Learn me coilover tuning

I'm assuming it's a simple answer, but I don't have experience screwing around with coilovers, so I just want to confirm.  I bought my permit-in-hand son a '97 Lexus LS400 a few months ago as his vehicle to learn to drive on, and be his DD once he has a license.  The car is absolutely spectacular, I love it.  Smoother than most modern engines, runs like a top.  Everything, and I mean every damn thing, works on this car.  Even the power seatbelt height adjusters.  It was meticulously cared for almost its' entire life by just one owner, and it shows.  Even the leather on the drivers seat looks nearly new.

However, I bought it from PO who had intended to run it in the Challenge.  So the only thing done with it from stock is to put a set of K-Sport coilovers on it.  He also replaced the rubber rear subframe bushings with aluminum.  On a smooth road, the ride is fine.  However, over bumps it is downright p-u-n-i-s-h-i-n-g.  It hops like a hella stance kid in a slammed Civic.  We have to literally stop and roll over a speed bump, otherwise a back seat passenger is going airborne.  I think it's lowered maybe 1" from stock, give or take.  How do I tune this to be much more compliant?  Is it as simple as highest ride height and softest setting?  Anyone have experience with k-sport?  Even if I do that, will it still ride like a suspension-less go kart?  I'm beyond thrilled with this car, it's fantastic, but the ride kills it.  Even my son is starting to get weary of it.  Here's a picture of its' current stance.

Find a stock setup. 

K-Sport is in the same garbage tier as the other Taiwanese brands.

Ride height isn't going to change how still the springs are. Do the shocks have enough damping for the springs?  I feel a spring swap is in your future. 

It might be cheaper than going to stock to find out what springs and dampers that are installed and switch to softer ones.

With coilovers you have flat ended springs and can ideally choose whatever rate you want.

Upping the ride height will help if it's running out of travel. Also make sure there are good bump stops in the system. Setting the shocks to full soft isn't necessarily the right answer as it might just be wildly underdamped like that. But like everyone else says, it's never going to ride well on that suspension. Get as much rubber in the system as possible and either go back to a stock suspension or upgrade to better coilovers.

K-Sport is a pretty cheap brand, the same company also sells under the D2 brand. I have plenty of experience with them, they're actually not bad value for the money, you get a proper fully-threaded shock body with independent height adjustment, but you get what you pay for in terms of the damping action. That said I have beaten cars with vastly more expensive struts with them

All you can do with those as-is is turn down the shock rebound with the top adjuster and give yourself some more ride height. You may also be running out of travel *at the top end* with the shock piston acting as a limiting strap, that feels rough and is bad for maintaining traction, you can add tender or helper springs to fix that.

If you want a cushy ride, sell these and go stock. They will never ride nicely.

Thanks.  I knew they'd never give a buttery smooth ride, but figured maybe I could make them a bit less like torture.  Sounds like time to find a budget stock set up.  I presume it's an easy and straightforward swap to go back to stock.

Klayfish said:

Thanks.  I knew they'd never give a buttery smooth ride, but figured maybe I could make them a bit less like torture.  Sounds like time to find a budget stock set up.  I presume it's an easy and straightforward swap to go back to stock.

Unless there was some hackery involved, it should be pretty straight forward.

GameboyRMH said:

K-Sport is a pretty cheap brand, the same company also sells under the D2 brand. I have plenty of experience with them, they're actually not bad value for the money, you get a proper fully-threaded shock body with independent height adjustment, but you get what you pay for in terms of the damping action. That said I have beaten cars with vastly more expensive struts with them

All you can do with those as-is is turn down the shock rebound with the top adjuster and give yourself some more ride height. You may also be running out of travel *at the top end* with the shock piston acting as a limiting strap, that feels rough and is bad for maintaining traction, you can add tender or helper springs to fix that.

If you want a cushy ride, sell these and go stock. They will never ride nicely.

Argh. There’s a lot of mistaken thinking in that. Maybe not the “cheap two-piece coilovers are crap” part, but the setup. I’m not on a device that’ll let me type much, so I’ll come back to this in a few days. 

According to this link, the spring rates are very high  

9.8k rear and 18k front 

I don’t know what stock Lexus spring rates are but that seems kinda nuts

https://shop.redline360.com/products/ksport-kontrol-pro-coilovers-lexus-ls400-1995-2000-clx090-kp?variant=21340127297616&currency=USD&gclid=EAIaIQobChMIiqWPo7WZ5AIVCNlkCh3g2wqlEAQYBSABEgLwxfD_BwE

I would start by raising the ride height to a more normal level  As low as those are, you don’t have enough shock travel for them to actually dampen any bumps  

Also soften the valving since they are ‘36 way’ adjustable  

These 2 options are free

Next, try to find some 2.5” diameter coil over springs with softer rates  You can buy Eibach coil over springs for 59 new  Might be able to find used cheaper 

Also, figure out where the aluminum bushings are in the rear suspension  Might want to revert to stock depending where they are 

Alternatively, go junk yard shopping for stock suspension :)

Keith Tanner said:

GameboyRMH said:

K-Sport is a pretty cheap brand, the same company also sells under the D2 brand. I have plenty of experience with them, they're actually not bad value for the money, you get a proper fully-threaded shock body with independent height adjustment, but you get what you pay for in terms of the damping action. That said I have beaten cars with vastly more expensive struts with them

All you can do with those as-is is turn down the shock rebound with the top adjuster and give yourself some more ride height. You may also be running out of travel *at the top end* with the shock piston acting as a limiting strap, that feels rough and is bad for maintaining traction, you can add tender or helper springs to fix that.

If you want a cushy ride, sell these and go stock. They will never ride nicely.

Argh. There’s a lot of mistaken thinking in that. Maybe not the “cheap two-piece coilovers are crap” part, but the setup. I’m not on a device that’ll let me type much, so I’ll come back to this in a few days. 

I'll be waiting, it's perhaps oversimplified, and arguably assumes that something is bottoming out at the current ride height and that the shocks are currently at a hard setting (although note I said "can do" not "should do" ), but I don't see what's *wrong.* On my own D2 coilovers I've had problems with running out of extension travel, this can happen easily when a strut has a single linear-rate spring that is hard for the amount of weight it's supporting. If the spring only compresses an inch under the car's weight, you only have an inch  (assuming 1:1 motion ratio) of extension travel, which can easily be taken up on the inside wheel in a corner or if the car bounces over a nasty obstacle.

18kg/mm front/9.8kg/mm rear sound like decent rates for an autocross setup on a car this heavy, and may not be bad on the track, but that's really hard for a street car, especially that front rate.

I would say get all-new stock stuff off of RockAuto and sell off the KSports. The ride in a stock 90's LS is grandpa's armchair-plush. But the only way you'll get that feeling back is to install new stock dampers.

Good news is that they sell everything, including the rear coil springs and pre-assembled front struts, brand new.

I'd start strategically playing with what you already have first, to more fully understand where you're actually at, before deciding where you want to go with it.

1) Make sure you're not topping (often overlooked) or bottoming out due to poor perch adjustment.

2) Once the expected available compression and rebound travel is confirmed, adjust the dampers BOTH directions to see how it changes the ride/handling characteristics.

3) Calculate the ride (not just spring) rates and put them into some comparatively understandable terms, like natural frequency, to better understand how much of the stiffness and/or harshness may be spring and how much may be damper.

What Driven5 said.   He is supposed to be learning car stuff, what better way to learn than to make changes, evaluate the result, and repeat.  What happens if you go full soft all around? Full stuff? Half way? Ride height up 1”? Down 1”, etc.  

Stock Lexus LS stuff is couch worthy. Friend has a newer 2000's model and its ridiculous how comfortable that car is on the highway. Find stock replacements if you can. Looks like most of the stock parts are available from Rock Auto. They have all parts separate(KYB GR-2's are available) and stock coil springs w/ and w/o air suspension.

Buy stock bushings as well, solid bushings will murder you and everything else in the car over high frequency bumps (expansion joints, potholes, cracks in the road, etc.)

Thanks all!  There's no harm in messing around with what's in it now just to see how it reacts, and help teach my son as Sonic pointed out.  Would be good learning lesson for me too.  However, if we don't like any of the results, a swap will be in our future.

GameboyRMH said:

Keith Tanner said:

GameboyRMH said:

K-Sport is a pretty cheap brand, the same company also sells under the D2 brand. I have plenty of experience with them, they're actually not bad value for the money, you get a proper fully-threaded shock body with independent height adjustment, but you get what you pay for in terms of the damping action. That said I have beaten cars with vastly more expensive struts with them

All you can do with those as-is is turn down the shock rebound with the top adjuster and give yourself some more ride height. You may also be running out of travel *at the top end* with the shock piston acting as a limiting strap, that feels rough and is bad for maintaining traction, you can add tender or helper springs to fix that.

If you want a cushy ride, sell these and go stock. They will never ride nicely.

Argh. There’s a lot of mistaken thinking in that. Maybe not the “cheap two-piece coilovers are crap” part, but the setup. I’m not on a device that’ll let me type much, so I’ll come back to this in a few days. 

I'll be waiting, it's perhaps oversimplified, and arguably assumes that something is bottoming out at the current ride height and that the shocks are currently at a hard setting (although note I said "can do" not "should do" ), but I don't see what's *wrong.* On my own D2 coilovers I've had problems with running out of extension travel, this can happen easily when a strut has a single linear-rate spring that is hard for the amount of weight it's supporting. If the spring only compresses an inch under the car's weight, you only have an inch  (assuming 1:1 motion ratio) of extension travel, which can easily be taken up on the inside wheel in a corner or if the car bounces over a nasty obstacle.

18kg/mm front/9.8kg/mm rear sound like decent rates for an autocross setup on a car this heavy, and may not be bad on the track, but that's really hard for a street car, especially that front rate.

 

Sorry, back in front of a keyboard.

"Independent height adjustment" is code for "generic shock cartridge with an adapter screwed on". It's touted as an advantage by the companies that build shocks this way, but it offers decreased overall suspension travel with no benefit. The shorter shock cartridge doesn't allow as much shock travel as a full length shock does, and there's really only one correct setting- short enough to allow full compression. Adjustable preload is another marketing term that's attempting to make a bug into a feature, but it's not really something that has any effect on vehicle dynamics until you get to edge cases where preload approaches the corner weight. A two-piece shock is a downgrade from a properly specified single-piece shock, but it's rare on cheap shocks because it's more expensive to build and takes more careful engineering.

If you are running out of droop travel and topping out the pistons, adding helper/tender springs will have no effect. That's a hard mechanical limit. You've run out of droop travel no matter what you do with springs. Now, if your springs are going loose before you get there, you may want longer springs or helper/tenders.

If this car is bottoming out hard, check to make sure it's not coil bind. It'll feel like metal on metal contact and it leaves characteristic marks on the springs where the coils have come together. The solution is to run longer springs if packaging allows, or to limit compression travel if not.

Note that you can't really assume spring rates without knowing a lot more about the chassis, especially motion ratios.

I added droop travel by sacrificing compression travel - moving the spring seat down so that the main spring alone would go loose, take up the slack with a tender spring, then move the lower mount to restore the previous ride height. You don't need much compression travel on the shocks on a lowered car with super-hard springs.

That's the tradeoff of those two-piece units. You have a limit to your overall travel, so you either have to sacrifice droop or compression. I think compression is a lot more important unless you're a rock crawler, but I will go to great lengths to make sure I get as much of each as possible. When you put the suspension into the stops, it basically stops working. There's always a bump big enough to do this, so you either make sure you have as much travel as you can get or you have to avoid those bumps.

The helper wasn't really part of your solution here, the solution was to simply make the shock longer overall which exchanges compression for droop.

Without the helper, the main spring could come unseated when I use any of my newly added droop travel, since I was running zero preload.

I haven't had any bottoming problems with the new setup and it fixed a problem I had in one corner where the car would start skipping diagonally. The car also no longer loses traction when crawling over pavement transitions or driving across deep cracks in the pavement.