More than you ever wanted to know about the 88-91 Honda Civic suspension

I had a chance this summer to do something I’ve been meaning to do - measure how much suspension travel my civic is capable of, without having to resort to too many custom bits.

At this point, I’m pretty strongly leaning away from getting the civic on stage, so this is more just to share, than anything else.

First, the setup:
1988 Honda Civic hatchback
All stock suspension components except for:
1990-93 (DA) Acura Integra Lower Control Arms on the rear. These arms move the shock mounting point ~1/2” inboard, providing more wheel travel for a given shock length and providing more clearance between the shock/spring and the trailing arm. More details and pictures on the difference here: http://crxcommunity.com/viewtopic.php?t=41148
96-00 (EK) shock “fork” to fit the dampers.
For dampers, I’m currently using:
Bilstein F4-BE5-2336-H1 - HD for 96-00 (EK) Front
Bilstein F4-B46-1605-H2 - HD for 92-95 (EG) Rear

The test apparatus:
I used a piece of PVC pipe with an OD of ~1.9” to substitute as a shock. To mock up a spring, I used a short piece of PVC with an OD of ~3.5” - comparable with the few 2.5” ID springs I’ve got to compare against.
As many bushings as possible were loosened during measurement to allow everything to move as freely as possible - I realize this may skew the reality of my measurements unless I’m planning on replacing the bushings with sphericals.

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KF7RWG
http://www.utahrallygroup.com

The Rear Suspension:

Full droop:


Full Bump:


Spring clearance at full droop:



Spring clearance at full bump:


UCA Clearance at full bump:


Numbers/Analysis:



18.4 cm of wheel travel, 14.2 cm of travel at the shock. Limit in bump was the tire hitting the wheelwell. Limit in droop was twisting the RTA bushing - I’m using a jack to press up on the forward point of the trailing arm, and at this point the body starts lifting. It can be re-clocked to give us more droop - assuming that gives us more travel, our limits move to the front end of the trailing arm hitting the chassis, and the compensator arm hitting the ‘frame rail’.

Fully compressed OAL, measured from top of the stock tower, to the bottom of the “shock” (not including the “fork” on the bottom) is ~31cm. It’s the back, so shock towers could be easily extended if needed.

I didn’t do any measurements of the actual shock on the rear to see what the off-the-shelf travel comes out to - but I’ve got a ‘feeling’ that it’s not as much as one might like - even with the spacers removed from inside the shock that should give an additional 15mm of extension at the shock.

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KF7RWG
http://www.utahrallygroup.com

Front Suspension:

Full Droop:


Full Bump:


Numbers:


Front Graph Notes (wheel bump):
1) Estimated Full Droop w/ spacer removed. (0.9 cm)
2) Off-the-shelf Full Droop (3.2 cm)
3) Bump Stop Contact (11.2 cm)
4) CV Axle is level (12.7 cm)
5) Bump stop compressed to lifting car (18.7 cm)
6) Full bump without Bump Stop (20.7 cm)

Fully compressed OAL is 26cm - measured from top of shock tower, to top of “fork”. Given the fact that there are off-the-shelf “top hats” which can raise the shock mount 1”, I imagine it would be possible to slightly extend the front towers if needed - or, if spring length is not an issue, construct “top hats” big enough to handle the 50mm bilsteins.

Unfortunately, didn’t take pictures of spring clearance, so you’ll have to take my word on it.

Using the stock UCA, there’s good enough clearance between the it and the spring, that I didn’t feel compelled to measure it. Depending what approach you use to get your ~-1* of static negative camber, there certainly might be an interference issue there.

Using the ‘EK’ fork that bolts up to the OTS bilstein, the spring does contact the knuckle at the maximum droop allowed by the balljoints. At <2cm of wheel bump, there’s ~1/4” of clearance - and plenty more as wheel bump increases. This contact is ~3.5” from the top of the fork, so if the spring perch can be higher than this, it may not be an issue. Obviously, if any negative camber is added, space between the spring and the knuckle will decrease.

Interestingly enough, if you use the stock fork from the car (that appears dimensionally nearly identical to the ‘EK’ fork), the spring clears the knuckle at full droop. The OD of the stub on the end of the OTS bilstein is 42mm, with ~5mm nominal wall thickness - decreasing where there’s a groove to clear the pinch bolt. I don’t appear to have a measurement for what the ID of the stock fork is, but I believe it’s ~39mm. Not sure if the stock fork could be bored out and/or the stub on the shock could be turned down, but that’s a possible solution to increase the room between the spring and the knuckle.
It appears that, with the OTS bilstein - with spacer removed - we can hit the 190mm of travel that JVL likes to shoot for.

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KF7RWG
http://www.utahrallygroup.com

Other assorted pics:

My best attempt at showing how much steering angle this car has:



just for fun...

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KF7RWG
http://www.utahrallygroup.com

HAha, the gif's are sweet. As is the mock up spring Cool info.

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Welcome to the cult of JVL drink the koolaid or be banned.

Excellent information. Thank you for that work!

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Robert.

"You are way too normal to be on Rally Anarchy." Eddie Fiorelli.

THose are 14" wheels, right?

Quote
krisdahl
THose are 14" wheels, right?

Yep, they're the OEM wheels off the 96-00ish Civic HX - ~12 lbs. 14x5.5 IIRC, mayyybe 14x6 but I doubt it. (I suppose I could just run down to the garage and double check, since they're still in the back of the car from our last rallycross 4 months ago)

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KF7RWG
http://www.utahrallygroup.com

I always thought the rear droop limit was going to be the toe link running out of room and throwing off your toe settings. I wonder how much more droop you get if you replaced the trailing arm link with the spherical bits that are out there. The only bushing in the car that isn't solid rubber is that trailing arm link so getting spherical joints might give up some of the twist limiting you experience.


I still think the front is pretty good for wheel travel as is on my Civic. I know the rear is a bit less and could maybe have some more work done to remedy it but never got there.

yep, if the trailing arm bushing was free-rotating, the next limit would definitely be the compensator arm hitting the unibody.

I imagine I might be able to get a little more travel using an OTS spherical piece on the front, since I didn't loosen the bushings on that arm at all. But, it'd probably be less than you'd hope, since the stock stamped arm is offset a little to clear better, whereas all the spherical pieces aren't really offset.

What you'd really want IMO would be a slightly curved arm, like this:


Although _that_ much curve would probably be unnecessary, since you'll hit the floor of the car with the front end of the 'trailing' arm pretty quickly. (not that that would be too hard to work around).

IMO, that's all pretty easy stuff though - the real kicker is that trailing arm bushing. Since it's a 'rotate in a billion axes PLUS slide side-to-side' movement, there's no easy answer. I know there's the PCI/pwjdm bearings, but I'm still skeptical. Certainly the best bang-for-the-buck is going to be the OEM rubber, with some testing to figure out exactly where they need to be clocked to get the most travel.

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KF7RWG
http://www.utahrallygroup.com

Great info here, thanks Aaron! I have a question for you: are you running off the shelf Bilsteins, or have they been lengthened at all?

I ask because my wife has an '89 CRX that she rallycrosses. We started out with a set of DA Integra shocks with Neuspeed progressive springs that I scored from the local pick-n-pull. The setup seems just about perfect except the shocks are shot so I'm hoping to replace them with some Bilsteins. Unfortunately, Bilstein doesn't make shocks for the DA Integra for some odd reason. The front shocks are just about the same, so I just put in EF Bilstein HDs. However, the Bilstein EF rears are significantly shorter, so I can't get the droop and ride height I want with them.

I called Bilstein to get some dimensions on the different rear shocks. They told me the EF shocks are 19.27" long extended and 14.92" long compressed (measured from center of bolt hole to underside of spring perch. The dimensions they gave me on the EG shocks are 18.48" extended/16.3" compressed. So they seem to be shorter overall and have only 2.18" of travel. From what I measured, the DA shocks are approximately 20.25" extended and 14.25" compressed, so that's very attractive. Too bad Bilstein doesn't make them!

I figured I'd ask here since you seem to be the expert on Honda rallycross suspension. Any advice is appreciated.

currently, the only modifications to the Bilsteins are extra circlip grooves to put the spring perches at the right height - other than that they're completely off-the-shelf.

I thought I remembered Bret @ Bilstein telling me the EF and EG rear HDs (F4-B46-1382-H1 and B46-1605-H2 respectively) were nearly identical, but searching through my email shows nothing of the sort.

99% certain that the shocks on the back of the car have more than 2" of travel - given the .77 motion ratio, I'm quite confident I've got more than 3" of total wheel travel in back.

Maybe Bilstein gave you the numbers on the "sport" shocks, rather than the HD?

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KF7RWG
http://www.utahrallygroup.com

Thanks Aaron. I think I'll try calling Bilstein again to get clarification. 2" of travel doesn't make much sense. Maybe you're tight and it was the sport shocks.

Any reason you chose the EG rears instead of the EF?

Quote
Erik Christiansen
Thanks Aaron. I think I'll try calling Bilstein again to get clarification. 2" of travel doesn't make much sense. Maybe you're tight and it was the sport shocks.

Any reason you chose the EG rears instead of the EF?

The EGs have some internal spacing that can be removed to give another 15mm of extension - and since the intent was to be able to use these for stage rally down the line, every little bit helps!

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KF7RWG
http://www.utahrallygroup.com

Took one of the rear shocks (F4-B46-1605-H2) off over the weekend and did some measurements.

for any measurements to the Upper Spring Perch (USP), I used a washer sitting on the shaft where it transitions from polished to rough - pretty close to where the perch would actually sit.

Bolt hole to USP - 18.735"
Bolt hole to very top of shock body - 12.75"
Top of shock body to USP - 5.5"
Lower (off the shelf, I think) circlip groove to bolt hole - 8.125"
Upper (added) circlip groove to bolt hole - 8.625"
Bolt hole to bottom of spring (with circlip installed on lower groove) - 7.875"

When compressing the shock by hand, it stops with about 0.25" of the chromed rod still showing.

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KF7RWG
http://www.utahrallygroup.com