A discussion on improving ride quality

[Apoc]

If Air Ride is good for Kirby.....

[stonenewt]

Originally Posted by wparsons

The issue is that stock the dampers are valved too stiff (not too soft) for the springs, going with stiffer damping will only make it worse.

Which is exactly want I said so I think you're not understanding the terminology.

Dampers quell movement. You do not stiffly or softly quell movement you quickly or slowly quell movement. A fast damper results in the suspension feeling stiffer as it slows down the movement of the suspension leading to the car body moving more. Slower damping has the reverse effect, but if it's too slow you get spring oscillation which is bad for ride quality & handling.

Suspension as a combination of springs & dampers can be stiff or soft as you’ve given the damping speed & spring force context. As individual components they are neither stiff nor soft.

[solidONE]

Originally Posted by stonenewt

Which is exactly want I said so I think you're not understanding the terminology.

Dampers quell movement. You do not stiffly or softly quell movement you quickly or slowly quell movement. A fast damper results in the suspension feeling stiffer as it slows down the movement of the suspension leading to the car body moving more. Slower damping has the reverse effect, but if it's too slow you get spring oscillation which is bad for ride quality & handling.

Suspension as a combination of springs & dampers can be stiff or soft as you’ve given the damping speed & spring force context. As individual components they are neither stiff nor soft.

I believe the GT86 and FRS BRZ have slightly different spring rates, the GT86 being much softer, at least for MY 13-14 FRS-BRZ or 2012 and 2013 GT86's. Perhaps the dampers are also different. So, I don't think were comparing apples to apples here.

I think you will be well served with a set of aftermarket Damper/Spring combo in terms of ride quality not to mention handling improvement over stock GT86.

SPRINGS Front/Rate Rear/Rate Part # MSRP
OEM Toyota 86 0.0"/2.3k 0.0"/3.3k TBD $---
OEM Toyota GT86 (EU)0.0"/2.3k 0.0"/3.3k TBD $---
OEM Scion FR-S M/T 0.0"/2.3k 0.0"/3.8k F:SU003-04144 $83.90
R:SU003-04147 $83.90
OEM Scion FR-S A/T 0.0"/2.3k 0.0"/3.8k F:SU003-04145 $83.90
R:SU003-04147 $83.90
OEM Subaru BRZ M/T 0.0"/2.7k 0.0"/3.5k F:20330CA010 $79.70
R:20380CA010 $79.70
OEM Subaru BRZ A/T 0.0"/2.7k 0.0"/3.5k F:20330CA020 $79.70
R:20380CA010 $79.70

[wparsons]

Originally Posted by stonenewt86505

Which is exactly want I said so I think you're not understanding the terminology.

Dampers quell movement. You do not stiffly or softly quell movement you quickly or slowly quell movement. A fast damper results in the suspension feeling stiffer as it slows down the movement of the suspension leading to the car body moving more. Slower damping has the reverse effect, but if it's too slow you get spring oscillation which is bad for ride quality & handling.

Suspension as a combination of springs & dampers can be stiff or soft as you’ve given the damping speed & spring force context. As individual components they are neither stiff nor soft.

Typically fast = soft damping, not the other way around. The softer the valving, the faster the damper will move for a given force.

When I say the damping is too stiff it means that the shock is responding too slow for the given spring rate.

Damping that is too fast would be underdamped, damping that is too slow would be overdamped.

[stonenewt]

Originally Posted by wparsons

Typically fast = soft damping, not the other way around. The softer the valving, the faster the damper will move for a given force.

When I say the damping is too stiff it means that the shock is responding too slow for the given spring rate.

Damping that is too fast would be underdamped, damping that is too slow would be overdamped.

Obviously we speak totally different languages & have different physics to you guys over the pond because if I talked to chassis guys in the UK with those definitions they'd look at me like I was really, really dumb!

[Ubersuber]

Originally Posted by stonenewt

Obviously we speak totally different languages & have differed physics to you guys over the pond because if I talked to chassis guys in the UK with those definitions they'd look at me like I was really, really dumb!

Your useage is correct. Don't assume that Canadians or Americans understand the poster you refer to any more than you and other UK english speakers would.

You are correct that dampers are described by reference to the response speed with which they damp spring vibration. The more quickly they damp the spring the "stiffer" the damper. That is what you wrote and anyone reasonably familiar with English would read you as having done so.

Dampers have two distinct valving elements: orifices designed for relatively slow speed spring deflections requiring smoothly controlled damper movements and bypass valving for rapid spring deflections requiring the damper to allow much more rapid spring deflections. Each of these functions operates in both compression (bump or jounce) and rebound (extension). Of the two, rebound action is by far the most important which is why most "adjustable" dampers are adjustable for rebound only.

From my experience with the stock rear dampers and the Bilstein B6 I fitted I conclude that the rear stock dampers are too stiff in high speed bump (high accelerations of the springs) and in high speed rebound. They are fine for the slower accelerations.

Pitch the car in very hard or drive over a sharp bump and the deficiencies of the stock rear dampers are manifested in a ridiculously hard and uncontrolled ride. The car pogos to some degree and the rear dampers lift the rear of the car very sharply. This causes wet or snowy handling to be very poor compared to what the chassis is capable of (I am sure about the wet and will very shortly learn about the effect in the snow). Even dry road handling is compromised.

The Bilsteins allow the sharp acceleration forces to be absorbed by the springs with less damping force and allow the rebound to return the spring to ride height much more quickly than the stock damper after a sharp bump or during rapid transient maneuvers. The key to the Bilstein advantage is they do this while also giving better damping forces for elimination of the spring harmonic. The Bilsteins allow rapid accelerations and still quell the spring harmonic rapidly. This is what you pay for buying Bilsteins and this is what you want for these cars.

When you add in the long and quite hard rear bump stops you get a car that will sharply decrease understeer and sharply increase oversteer as the body rolls onto the outside bump stops. The suspension will start riding the rear bump stops earlier than the fronts for any given wheel movement (because of the motion ratio difference and the very small length difference between the front and rear bump stops, less than 1/8 inch). As the rear bump stop is much harder than the front the balance of the car shifts rapidly pushing roll resistance to the rear axle prematurely and often startlingly. The bump stops are essentially undamped because their compression rise is very, very steep and the bump resistance of the damper becomes irrelevant once the bump stop has been compressed significantly. Presumably, the rebound of the bump stops is comparable but nobody has tested this by measuring the rebound force, only the compression resistance. Likely they are similar because polyurethane foam is in reality a kind of air spring. It works because the enclosed air bubbles (micro sized) compress under pressure. Air of a certain volume and temperature exerts a linear force change with pressure increase or decrease and I doubt polyurethane has much compression or rebound without entrained air. I disregard the distortion effects of the bump stops because the urethane foam is dimensionally quite stable, the collapse rate of the "necks" of the bump stops along the damper shaft keeps the bump stop more or less in line as it compresses and, basically, it is what it is. Any stretching deformation of the bump stop outside the vertical will slow the compression rate of the air bubbles but that is what it is, non-adjustable. Only the length of the bump stops can easily be changed and you can change the compressibility rates by choosing where to cut out the length. Drilling the foam will reduce the spring rate of a bump stop but you are totally on your own as to where to drill and by how much.

[wparsons]

Originally Posted by Ubersuber

From my experience with the stock rear dampers and the Bilstein B6 I fitted I conclude that the rear stock dampers are too stiff in high speed bump (high accelerations of the springs) and in high speed rebound.

Funny, considering all other sources suggest that the Bilsteins have stiffer valving that stock.

Also, the fronts are more over damped than the rears which if anything drives the bias forwards (creating more understeer) in transitions.

Another problem with your theory is with how damping actually affects handling. In a steady state corner the damping (assuming no bumps) has zero influence on balance. Damping only influences balance in transitions. So unless you're getting oversteer right at turn in, it's not the damping.

Originally Posted by Ubersuber

The suspension will start riding the rear bump stops earlier than the fronts for any given wheel movement (because of the motion ratio difference and the very small length difference between the front and rear bump stops, less than 1/8 inch). As the rear bump stop is much harder than the front the balance of the car shifts rapidly pushing roll resistance to the rear axle prematurely and often startlingly.

You do realize that the motion ratio actually means you get MORE wheel travel at the rear for the same amount of shock travel, right? The motion ratio is irrelevant until you look at the amount of available bump travel before the bump stop is engaged at both ends though. IIRC, the front actually has less bump travel before you're on the bump stop, but I've never measured.

You also realize that with the motion ratio differences, the bump stops in the rear would have to be almost twice as stiff as the fronts to have the same effective rate at the wheel, right?

Based on motion ratios (assuming front is 1, rear is 0.75 which is very close to accurate) the wheel rates are:

Front: spring rate * 1
Rear: spring rate * 0.5625 (0.75^2)

BRZ:
Front: 2.7k * 1 = 2.7k
Rear: 3.5k * 0.5625 = 1.97k

FRS:
Front: 2.3k * 1 = 2.3k
Rear: 3.8k * 0.5625 = 2.14k

You should do yourself a favour and read this thread (including the linked pages):

http://www.ft86club.com/forums/showthread.php?t=9936

Originally Posted by Ubersuber

Likely they are similar because polyurethane foam is in reality a kind of air spring. It works because the enclosed air bubbles (micro sized) compress under pressure.

Nice to see you finally agree that they are springs, despite your previous protests.

[Ubersuber]

I find the Bilsteins improve the ride quality noticably. Sharp bumps are dealt with much more effectively and wheel control seems much better especially in rebound. It will be interesting to see what supplier Subaru has turned to for the 2015 rear shocks.

High pressure gas shocks will always give a more comfortable ride all other things being equal. Compression resistance is lowered and rebound resistance is increased merely by the presence of the high pressure gas chamber (30 Bar or so) even if no other valving is altered.

In the real world dampers are always active. No real person drives around a corner on a road or a track in steady state. Even Parabolica has an apex.

I'm not sure bump stops act truly as springs in the sense that the spring rate is the same in compression as in "rebound". I'm virtually certain they don't need damping which suggests they don't behave as normal springs would. It is useful to note that they have a spring rate in the sense that they compress progressively but not useful to consider this to be a spring rate as that term is usually used in connection with suspension. The compression pattern produces an extremely progressive spring rate rise which is unfortunate.

If the front wheel on the BRZ compresses by the same amount as the rear wheel then the rear bump stop will be contacted first. Just ask yourself if you put a 2 inch long obstruction into the stroke of the front shock and the same 2 inch obstruction into the stroke of the rear shock which will touch first.

Then note that the rear bump stop is much stiffer in compression than the front and you understand why the bump stops may affect the handling so markedly. They certainly adversely affect the ride.

A link to the comparison graphs of the damping curves of the Bilstein B6/B8 to stock dampers would be useful. Anyone actually done this? It seems the B8 differs from the B6 only in the position of the internal rebound bump stop, from the cutaways I've seen of the two models. The shorter stroke of the B8 is achieved by raising the position of the internal bump stop, so rebound stroke is reduced. There would appear to be no performance advantage to this.

[wparsons]

Originally Posted by Ubersuber

If the front wheel on the BRZ compresses by the same amount as the rear wheel then the rear bump stop will be contacted first. Just ask yourself if you put a 2 inch long obstruction into the stroke of the front shock and the same 2 inch obstruction into the stroke of the rear shock which will touch first.

Have you actually measured to see how much bump travel (on the shock shaft) there is front and rear before contacting the bump stop? If there is equal travel at the shock, then there is actually MORE wheel travel in the rear than in the front.

Originally Posted by Ubersuber

Then note that the rear bump stop is much stiffer in compression than the front and you understand why the bump stops may affect the handling so markedly. They certainly adversely affect the ride.

Did you completely ignore the explanation above about why the rear bump stop being stiffer isn't the reason, unless it's twice as stiff as the front? The difference in motion ratio makes a huge difference in effective wheel rate vs actual spring rate front to rear.

[Ubersuber]

Hmm, front wheel goes over a two inch high bump, wheel compresses by two inches and then returns to ride height. Rear wheel goes over same bump and compresses by how much I wonder?

Hmm, effective rear spring rate is softer than the front and the shock free travel is about the same (not that this matters to the thought "experiment"). Car goes over a two inch bump, does the spring rate matter?

Car is in roll, and rear spring rate is softer than the front rate, does the rear suspension compress more than the front suspension?

I guess I am ignoring stuff.

[wparsons]

Yes you are, lots of things.

For bump travel, you're still missing the amount of bump travel before the bump stop is engaged, plus the difference in weight distribution, how much of the bump is absorbed vs the body of the car rising up over it, etc.

For roll in a turn, you're missing everything from bumps and have completely ignored sway bar rates as well.

if you would bother to read real information about suspension balance and spring rates you would see that the ideal spring rates factor in many variables, not just the measured rate of the spring.

At the end of the day, you're still claiming to have found a way to defy the laws of physics, so congrats?

[EAGLE5]

I just wanted to remind everyone that there is an ignore feature on this website. You can ignore users who you might feel add nothing to the discussion.

[Dipstik-sportech]

Originally Posted by jsimon7777

I just wanted to remind everyone that there is an ignore feature on this website. You can ignore users who you might feel add nothing to the discussion.

Can you do this on Tapatalk?

[EAGLE5]

Originally Posted by Dipstik-sportech

Can you do this on Tapatalk?

No idea. I HATE that shitty spyware. But you can try blocking a person on the web site then see if it works in Crapatalk.