I think Toyota/Scion is making a BIG mistake with the FR-S' suspension tuning

[OrbitalEllipses]

Originally Posted by delongedoug

You're right, humans shouldn't be allowed to drive. Can't trust them.

A lot of them, yeah. No more congestion either. And this is a bad idea, how? Driving's a privilege, not a right.

[Zgrinch]

Originally Posted by OrbitalEllipses

A lot of them, yeah. No more congestion either. And this is a bad idea, how? Driving's a privilege, not a right.

Let all the dumb humans ride the bus.

[Maxim]

From what I've read, Subaru's tuning will likely result in slightly better lap times and stability, and Toyota's tuning will result in a slightly more "playful" demeanor.

Given that the vast majority of my driving will be on public roads, and when I hot-shoe it I will, for safety's sake, be more like 8/10ths instead of 10/10ths, I think I'll prefer the Subaru's settings. Just a little bit of safety net built in for when there's some extra dust on the road that I'm not anticipating, etc. The reviews have said that it's quite easy to transition to oversteer with the Subaru, so I doubt there will be any issue of "losing fun."

Stability control and traction control go "off" when I play. I've never had either of them "save" me and have been driving powerful rear wheel drive cars for years, many times in snowy conditions. They're great for drivers who don't care about driving and just want some additional security, and they're great in panic situations like having to swerve away from a deer or somebody who wandered into your lane on the highway. Thus I leave them on when I'm doing everyday things.

Basically, Toyota/Scion have tuned the car to appeal to the drift generation...to which I do not belong. The car has a slight front weight bias, it SHOULD have a small amount of steady-state understeer. Tuning it to oversteer leads me to believe that a bit of overall grip was given up to do so.

Subaru has done what they always do for their performance cars. They've tuned it to reliably go fast as hell in a variety of conditions, with a little bit of safety net built in because in the real world you never know the exact amount of dust or moisture on the road. That comes from their long history of rally racing, and that kind of tuning produces a faster more stable vehicle in real world conditions.....

[ZDan]

Originally Posted by Maxim

Basically, Toyota/Scion have tuned the car to appeal to the drift generation...to which I do not belong. The car has a slight front weight bias, it SHOULD have a small amount of steady-state understeer.

Not true. Exceedingly easy to tune out understeer with spring and sway bar rates. Slight front weight bias => slightly more rear roll bias = neutral. They will have tuned to achieve the handling balance they wanted, which is not strictly dictated by the 53/47 weight distribution. Easy enough to tweak front/rear roll stiffness to get even load distribution between the outside front/outside rear, which would maximize total lateral grip and reduce understeer.

Tuning it to oversteer leads me to believe that a bit of overall grip was given up to do so.

There's no way they will have "tuned it to oversteer". Maybe tuned to understeer less. In which case it would have slightly more total grip at max cornering than the BRZ, not less.

Realistically, the cars are going to be very similar. With the same toe and camber settings, they're going to be close to equivalent of course.

Subaru has done what they always do for their performance cars. They've tuned it to reliably go fast as hell in a variety of conditions, with a little bit of safety net built in because in the real world you never know the exact amount of dust or moisture on the road. That comes from their long history of rally racing, and that kind of tuning produces a faster more stable vehicle in real world conditions.....

If not at the track or autoX...

But again, the performance is going to be *very* close between the two.

[Maxim]

Originally Posted by ZDan

Not true. Exceedingly easy to tune out understeer with spring and sway bar rates. Slight front weight bias => slightly more rear roll bias = neutral. They will have tuned to achieve the handling balance they wanted, which is not strictly dictated by the 53/47 weight distribution. Easy enough to tweak front/rear roll stiffness to get even load distribution between the outside front/outside rear, which would maximize total lateral grip and reduce understeer.

There's no way they will have "tuned it to oversteer". Maybe tuned to understeer less. In which case it would have slightly more total grip at max cornering than the BRZ, not less.

Realistically, the cars are going to be very similar. With the same toe and camber settings, they're going to be close to equivalent of course.


If not at the track or autoX...

But again, the performance is going to be *very* close between the two.

Tuning to understeer less without major changes like camber adjustment, tire size/compound changes, or weight distribution = tuning the rear to let go easier = reducing rear grip in the name of "balance".

I've experienced this plenty. WRX guys are always trying to "fix" their understeer-prone front heavy cars. They tighten up the rear sway bar, they get more oversteer....but they haven't changed the amount of front grip, which means the only thing it accomplished is the rear of the car is letting go sooner.

You said yourself, the major settings between the two cars are the same. The parts are the same. The spring and damping rates appear to be the only differences. Toyota went with softer springs and higher damping rates, which is going to result in more weight transfer, which absolutely can help cause oversteer because it means the rear axle is transferring more stress to the outside wheel and less to the inside...which will reduce overall grip. Subaru went with tighter suspenders and less damping, and that will result in more even distribution of weight under load. At that point, the natural balance of the car will come out more....and with a slight front bias, this car will naturally have a little steady-state understeer.

I would bet that the scion/toyota version will post ever-so-slightly lower skidpad numbers, reflecting a small reduction in rear grip.

But yeah as you said the differences are likely to be extremely minor and almost a non-issue for most driving. .01 or .02 on the skidpad is not going to be noticable to most people.

[delongedoug]

Originally Posted by OrbitalEllipses

A lot of them, yeah. No more congestion either. And this is a bad idea, how? Driving's a privilege, not a right.

Except you damn well know there's no way to do anything about it. Heck, you can't even take the license away from a blind 90 year old in a wheelchair. So to regulate them, we have to regulate all of society down to their level and we continue to get dumbed down to the same low benchmark. And so on and so forth.

.001% of the population uses cold medicine to cook up meth. Well then, lets check 100% of the population's IDs when buying cold medicine.

[Racecomp Engineering]

Get this political discussion BS out of here!

Originally Posted by Maxim

I've experienced this plenty. WRX guys are always trying to "fix" their understeer-prone front heavy cars. They tighten up the rear sway bar, they get more oversteer....but they haven't changed the amount of front grip, which means the only thing it accomplished is the rear of the car is letting go sooner.

While I agree with you that many throw on a big rear swaybar and do not necessarily make the car faster, a rear swaybar does improve front grip...it doesn't just remove rear grip. If the rear has some grip to spare and understeer is a problem...improving front grip through a rear bar while slightly reducing rear grip may result in a net improvement in total grip. Of course all of that depends on a lot of factors and throwing on a massive bar with no thought usually doesn't work out well.

I do not expect much difference between the two cars in terms of numbers at least. We do plan to measure spring rates for both and shock dyno both cars dampers though.

- Andrew

[Racecomp Engineering]

Originally Posted by Maxim

Toyota went with softer springs and higher damping rates, which is going to result in more weight transfer, which absolutely can help cause oversteer because it means the rear axle is transferring more stress to the outside wheel and less to the inside...which will reduce overall grip. Subaru went with tighter suspenders and less damping, and that will result in more even distribution of weight under load. At that point, the natural balance of the car will come out more....and with a slight front bias, this car will naturally have a little steady-state understeer.

Stiffer front springs (while keeping the rear the same) will increase weight transfer at the front of the car. Since total weight transfer will stay the same for a given car in a given corner (on a given day, at a given latitude, etc.) this means the rear will experience less weight transfer.

This means the rear tires are more equally loaded compared to before, since less weight has been transferred, and you have an increase in rear grip. Front grip may decrease due to increased weight transfer and the likelihood that you will overload the now more heavily loaded outside tire, but it's tricky since we're also reducing roll and camber loss, which can be a very big deal on a strut based car and when starting from a pretty soft starting point (OEM). The stiffer springs also help the car react faster and improve response.

Hope I helped.

- Andrew

[ZDan]

Originally Posted by Maxim

Tuning to understeer less without major changes like camber adjustment, tire size/compound changes, or weight distribution = tuning the rear to let go easier = reducing rear grip in the name of "balance".

If you've got steady-state understeer in a slightly front-heavy car, you will increase total grip by tuning in relatively more rear roll stiffness. You were overloading the outside front, retuning for less understeer alleviates outside front load and increases grip/load up front by allowing the inside front and outside rear to do more cornering work.

If you had been overloading the front, you will gain more front grip than you lose at the rear. To a point, but as long as we're talking about reducing a terminal understeer situation and not inreasing a terminal oversteer situation, this will hold true.

I've experienced this plenty. WRX guys are always trying to "fix" their understeer-prone front heavy cars. They tighten up the rear sway bar, they get more oversteer....but they haven't changed the amount of front grip, which means the only thing it accomplished is the rear of the car is letting go sooner.

You absolutely do increase the front grip by adding rear roll stiffness. You are taking load off of the overloaded outside front, giving it more grip per unit load, and adding load to the inside front, which at its low load level is still in the linear range of the grip/load curve. With more rear roll stiffness, under steady state cornering, you are adding total grip to the front and taking it away in the back.

Toyota went with softer springs and higher damping rates, which is going to result in more weight transfer,

In steady state cornering at the same speed, left to right weight transfer is a function of c.g. height and track width. So whatever the spring/damping rates are, at a given constant cornering speed, weight transfer will be identical.

Subaru went with tighter suspenders and less damping, and that will result in more even distribution of weight under load.

No it won't. Steady state cornering, weight transfer = cornering gs * c.g. height divided by track width, period. The stiffer-sprung car will NOT have more even left/right distribution.

At that point, the natural balance of the car will come out more....and with a slight front bias, this car will naturally have a little steady-state understeer.

(sigh) Again, this doesn't have to be the case. Tune roll stiffnesses to give more even load between the outside front and outside rear and you will reduce understeer and add to overall grip.

I would bet that the scion/toyota version will post ever-so-slightly lower skidpad numbers, reflecting a small reduction in rear grip.

Realistically, the differences are likely to be too small to measure, but again the advantage in overall grip will be to the car that doesn't overload the outside front as much, which (sounds like) should be the Toyota.

But yeah as you said the differences are likely to be extremely minor and almost a non-issue for most driving. .01 or .02 on the skidpad is not going to be noticable to most people.

Any difference is most likely to be smaller than car to car variations.


Consider a 2900 lb. 53/47 car, 18" high c.g., 65" track, steady-state cornering in a right-hander at 1g. With roll stiffness also at 53/47, you'll have:
1194 lb. LF, 343 lb. RF
1059 lb. LR, 304 lb. RR

You could add rear roll stiffness/take away front roll stiffness to get:
1126.5 lb. LF, 410.5 lb. RF
1126.5 lb. LR, 236.5 lb. RR

This would add MORE grip up front than you take away in the rear, due to the nonlinear nature of tire grip vs. load. In the 1st case, the outside front is making less grip per unit load than it or the outside rear are in case #2. The inside tires are so lightly loaded that they're in the linear region of grip/load.
Case 2 = more total grip and less understeer.

In reality, I bet that the roll stiffnesses on both cars actually bias more load onto the outside front, as this is normal for most cars. If the reports are true, the Toyota would do this to a lesser degree. Again, more total grip vs. the BRZ's greater overloading of the outside front.

But again these differences are going to be very minor and very subtle.

[Racecomp Engineering]

Originally Posted by ZDan

In steady state cornering at the same speed, left to right weight transfer is a function of c.g. height and track width. So whatever the spring/damping rates are, at a given constant cornering speed, weight transfer will be identical.

You nailed it. The one thing to point out is that while total weight transfer will stay the same, you can alter the distribution of that weight transfer (which it appears you understand, just clarifying for everyone).

Big front sways got popular for Subarus because of dynamic camber and geometry considerations...plus they "felt" good in terms of response and turn-in. Important things on mac-strut car. Many have moved on to a more balanced set-up though and that's the approach I recommend.

- Andrew

[Maxim]

If stiffer suspension didn't affect weight transfer, we'd all be riding on pillows.

A stiffer suspension, or thicker roll bars, absolutely will affect how much weight is transfered from side to side during cornering. The whole body of the car moves over the unsprung portion of the vehicle. The total weights being transferred are of course the same, but the rate at which they are transferred is going to be different....which is going to affect how much load each tire is bearing, because it affects how the suspension "sets up."

Squishier suspenders = more side-to-side shift in weight distribution during cornering = less even load on each tire = reduced grip.

This is the exact same reason that it is easier to launch more softly sprung (rwd) cars. Upon launch, the softer springs allow more weight transfer to the rear, which increases rear grip. Conversely, stiffly sprung FWD cars are easier to launch, since less weight transfers away from the front tires...

Just to check on my reasoning, I loaded up Forza 4 last night and did some experimentation. I used a car with 53/47 weight distribution (RWD converted last-gen celica). Set up on as close to stock settings as I could get with an adjustable suspension, keeping camber and toe the same, a small reduction in spring rate accompanied by a small increase in damping rate...lowered the lateral grip figure by .01 at 60mph (no change at 120) and resulted in a slightly looser tail, especially during trail braking or throttle lift, because the rear was moving around more. Meanwhile, increasing the suspension stiffness a bit while decreasing damping rate resulted in no change in lateral grip but a little bit of understeer.

Increasing rear roll stiffness increased oversteer (dramatically increased it over uneven surfaces) but did not change total grip, while increasing front roll stiffness increased understeer but resulted in much better steering response.

These are the predictions I made beforehand.....so....yeah. ?? I strongly suspect that I am using terminology differently than you two and it's resulting in some confusion. The stuff you just described as weight transfer, I would have called weight distribution....when I think weight transfer, I think of dynamic changes in suspension load and the weight of the car actually shifting around before the suspension takes a set. Is this the source of the confusion?

I'm trying to get at what happens DURING suspension movement (while lateral forces are changing), and from what I can tell you're addressing the balance of the car once the suspension has taken a set (once lateral forces are constant)

To put it another way, yes, I understand how increased rear stiffness will cause weight to be more evenly distributed at the front tires, theoretically increasing front grip, but the trade off for that is that at initial turn-in, one of the rear tires is going to be recieving a much higher "spike" of the lateral acceleration, since the total amount of energy being transfered is the same, but the time in which it is transfered is shorter due to increased suspension stiffness. With a higher spike in instant load to the outside rear tire, that tire is more likely to exceed the available amount of traction and thus begin to slip, and at that point the inside rear tire will not have enough traction to make up the difference, which is going to result in the entire rear beginning to slip, causing oversteer.

It sounds to me like this is exactly what is happening with the cars, per the reviews I've read. The Toyota has softer front settings than the Subaru (I've specifically read that), which means the rear is stiffer in comparison to the front than on the Subaru (which is going to increase oversteer, because the rear tires are subjected to higher instant-load during initial turn in), while the Subaru is a little stiffer overall, but harder in the front than the rear, which is going to lessen instant-load on the outside rear tire (and increase it on the outside front) which will cause understeer.

The car and driver review of the Subaru mentioned this, how the car displays a little bit of understeer at turn-in.





Again though, the differences are really really small....most drivers probably won't notice much difference between the cars, except maybe that the ride in the Subaru is just a little harsher due to the spring rates.

[old greg]

Originally Posted by Maxim

Squishier suspenders = more side-to-side shift in weight distribution during cornering = less even load on each tire = reduced grip.

Load transfer is not caused by suspension movement. Suspension movement is caused by load transfer. Even if you replaced your springs/struts with solid steel bars your lateral load transfer per g would remain unchanged.

All you can change with springs, bars and damping is load transfer distribution. The total amount of load transfer is governed by the track width, unsprung mass, cg height and lateral acceleration. It's the laws of physics.

[Maxim]

Originally Posted by old greg

Load transfer is not caused by suspension movement. Suspension movement is caused by load transfer. Even if you replaced your springs/struts with solid steel bars your lateral load transfer per g would remain unchanged.

All you can change with springs, bars and damping is load transfer distribution. The total amount of load transfer is governed by the track width, unsprung mass, cg height and lateral acceleration. It's the laws of physics.

Again, missing what I'm trying to say. Yes, I'm aware that the actual amount of total energy being transfered is a constant that suspension settings will not change, but suspension settings absolutely will change how quickly that energy is transfered to the road via the tire, and that absolutely will affect the handling.

Jumping off of a 30 foot building and landing on a big cushy mattress is still going to transfer the same amount of energy to the ground as jumping off and landing directly on the ground. However, I think we can all agree that the affect on your body is somewhat.....lessened....by utilizing the mattress to spread the energy transfer over the medium of time, rather than transferring it all instantly. A suspension does the same thing. Total energy (weight) being moved around is the same but suspension settings can dramatically alter how quickly the tire is subjected to that energy, and good settings can help avoid overwhelming the contact patch by letting all the energy hit at once.

[old greg]

Load wrt. time has a lot more to do with damping ratio and roll inertia than with spring rates (unless your springs are soft enough that you are hitting the bump stops).