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Originally Posted by wootloops
This is great info, thanks!
You're right, I am not running aero yet so I probably don't need to go as stiff. The YCW Recommendation of 8k/16k I believe equals 448/896 so that would be a little softer. Based on your comments, The spring ratio would be 1:2 front/rear which may be a tad oversteer prone, but I can probably dial that out with a stiffer front sway bar if needed. It should fall somewhere between your 450/1050 and 650/1100 in terms of front/rear bias.
Thanks again, your build is a big inspiration.
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I run the YCW with 8k/16k but i sent them out to be custom valved for it. I like this setup the best I've had on the car. 4k/12k "street" setup they sell is too soft. Maybe for a stance car it would be good. I ran 6k/16k for a while and it was pretty good until I tried 8k/16k. The little bit of extra front spring rate gives you a little more front bump travel without being so stiff that you then need helper springs. I like where the car is at right now but it could be stiffer. I am now running 285s all around. Going to be moving to ohlin's dedicated track soon which is 12k/18k So I am curious to see how that feels... I hear a lot of hype.
Moving from 6k/16k to 8k/16k definitely induced a little under-steer in slow speed corners in autocross. However, the car also slaloms way better now for a net gain (I've been faster). Driving style matters for sure and you'll need to adjust/re-learn every time you make a change.
I know I have preached on here a lot about ride frequency and how the rear motion ratio is low... but that is usually said within the context of people complaining about terminal under-steer and how to fix it. Run more balanced spring rates. However, many people's counter arguments in those conversations are also true... that a race car doesn't need to be tuned for flat ride. I think due to braking and what not it's more realistic for a racecar to have more of a 60/40 spring rate bias. Spring rates like 650/1100 result in about a 62% front spring rate bias which is a little high. With sway bars tuned for more front roll stiffness that number likely increases to closer to 70% front roll couple distribution depending on what sways you run. That's where it becomes a balancing act of staying within that golden range where a little front bias might help but too much and you'll just induce excessive under-steer leaving time on the table. 450/900 (8k/16k) is closer to 57% front spring rate bias and before factoring in sways feels like a pretty good starting place on paper.
IDK if I am using all of the terminology correctly and explaining it well.. I am paraphrasing from resources like this:
https://robrobinette.com/Suspension_Spreadsheet.htm
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*Front Roll Couple Percentage describes lateral load transfer distribution front to rear and subsequently the handling balance. It is the front roll stiffness divided by the total roll stiffness which is a ratio, front to rear, of the vehicle's total roll rate. Higher than 50% means the front wheels take more weight while cornering and the handling progresses toward understeer but for most cars around 55% gives balanced handling on the track while approximately 75% is best for autocross. For powerful cars a higher FRC% can help prevent power-on oversteer so a turbocharged Miata will typically need a higher FRC% than a normally aspirated Miata.
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