Lexus IS Forum - View Single Post - Do stiffer springs reduce/eliminate the need for sway bars?
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post #3 of (permalink) Old 04-07-2017, 03:28 PM
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Lots of racers in things like Honda Challenge don't run sways. Sways are just tuning tools. How about trying the stock sways again before tossing them out completely? It won't hurt to take them off and try it. I don't consider the TRD's to be particularly stiff.

The car is very balanced all around, no oversteer or understeer. Problem is, it grips until all 4 corners break lose at once, and there's no saving it.
That's what a neutral handling car does. If you want more understeer I'd probably try reducing the rear springs to 10K and see if you like it. Maybe just remove the rear sway bar and leave the front.

The fact you say "no saving it" suggests you might need to train the driver more to feel it nibbling at the edges of grip. Biggest mistake people make when the rear steps out is to release the gas pedal, this can even make an under-steery car come around. It can make a neutral car snap around. When the rear steps out and you let off the gas, you cause a massive decrease in rear grip. What you should do is feather the throttle or even keep it at the same position and handle it with counter-steer.

If you find the car coming around too quickly on you and you haven't lifted, it suggests you're not counter-steering enough or fast enough. At that point you need to consider where you're looking. If you're looking at the curbing, you'll probably drive there. When it steps out you need to be looking where you're going.

Like, if you corner hard, the outside wheels are pulling up on the sway bars, which in turn pulls up on the inside wheels. I understand wanting to be flat and all, but at a certain point, your inside wheel will come off the ground and be useless, especially in a car like mine without LSD.
The inside tires don't do all that much. If you're going properly fast in a corner, most of the weight has shifted to the outside. My M3 used to corner with the inside tire a foot in the air. You couldn't even tell while driving it.

When is too much stiffness too much, to the point of losing grip in the corners?
You can't get more than 100% out of the tires. That's just how it is. It the tires have the proper camber so they're laying flat on the ground during cornering and you find yourself sliding sideways, I suspect you're simply out of grip. If you hit a bump in a corner and the car hops so you lose grip, then your suspension might be too stiff.

What's the chance your shocks are too stiff and the car is hopping instead of complying with the track.

My own personal opinion is that I like a bit of understeer on track. I can always induce oversteer by lifting if I want and it means I can power out of the exits without the rear stepping out on me.

14K = 770 lbs/in
12K = 660 lbs/in.

This is decently stiff but the Honda challenge guys with similar suspensions often run a bunch more. I used to run 650 lb/in in my M3. The IS300 has a motion ratio of close to 50-60% meaning the 770 is only effectively 450-500). I'm not certain of the IS300 motion ratio. It's related to where on the lower control arm the spring pushes. On struts it's almost 100% on the wheel. In the IS300 because the spring is pressing on the lower control arm. The leverage from the arm means it's effectively a lower spring rate for the same lbs/in
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