can justify about any curve shape. I don’t believe there is a ‘perfect’ curve shape generically or even any perfect curve shape for a given car. It’s all the factors including car, tire and road input.

I tend to run springs on the soft side to gain mechanical grip. The downside to reducing spring rates is that the car will gain compliance, but lose response to the driver. When the driver reports a lack of response and vague car feedback, that’s a pretty good clue you’re too soft. However, if you run higher damping forces in the range of inputs which relate to driver feedback, you find the spring rate floor become lower. It’s a trade which is usually beneficial to make.

Lastly, I want to calm concerns about too much compression. I’ve often been told that too much compression will cause the tire to skip and lose grip. I think this has been found by people who are already running excessive rebound. What they’re bumping up against is too much damping overall. It’s not that compression per say is too high, it’s that it’s too high for the existing amount of rebound. By reducing the rebound, I’ve found compression forces can be safely increased without causing compliance problems.

I don’t particularly want anyone to believe what I’m saying. I’m not writing a gospel or trying to convince everyone I’m ‘right’. I’m simply explaining my process and providing some food for thought. I’m interested to see its reception.
I can corroborate 95% of this anecdotally with my own trial and error. I would agree that low speed can be 1.0< (critical) especially if chassis control was very important to the engineer or driver. It's not wrong. The car wants what the car wants for a given setup at a given track.

I will say that the 70% of critical did not "appear from thin air" I think RCVD does a good job explaining where that came from for a non aerodynamic race car:

070CritD.JPG

Take a look at the oval table below the non aero table and you will see 0.71 is out the window with ease
070CritD2.JPG
 
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323
318
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
That wasn't the exact graph in my head, but it will do. So, do you believe that a book refers to a paper which puts a number on a chart and this is now the prefect answer for every non-aero car forever? Stop following books and start following stopwatches.
 
77
56
Exp. Type
HPDE
Exp. Level
Under 3 Years
TX
That wasn't the exact graph in my head, but it will do. So, do you believe that a book refers to a paper which puts a number on a chart and this is now the prefect answer for every non-aero car forever? Stop following books and start following stopwatches.
Nnno... That is not what I said at all. I just wanted to show it was not a number pulled from thin air. There is no commandment "Thou shalt trust and not verify". In fact, I said

"I would agree that low speed can be 1.0< (critical) **edit got my greater than sign wrong** especially if chassis control was very important to the engineer or driver. It's not wrong. The car wants what the car wants for a given setup at a given track."

The math is valid but is just one of many tools that gets you in the ballpark, then the driver + all of the real world conditions / variables will dictate final configuration(s).
 

Dave_W

Cones - not just for ice cream
984
1,277
Exp. Type
Autocross
Exp. Level
20+ Years
Connecticut
Some interesting tidbits under the "Limit Handling" section in that text. I wonder how long it actually takes one of our cars (with some of the typical spring & shock changes) to move through the damping resistance and reach steady-state.

Another piece of information in this link. Note the part about "driver feel" vs actual speed/time as well.
Yeah, just "some guy on the Internet" to most, but he's won SCCA Solo National events, helped start the entire Street Modified category, worked rebuilding race shocks, and most importantly has data logged nearly every run he's taken in his car over years of competition. Read the Acknowledgement page. And the Caveat Lector page.
 
77
56
Exp. Type
HPDE
Exp. Level
Under 3 Years
TX
Some interesting tidbits under the "Limit Handling" section in that text. I wonder how long it actually takes one of our cars (with some of the typical spring & shock changes) to move through the damping resistance and reach steady-state.

Another piece of information in this link. Note the part about "driver feel" vs actual speed/time as well.
Yeah, just "some guy on the Internet" to most, but he's won SCCA Solo National events, helped start the entire Street Modified category, worked rebuilding race shocks, and most importantly has data logged nearly every run he's taken in his car over years of competition. Read the Acknowledgement page. And the Caveat Lector page.
The far north site has some good info. I regularly refer people to that site because of how well the info is explained.
 
323
318
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
Nnno... That is not what I said at all. I just wanted to show it was not a number pulled from thin air. There is no commandment "Thou shalt trust and not verify". In fact, I said

OK, fair enough, but the justification was simply more research. There is nothing presented which derives these numbers from first principles (which *no one* can do, btw). It might be accurate so say that 0.71 is the best compromise for the inputs which they used, but the conclusion that this is somehow universally applicable is not supported. At best, it's a good 'first cut' baseline. There's no reason why the claim of 0.71 is any better than Grant's claim of 0.65 or mine, which varies. It is important to appreciate the damping research in that paper had nothing to do with racing (Electronically Controlled Shock Absorber System Used as a Road Sensor Which Utilizes Super Sonic Waves, 851652). Further, it's from 1985. There have been massive advancements in dampers in the last 35 years.

Grant's histogram argument is from Claude Rouelle, who gives race car engineering seminars. It's worth understanding that Claude has no mathematical justification for his hypothesis. The argument falls back to "It is intuitively obvious that..." Well, I don't agree that the historgram really tells us anything. In fact, I'd say it's looking at damper data in a fundamentally incorrect way, but that's a different story.

Lastly, we're all just "Some guy on the internet". None of us have all the answers. I'm giving my approach. It's worth every cent what you've paid for it.
 
323
318
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
Some interesting tidbits under the "Limit Handling" section in that text. I wonder how long it actually takes one of our cars (with some of the typical spring & shock changes) to move through the damping resistance and reach steady-state.

Another piece of information in this link. Note the part about "driver feel" vs actual speed/time as well.
Yeah, just "some guy on the Internet" to most, but he's won SCCA Solo National events, helped start the entire Street Modified category, worked rebuilding race shocks, and most importantly has data logged nearly every run he's taken in his car over years of competition. Read the Acknowledgement page. And the Caveat Lector page.

On the 'Caveat Lector' page, Grant sums things up by writing, "Don't just take my (or anybody else's) word for it - GO TEST IT!" I couldn't agree more.

I couldn't find 'Limit Handling', but on the 'Balancing the Car' I do disagree with a couple of his statements.

First was tuning for oversteer. I tune for a small, consistent understeer for a couple reasons. The first (which Grant mentions) is that O/S limits driver aggressiveness on corner entry. This is the first and easiest way to introduce problems later in the corner. The driver must have absolute confidence, particularly in the rear, of the car on entry. Also, steady state oversteer will limit the ability to accelerate out of a corner because the rear tires are already saturated with cornering load. I don't tune for U/S because I'm scared. Racing has little to do with bravado. I do so because it's faster. Admittedly, an autocross car, which is always at a relatively low speed and has to negotiate very tight corners is a special case which probably means U/S should be reduced to a minimum, but we have to appreciate that a driver can influence balance *way* more with his feet than we can move with any of our tools. We need to supply a predicable platform for that to happen.

The second thing I disagree with not using the dampers to influence handling balance. Dampers are one of the better tools to use to influence balance of the car in transitions because that's when they're active! Very often, if you improve the transitions of the car (particularly on corner entry), you'll find whatever steady-state problem you have will either diminish or completely vanish. This happens because we're allowing the driver to modify his actions. None of our changes happen in a vacuum, they're all part of the feedback loop which includes car and driver.
 

Dave_W

Cones - not just for ice cream
984
1,277
Exp. Type
Autocross
Exp. Level
20+ Years
Connecticut
Admittedly, an autocross car, which is always at a relatively low speed and has to negotiate very tight corners is a special case which probably means U/S should be reduced to a minimum, but we have to appreciate that a driver can influence balance *way* more with his feet than we can move with any of our tools.
Exactly, most of Dennis' real-life tuning examples are based on autocrossing his Street Mod Eagle Talon, which had AWD, lots of power, and grippy tires. His whole driving style revolved around being able to rotate the car on entry, get hard on the throttle as soon as possible, and have the AWD pull the car out of the corner. The whole site/e-book is based on autocross.

I had very much the same style when I was autocrossing my FWD Neon back in the 90's - 225 tires on front, 205 on the rear, -2.5F/-0.5R camber, 1/4" total toe out on front, and a hair toe out in the rear. To say it was twitchy is an understatement. But I could enter a corner using left-foot braking and a bit of steering to point the nose, use the throttle against the brakes to adjust the F/R braking balance and rotation into the apex (had to unlearn that for RWD), and by the apex have the steering nearly pointed straight and be full on the gas as I carried a slight 4-wheel drift out. Worked great at autocross, but off-ramps in the rain could be a white-knuckle experience. I'd never use that setup at a racetrack. I definitely agree that mild understeer is a much better scenario for the higher speeds and longer corners on a track.

Ideally for a fast driver, you want even an RWD autocross car to have slight oversteer on corner entry to help rotation, then transition to neutral when on the throttle on corner exit. I've used dissimilar brake compounds on my Miata like a lot of TMO track guys, but I put the more aggressive compound in the rear to shift the balance to oversteer during trail-braking. Again, not something you'd do for the track but works for the lower speeds and tighter corners in autocross. You also need an autocross driver who understands the entry-loose condition and can use it to their advantage.

For my club's Autocrosser of the Year Runoff, all the class champions for the year drive 3 runs in the same Miata for best time and the big trophy. That car I've set up with slight understeer in all phases, as it inspires confidence, as you say. Because there are a bunch of drivers coming from their own widely-different cars and jumping into the Miata "cold" I wanted it to be as predictable and confidence-inspiring as possible. In fact, in this particular situation, setting up the car to be predictable and confidence-inspiring is much more important than it being fast.
 
77
56
Exp. Type
HPDE
Exp. Level
Under 3 Years
TX
Exactly, most of Dennis' real-life tuning examples are based on autocrossing his Street Mod Eagle Talon, which had AWD, lots of power, and grippy tires. His whole driving style revolved around being able to rotate the car on entry, get hard on the throttle as soon as possible, and have the AWD pull the car out of the corner. The whole site/e-book is based on autocross.

I had very much the same style when I was autocrossing my FWD Neon back in the 90's - 225 tires on front, 205 on the rear, -2.5F/-0.5R camber, 1/4" total toe out on front, and a hair toe out in the rear. To say it was twitchy is an understatement. But I could enter a corner using left-foot braking and a bit of steering to point the nose, use the throttle against the brakes to adjust the F/R braking balance and rotation into the apex (had to unlearn that for RWD), and by the apex have the steering nearly pointed straight and be full on the gas as I carried a slight 4-wheel drift out. Worked great at autocross, but off-ramps in the rain could be a white-knuckle experience. I'd never use that setup at a racetrack. I definitely agree that mild understeer is a much better scenario for the higher speeds and longer corners on a track.

Ideally for a fast driver, you want even an RWD autocross car to have slight oversteer on corner entry to help rotation, then transition to neutral when on the throttle on corner exit. I've used dissimilar brake compounds on my Miata like a lot of TMO track guys, but I put the more aggressive compound in the rear to shift the balance to oversteer during trail-braking. Again, not something you'd do for the track but works for the lower speeds and tighter corners in autocross. You also need an autocross driver who understands the entry-loose condition and can use it to their advantage.

For my club's Autocrosser of the Year Runoff, all the class champions for the year drive 3 runs in the same Miata for best time and the big trophy. That car I've set up with slight understeer in all phases, as it inspires confidence, as you say. Because there are a bunch of drivers coming from their own widely-different cars and jumping into the Miata "cold" I wanted it to be as predictable and confidence-inspiring as possible. In fact, in this particular situation, setting up the car to be predictable and confidence-inspiring is much more important than it being fast.
All in agreement here it seems, I always aim for slight O/S in low speed and slight U/S in high speed turns. It takes a lot of guess work out of the equation and I can focus on driving more than "managing" the car, if that makes sense.
 
323
318
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
We've got too many variables here.

The first is track or autocross. An autocross car definitely has to have a lot of 'turn' in it, but whatever entry rotation we allow, we need to make sure we don't get excess. I'll always err on the side of stability because rotation overshoot is a much bigger problem than too little. Secondly, we always need to be able have good powerdown off the corner. We've all seen BlackSheep's car. That is not just a stick axle phenomenon. This means we have to maintain a little excess cornering capacity on the rear. Big heavy cars like ours make time in straight lines, not the middle of the corner.

The second variable we need to isolate is the car. A Miata needs a different balance than a Mustang. An AWD Talon will want a different balance than those two. The Neon will be yet a third variation. None of these will want the same balance as a Mustang/Camaro GT car. It's very difficult to draw parallels among these cars any more than to say we want to optimize each towards their individual strength and minimize the effect of their weaknesses.

Off the top of my head:

Miata:
  • Maintaining high rolling speed through corners is a must
  • Low weight, excellent direction change
  • Low power, wheelspin is not a major issue
  • Braking is a relatively minor issue because of lower straight & higher cornering speeds
All of these things conspire to push us in a direction which has very little understeer. This car does not have an excess of power, so we produce the best lap time by relying on high corner minimum speeds and nimbleness to offset the lack of forward acceleration. That's completely reasonable and explains why we always see a Miata at large yaw angles and it also explains why they're such a barrel of monkeys to drive.

A front-drive Neon and AWD Talon are also significantly different to a GT car to the point where we would compromise their respective setups in an effort to optimize their individual advantages. My greater point is not only that we have to optimize each car based on that particular car's performance envelope, but that those strategies will be based on the relative strengths of that particular car. My damper approach is agnostic on the car in question. I've used it on radically different cars and never had the scenario where it was either slower or produced unfavorable driver comments. My comments concerning chassis balance is very much car-type specific. I don't think the same understeer gradient should be used for a Miata and a GT car. They have significant differing strengths and weaknesses.
 
323
318
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
"I would agree that low speed can be 1.0< (critical) **edit got my greater than sign wrong** especially if chassis control was very important to the engineer or driver. It's not wrong. The car wants what the car wants for a given setup at a given track.

I think I see one if our conflicts. I don't damp low-frequency inputs @ >1 critical just for chassis control. Certainly that's a reason, but it's not the only one. I do it specifically because it also increases grip by reducing the chassis response to low frequency inputs. It's important to note l use this approach to keep the tires in contact with the ground as much as to limit excessive chassis motion.

It's not just that I *can* do it, but that I get the opportunity to do so.
 

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