Fit/CRZ suspension design

[BlackNDecker]

I'm including the Fit in this discussion because the cars are virtually identical (same subframe, same axles/half shaft, same torsion beam rear suspension, same rear shocks, etc). The CRZ has aluminum front LCAs and different part numbers for the some of the components of the front shocks (different bump stops, different springs)....but that is about it.

A little background:
Honda adopted the McPherson front strut starting with the 7th gen civic (2001-2005), RSX (2001-2006), and EP3 (2002-2006 civic Si) and has carried the design forward with minor changes through to the current civic, TSX, and now the CRZ and Fit.

I have copied and pasted the following from a thread Mustclime created on clubep3.com. This is quite possibly the best info on tuning the McPherson strut font suspension. (source: EP3/DC5 suspension design - Club EP3 Message Board)
The following is a look at how to "tune" the ep3/dc5 suspension from a design point of view. First I would like you to really look at the front suspnsion......

Originally Posted by mustclime

First, look at the top pic, that is looking at the stock suspension from the rear. You will notice the LCA is angled down from center of the car. The tie rod is angled up from the center of the car. The suspension design is greatly effected by ride hight . What does that mean? Well, look at the top pic again. As you lower the the suspension the LCA goes flat and then past one inch of drop it starts to angle up. This is very bad for the suspension when you look at side loads( cornering forces). If the LCA is angled up and the weight of the car pushing side ways while the tire is trying to stick to the road, this force will "tend" to push the LCA up more and cause the suspension to blow through its travel. If the LCA is flat or angled down, the cornering loads are directed down the LCA in to the sub frame.

Cliff notes: LCA angled up from the center of the car = you blow through your suspension travel and get lots of under steer. So do not lower the car more than one inch.

Next issue to look at with the top pic is camber......Camber is a term used to describe what angle the tire is set at with regard to the road. In stock form, camber is not adjustable and the stock suspension is set for about zero degrees camber. This is great for drag racing and making tires last for 60,000 miles but it sucks for generating grip in turns. Having a couple degrees of negative camber helps the outside tire to take a set and helps keep the tire tread on the road surface. There are 3 ways to get more camber in a ep3/dc5.
1) Camber plates, these angle in the top of the strut and as a result angle the tire.
2) Crash bolts, these mount where the strut and the bearing carrier connect. This allows you to angle in the bearing carrier and allows you to angle in the tire inward.
3) Type-r LCA, these are wider than stock and as a result angle the tire inward. WARNING! If you decide to use these, you should not use your stock axles and you will need type-r front sways because of the extra width of the LCA.

What is the best camber setting for the front suspension? It depends on what you are doing and what tires you are using. As a general rule I would say -1 to -1.5 degrees for dd and about -3 for the autoX guys.

Cliff notes: Negative camber good for cornering in the front suspension.

Now look at the lower pic, the first thing I want to to look at is the front bushing on the LCA. That bushing is there to change toe settings as the cornering loads increase. It adds toe in as the gee forces go up, this = increasing under steer! Anyone that is trying to get our cars to handle needs to replace this bushing asap. Both Mugen and Energy Suspension make kits for this.

Cliff notes: The front bushing in the LCA needs to be replaced to make our cars handle.

Now I want to address the Caster angle of our suspension in the front. If you look at bottom pic you will notice the strut is almost strait up and down. The stock caster angle is around 1.5 degrees.....this sucks for handling and strait line tracking. If Honda screwed up anything with our cars suspension, this is the biggest thing. It is also the hardest to fix but it can be fixed. K-Mac makes a Camber/Caster plate for this. The strut towner's can also be re-drilled to angle the strut back. For road racing there are bushings for the LCA that shift the LCA forward to angle the strut back.

Cliff notes Caster good but hard to get.

Now the rear suspension:

While the 8th gen civic and TSX were blessed with a multi-link rear suspension, the RSX and 7th gen civic suffered from a dual control arm rear suspension that truly hampered these cars handling potential. The situation is much worse with the CRZ and Fit...Honda adopted a torsion beam rear suspension. Basically limiting rear suspension options to ultra-stiff springs and a sway bar.

Know your enemy:


I'm hoping this helps generate some technical discussion of the CRZ/Fit suspension design.

[BlackNDecker]

So how/when do roll center adjusters (RCAs) help?

Here is some good info to illustrate the difference/benefit/cause/effect of lower your car, steering geometry etc etc...(originally posted by speedstar808 on clubrsx.com)

Due to the massive lowering, the angles of the suspension geometries are no longer optimum. Take a look at the below picture which shows the arms and tie-rods angled upwards. A Bumpsteer Kit (reverse tie rods) and a set of Roll Center Adjusters (RCA) should fix this problem.




What is Bumpsteer? A bit of an explanation: Bump steer on the front wheels is illustrated in the diagram below, and it can be seen that it is caused by unequal angles between the steering tie rod and the lower arm. Depending on the difference in the angles, the wheel will either exhibit toe in or toe out on bump.
Lowering a car changes the angles between the lower arm and the steering tie rod, this in turn increases the bumpsteer on the front wheels, hence the benefits of a lower mass center is not seen because of the bumpsteer.





Why use Roll Center Adjusters? Refer to the diagram below: At standard ride height, the roll center is set by the angle of the arms and the roll center is an imaginary point where their lines would intersect. Ride & Handling guru John Miles advises that roll center is set between 40mm - 60mm above the ground for stability, and from this baseline the handling geometries can be set.




When you lower a vehicle, the wheels "move up" into the body and the angle of the arms is no longer optimum, in some severe cases they push the roll center low down below ground level. This would result in more roll than standard therefore the benefits of lowering the vehicle would not be realized. This is why you may read in some magazines and documents why lowering a standard car too much without geometry change is actually dangerous and adversely affect handling.

[BlackNDecker]

BTW, the Moonface front RCAs for the CRZ are an astronomical rip-off...I don't know where they get off charging $900 for these. Buddy Club and Js Racing sell them for around $250 (unfortunately nothing released for the Fit/CRZ yet).

[human668]

Originally Posted by BlackNDecker

Honda adopted the McPherson front strut starting with the 7th gen civic (2001-2005), RSX (2001-2006), and EP3 (2002-2006 civic Si) and has carried the design forward with minor changes through to the current civic, TSX, and now the CRZ and Fit.

No, TSX doesn't have McPherson front strut.

[BlackNDecker]

Thanks for the correction...the TSX is doubly blessed with double wishbone up front and multilink in the rear.

[roddy]

there's this for the fit. i've asked ben from ajr to see if he could import this, even though its stupid expensive.

maybe it'll transfer over to cr-z?

‚f‚dƒtƒBƒbƒgƒŠƒ„ƒAƒNƒXƒ‹

[northbridge]

Originally Posted by BlackNDecker

BTW, the Moonface front RCAs for the CRZ are an astronomical rip-off...I don't know where they get off charging $900 for these. Buddy Club and Js Racing sell them for around $250 (unfortunately nothing released for the Fit/CRZ yet).

thanks for all the information. i was going to put on a set of coilovers and call it a day. my TSX was much simpler in terms of suspension mods. I did think the moonface parts were a bit expensive as Spoon also makes roll center adjusters for the CL9.

Have you lowered your fit? what did you do about this? My next purchase is coilovers, i dont want to lower the car and end up with problems though so id like to get all the parts first.

[BlackNDecker]

Originally Posted by roddy

there's this for the fit. i've asked ben from ajr to see if he could import this, even though its stupid expensive.

maybe it'll transfer over to cr-z?

‚f‚dƒtƒBƒbƒgƒŠƒ„ƒAƒNƒXƒ‹

Are you referring to the rear axle...I don't see how this will solve the problem of unstable handling from lowering the car? The problem can't be fixed by adding camber...roll center adjusters and inverted tie rod ends (but only for extremely lowered cars) can serve as a mediocre band-aid for cars lowered beyond 1.5".

Unless you're asking if it will fit, then I'm not sure...the part #s are different for the CRZ and Fit rear axles, but I would be shocked if they weren't swappable. I wonder if the CRZ's rear axle is lighter or has a different offset:
CRZ:
Cart Contents Honda Parts at HondaPartsDeals.com: Honda Accessory, Honda Car Parts, Honda Auto Parts, Honda Accord Parts[ProductID]=CR-Z&Label[YearID]=2011&Label[DoorID]=3&Label[GradeID]=BASE&Label[AreaID]=KA&Label[TransmissionID]=6MT&Label[SectionID]=CHASSIS&Label[IllustrationGroupID]=REAR+AXLE&ProductID=28&YearID=42&DoorID=2&GradeID =21&AreaID=2&TransmissionID=8&SectionID=6&Illustra tionGroupID=18794

FIT:
Cart Contents Honda Parts at HondaPartsDeals.com: Honda Accessory, Honda Car Parts, Honda Auto Parts, Honda Accord Parts[ProductID]=CR-Z&Label[YearID]=2011&Label[DoorID]=3&Label[GradeID]=BASE&Label[AreaID]=KA&Label[TransmissionID]=6MT&Label[SectionID]=CHASSIS&Label[IllustrationGroupID]=REAR+AXLE&ProductID=28&YearID=42&DoorID=2&GradeID =21&AreaID=2&TransmissionID=8&SectionID=6&Illustra tionGroupID=18794


I think the only decent solution for the rear would be to work a damper into the shock that allows for more travel or figure out a way to lower the rear roll center...I'm not sure how this would be accomplished with a rear torsion beam sussy.

[BlackNDecker]

Originally Posted by northbridge

thanks for all the information. i was going to put on a set of coilovers and call it a day. my TSX was much simpler in terms of suspension mods. I did think the moonface parts were a bit expensive as Spoon also makes roll center adjusters for the CL9.

Let me be clear, I'm not a suspension expert...just trying to learn more myself. These are posts that I have found helpful.

Originally Posted by northbridge

Have you lowered your fit? what did you do about this? My next purchase is coilovers, i dont want to lower the car and end up with problems though so id like to get all the parts first.

My car is lowered minimally on Progress springs. Something like 0.8" front and rear...1" is probably as low as you'd want to go before negatively impacting handling...but it really depends on the angle of the front lower control arms as I mentioned above.

Here are some pics of my drop...people complain about the wheel gap but it doesn't bother me. I went the lightest tire and wheel combo I could find...Enkei RPF1s and Toyo Proxes4 UHP tires.












And one of my favorite Fits evah...mmmm J's racing bumper

[roddy]

i just want that rear part to be able to adjust camber.

blackndecker, from fitfreak right? sn looks familiar