I got 2 sets of 250# springs and a set of 400# springs.
Stock is around 100# front and rear. We have been racing on 150# front and 100# rear. Car was good but a little pushy.
I'm looking for higher cornering speeds and more neutral handling + better outside edge tire wear.
The car has no toe front of rear, 3.2 camber in front and 1.75 camber in rear. It also has 6 dey faster in front.
What say you grm?
If 150/100 pushed a little, then 400/250 would probably push as well. And 250/400 would likely be a drift machine. I'd try 250/250 first and see what happens.
Toe the front out a hair, see if the push goes away at turn in.
250/250 seem light but completely depends on tire selection. The more grip the more spring needed.
According to an old GRM article, the Speed Source ITS FC used 300-400lbs front, 200-275lbs rear.
My FC seems to be extremely sensitive to rear alignment changes, and runs a stiffer rate up front than out back w/ no sway bars. I would think 400F 250R without sway bars could be a good choice. Maybe reduce the rear toe-in a bit to get rid of the push? Or get your drivers to trail brake more. 
We have zero toe in the rear. Do you run without front and rear swaybars?
Yes- but remember I'm not on pavement either. My rates are closer to 300F 220R I think.
¯\_(ツ)_/¯ wrote: but remember I'm not on pavement either
Depending on suspension geometry and how the suspension behavior changes with roll, that can make a big difference. I've seen cases where a car pushes on pavement, but drive it down a dirt road where you get very little roll before running out of grip and suddenly it's tail happy if there's any kind of speed involved, especially on lift-throttle.
Play around with this spreadsheet, to get to it, you go to Fat Cat's website click education, then resources, tech info and online suspension calculator then pick your car from the list. You can play with the variables, including weight of the driver, car, spring rates etc and it spits out information. Read up on bounce frequency ratio and its effect on suspension for spring rate choices.
I ran my FC on track using 7kg/mm front (390 lb/in) and 5kg/mm rear (280 lb/in) with a Racing Beat front sway bar and stock rear bar. It pushed just a little bit, but could be made to oversteer with the proper technique. The 400/275 spring rates were apparently the standard recommendation from Mazdaspeed for a good stating point in ITS racing for the car and I felt that it was indeed a good place to start.
So your 400/250 springs should work, depending on what sway bars you've got for it.
Stock bars.
If you have coilovers, the other thing that seems to impact my FC's handling is rake- the higher the ass is relative to the front, the less stability the car has. I think this is thanks to the different amounts of toe change in the rear at different points in its' travel- the way my car corners is very much this order:
-Transfer weight forward, rear toes out
-Turn in, get car rotating to your liking
-Get back on throttle to transfer weight back, rear toes in
-Balance throttle and steering to maintain slip angle (rear is now toed in, making this easy)
-Allow car to straighten as you track out
If you don't do step one, you get understeer, and I'm not sure tuning around it would be beneficial.
With stock bars I'd definitely try those spring rates. If you're able and willing to put in the effort, it might also be a good idea to modify the stock bars to make them adjustable by cutting off the stock ends and welding on some bar stock as new ends with more holes.
You'll need to log in to post.
