Suspension "slaps" "thuds" with road imperfections
#26
Senior Member
Thread Starter
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.
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.
#27
Racecar - Formula 2000
Also, all tires are not created equal - some have stiffer constructions than others of the same size - it would be good to research ride quality ratings to assess what you want to buy.
Last edited by DaveW; 12-07-16 at 10:14 AM. Reason: added last sentence
#28
Full Member
iTrader: (3)
When the FD was engineered over 20 years ago, they had a wheel diameter and tire size in mind when doing suspension design. You are a +2 in wheel size with a larger contact patch and significantly more unsprung weight than they would have designed for. Some manufacturers, like Porsche, will even issue a maximum wheel diameter recommended for each model based on suspension design. Ever lift a stock FD wheel? They are LIGHT, a little under 16 lbs. Even a very lightweight 18" wheel will be in the 18 lbs range, and most are 22-25 lbs. Your tire with the 18" size will be heavier as well. I suspect if you dropped back to either OEM 16" or even a lightweight 17" that you would feel a significant improvement in steering response, nimble responsiveness, noise, and ride quality.
#29
Rotary Motoring
iTrader: (9)
^^
This is true.
The Yamaguchi FD book states that there was a last minute on the production line recall to add a reinforcement to the boxed section in the lower sill in front of the rear wheel- added to increase chassis rigidity because the car was slapping going over freeway expansion joints (you can actually see the cut/weld where they added it).
But still, the rest of us aren't complaining of whacks going over normal road features in our FD with 18s.
Either the OP likes to drive with windows down and is more sensitive to sounds than the rest of us, its the tires he has chosen or there is something up with the car/part he has added.
This is true.
The Yamaguchi FD book states that there was a last minute on the production line recall to add a reinforcement to the boxed section in the lower sill in front of the rear wheel- added to increase chassis rigidity because the car was slapping going over freeway expansion joints (you can actually see the cut/weld where they added it).
But still, the rest of us aren't complaining of whacks going over normal road features in our FD with 18s.
Either the OP likes to drive with windows down and is more sensitive to sounds than the rest of us, its the tires he has chosen or there is something up with the car/part he has added.
#30
Put it in the microwave!
iTrader: (22)
Was this ever resolved ? I have ohlins DFV as well and new toelinks trailing arms and new pillow ***** with a poly diff bushing and I know exactly what op is describing. Everything is great . But when ever you go over little cracks in the road or little gaps/tiny pumps / lane markers , the rears seems like there is no traveling almost like the rear justs drop into the hole and bounce back up making the slap thud noise. Very annoying
Makes the rear sound like a rattle can and things are about to all let loose . Oh. And I'm on 16inch stockers with brand new tires. So I know it's not a wheel tire size issue. Could be messed up swaybar links ?
Makes the rear sound like a rattle can and things are about to all let loose . Oh. And I'm on 16inch stockers with brand new tires. So I know it's not a wheel tire size issue. Could be messed up swaybar links ?
#36
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Was this ever resolved ? I have ohlins DFV as well and new toelinks trailing arms and new pillow ***** with a poly diff bushing and I know exactly what op is describing. Everything is great . But when ever you go over little cracks in the road or little gaps/tiny pumps / lane markers , the rears seems like there is no traveling almost like the rear justs drop into the hole and bounce back up making the slap thud noise. Very annoying
Makes the rear sound like a rattle can and things are about to all let loose . Oh. And I'm on 16inch stockers with brand new tires. So I know it's not a wheel tire size issue. Could be messed up swaybar links ?
Makes the rear sound like a rattle can and things are about to all let loose . Oh. And I'm on 16inch stockers with brand new tires. So I know it's not a wheel tire size issue. Could be messed up swaybar links ?
I think you'll have much better luck with the OEM bushings in the diff carrier.
M2 style links and arms don't make noise going over bumps but could make some noise under heavy braking or cornering if they become worn/sloppy.
#38
Rotary Motoring
iTrader: (9)
But the diff/axles are like 60lbs suspended by just the two bushings to the subframe.
When the body of the car drops into a dip the inertia of the differential could cause clunking in the harder diff bushings or even pull the subframe in a way that causes a clunk in the subframe to unibody interfaces.
Mazda was getting a slapping in the rear of the FD over expansion joints from just too much flex in the unibody and had to add the box section in the rocker below the door that left that short vertical seam at the last moment.
If you want OEM NHV you must use OEM components.
When the body of the car drops into a dip the inertia of the differential could cause clunking in the harder diff bushings or even pull the subframe in a way that causes a clunk in the subframe to unibody interfaces.
Mazda was getting a slapping in the rear of the FD over expansion joints from just too much flex in the unibody and had to add the box section in the rocker below the door that left that short vertical seam at the last moment.
If you want OEM NHV you must use OEM components.
#39
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The diff is 80lbs and those bushings may as well be metal because there is no give and the sleeves are metal
That said overall it's worth using stock bushings just to get rid of the tire noise, the jolts, etc....etc....
Bottomline: those bushings are a nightmare on a street driven FD.
#40
Senior Member
Thread Starter
I have stock diff bushings! It's not the diff bushings
#41
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I'm from Sacramento as well and have this same exact issue. I have Ohlins DFV suspension, all new powerflex bushings everywhere, new pillowballs, new inner and outer tie rods, new front sway bar links, and stock wheel sizes. Been slowly tackling different areas to see if the noise would decrease but so far it hasn't. Will probably try wheel bearings next to see if that fixes anything.
#42
Put it in the microwave!
iTrader: (22)
I'm from Sacramento as well and have this same exact issue. I have Ohlins DFV suspension, all new powerflex bushings everywhere, new pillowballs, new inner and outer tie rods, new front sway bar links, and stock wheel sizes. Been slowly tackling different areas to see if the noise would decrease but so far it hasn't. Will probably try wheel bearings next to see if that fixes anything.
#45
Racecar - Formula 2000
I'm from Sacramento as well and have this same exact issue. I have Ohlins DFV suspension, all new powerflex bushings everywhere, new pillowballs, new inner and outer tie rods, new front sway bar links, and stock wheel sizes. Been slowly tackling different areas to see if the noise would decrease but so far it hasn't. Will probably try wheel bearings next to see if that fixes anything.
At the risk of stating the obvious and being redundant, but knowing a bit about NVH and handling, the list of harshness suspects are, mostly in decreasing order:
o Tires - pressure, construction, tread wear. High pressure means more harshness. Some tires have hard sidewalls for quick response - those are usually harsh. Low profile tires are harsher than ones with taller sidewalls. Worn tires transmit more noise, etc.
o Suspension bushings - softer is generally quieter. Aftermarket ones are by design stiffer for more crisp handling.
o Shocks - too-high damping levels increase impacts and road noise. Softer will ride better, but can degrade response and handling.
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