My Suspension Plan What you Think

[bnightstar]

What comments did you get from the pro driver who ran 1:08's (against your 1:10.x)?


Aside from the jacking rails, Shogun has covered most of what I'd have posted. What I really think you need to do is make your wheel and tire upgrade first, and by itself. Plan on making adjustments to your alignment, see where just that much puts you, and go from there instead of trying to guess from here.


Norm

Thanks for coming back Norm. I was at Dracon yesterday did 1:09.774 so I'm improving however the car blow a flex pipe :( which is super pricy here. Anyway the comment from the pro drive was that the car is way to soft and he suggest I move to coilovers and if I want fastest times slicks as well.

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[TeeLew]

515/800 is negative 34% frequency. You want positive 3-10%.

This is not the end-all/be-all. I suspect that 500#/in on the front a little high (especially for a street tire) and agree that 800#/in is relatively low (even for a street tire), but flat-ride is much more useful for a first cut at springs on a minivan than it is on a track car.

 

[Norm Peterson]

This is not the end-all/be-all. I suspect that 500#/in on the front a little high (especially for a street tire) and agree that 800#/in is relatively low (even for a street tire), but flat-ride is much more useful for a first cut at springs on a minivan than it is on a track car.

Just about any street-intended car, actually.


Norm

 

[TeeLew]

If we're strictly concerned with street use, OK, I guess. In that scenario, why are we changing springs? I'll concede there is a practical use for it on things like expansion joints at freeway speeds. Beyond that, It's just not a concern and does nothing to intrinsically improve handing. It was a thing which the early pioneers in vehicle dynamics used to make better cars, but they had to do things like this because they were stuck with emulsion dampers which were nearly useless. It was better to have the car bouncing down the road in a slow heave 'pogo' motion instead of a slow pitchy 'porpoising' motion.

On track, you're never at a constant speed and we almost disregard chassis motion on the straights. 'Flat-Ride' rates suggest either a relatively soft front or a relatively stiff rear. Either has it's drawbacks. While some tracks do have 2-wheel bumps which concern us, they're the exception, not the rule.

I don't want to completely disregard the idea, but I feel it's an error to use it as a setup bogie.

 

[Norm Peterson]

If we're strictly concerned with street use, OK, I guess. In that scenario, why are we changing springs? I'll concede there is a practical use for it on things like expansion joints at freeway speeds. Beyond that, It's just not a concern and does nothing to intrinsically improve handing. It was a thing which the early pioneers in vehicle dynamics used to make better cars, but they had to do things like this because they were stuck with emulsion dampers which were nearly useless. It was better to have the car bouncing down the road in a slow heave 'pogo' motion instead of a slow pitchy 'porpoising' motion.

On track, you're never at a constant speed and we almost disregard chassis motion on the straights. 'Flat-Ride' rates suggest either a relatively soft front or a relatively stiff rear. Either has it's drawbacks. While some tracks do have 2-wheel bumps which concern us, they're the exception, not the rule.

I don't want to completely disregard the idea, but I feel it's an error to use it as a setup bogie.

You can still pay some attention to it, certainly you'd be more likely to do so for a dual-purpose street/track car than you would for a dedicated track car (like time trial or W2W and caged). Of course, at that point you're also going to be running relatively firm damping, which quiets suspension movement and pitch down rapidly anyway.

The thing is, "flat ride" is not something that only applies at one speed, even though that's what the simplified calculation can lead one to believe. When you consider there to be some acceptable amount of "out of flatness" in the ride, that will determine a range of speeds - or a range of front vs rear spring stiffness - over which the end result is close enough to flat ride. How much is acceptable, well, I guess "it depends" . . .


Norm

 

[TeeLew]

The thing is, "flat ride" is not something that only applies at one speed, even though that's what the simplified calculation can lead one to believe. When you consider there to be some acceptable amount of "out of flatness" in the ride, that will determine a range of speeds - or a range of front vs rear spring stiffness - over which the end result is close enough to flat ride. How much is acceptable, well, I guess "it depends" . . .

Norm

I understand that it's not only applicable at a single speed, but it's benefit is reduced the further one varies from that optimal scenario. In terms of how to quantify the acceptable out of "out of flatness" we can use, we have 2 good data points. The first is the driver feedback and the second is the stopwatch. In my experience, as long as the car is balanced in terms of handling, the former doesn't care and the latter argues against it.

 

[Norm Peterson]

I'm sure that driver preferences and technique are also involved. Otherwise "one size fits all" would apply, we'd already have the end-all, be-all solutions, and there wouldn't be any need to talk about this stuff at all . . .


Norm

 

[bnightstar]

I'm sure that driver preferences and technique are also involved. Otherwise "one size fits all" would apply, we'd already have the end-all, be-all solutions, and there wouldn't be any need to talk about this stuff at all . . .


Norm

Leaving aside the question for the 800 lbs rear springs (maybe will need more).

I just wanted to know if my plan sounds reasonable for a car that will see both street/track driving. Vorshalag said that from all the dumpers they tested the Ohlins were best on the street and good enough on the track in there stock form which is why I want to go with them. As I said based on feedback from Pro driver the car is to soft for the track and I need to address that if I want to progress with my driving.

 

[Norm Peterson]

"Too soft" doesn't automatically mean going straight to shopping for dedicated race car spring rates, especially if there will be a significant amount of street driving involved. BMR's SP083 springs (about 50% stiffer than OE) or Steeda's Comp Dual-Rate springs (closer to double OE) might well be enough at least for a while. Perhaps with a bit more sta-bar stiffness at one or both ends.


Norm

 

[bnightstar]

"Too soft" doesn't automatically mean going straight to shopping for dedicated race car spring rates, especially if there will be a significant amount of street driving involved. BMR's SP083 springs (about 50% stiffer than OE) or Steeda's Comp Dual-Rate springs (closer to double OE) might well be enough at least for a while. Perhaps with a bit more sta-bar stiffness at one or both ends.


Norm

I agree but I'm like if you are doing something do it right the first time. Which is Why I plan to go with Coilovers.

 

[shogun32]

I agree but I'm like if you are doing something do it right the first time. Which is Why I plan to go with Coilovers.

"coilvers" are not magic. The good stuff costs $3000 and more, so going Ohlins there is the cheapest acceptable product. Since the rear is divorced spring, aside from headache of the swap it's fairly easy to play with rates.

 

[TeeLew]

I'm sure that driver preferences and technique are also involved. Otherwise "one size fits all" would apply, we'd already have the end-all, be-all solutions, and there wouldn't be any need to talk about this stuff at all . . .

Norm

And that's 100% true. There are a million and one ways to 'skin the cat'.

I guess if I step back and try to explain why I shy away from a F.R. spring lash-up, it goes back to my personal tuning biases, but these biases have not been arbitrarily formed. I have two main tuning bogies. The first is that the rear of the car has to be rock-solid stable on entry. The instant the rear gets unstable on corner entry, it hurts confidence and lap time goes into the toilet. If you ever find yourself driving with your fingertips, that car is either too loose or too unstable (not necessarily the same thing) to drive hard into the corner. My second tuning bogie is to optimize powerdown on corner exit. The more HP you have, the more of an advantage it is to get the nose pointed down the straight and be full throttle. If you're drifting the tail out to the exit of the corner, then you're spending time at partial-throttle going *across* the track, not full-throttle going *down* the track.

The front of the car is _mostly_(probably 80%) in control of corner entry stability. What makes for a stable braking platform? A relatively large front spring. We can over-do it, for sure, but that's usually not too tough to identify. If the front is skipping and loses compliance over bumps or is just generally numb on the brakes and easy to lock wheels, those are some good signs you're too stiff. Beyond that extreme, though, a relatively stiff front spring almost always inspires confidence on corner entry.

Reducing wheelspin and putting power down is my focus on corner exit. I want the driver to be able to apply full throttle pretty damned quick. If it takes more than about a second to go from 0 to 100% throttle, then you're either on the wrong line or the rear isn't strong enough. A smart old racer once said, "A car is like a primate, it has to squat to go." That was a long time ago, but it's still applicable. Soft rear springs improve exit traction.

Now you can appreciate what pushes me away from F.R. springs. There's also a fair question to come out of this. If you've got a relatively stiff spring on the front and a relatively soft spring on the rear, don't you to deal with understeer? The short answer is, "Yes." It's the compromise I'm willing to accept, but it's also facilitating and encouraging the driving style that I believe one needs to use. If the car is understeering early in the corner, what should the driver do? Keep the vertical load forward in the car with brakes. So, you'll need to trail the brakes into the corner to make the car turn. You'll also need to reduce your corner minimum speed below that of a more 'neutral' car, because it just doesn't have that lateral capacity (which we've traded for improved longitudinal capacity). Once off the brake pedal, you'll need to be patient before initiating throttle. Don't add throttle until the car is pointed in the right direction. Once it is, apply the throttle as quickly as possible.

I'm not in any way encouraging a 'one-size-fits-all' approach. Nothing has a bigger effect on the car than driving. Being able to effectively manipulate the load transfer in the car is vital. As a driver becomes better at managing the load transfer, they also tend to favor a car with its grip more biased towards the rear. The closest thing I've ever come to a tuning universal is that the better or faster the driver, the more understeer they require to go fast. No one...and I mean *no one*...likes to drive a genuinely loose car on a racetrack. It sucks when you're spending all your time just trying to keep the thing on the track and, ultimately, it's slow.

 

[bnightstar]

"coilvers" are not magic. The good stuff costs $3000 and more, so going Ohlins there is the cheapest acceptable product. Since the rear is divorced spring, aside from headache of the swap it's fairly easy to play with rates.

they are the only way to go over 300 lbs front spring though.

 

[Norm Peterson]

The question then becomes whether you really need more than 300 lb/in up front.

I suspect that more than 300 would be worth more at autocross where the transitions are pretty much on top of each other than out on the "big tracks".


Norm

 

[Norm Peterson]

And that's 100% true. There are a million and one ways to 'skin the cat'.

I guess if I step back and try to explain why I shy away from a F.R. spring lash-up, it goes back to my personal tuning biases, but these biases have not been arbitrarily formed. I have two main tuning bogies. The first is that the rear of the car has to be rock-solid stable on entry. The instant the rear gets unstable on corner entry, it hurts confidence and lap time goes into the toilet. If you ever find yourself driving with your fingertips, that car is either too loose or too unstable (not necessarily the same thing) to drive hard into the corner. My second tuning bogie is to optimize powerdown on corner exit. The more HP you have, the more of an advantage it is to get the nose pointed down the straight and be full throttle. If you're drifting the tail out to the exit of the corner, then you're spending time at partial-throttle going *across* the track, not full-throttle going *down* the track.

The front of the car is _mostly_(probably 80%) in control of corner entry stability. What makes for a stable braking platform? A relatively large front spring. We can over-do it, for sure, but that's usually not too tough to identify. If the front is skipping and loses compliance over bumps or is just generally numb on the brakes and easy to lock wheels, those are some good signs you're too stiff. Beyond that extreme, though, a relatively stiff front spring almost always inspires confidence on corner entry.

Reducing wheelspin and putting power down is my focus on corner exit. I want the driver to be able to apply full throttle pretty damned quick. If it takes more than about a second to go from 0 to 100% throttle, then you're either on the wrong line or the rear isn't strong enough. A smart old racer once said, "A car is like a primate, it has to squat to go." That was a long time ago, but it's still applicable. Soft rear springs improve exit traction.

Now you can appreciate what pushes me away from F.R. springs. There's also a fair question to come out of this. If you've got a relatively stiff spring on the front and a relatively soft spring on the rear, don't you to deal with understeer? The short answer is, "Yes." It's the compromise I'm willing to accept, but it's also facilitating and encouraging the driving style that I believe one needs to use. If the car is understeering early in the corner, what should the driver do? Keep the vertical load forward in the car with brakes. So, you'll need to trail the brakes into the corner to make the car turn. You'll also need to reduce your corner minimum speed below that of a more 'neutral' car, because it just doesn't have that lateral capacity (which we've traded for improved longitudinal capacity). Once off the brake pedal, you'll need to be patient before initiating throttle. Don't add throttle until the car is pointed in the right direction. Once it is, apply the throttle as quickly as possible.

I'm not in any way encouraging a 'one-size-fits-all' approach. Nothing has a bigger effect on the car than driving. Being able to effectively manipulate the load transfer in the car is vital. As a driver becomes better at managing the load transfer, they also tend to favor a car with its grip more biased towards the rear. The closest thing I've ever come to a tuning universal is that the better or faster the driver, the more understeer they require to go fast. No one...and I mean *no one*...likes to drive a genuinely loose car on a racetrack. It sucks when you're spending all your time just trying to keep the thing on the track and, ultimately, it's slow.

Agreed, though I feel it depends on whether you're coming from a car with better power (power potential, at least) than lateral grip, or from a car with better lateral grip than power. In the first case, you probably would end up building in somewhat more understeer. In the latter case, what you'd have is more of a momentum car, and you'd want less understeer than you would in a more muscular point and shoot car.

You can always add more front bar stiffness, which would at least slightly help the camber situation for all four tires.

I wouldn't want to drive a genuinely loose car anywhere except for playing around on a snow-covered parking lot where there wasn't anything to hit. Been in a too-loose car (experimentally) on dry pavement at somewhat higher speeds than that, where it was loose no matter whether I was on-throttle or off-throttle, and it was not fun at all. Randy Pobst is absolutely on point with the notion of maintaining a little understeer in your ride.


Norm

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