I currently running Koni's with 450F/375R lb coilovers. Front sway bar is the Tripoint .188 wall and the rear is stock 93FD 17.3mm. My desire is to soften the rear. I would like to try 350 lb springs and the 95 FD rear bar 15.9mm. My question is, how much % of reduction would have taken place. Thanx much...

 

Have you adjusted your Koni's yet? I find that you never adjust them to either full soft/hard as the last 1/2 turn is no makes adjustments in a linear fashion. In regards to softening the rear, what are you trying to accomplish? Does the car tend to oversteer too much? If it does, I'd first adjust the Koni struts slightly softer, then tire pressure down to increase grip.

What do you want with the % reduction? To my knowledge there is no special ratio between sway bar size and spring rate. But to find % change, here is a formula.
(Final- Initial)/100= %change

 

Your best bet is to try one change at a time and see how you like the feel. All the numbers and data will solve major issues but the final say has to come from the driver not the calculator.

 

You cannot solve that problem because spring rates:mm in sway bar.

I have springs for your car. I would suggest 225-250 in the rear. 375 is WAY WAY WAY WAY WAY WAY to heavy. What are you doing with the car racecar/autocross/street/drift?

 

You did notice that this car is an FD?

375 in the rear is hardly too stiff in an FD.

 

Depends on what you want the car to do .... Hook up ... 375 will not allow the rear end to squat and hook...

 

^^^^

I don't think we're all talking about the same car. I'm running 650/500 on my FD, and the "typical" track rates are at least 500/400.

 

375 is a bit on the soft side.

I run 700/500.

 

650, 375 is what all the Speedsource cars come with. That is what I used, no rear anti-sway bar. FC however...but that should be similar weight. Just my 2 cents. Best of luck

 

This does not answer the spring plus bar question of yours, but a prime reason for sway bars is to adjust side rates independent of pitch rates. Springs effect both, bars side only. While your rates are very close to what Howad Coleman likes, the front to rear ratio may be too close, i.e. increase front rate or reduce rear rate.

From Mazdaspped:

Suggested Spring Rates with Coilovers
1993 and later SPRING RATES WITH COIL-OVER SETUP
Spring rates tested with GAB shock (super HP model)

Smooth Track (recently paved)
650 - Front
350 – Rear (54% of front)

Slightly weathered track surface
350 - Front
225 – Rear (64% ratio)

Rough Track
200 - Front
150 – Rear (75% ratio)

Stock
263 – Front
195 – Rear (74%)

 

Don't FCs have mcpherson struts?

 

Yes they do, as well as semi-trailing rears, so the comparison isn't 100% accurate.

 

I think FC to FD suspension is like comparing apples and oranges. You have totally different motion ratios and sprung and unsprung weights. The cars may be close in total weight but the springs have way different geometry to deal with.