Need Maths Help

[Dubeckyj]

Hey all, I'm trying to mathematically figure out a good starting point for coilover spring stiffness. It's for a G3 but I'm hoping for more attention and expertise here. I remember reading in multiple places that a good wheel frequency for road cars with light track duty is between 1-1.5 hz. I did some rough calculations a while back when I got bored, and assuming the total weight of the car with me in it is ~3630lbs with 66% front, I got between 0.6-0.7hz front and rear. So I thought, easy maths, I'll double the spring rates which should double the frequency, add a little to the rear to cancel out front-rear oscillations and I'm done. Because I haven't done math in a while.

I stumbled upon this yesterday, and now I'm confused. I guessed at an unsprung weight of 80, but changing it between 60-120 only affects the frequency by 0.05hz. The link should plug in the values I have for the front, which shows me a 1.16hz frequency stock? Is this right?

My original scribbling left me with 350# front 250# rear springs, which now puts me at 1.75hz front and 1.84hz rear. Does this still make sense? Or am I doing something wrong? The 450/300 combo from the SHOsource coilovers just seem a little extreme for a DD car that barely sees the track.

Appreciate any input.

 

[rubydist]

the natural frequency of a spring / mass system w = sqrt(k/m)

that means to double the natural frequency of the system, you must quadruple the spring rate.

iirc, the weights f/r are not 66/33, but more like 58/42 or 60/40, somewhere in that range.

 

[SHOspazz92]

The 450/300 combo from the SHOsource coilovers just seem a little extreme for a DD car that barely sees the track.

Appreciate any input.

I will say this, having actually put more then a few 100 miles on the SHOsource coil-overs in a full weight (Probably heavier then stock) 95 MTX with a Gen III Subframe.....They ride great!

I had mine set on full soft and the ride was better then any Koni/Intrax/Eibach setup I have ever had. The only problem I had was when I was stuck behind a school bus doing 25 MPH on a two lane road. There was some washboard in the road and the rear ride got a little bouncy. At speed, this was never a issue. However, If I would have stiffened up the rear coil-overs a bit this wouldn't have been a problem. Also, my car had a 29mm rear sway bar, which makes the rear end of any SHO ride like complete shit. I also had my car set fairly low.

Go with the stock springs and adjust the coil-overs accordingly from full soft until it reaches your liking. You will not be disapointed with the drive-ability of these things. I was shocked on how well they rode.

-Sam

 

[Dubeckyj]

the natural frequency of a spring / mass system w = sqrt(k/m)

that means to double the natural frequency of the system, you must quadruple the spring rate.

iirc, the weights f/r are not 66/33, but more like 58/42 or 60/40, somewhere in that range.

Actually, the G3 is 66/34. And thanks. I know my math was wrong, but I don't know where. Did you check out that calculator to see if it makes sense?

I will say this, having actually put more then a few 100 miles on the SHOsource coil-overs in a full weight (Probably heavier then stock) 95 MTX with a Gen III Subframe.....They ride great!

I had mine set on full soft and the ride was better then any Koni/Intrax/Eibach setup I have ever had. The only problem I had was when I was stuck behind a school bus doing 25 MPH on a two lane road. There was some washboard in the road and the rear ride got a little bouncy. At speed, this was never a issue. However, If I would have stiffened up the rear coil-overs a bit this wouldn't have been a problem. Also, my car had a 29mm rear sway bar, which makes the rear end of any SHO ride like complete shit. I also had my car set fairly low.

Go with the stock springs and adjust the coil-overs accordingly from full soft until it reaches your liking. You will not be disapointed with the drive-ability of these things. I was shocked on how well they rode.

-Sam

Thank you! I've been waiting to hear some feedback from the coilovers. My plan is to disconnect the front sway bar and drop back to a 19mm in the rear, so I shouldn't have any solid-axle feel in the rear. Who else has their coilovers working? I'd like to hear more feedback about the spring rates out of curiosity.