Poly, Delrin vs Rubber bushing fitment

[dhutton]

DSE uses delrin in all their front control arms and only uses rubber in the rear on their swivel links but Don's point stands and I agree.



However, changing those bushings to rubber is not what I would call low hanging fruit nor do I think it will have a significant impact on your harshness issue.

Tire pressure is a big deal and is free. I'd give it a shot. After that, I would revalve the shocks. Does Hotchkis send dyno sheets with their shocks?

I stand corrected! Thanks Donny.

Don

[dhutton]

I adjusted the tires down from 36 psi to 30 and it made a big difference! Not gone but WAY,WAY BETTER.

Awesome!

Don

[67-LS1]

Since the subject of shocks is up I'll add my .02. One of the first things I would want to do is to determine how much of my shock travel I am using in my typical driving. An easy way to do that is to smear some grease on the shock shaft and then drive around & see what got wiped away. If you have shocks apart I like to put tight o-rings on the shafts for markers. Then investigate where your bump stops come into play in normal driving. You need to verify that you are using your compression travel without slamming the bumps too hard in normal driving. Personally I feel that most of the harshness that people encounter is due to the rapid change of direction between compression to rebound. Slamming the bumpstops can cause this along with weak rebound. For my "soft" setups (on properly matched shock/springs) I run soft compression and a lot of rebound. It sounds like you may need softer high speed compression as I am assuming the the "cracks" in the concrete are not compressing your suspension much. I also find that if the car has very much bump steer that I perceive it as being rougher when I hit rough areas. Have you attempted to determine the frequencies front & rear?

My suspension bump stops have tons of clearance. And there is not a mark on the frame/arm where they would contact
If there are bump stops within the shocks I wouldn’t know. The shocks were part of the Hotchkis kit so I assume they were matched with the intended use which was a small block. After a very short while I did change out the Hotchkis springs for lighter rated springs. I could barely budge the front end they were so stiff. I can bounce it a little now and it really was an improvement. I did not change the shocks at that time so the shocks in the front of the car may be designed to work only with the much heavier spring??
I don’t know what you mean by the “frequencies” front and rear.

[CSG]

You can google "car spring frequency" and get a better description than I could give. I had a discussion with some OEM suspension engineers a long time ago and they were pretty big on having the right front to rear frequency ratio for comfort. From my little bit of experience, with the limitations most of us are not going to put the fab work into overcoming, the frequency ratio is not as important on a race car because it is not always "balanced". For a 100% street car I believe it would be worth investigating. Of course after that then the shocks have to match the springs...

[dhutton]

You can google "car spring frequency" and get a better description than I could give. I had a discussion with some OEM suspension engineers a long time ago and they were pretty big on having the right front to rear frequency ratio for comfort. From my little bit of experience, with the limitations most of us are not going to put the fab work into overcoming, the frequency ratio is not as important on a race car because it is not always "balanced". For a 100% street car I believe it would be worth investigating. Of course after that then the shocks have to match the springs...

Interesting. I think maybe this refers to the natural frequency of a second order control system. The natural frequency combined with the damping ratio of the shocks will determine the response of the system to a step input. At least this is my SWAG...

Don

[stab6902]

Ride frequencies are a big topic, but here's a nice intro: http://downloads.optimumg.com/Techni...Tech_Tip_1.pdf

Modern performance oriented production cars tend to have ride frequencies in the 1.5 Hz range (+/- a few tenths), with the rear ride frequency being 10-20% higher than the front. The article above does a nice job explaining why.

Spring manufacturers are well aware of this stuff, and as long as you have a 'typical' car with a matched set of springs, you should be in the ballpark. If your vehicle weight and/or weight distribution is way different from stock or you're mixing and matching parts, it'd be worth looking into.

You can roughly determine your vehicle's ride frequency by doing a simple "bounce test" (with the vehicle parked) and counting the number of oscillations in a 30 second increment for example (Hz = cycles per second). So if the rear of your car bounces 40 times in 30 seconds, your ride frequency would be 40/30= 1.33 Hz. Each end of your car will have a frequency it naturally tends to oscillate at (that's why it's called a natural frequency) with minimal effort; like pushing a swing. Damping has an effect on frequencies as well, but not as much as you might think. I prefer to determine the natural frequencies with the shocks removed, and once I'm happy with them, reinstall and adjust shocks to application/preference. I'm a nerd so I use the accelerometer in my phone and Matlab to measure and analyze ride frequencies and damping, but at the end of the day it's all about how you want it to feel going down the road.

[dhutton]

Ride frequencies are a big topic, but here's a nice intro: http://downloads.optimumg.com/Techni...Tech_Tip_1.pdf

Modern performance oriented production cars tend to have ride frequencies in the 1.5 Hz range (+/- a few tenths), with the rear ride frequency being 10-20% higher than the front. The article above does a nice job explaining why.

Spring manufacturers are well aware of this stuff, and as long as you have a 'typical' car with a matched set of springs, you should be in the ballpark. If your vehicle weight and/or weight distribution is way different from stock or you're mixing and matching parts, it'd be worth looking into.

You can roughly determine your vehicle's ride frequency by doing a simple "bounce test" (with the vehicle parked) and counting the number of oscillations in a 30 second increment for example (Hz = cycles per second). So if the rear of your car bounces 40 times in 30 seconds, your ride frequency would be 40/30= 1.33 Hz. Each end of your car will have a frequency it naturally tends to oscillate at (that's why it's called a natural frequency) with minimal effort; like pushing a swing. Damping has an effect on frequencies as well, but not as much as you might think. I prefer to determine the natural frequencies with the shocks removed, and once I'm happy with them, reinstall and adjust shocks to application/preference. I'm a nerd so I use the accelerometer in my phone and Matlab to measure and analyze ride frequencies and damping, but at the end of the day it's all about how you want it to feel going down the road.

Good info. Thanks!

Don