A discussion on improving ride quality

[HI]

Originally Posted by cdrazic93

My favorite FWD car is a supra in reverse...

This may have been the best thing I've ever read on the forums

[NissanGuy]

Originally Posted by Ubersuber

My view is that the rear shocks are not stiff enough in rebound to properly control the spring. Hitting the rear bump stops too early in the shock stroke just exacerbates this weak damping problem. The symptom is an annoying pitch which fitting the four Bilsteins eliminates completely.

I am now of the view that the stock front shocks are too stiff in jounce which contributed to the pitching. Once I fitted the Bilstein struts the pitching has been eliminated.

What is this pitch of which you speak? I find that my car exhibits two annoying pitches, both of which could be the result of dampers. The first type is wheel hop, primarily encountered when accelerating at full speed out of a corner. The second type is when cruising on the freeway the vehicle traces the road surface exactly, as if there were no suspension; choppy pavement, over which most vehicles glide, causes a very controlled but very uncomfortable rhythmic pitch motion. I want to get the Bilsteins myself!

In fact, the new shocks and tires I fitted are so solid I can now feel the inadequacy of the stock rubber bushings...

Round and round we go, haha. I kept finding the next weakest link and accidentally built my Altima into a ghetto racer. Which bushing do you feel is inadequate? I've definitely found that the rear subframe bushing inserts made the car feel much better over bumps. Not more cushy, but firmer; that grey area between ride and handling...

[Ubersuber]

I think the wheel hop experienced in tighter low speed corners results from the action of the Torsen. These cars have insufficient power to hop a wheel otherwise. The Bilsteins control this better than the stock shocks but because it isn't really wheel hop per se but more of a slip grip effect the Bilsteins won't eliminate this sensation of the inside rear wheel trying to hop off the road (the actual bounce isn't enough to break traction in any meaningful way, the Torsen will just rapidly shuffle the torque back to the outside wheel).

The pitch I refer to is the secondary rebound of the rear spring after a sharp bump, such as a pothole or a speed hump. On certain road surfaces this can also lead to a harmonic oscillation although we don't have road surfaces like that here. The sharpness of this secondary bounce was actually causing me back discomfort and now the car is very smooth and causes me no issues with my lower back.

The stock rear shocks do not completely control the rebound of the spring over sharp bumps, the Bilsteins do. If you ride a sharp bump through a corner the Bilsteins allow the tires to remain fully loaded on the road through the bump, the stock rear shocks allow a sideways slip. In addition to this I felt that the front struts were too stiff in sharp bounce motion, which is a sign of saving money on strut development. Good low resistance in bump is tricky to design in at the same time as you are trying to get good rebound action.

It's possible Subaru deliberately underdamped the rear to allow a drift to be more easily provoked. Certainly the slow speed resistance of the stock shock in both directions is less than for the Bilstein. The secret to control over sharp bumps is the rebound rate, all shocks are designed to bypass resistance to sharp compression over bumps but the valving controlling the rebound of the spring is the tricky part. You want a rapid wheel movement as the spring decompresses (low shock resistance) followed by a steadily rising resistance as the spring extends so that the spring does not try to recompress itself as the car resumes travel on the smooth road after the bump. This is why rebound damping is usually the adjustable function on adjustable street shocks and compression valving not usually because for most purposes only rebound damping is important.

If you need to get into adjustable compression damping you really need to understand what you're doing.

In reality, adjustable shocks are only useful if you track the car as for street use there is usually one sweet spot for the driving you normally do. Most adjustable shocks are set once, correctly, and then left alone.

Coilovers are only beneficial if you want to adjust ride height as well. Most cars do not need either adjustable shocks or adjustable spring perches. Most coilovers get installed, set and left.

Frankly, the stock spring rates on these cars are pretty good. Better damping allows those factory settings to shine through. Lowering this car likely creates more handling issues than is worth the effort since the CG is already lower than a "badger's badger" as Clarkson put it.

[Dezoris]

I have been on 16" blizzaks on stock suspension and with Ohlins. The softer/larger sidewall helps. But the stock suspension is over dampened still. In summer with Ohlins even on soft with RS3s its firmer than stock. More controlled, however when I get into my stock AP2 S2000 with RS3s it feels like a luxury car compared to FRS in terms of ride smoothness.

I think your best bet is maybe 130lb springs, stock ride height and custom valved dampers with non agressive rebound. I just dont see much aftermarket setups doing what you want.

[emutcfut]

Originally Posted by Ubersuber

I cut one half inch out of the hard top section of the rear bump stops and glued the two remaining bits together and installed Bilstein HD rear shocks (B6 standard length).

I've read multiple times that this car is very bumpstop active. Does cutting your bumpstops or increasing damper stroke with tophats increase the amount of body roll as it needs to compress more before it can settle on the bumpstops in a turn?

[KoolBRZ]

Originally Posted by RYU

So what have you tried? Please share your mods.

I'd also like to take a moment to note the following:
One of the biggest flaws with the online world of suspension reviews is that the person reviewing can only speak to their universe and their experiences. Please don't tell me the KW V3s ride comfortably because they are firm at any setting and also a bit jarring on rough roads. Same with the Bilstein B14s in varying degrees. Even in stock form the car is still firm.

Before I throw in the towel, I'm hoping to ask the community for ideas on areas I may not have thought about.

FYI: I've gone thru 5 different suspension setups in the BRZ. With my limited research, I've concluded that the rear suspension travel is lacking (i.e. too short) after exhausting all the options.

I'm ready to install offset rear LCAs that increase rear damper stroke by 20mm. I'm not sure that's enough and would also cause the need to screw around with spring heights and potentially helper springs.

I like to be around 15-20mm lowered which isn't asking for a lot I thought. I recently rode in a stock BRZ and realized the ride isn't really too much more comfy even in a stock car. Its been so long I had forgotten that..

You are not alone. I'm personally disappointed by how badly the Toyobaru triplets have failed the Initial "D" tofu test. Any sheets of tofu hauled in this car would be torn to shreds in no time. I've tried Airlift struts, KW V3's, Bilstein B4's, and have gone back to the Airlift's. The KW V3's taught me how to adjust the dampening, so when I went back to the Airlifts, I knew to adjust for the best "firm" suspension I could get. I have to have stock height or higher, because I go off-road occasionally. The best you can get would be to replace your control arm bushings with bearings, the springs with airbags, the sway bars with electronic locking bars, and the struts with Bilstein Damptronics. Short of that I would recommend the Airlift digital package. Once installed correctly, nominal ride height is at the center of the strut travel. I have mine adjusted for 25 from full hard in front, and 26 from full hard in back. It still mauls me on big bumps at slow speeds, but handles pretty well otherwise.

[Ubersuber]

Originally Posted by emutcfut

I've read multiple times that this car is very bumpstop active. Does cutting your bumpstops or increasing damper stroke with tophats increase the amount of body roll as it needs to compress more before it can settle on the bumpstops in a turn?

Damper stroke is controlled by suspension travel only. Active spring length affects suspension travel. Top hats allow you to lower the car without shortening the spring, they can't increase shock stroke. Only changing the spring rate (lower rate) can increase shock travel by allowing the suspension to move over a longer distance.

Bump stops increase the effective spring rate by supplementing the steel spring rate plus steel roll bar rate (divided by 2, the effective rate of a bar is half the specified rate because it has to push up on one spring while pulling up on the other spring) with the effective spring rate of the polyurethane foam bump stop. These are shaped to provide a tailored progressive rate that increases in a designed manner as the bump stop is compressed.

Anything that changes the spring rate of one wheel will change the body roll characteristics, lower total effective spring rate will increase body roll.

However, total body roll depends on the spring rates at each end of the car also. The roll forces are considered to act through a line connecting the front and rear roll centres. The higher the roll center the less body roll will change with a given change in spring rate at that end of the car. Be aware that roll centers and roll axis are not usually fixed as they depend upon the changes in suspension geometry resulting from suspension compression and rebound. For design purposes the roll centres and roll axis are determined from static position of the suspension at rest, then the movements are allowed for. It is very difficult for an amateur DYI to know what to change to correct any roll center effects.

What I tried to do was raise the height at which the shock would bottom out against the bump stop (increasing the free travel of the shock before it touched the bump stop), so reducing the roll resistance over that increased range of motion. By cutting out a slice of the hardest part of the bump stop I also reduced the spring rate of the bump stop itself. If you just cut the soft end off, which is easiest, you may postpone the contact but then the effective spring rate rises even more rapidly once the shock bottoms onto the bump stop. I felt that the effective spring rate of the factory bump stop was too high and began too early in the roll provoking oversteer forces in the rear axle earlier than was optimal. This is why I caution anyone against doing this if they want to drift the car for any reason as I'm pretty sure the drifting effect is facilitated by this long bump stop design.

My experiment cutting one half inch out of the rear bumps stops has had the predicted and desired effect. The ride is better at the rear (which is where you really notice a hard ride) and the handling is, for me at least, sweeter and more progressive as you load up the rear axle.

A similar effect could have been achieved by fitting a smaller rear roll bar (if one exists which is doubtful) or fitting a larger front bar to move some additional roll resistance to the front of the car.

I decided I liked the factory spring rates front and rear just fine. I objected to the sudden increase in roll rate (i.e. effective spring rate, the rate of body roll decreases of course if the roll spring rate increases) at the rear when the suspension compressed onto the bump stop on the outside wheel.

As for the movement I now feel in the rear axle I put that down to more bushing movement caused by higher cornering forces from the upgraded Michelin tires. Whether it is subframe movement or twist in the suspension arm bushings is not easy to determine from the driver's seat but it seems likely it is the subframe being deflected as it does not feel as if the rear wheel alignment is changing under cornering forces.

[NissanGuy]

Dang, you speak the truth. If I wasn't sold on Bilsteins, I am now.

I was paying a bit closer attention to the car's rear in the canyons yesternight, I realized I can totally feel the rear bump stops, and the soft rear rebound damping. The way it manifests to me is that two large rapid bumps sends me flying, I never noticed that only the rear loses composure. It's a really strange balance.

I don't want to drift, per se, but I do want oversteer. Certainly I can find a better way to that end than using the bump stops like pogo sticks. You cut the top 1/2" off, you say... Is that just the top third of it?

[solidONE]

Originally Posted by Ubersuber

Damper stroke is controlled by suspension travel only. Active spring length affects suspension travel. Top hats allow you to lower the car without shortening the spring, they can't increase shock stroke. Only changing the spring rate (lower rate) can increase shock travel by allowing the suspension to move over a longer distance.

Bump stops increase the effective spring rate by supplementing the steel spring rate plus steel roll bar rate (divided by 2, the effective rate of a bar is half the specified rate because it has to push up on one spring while pulling up on the other spring) with the effective spring rate of the polyurethane foam bump stop. These are shaped to provide a tailored progressive rate that increases in a designed manner as the bump stop is compressed.

Anything that changes the spring rate of one wheel will change the body roll characteristics, lower total effective spring rate will increase body roll.

However, total body roll depends on the spring rates at each end of the car also. The roll forces are considered to act through a line connecting the front and rear roll centres. The higher the roll center the less body roll will change with a given change in spring rate at that end of the car. Be aware that roll centers and roll axis are not usually fixed as they depend upon the changes in suspension geometry resulting from suspension compression and rebound. For design purposes the roll centres and roll axis are determined from static position of the suspension at rest, then the movements are allowed for. It is very difficult for an amateur DYI to know what to change to correct any roll center effects.

What I tried to do was raise the height at which the shock would bottom out against the bump stop (increasing the free travel of the shock before it touched the bump stop), so reducing the roll resistance over that increased range of motion. By cutting out a slice of the hardest part of the bump stop I also reduced the spring rate of the bump stop itself. If you just cut the soft end off, which is easiest, you may postpone the contact but then the effective spring rate rises even more rapidly once the shock bottoms onto the bump stop. I felt that the effective spring rate of the factory bump stop was too high and began too early in the roll provoking oversteer forces in the rear axle earlier than was optimal. This is why I caution anyone against doing this if they want to drift the car for any reason as I'm pretty sure the drifting effect is facilitated by this long bump stop design.

My experiment cutting one half inch out of the rear bumps stops has had the predicted and desired effect. The ride is better at the rear (which is where you really notice a hard ride) and the handling is, for me at least, sweeter and more progressive as you load up the rear axle.

A similar effect could have been achieved by fitting a smaller rear roll bar (if one exists which is doubtful) or fitting a larger front bar to move some additional roll resistance to the front of the car.

I decided I liked the factory spring rates front and rear just fine. I objected to the sudden increase in roll rate (i.e. effective spring rate, the rate of body roll decreases of course if the roll spring rate increases) at the rear when the suspension compressed onto the bump stop on the outside wheel.

As for the movement I now feel in the rear axle I put that down to more bushing movement caused by higher cornering forces from the upgraded Michelin tires. Whether it is subframe movement or twist in the suspension arm bushings is not easy to determine from the driver's seat but it seems likely it is the subframe being deflected as it does not feel as if the rear wheel alignment is changing under cornering forces.

Cusco make a set of undersized anti-sways. 16mm front and 14mm rear hollow bars IIRC.

http://www.cuscousainc.com/vehicle-r...&modelname=475

[Ubersuber]

Originally Posted by NissanGuy

Dang, you speak the truth. If I wasn't sold on Bilsteins, I am now.

I was paying a bit closer attention to the car's rear in the canyons yesternight, I realized I can totally feel the rear bump stops, and the soft rear rebound damping. The way it manifests to me is that two large rapid bumps sends me flying, I never noticed that only the rear loses composure. It's a really strange balance.

I don't want to drift, per se, but I do want oversteer. Certainly I can find a better way to that end than using the bump stops like pogo sticks. You cut the top 1/2" off, you say... Is that just the top third of it?

I like Bilstein because a monotube shock feels different to say a Koni twin tube type. Bottom line, better shocks really improve the roadholding of this car, especially at the rear. Which brand you buy and fit is a personal choice, better damping from any good brand.

I elected to cut one half inch out of the top hard part of the rear bump stops. Because the very top is bevelled to fit the stock dust shield and also has an internal groove to engage the bump stop onto a ring on the top of the damper shaft (retaining the bump stop at the top of the damper travel) I sliced the half inch out from beneath the bevel and above the first pinched in section and used Goop auto silicone to glue it back together. Don't know if this works or not. Time will tell but to be sure I'd have to take it all apart again so I will await any symptoms of failure before I bother to do that.

I'm not sure you want to cut a whole section off or out of the bump stops but replacements are cheap enough and R&R the rear shocks is a pretty simple job so you could experiment. The rears are coilover style so they unbolt and remove much like a strut but you don't have to take the hub bolts out. You MUST use a spring compressor though for safety as you take the spring off to R&R the bump stop.

I think the Torsen will give enough torque to the rear wheels to unstick them in the wet. Also, throwing the car in hard will still put you on the outer rear bump stop enough to provoke a little tail action if you are hard on the gas in low gear.

Oversteer is generally slow except for very tight low speed corners. Fun but slow.

[Ubersuber]

Originally Posted by solidONE

Cusco make a set of undersized anti-sways. 16mm front and 14mm rear hollow bars IIRC.

http://www.cuscousainc.com/vehicle-r...&modelname=475

Hmmm, this must be for guys who want to up their spring rates by quite a bit and find the single wheel bump rate too high with stock bars.

Fitting only a softer rear bar would increase understeer a bit. I think stock springs and a slightly stiffer front bar would be a better solution to needing more understeer.

Once I SC this engine (if I do after the warranty is complete) I think I may find a stiffer front bar is needed. I'm still a bit disappointed that TRD or STI has not released a warranteed SC kit. Toyota obviously knows how to do a supercharger and there's nothing Subaru don't know about boosting engines. Either this car is still selling too well to warrant issuing such an improvement or Toyota doesn't want the possible liability issues that might arise from someone fitting a factory supercharger without first understanding how to control power oversteer.

No matter what you do I think this chassis will still oversteer when traction conditions are poor. More power will make this car quite tail happy I expect. Not a problem except for winter....

[solidONE]

Originally Posted by Ubersuber

Hmmm, this must be for guys who want to up their spring rates by quite a bit and find the single wheel bump rate too high with stock bars.

Fitting only a softer rear bar would increase understeer a bit. I think stock springs and a slightly stiffer front bar would be a better solution to needing more understeer.

Once I SC this engine (if I do after the warranty is complete) I think I may find a stiffer front bar is needed. I'm still a bit disappointed that TRD or STI has not released a warranteed SC kit. Toyota obviously knows how to do a supercharger and there's nothing Subaru don't know about boosting engines. Either this car is still selling too well to warrant issuing such an improvement or Toyota doesn't want the possible liability issues that might arise from someone fitting a factory supercharger without first understanding how to control power oversteer.

No matter what you do I think this chassis will still oversteer when traction conditions are poor. More power will make this car quite tail happy I expect. Not a problem except for winter....

When I do eventually go with higher spring rates after I move up from stock class I plan on removing the rear bar completely. I've actually tried this on stock suspension and the increased rear grip from the independent articulation in the rear was fantastic, but the 'soft' stock rear springs caused the rear to rebound off the bumpstops. I was able to get on the throttle early and hard with confidence and the rear tires seem to just clamp down. Before it starts bounce off the bumpstop, of course.

[EAGLE5]

So... shortened rear bump stops. Get rid of the rear roll bar. Put raised rear top hats with longer shocks and springs on the back so you get more travel. Make the springs stiff enough to stay off the bump stops almost all the time. Use quality monotubes. Lighten the brakes and tires. Install adjustable lower control arms. Are we done yet?

[NissanGuy]

Originally Posted by jsimon7777

So... shortened rear bump stops. Get rid of the rear roll bar. Put raised rear top hats with longer shocks and springs on the back so you get more travel. Make the springs stiff enough to stay off the bump stops almost all the time. Use quality monotubes. Lighten the brakes and tires. Install adjustable lower control arms. Are we done yet?

Stiffen the body! Someone mentioned installing front strut bar made it feel like his front tires were 10 psi low, judging from ride quality. And of course the car will go faster too haha.

In my opinion, stiffening the body is dangerous because you expose the next weakest link, and then you want to stiffen that part as well. One roll cage later your sportscar will ride like a Lexus haha. What I'm planning to do, to avoid this weakest-link process, is to purchase all my reinforcement bits from one company, figuring they've tuned it for balance (literal tuning, that's harmonic balancing). So, TRD for me.