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View Full Version : Adjusting Suspension - MKIV Koni Reds



JMD
06-16-2025, 05:00 PM
Ok, I've done a lot of searching and yes, there is tons of random info on the forum about the koni red shocks and FFR standard springs (#500F/#300R), but I don't really see much out there about fine tuning or making adjustments other than 'put the setting to softest' and that's about it.

I find the ride very bouncy, the car feels unsettled going over even moderate bumps at 30-40mph. I've driven light cars before so it's not just it being different than a 'normal' or modern car. It certainly handles like a go kart, which is great...but it almost feels nervous and jittery in a bad way, not really planted and secure. My car is 100% completed mechanically, body on, shocks double checked to be in softest position, alignment done to recommended specs, and no sway bars attached. Ride height is right around 4.5" front, 5.25" rear. Riding on 15" wheels (maybe that's part of the problem!), tire pressure around 25psi.

My first thought is to increase the damping on the shocks to reduce the 'bounce', which feels like too much rebound after initial compression. If this is a common experience with this car I expected to see a lot more threads about how builders are finding it better to firm up the shocks or make adjustments other than what we are told to set things to initially, but I'm not.

I know this is just the beginning of getting the car sorted out. It's going to take time and part of the decisions made are personal preference, but I was wondering if anyone had experience with these stock spring rates and shocks who could give some pointers or share what's worked best for you after you made adjustments after initial setup. I refuse to believe everyone is just sticking with the initial settings and not making any changes.

Firming up the shocks is my next step, I think...will see what happens from there. I do believe this is a decent enough chassis to be able to handle well with the right adjustments and parts. Would love to hear from some of you who have experience with this.

Whether it be improving ride quality or setting your car up for autocross or track...let me hear what's worked for you!

CraigS
06-17-2025, 06:36 AM
I don't care for the 300# rear springs. I prefer 200-250 springs. One thing I do wonder about though is your ride heights, especially the rear is quite high. I'd try 4.0"F and 4.5" rear. Also experiment w/ dropping tire pressures to 20-22.

Jeff Kleiner
06-17-2025, 07:44 AM
I agree with Craig that your right heights are higher than what's common but that won't actually affect how the car rides. I went the other way with springs primarily for autocross and track use with 750# front and 500# rear. When making this change I turned the rebound up one click. Firm but not harsh and definitely not "bouncy". Tell us more about what you're calling "unsettled"...is it actually bounce or is it lack of stability? I see that you have power steering; what are your alignment settings?

Jeff

Railroad
06-17-2025, 09:14 AM
Tire pressure gauges can vary greatly in accuracy. I would drop the TP to 22psi and see how that feels.
I bought one from Summit racing, supposedly accurate and is graduated to easily adjust the pressure to within fractions of a pound.
I like!

gbranham
06-17-2025, 09:26 AM
I don't have mine aligned by a shop yet, but I've got it rough aligned with string and levels. Mine feels a little jittery or "darty" in the curves, but feels great driving on straight roads. I know a final alignment will help substantially. One thing I've noticed is the power steering is super "light" if that makes sense. I'd almost prefer more resistance when turning the wheel at speed in curves. Again, maybe a final alignment will help with this.

Greg

JMD
06-17-2025, 12:05 PM
Thanks for the responses.

Craig, I double checked ride height and am at 4 1/2" front, 5 1/8" rear. I don't think that is something that would have a noticeable effect the ride. Will double check tire pressure and maybe pull it down closer to 22.

Jeff, what I mean by 'unsettled' is pretty much the way the rear end is behaving. The front end seems steady and pretty stable, but the back end seems to amplify any big bumps in the road. It doesn't feel unstable side to side, but feels light and overly reactive going over bumps. It seems to unload the rear end on moderate bumps and at moderate speeds, which makes me a bit nervous about how it will act at higher speed or how it will behave in similar conditions under a lateral load. If the back end is unloading due to undulations in the road in the middle of a turn that feels like a recipe for snap oversteer. I think ultimately that's what I'm afraid of. It's not a big deal at 30-40mph, but I'm afraid of what I'm feeling at moderate speeds might mean at higher speeds and with more vehicle dynamics involved.

Here is my current alignment:
Front
Camber : -0.5
Caster : 8 degrees
Toe: -0.10 degrees (in)
Rear
Camber : -0.5
Toe: -0.15 degrees

The steering is light and responsive but not twitchy. No concerns there. I do have power steering, but installed a flow restrictor that reduces the pump to 2 gal/min. No complaints.

The car feels fine on a straight road with the exception of the rear end bouncing more than it should over bumps. The front is a little bouncy, too, but much less so.

I'll make sure tire pressures are at 22 and firm up the rear shocks by 1 click and see how that changes things. Would still love to hear from more owners about what they've done with their suspension setups.

gbranham
06-17-2025, 03:36 PM
I'm sure you've checked, but are you sure you have the front springs on the front, and the rears on the rear?

Greg

JMD
06-17-2025, 06:46 PM
Ok, so today was a great illustration of why we double and triple check what we think we know to be true.

My rear tire pressure was at 30, not 24 like I thought. Aired it down to 24 and I'm sure that will make a difference.

After double checking my build thread, yes, I do have the springs in the correct positions, but the rear springs FFR sent me are 400# springs (not 350). With that high of a spring rate I would guess setting the shock to the second click from full soft instead of full soft might be more appropriate.

Jeff Kleiner
06-17-2025, 08:26 PM
400 is correct for the IRS. Keep the rebound on full soft.

Jeff

CraigS
06-18-2025, 09:03 AM
Sorry I missed that you have IRS. So yeah 400 is fine.