Excellant write up. Stickied [thumb]

 

That didn't take long! Thanks......

 

How do you move the pivot points on the front LCA?

 

Cut, move, then weld in new position with some re-inforcement to stiffen strucutre as much as posssible within class rules.

Nice writeup! I love hearing from people that knows what they are tallking about. Unless of course your copy and paste skills are as good as mine....
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No "cut and paste" but simply a repetition of various info from books and online articles in my own words. Like I said in the original post, this is somewhat common knowledge for those that have had enough interest to do the research, but it is an often underestimated or unexpected impact when lowering suspension.

I think most people assume lowering a car always means it will handle better, which it can, but you have to be aware of the trade offs.

I've been dealing with these tradeoffs too. my car is quite low, probably too low, but it looks good dammit.

My plan to deal with the loss of camber gain was huge static camber. I bought LCR plates to do this. I found, as you mentioned above, that i had lost too much acceleration and braking traction.

My solution was to swap the camber plates from driver to passenger (and vice versa) and rotate 270º. What this did for me was to give me enough negative camber adjustment for my needs, but also gave me appeciable castor.
So now, when i auto-x. i have good straight line accel and braking, and when i corner, the castor provides more camber than I lose through the position of the control arm.
win-win in my opinion.

I dont have any alignment printouts from this setup, because I do my alignments (mostly toe adjustments) in my driveway, and now I'm on my winter springs. So in the spring when i go back to coilovers and LCR's. i can put it on a rack and let you know.

I think LCR is making a new camber plate design for this year that provides both camber and caster adjustment, check out the LCR forum. Also there is a company called K-MAC, that offers a strut mount that offers similar advantages.

I had a friend of mine fabricate some custom plates similar to the K-MAC plates, but with a more extreme range or movement that will allow up to about 6 degress of positive caster and a good 5 degrees negative camber. Not that I expect to go that far with my alignment, but if I ever trade paint with someone on track, I wanted to have a little extra movement to offset crash damage and not have to worry about getting the strut towers back into perfect alignment.

I love the idea that this has stirred up some good dialog. Dealing with a simple mac strut suspension and trying to find the best balance of trade offs for your type of competition and driving style is not easy. This is reflected in my class rules that allow cars with mac strut suspension to reduce thier minimum weight by 50 lbs. ( I also get another 50lb credit towards min weight for FWD)

 

Sure makes a lot more sense when you explained it here. Nice.

 

Nice writeup! I love hearing from people that knows what they are tallking about. Unless of course your copy and paste skills are as good as mine....
Posted via FF Mobile

 

One other thing to note is that the body roll of a vehicle also adds positive camber to the outside tire while you are in a turn. So we have suspension compression and body roll contributing to the camber angle of the tire.

Stiffer sway bars can help to reduce this body roll impact, but the tradeoff is lift up and spin of the inside front tire on corner exit (even with a torsion style differential) from the weight transfer by the sway bars. Stiffer springs can help reduce the body roll, but you can compromise suspension motion.

Long story short, suspension modification is a constant battle of trade-offs.

 

I've been dealing with these tradeoffs too. my car is quite low, probably too low, but it looks good dammit.

My plan to deal with the loss of camber gain was huge static camber. I bought LCR plates to do this. I found, as you mentioned above, that i had lost too much acceleration and braking traction.

My solution was to swap the camber plates from driver to passenger (and vice versa) and rotate 270º. What this did for me was to give me enough negative camber adjustment for my needs, but also gave me appeciable castor.
So now, when i auto-x. i have good straight line accel and braking, and when i corner, the castor provides more camber than I lose through the position of the control arm.
win-win in my opinion.

I dont have any alignment printouts from this setup, because I do my alignments (mostly toe adjustments) in my driveway, and now I'm on my winter springs. So in the spring when i go back to coilovers and LCR's. i can put it on a rack and let you know.

 

A good, clear discussion. Well worth the sticky. Thanks, and rep given!

 

The reason MacPherson strut equipped cars have this problem is because the angle of the lower control arm relative to the chassis changes as you lower the car. Lower too far and the arm tilts the "wrong" way (up), lower on the chassis side and higher on the strut side--and the rolling of the car has a greater mechanical advantage on the strut causing it to compress the spring easier as the weight shifts to the outside. That change in geometry is what changes the roll center.

When you lower a car with MacPherson struts the roll center lowers farther/faster than the CG. So if at the stock height the roll center is, for example, 4 inches below the CG, when you lower the car 2" the CG drops 2" but the roll center drops say 6". The actual tendancy of the car to lean during cornering then increases. To counter that tendency you need MUCH larger springs. Not ordinary lowering springs in the 200-400lb range--but 500-600lb race springs.

"If you can imagine picking up a barbell with a weight on just one side---if you pick it up close to the weight it's easy to lift/handle, but if you pick it up at the opposite end of the weight (which is a great forearm workout) it becomes more difficult as you lose mechanical advantage. The length or arm length creates a greater "polar moment of inertia" (distance from roll center to Center of Gravity). So with stock geometry your CG and roll center are close together (like grabbing the bar next to the weight which requires less effort or less springrate to control the roll) but as you lower the car the roll center drops quicker than the CG creating more mechanical advantage (makes the car top heavy)/longer arm/requiring more spring rate"---like I said above, quite a bit more.

Here is a good illustration:

http://www.modified.com/tech/0508_sccp_making_it_stick_part_3/index.html

Here is a real-world example http://buildafastercar.com/tech/Roll-Centers : ...go back to the example earlier where we found that lowering a Subaru WRX STI drops the front roll center by 2.6 times as much as the chassis height (which also means 2.6 times as fast as the chassis's center of gravity). As it turns out, a one-inch lower ride height actually increases the vehicle's roll couple by about 18%, which means body roll will also increase by 18% unless firmer springs are used to resist this force. The springs would need to be 18% firmer just to maintain stock-like chassis roll numbers. Again, that's 18% just to break even!

 

^^Yeah, that's the explanation I was originally looking for, I remember reading that article a long time ago

I imagine Auto-x-zts has done a lot of study on this, trying to catch up to those spec civics in a ZX2

 

^^Yeah, that's the explanation I was originally looking for, I remember reading that article a long time ago

I imagine Auto-x-zts has done a lot of study on this, trying to catch up to those spec civics in a ZX2

We're certainly trying to reel 'em in. We're seeminly inside of 2 seconds on 60second courses right now (vs. National 2nd and 3rd in 2009).

Our car runs just-a wee-bit-past-level LCAs--but we're on 650# front springs too.

 

So, if the top of my rear tires tilt inward is that ok? is it going to put excessive wear on the tires? if so, how can i fix it?

 

that's ususally OK, but if it's too severe you will wear the inside edges.

The only way to minimize tire wear is to have a quality 4 wheel alignment.

IF you have lowered the car and need to correct camber in the rear to improve tire wear and get the alingment back into factory specs there are simple "eccentric bolts" that can be used to correct the alignment.

Check out some of the Focus part suppliers' web sites. I know FSWerks, and Central Florida Motorsports carry these bolts.

Also these bolts are also available from many autoparts stores, and they are also referred to as "crash bolts" by garages and bodyshops etc since they will allow corrections to alignment when there is very mild frame damage and they just want to get the car to align and drive correctly.

 

Tb1999 this is good stuff, I'm going through this in school (I go to a tech school) and your spot on with everything. It makes it alot simpler to adjust your alignment with a lowered car and the effects of it. Added some rep points for this useful information.

I'll keep this in mind for dropping my focus, though I'm thinking of just going from a ZX3 to an SVT setup for daily driving. Though the h&r cup kit looks sooooo nice

 

So, it sounds like on tight tracks, you need less camber so you can get more bite off the corners & use more brake. And on bigger tracks w/ more momentum ,you can use more camber. I really enjoy these kinds of write-ups, awesome!

 

I believe it's just the opposite. On tight couses more camber is OK. On long fast courses reduced camber because you want lots of tire on the pavement for straight line stability. It's better to tune with spring and sway bar stiffness than relying on camber alone.

 

the one other major influence on making a descison on chassis set-up is that you always want to optimize for faster corner exit/accel vs corner entry/braking. The reason being, is that you are only braking for a very short time, carrying an extra MPH or 2 into the corner only lasts for a brief moment, but if your corner exit speeds are 2 MPH faster, then you will be close to 2 mph faster for the entire distance of the track before the next turn.

That's why it's always a better investment to install the best shocks/springs and a limited slip diff, rather than investing in a big brake kit. ( at least with cars in our general HP/top speed ranges)

the only time you need to install bigger brakes, is if you get brake fade due to over heating, or can't generate enough stopping power to lock up the brakes at the top end.

I carefully calculated my car's braking needs using Fred Puhn's "Brake Handbook" . The stock 11" rotors are pretty much good for stops from 135 > 60 provided you are using race componds on the pads and there is proper brake cooling.

 

I second picking up "Tune to Win" excellent guide to every thing racing, even for FWD guys like ourselfs.

 

I third that motion.......all of Carroll Smith's ".....to Win" books (there are several) are helpful in preparing and driving any performance car. They're mandatory reading for those aspiring to be a car builder, driver and just understanding vehicle dynamics.

 

Effects of lowering on suspension geometry

TB 199 is absolutely correct about the adverse effect that lowering can have on front suspension geometery. However, in addition to camber, lowering also severly effects toe in and toe out. When the car is lowered, the steering rack ends up lowered also, but the steering knuckle stays at the same height it was before the car was lowered. Because the tie rod connects the outer end of the rack with the steering arm on the knuckle, the inner tie rod pivot ends up lower than the outer tie rod pivot. Now, as the suspension compresses under braking, the tie rod pulls the steering arm in toward the center line of the car, and when the usupension expands under acceration or over a bump, the tie rod pushes the steering arm outward. Because the rack on a Focus is mounted behind the front axle centerline (called "rear steer"), this results in unwanted excessive toe out during braking, and excessive unwanted toe in during acceration. The technical term for the unwanted changes in toe is called "bump steer." To regain correct toe, the rack or the rack end of the tie rod must be raised, or the steering knucle end must be lowered, by the amount the car was lowered.
Actually, the only way to check toe completely is to remove the front springs, reinstall the strut, clamp a flat plate onto either the tire or the front hub or brake disc, line up two dial indicators at the height of the front spindle, with the indicators spaced apart equal to the tire diameter, one in front of the spindle one half the distance of the tire diameter and the other the same distance in back of the spindle. Then with a jack under the suspension, raise and lower the suspension from standing right height and measure the changes in toe that shows up on the dial indicators. Usually two to three inches up and two to three inches down covers most normal suspension movement. Raise the rack or inner tei rod pivot or lower the outer tie rod pivot until the dial indicators show the least amount of toe change during suspension travel. Ideally, toe change should be as little as possible, such as under .010 on a race car, somewhat more on a street car. Lowereing the car also effects caster, because the bottom of the strut usually ends up farther forward in relation to the top of the strut after the car is lowered. This reults in increased negative caster, but as long as the increase is not excessive, slightly more caster helps keep the car steering straingt ahead, although steering effeort may be slightly increased. Excessive caster causes one side of the front suspension to actually raise the car up higher during cornering, which is not good.

 

Reading all this a few years after the original post, but still great stuff!! Thanks for the post! Suspension is indeed a huge compromise game! At least we've got independent rear suspension to work with now. On my '82 Mercury Capri RS 5.0 I had to deal with all this and a live rear axle too! Impossible to hook up! Yikes!!

 

Fresh "Stickie" status to get more looks.

Lots of good info. to think on here!

 

I've been away from this forum for so long, its great to see a discussion this old still getting respect as a stickie, and all the great comments from others adding to the discussion. So much is discussed about engine building and bolt on mods, its great to see some hardcore suspension junkies on here...

 

This^^^^[thumb]

 

felix. if i searched "this^^" what would come up?

 

You'd probably find more about foxbody/sn95 Mustangs,,,,Lowering a Mustang any big degree & you'll want to use Steeda X2 ball joints w/ a Steeda or Baer bumpsteer kit & then you'll need a bbk as they wouldn't work w/ stock brakes unless your starting out w/ big brakes to begin with or a Cobra/mach1,,,,,,,,,,,,,[thumb] Lots of work to make a Mustang corner vs gen3 Camaro's,,,,,,,,,[thumb] Get me started w/ Mustangs= I've got you covered,,,,,,,,,,,,

 

come work at the dealer. we need a guy who knows mustangs in service. we sell shelbys all the time

 

Ha, I've worked at dealers for yrs. Last time was over 10+ at a Ford bodyshop. Have fun installing long tubes on a Shelby gt500 & I have no idea why some of them want to swap out the dual disc clutch for a single disc.

 

Oh man, I need to get that book now

Sent from a man with a broken focus

 

Lots of cool suspension/brake books,,,,,,,,,,

 

I want to install coilovers, after installation will answer)

 

Got to say= Don't cheap out on suspension.....K/W, Bilstein, H&R are the major players...