darreng505 Posted June 18, 2013 Share Posted June 18, 2013 Hello racers, I have a 2012 Boss 302 as a full time track car. Completely upgraded suspension. All adjustable. I have the Ford Racing M-18000-C D-spec struts/shocks and the Eibach sportline springs which have a rate of 425 front, 275 rear. I just bought a set of H&R Race Springs to try. 325 front, 385 rear. Sounds kind of low in the front, but was the stiffest available from H&R. What can I expect from this new spring rate and rear bias? I run 295/40/18 square Hoosier R6's. Front sway bar 35mm on full tight, rear 25mm bar on loosest setting. Not sure where to start with the dampening settings (more even maybe). The D-specs are continuous so right now I am -2 turns front, -1 turn rear. But I am constantly changing the dampening as the tires wear... Your tips and knowledge most appreciated! Quote Link to comment Share on other sites More sharing options...
Al Watson Posted June 26, 2013 Share Posted June 26, 2013 I would suspect the car to severely oversteer and be tail happy everywhere. Typically a nose heavy car would require morefront spring than rear for balance. Ibet the original 425/275 springs to be close to balanced. Quote Link to comment Share on other sites More sharing options...
soundguydave Posted July 11, 2013 Share Posted July 11, 2013 I won't throw a dart at the final result, but you need to remember that on the S197, the stock rear spring location is quite a ways inboard from the shock mount, and that introduces an "interesting" motion ratio into the rear equation. In straight bump, yes, the rear springs sound a tad on the high side compared to the front, but in roll, you factor in the motion ratio (IIRC 0.6848), the wheel rate winds up being quite a bit lower. For example, with the quoted 385 lb/in rear spring rate, the wheel rate winds up being roughly 180lbs/in. (motion ratio squared times spring rate)*(SIN(spring angle)) For simplicity's sake, I elected to just blow off the SIN term, since the spring is close enough to vertical not to have a major impact. IF, however, you convert to a true coil-over setup in the rear, then the SIN term does come into effect, as the damper (and thus the spring) is inclined, and is also at a much different mounting point. FWIW, I'm running 350 in front, and 300 in the rear, and I feel undersprung pretty much all the way around, but particularly in the front. Quote Link to comment Share on other sites More sharing options...
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