911F1

I went on a spirited drive last weekend with some Rennlist members. I noticed the front end bouncing when the weight gets transferred during turn in. Both front corners are doing it. I checked my shocks and they seem ok. I have Bilstein HD's with ROW M030 springs. Michelin PS2 tires with 32F 34R PSI. ROW 22mm and 21mm rear sway bars. I get the feeling the springs are to soft for the Bilsteins. Would a stiffer spring do the trick? H&Rs for example. Could alignment cause a bounce effect? Can to much front rake cause the bounce? I tried searching this topic and all I found was people concerned with the front end feeling floaty. My car doesn't feel floaty. More of a bounce or hop effect in mid corner. Maybe I need PSS10's and I'm just not liking my suspension setup.
Any feedback would be great. Or if someone can provide a link if the topic has been discussed already. Thanks

Edit:
I forgot to mention I have the Walrod front A arm bushing also.

jscott82

Tire pressure is WAY too low(assuming 18in wheels) Go with the recommended pressures. Lower pressure does not improve grip.

Bouncing is uncontrolled movement. It's either:
Something is loose (or binding)
Or
A mismatch between spring rate and damping factor of the shock. But since HD + mo30 is a common setup,, I doubt that is the problem.

Bump steer can feel like it's bouncing, but at mo30 ride height, should not be a big issue.

Short of putting a shock on a shock dyno, you can't really check them. But again, bilstein HD have a pretty good reputation for durability.

I would get the car on a lift and check for play in all suspension components, front and rear... then re check kinematic toe in the rear.

Just my 2 cents... good luck

911PERVY

How low are you? Bump steer could be the issue if lower than stock. RS/GT2 uprights will sort that out

NYC993

Misalignment can cause all kinds of weird behavior.
I have hard time visualizing what you are talking about.
What happens to the front end when you are "bouncing"? Are you starting to oversteer/udnersteer? Do you need to do steering wheel correction? Is this during braking or acceleration?

Drisump

My experience as well but since you seem to be running euro height, it should be good. I do run lower tire pressures than stock in my 18"s. I used to run stock psi but while on a drive With some other Rennlisters they recommended lower pressures as well. I found that when road temperatures got hot, my tires set to stock psi were feeling a little greasy. Lowering pressures really helped. I can't comment on the spring rate question....perhaps Bill V. Will chime in.

NYC993

When one talks about tire pressures it needs to be specified if it's cold, warm or hot. It's 8-12 psi difference between cold and hot tire.

OverBoosted28

Lowering tire pressures would most likely feel more "greasy".

911F1

My ride height is between ROW and RS. 129mm front and 114mm rear.
I'm thinking its either bumpsteer I'm feeling like 911PERVY suggest or mismatched spring to damping factor that JSCOTT82 mentioned. I will raise my tire pressures and go for a drive. But doubt thats it. Then I'll raise the car to ROW height and see if bumpster is the problem. If its still bouncing then I really do think the ROWM030 springs are to soft for the Bilstein HD's. When I was adjusting the Bilstein spring perches the other day I could feel that the springs are very soft. You can grab them by hand and compress them quite a bit. I was surprised actually. Thanks for everyones feedback. Any more suggestions are greatly appreciated.

JM993

Did this happen consistently or just in bumpy corners? My experience with Bilsteins is that the compression dampening is way too firm. This translates into unsettling the car in corners with less the smooth pavement.

911F1

No it wasn't happening consistently. Good point. I thought it was the type of corner. Tight vs long sweepers. It seem to happen in the tight
corners and I thought it was the weight being transferred more suddenly. But maybe those turns had a very uneven surface. I'm going to go for another drive and really pay attention to the road surfaces next time. Before I make any modifications to my setup. What suspension would do best when driving on uneven surfaces? Full coilovers like PSS10's or a package that has a well matched spring and shock setup?

JM993

I'm not a big fan of Bilsteins. I purchased the same setup you have and ended up removing them from the car and installing KW Variant 3s. I like them a lot. They're double adjustable (rebound and compression) and are supple enough in the softer settings to deal with the uneven/bumpy roads encountered on the street. I've also had good experiences with Konis, but haven't tried them on 993s.

Incidentally, one of my other cars has PSS10s installed by the previous owner. While not as bad as the Bilstein HDs I had, these too have too much compression dampening even on the softest setting.

911F1

JM993, Thanks for the feedback. Maybe I should get in on that KW V3 group buy thats good till the end of the month Another question you might know the answer to. How can you tell if your upper strut mounts are bad? Can this cause the bounce/hop I'm feeling?

phoneyman

I havent driven with the Bilstein setup, but I have KW3's also and really like them. I've slowly adjusted them to settings that I consider great for me.

Also, check the fasteners on your upper strut mounts. Right when I bought the 993, I noticed that 2 bolts on the same side were loose. I hadnt driven it much so cant say it made the steering noticeably bad, but I cant imagine that was a good thing. I added a front strut brace and the front feels great. They arent for everybody, but I like the car being really stiff.

I added the front brace to help with windshield creak as I saw on RL that some people tried that. It did not work for me unfortunately, but I like the brace for other reasons.

TJ993

I Agree whole heartedly with your comments and based on my experience, having the ROW Springs.
I would add atleast 2 pounds of air front and possibly four in the rears.
Street 34 frt and 36 or 38 rear depending on roads
But u said spirited driving so 36 frt and 38 or 40 rear and give her a run.

Dependant on tread depth I anticipate an additional increase of 2 pounds front and 3-4 pounds pressure increase Rear when hot - if using 18 inch rims??

I would like to add that the ROW Spring may be a factor in over all handling. It was suggested to me that the H&R may be the Better Match to ROW Springs unless you wish to move to a superior strut system?

These row springs bring other issues so I will send u a pm.
RE HD struts - this is what I have been told and my experience having them on my car 45,000 Miles.
They are sprung too stiff unless the car spends most of its time on a Highway.
Spring Rate issue.
I was told they are built adequately for 80% of cars but not 80% of the drivers. They are slated to last 80,000 Miles b4 rebuild.

The 21mm rear sway will stiffen up the car more than mine with the 20.
To start, up the tires and see how she feels.

If u recently jacked up the car, check the Front Springs are in their perches.
Mine get very loose, for example if I raise the rear of the car.
Thinkin H& R if the front end is in order - as recomended by JScott 82
See the pm I sent. ROW Springs - The real Issue.
Cheers TJ

TJ993

i think JM993 has nailed it!!
H&R is likely the cheaper solution - based on the advice I received herein but I have yet to make the final decision.
The KW may be calling here, if u need a reason LOL or excuse.
Good Luck with her
TJ