I've noticed the spring rates on the FD are (relative to the TurboII) *incredibly* stiff. Anyone know if it would be a problem on the street to upgrade to FD type spring rates on a TurboII?

Is the FD just an incredibly bumpy ride or something? Or is the TurboII just really really soft for a sports car? I think the turboII is like 120 lbs front stock, the FD is somewhere around 220 or so, but they're about equivalent in weight.

Anyone have any details on this?

 

Actually, the stock FD rates are about 280/200.

The FD rides stiffer than the TII but the suspension geometry is completely different -- Mac strut vs double-wishbone. I doubt the wheel rates are as different as the spring rate.

As far as spring rates, talk to Tri-point or Ground Control, they will know appropriate spring rates for an FC.

 

FD runs stiffer due to different suspension geometry.

You can run the *stock* FD spring rates on the FC, but that is not the most stiffest rates possible.

I run the old GC set-up, and my springs are 400 front, 325 rear.


-Ted

 

i was wondering when wheel rate versus spring rate was going to come up on the forum...

the fc has a strut front suspension. as such the spring rate is the wheel rate. so a 400 pound spring is very close to 400 pounds at the wheel. ..(wheel rate)

wheel rate, not spring rate, is the proper method to compare different cars suspension dynamics.

the fd has double A arms. the shock is roughly in the middle of a lateral lever arm (the lower A arm).
for every inch of wheel travel (up or down) the shock and spring move only .605 front and .68 rear.

that means that a 400 pound front spring is like a 240 fc spring at the wheel.

wheel rates relate to corner weights most directly.

when i look at a new car and attempt to put the right spring on it i determine the wheel rate in relation to the spring rate ( often referred to as the 'motion ratio') and then use a formula relating the wheel rate to the corner weight. various multiples deliver buick-like ride to buckboard characteristics.

howard coleman

 

howard, I just wanted to say that evertime I have read one of your suspension related posts, I always learn so much worthwhile information. Thank you for spreading your great knowledge to the community, it is greatly appreciated.

 

Agreed. Hopefully, Howard will stick around for a while, but most truly knowledgable people get fed up with the typical forum member and leave/quit posting.....

 

Wow, never heard of wheel rate before. I did know the FD had unequal length A-arms to lessen the need for negative camber for hard driving, but didn't know about wheel rate. So that would mean that:

An FD has 280/200 spring rate - 169.4/136 wheel rates
An FC has somewhere around 100/90 spring and wheel rates?

So basically if I put 200 lb front, 160 lb rears I'd have a slightly stiffer wheel rate than a stock FD? Might go with that, but the rates I found with another spring company was like 200/120, weird.

 

the rear fc suspension, being independent, probably has a different wheel/spring rate relationship than 1 to 1.

howard coleman

 

I put "wheel spring rate" in the search window and I get over 100 hits. You guys must not read much

Wheel rate is the load from the spring which the wheel actually sees. Since the spring is mounted on a lever (the suspension arm) the farther away from the wheel the spring is mounted the higher the rate of the spring will need to be in order to give the same wheel rate.

When comparing different cars with different suspensions wheel rate is what counts.

 

did you read ANY of those results? most of them have nothing to do with wheel spring rate, but rather just have those three words somewhere in the posts

 

A quick search finds it here, here and here.

Of course not all 100 hits actually discuss wheel rate, that's why there is a little bit of the message shown in the window when you get your results so you can read the ones that matter and ignore the rest...