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Project DC2 Integra: Starting the Journey Toward Better Lap Times with KW Suspension

by Mike Kojima

 

If you've been paying attention to our DC2 project car, then you know in the last installment we took our car to Buttonwillow Raceway (CW13) to record its baseline lap times and to get some driving impression of its 150,000-mile suspension and tires. Surprisingly the old DC2 was not horrible and not the slowest car entered in Global Time Attack's first ProAm event of the year. 

A lot of this had to do with the skills of our test driver, Karla Pestotnik, but it also spoke well of the DC2's innately good design and excellent stock balance. The old Honda "fun to drive" factor that seems to be missing from most of the cars they produce nowadays. 

However, Karla was complaining of the old, "weak in the knees stock suspension".  Our car was equipped with state of the art suspension circa 1995- Koni yellow single adjustable shocks and Eibach Pro-Kit stock replacement springs.  Although this was the hot setup then, it pales to what modern coilovers are like now. 

 

Our DC2 Integra Project at the ride height we got it with, (with Koni Yellow shocks and Eibach Pro Kit Springs, a 1.2" drop from stock) getting ready for its baseline laps around Buttonwillow Raceway's CW13 configuration. Be sure to check out our video for our impressions and base lap time.

 

The poor Konis were well-worn, so adjusting them didn't make much difference, leaving the chassis wallowy and blowing through the travel at track speed. The stock DC2 springs are around are about 3.5kg front and 1.7kg rear. This is a pretty amazingly soft rear spring rate for an FWD car! The Eibach Pro-Kits are 5.2 kg front and 3.8 kg in the rear, lowering the car about an inch and a half, but with a front harder bias. This would probably lead to understeer with a modern set up.  

 

We went out with the old and in with the new, thoroughly modern, KW Variant III coilovers.

 

The Variant III is KW Suspension's line of ultimate daily driver coilovers. The springs on the DC2 Variant III are progressive for a smoother ride potential and to reduce noise and vibration. The springs are custom wound to use the factory rubber isolated upper mounts. 

This does not affect handling on the multi-link suspension equipped DC2 as much as it would a McPherson strut car, as flex in the factory mount does not affect the lateral location and the geometry of the front suspension like it would in a strut. 

Since much of the noise of a coilover is transferred through pillow ball mounts into the cabin, rubber isn't a bad idea in this daily driver application. 

 

The front Variant III coilovers sport a spring rate of around 6.3kg (this is preloaded at ride height and gets stiffer under compression since the spring is progressive). This is almost two times stiffer than stock, but overall a reasonable spring rate. This is also considering the suspension is multi-link and the motion ratio of the front suspension is around .6, which considerably reduces the wheel rate. 

 

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Comments
Hayden 01
Hayden 01link
Monday, August 14, 2017 4:27 AM
I get that KW makes an amazing product, but I wish you would have tested a more affordable coilover for those of us who can't afford KWs. If you tested a budget brand and said it wasn't as good as the KW or equivalent but still was a good product, I would trust that. I'm sure there are good quality coilovers out there at a lower price point.
MDR
MDRlink
Monday, August 14, 2017 6:49 AM
@Hayden: You mean your coilovers aren't worth more than your car? :)
Mike Kojima
Mike Kojimalink
Monday, August 14, 2017 8:42 AM
We wanted KW's because we have big plans for this car!
ED9man
ED9manlink
Monday, August 14, 2017 9:03 AM
Very interested to see what you do, I considered KW v3 for my track EK, but the F/R spring rate bias seemed really sub-optimal for maximum performance based on my understanding.
ThisGuy
ThisGuylink
Monday, August 14, 2017 12:06 PM
Mike, I know on these cars it is common to raise upper shock mount on the hat to keep the shaft from bottoming out in lowered cars. Even shortening the shock body to be able to keep the bump stop in a reasonable spot. Can you comment to shock body length and bumpstop location on the KW VIII?

Also the Type R shock mounts both front and rear have practically solid bushings. They are a really good alternative when budget is in mind.
Mike Kojima
Mike Kojimalink
Monday, August 14, 2017 1:51 PM
ED9 Man, I feel that this is going to be good for street but for track use, the rear spring rates are probably gonna need to be raised. My gut feeling is something like 6 kg for starts, however, there is some binding in the trailing arm bushings that people don't take into account and I don't like the hard rotation as soon as you weight transfer that many race guys in Honda Challange set their cars at. So we will see. I do know what you are talking about but let's see if the heavy rear spring trend in grassroots racing is the right approach for a good balance here. I did go stiffer in the rear for our EP3 because it doesn't bind as bad and because of the motion ratio.
Mike Kojima
Mike Kojimalink
Monday, August 14, 2017 1:53 PM
This guy, I know that GC and other companies raise the rear top mount but we seem to have sufficient bump travel in the condition that we want to run the car at with this setup.
Julian ITR
Julian ITRlink
Tuesday, August 15, 2017 5:07 PM
Nice that you are doing an Integra, I am really curious on your take on the whole rear suspension situation on those cars. Do you think the Type R rear lower arms are really worth it? The EK9 Civic Type R had regular stamped steel ones, and I'm not sure for what reason they need to even be strong in torsion/bending. Is it just because of the sway bar trying to twist it? Wouldn't reengineering the sway bar mount so it doesn't cause torsion in the first place a better idea?
I feel the rear trailing arm bushings are kind of an unwinnable situation on those cars, if you make the trailing arm bushing hard/solid you lose the point the suspension was designed for in the first place, and basically carry around a super heavy trailing arm for no reason imo.
Mike Kojima
Mike Kojimalink
Tuesday, August 15, 2017 5:31 PM
Julian, I agree with you, I want to understand the OEM logic to having the expense of a different lower arm for a limited production car where it would make a minimal difference. The most important thing is not to use a solid bushing for the trailing arm, that is a common mistake and is bad on this car.
SM_Clay72
SM_Clay72link
Tuesday, August 15, 2017 9:34 PM
I hope you are going to run the same old crap tires in your next test so we can have some real comparo!
Mike Kojima
Mike Kojimalink
Tuesday, August 15, 2017 11:07 PM
To do the test on old tires is meaningless. Better tires require more damping and roll stiffness which is provided. To have that on old tires is a mismatch.
ginsu
ginsulink
Wednesday, August 16, 2017 6:06 PM
That's true, the point you guys are making on the trailing arms. AFAIK, Honda designed it to be a 'semi-trailing double-wishbone type suspension' which I think is unique to Honda. It is supposed to 'toe-in' during hard braking to keep the rear end from wagging too much as the load is summarily reduced. You can see how this works, quite easily, when viewing the suspension from above on a Freebody diagram.

Obviously, introducing a solid bushing eliminates the movement, although, the 'front toe-link' will still toe-in the whole trailing arm under bump.

As for that rear trailing arm, there are reasons why Honda produced a different set of parts for the Type-R chassis. I'm pretty certain that it is a stiffer part, specifically for the 21mm sway bar. The stock mount on the DC2 chassis is in single shear, and from what I can tell, the Type-R mount upgrades it to double shear. There is also another upper arm, that is made of tubular steel instead of the stamped piece, but the tubular part is specifically made for the Type-R, and it was really difficult to get in America, you have to just get an aftermarket adjustable type here.
Julian ITR
Julian ITRlink
Wednesday, August 16, 2017 7:44 PM
ginsu, do you refer to the picture in the book "The Automotive Chassis" on page 62? ;) At least that's one that illustrates what you wrote about.

You are correct on the single vs. double shear situation, but the EK9 Type R also used a 22mm rear sway bar, with no bespoke control arms. That's why I am not sure how much of a difference the stronger arms really make, especially as the torsion of the arm is initially only limited by the damper bushing.

The upper arms are maybe stronger against buckling, but how much side load would you need to have until that becomes even relevant. And I guess in that situation, adjustable parts are used anyways.

My favorite rear suspension design on FWD is what VW and Ford are using.
You can basically use solid bushings for everything except the trailing arm. The trailing arm only takes longitudinal loads and is soft against bending, so camber and toe do barely change by the longitudinal movement as they are set by the control arms you used spherical bushings on. So it's "comfy", precise and also much lighter than the Honda design.
SM_Clay72
SM_Clay72link
Thursday, August 17, 2017 9:25 AM
Yes, and in that case it would have been nice to see the inverse with good tires on the old suspension.

Basically what I am trying to say is it would be nice to see what a modern performance tire can do on it's own. Tire tech has come incredibly far since that car was built.
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