Suspension "slaps" "thuds" with road imperfections
 

Since the day I've had the car it's pretty much always done this. Got it with 130k now 160k

Suspension now is Ohlins DFV with 13k/9k swift, Racing beat front sway bar stock 94 rear. Did the same thing on stock bilsteins and konis with racing beat springs.

All stock control arms appear to be in good shape nothing is loose.

18" wheels 245 front 265 rear pilot super sports

It's very smooth over bumps and the kind of road imperfections that most sports cars struggle with, but over little bumps (like lane markers or cracks) there is loud / annoying noise and jolts.

I've driven another FD with Zeal coilovers and it's not as smooth but has much less of this problem. That car was on 17s with 265s all around, again stock control arms in good shape.


Is this just the nature of the car of with 18 inch wheels? I've been thinking about going to 17s anyway. I haven't driven other fds with 18s....

Pillow balls in the rear suspension would be my first guess

Wouldn't they be loose if they are bad?

did you replace the end links when you put on the racing beat sway bar? My guess is that they're shot.

No, but there is no play. Car came with the sway bar, so they may have been replaced. They definitely look to be in good shape

It sounds like you are describing noise associated with running wide low profile tires. If there is a problem in the suspension it will be a pretty apparent metallic knocking. FD's were built back when minimal sound deadening was used, and was originally designed with 50 series sidewalls. Changing to wide 18's would certainly exacerbate tire slap over small road imperfections. Maybe try to borrow some stock wheels to see if the problem is relieved. If so I would try 17's with a 40 series sidewall. I actually prefer the look of 17's with stock body anyway. Good luck.

That's what i've been assuming for a while :/

It's not a metallic noise. Just a hardness and interior noise from specific road issue. Potholes, lane markers, and gaps or slight steps up really bang the car. Everything else is exceptional with the ohlins :)

My sw20 mr2 has 17s with less tire profile and doesn't do this at all, yet gets upset over things the rx7 glides over (big bumps / undulations)

Frustrating!

I used to have an SW20 turbo. They are extremely solidly built and vaultlike for their size. Just feel how heavy the front hood is as an example. I do think it would be worth it for you to change all the rubber bushings in the car. At 160k and 25+ years old, it is probable that they have degraded to the point where they are transmitting more NVH into the car than originally intended. If you are attached to your 18s I'd try that first.

I'm not attached to the 18s (though I love the tires, super sports are amazing!)

Which bushings are most likely worn? They all look pretty good. The previous owner may have changed a few here and there.

The issue is probably 75% in the back btw

Sounds like the tire noise that's typical of high performance tires.
Time for an education.
http://scholarworks.rit.edu/cgi/view...context=theses

Thats great, but I have the same tires on my mr2 (though different sizes)

And we use these tires on many, many sports cars at my shop and I've yet to hear / feel this.

Mine makes similar noise in the rear and I have pretty much new Ohlins DFVs, Powerflex bushings front and rear, new pillowballs, etc. I think the noise over those types of bumps is simply the lack of weight in the rear of the car and the lack of sound deadening. My car has always had this noise even before I swapped everything out. I wouldn't worry about it if you are sure everything in your suspension system is up to spec.

You can't tell by looking, you have to physically manipulate them. You can try first with everything on the car by jacking it up and wiggling parts. Next is to disassemble and wiggle individual bushes. My FD has only 60k and the only bushes that were good were the trailing arms. All the pillows were shot. Since they are rather expensive, my guess is the PO may not have replaced them. The differential bushes are a pain to get to, so those may be original as well, but those don't see the wear like the pillows. That said, those are generally recommended to be replaced/upgraded regardless of condition to improve handling.

I definitely can't feel and looseness tugging around on the wheel... But I know that doesn't really mean they are good...

I do know what i'm doing here btw (I work on million dollar cars every day and have been in the automotive industry for 14 years!)

Maybe i'll just go in and replace everything,

The diff mounts are newer - replaced the diff with low millage JDM unit that had nice bushings.

Also check the rear mounting bolts holes of the power plant frame to see if they are cracked.

Mine were cracked and the front of the differential moving against the power plant frame as well as the transmission tunnel brace that goes through the power plant frame hitting it over bumps in the rear was loud and annoying over small sharp impacts like you describe.

I have a samberg fd diff mount :)

But it did the same things with the stock powerplant

Check that your coilovers are preloaded. Jack car up and make sure the springs are tight.

yes - i installed them. And like I said, was the same with other suspension that was in the car.

i'm not convinced that it's the pillow balls, I have no low speed noise or clunking

halp

Put a video up here from inside the cabin with the noise happening?

If it is a rubbery whack sound it could just be the low profile tire.

It could be anything else too though.

I have had pillow balls with no slop make this noise.

Basically, I have found that if a pillow ball moves freely with very little friction, it is shot and will make noise.

That is good information. I don't have any low speed clunking. But there is a roughness over sharp bumps and a noise that goes with it. The most obvious thing is lane markers on the highway. You can feel everyone of them and it makes way too much noise vs almost any other car.

New pillow balls didn't change anything about this problem. But the car does feel a bit tighter in the rear end.

Still looking for a solution

I think you are looking for a non-existent solution as long as you are using wide low-profile tires (18" 245 & 265) on a very light, minimally-sound-insulated car with performance tuned suspension and bushings.

The logical solution, as others have mentioned, is higher-profile tires on smaller wheels.

That is one of the reasons I kept my stock wheels with 225/50R16 tires - I wanted to drive the 7 on trips w/o getting beat to death. The other reason is pot-holed roads in NE Ohio - 45 or 50 series is as low as I think is practical around here.

BTW, when I was working with OE's on air suspension and tires, the rule of thumb on ride noise and harshness issues was to look at, in approximate order of importance:
1. tires and tire pressure
2. suspension friction
3. damping (shocks) and the damping present in the air springs
4. suspension bushings
5. everything else