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Discussion Starter #1
This subject came up in my D23 race engine build thread, so I needed to spin-off this subject to the suspension forum!

While I'm waiting to get my hands on the valve seat cutting tools from a friend, and the block is still out at the machine shop, we might as well cover this whole suspension drop issues and how it impacts the suspension geometry. There are tons of books and internet references to this, but I'll take a stab at it on my own here.....

Here's why lowering a Focus (or any car)can "tamper" with the suspension geometery, and specifically its impact on camber.

FYI -

Camber is the tilt of the top of the tire as viewed from above, tilt the top outwards for positive camber, tilt the top inwards, you have negative camber.
Camber "gain" is the change created in this angle as the suspension moves through it's range motion. If the top of the tire angles outwards as the suspension compresses, this is "positive camber gain", and when the top of the tire angles inwards, this is "negative camber gain".


Ususually you want to have a "negative camber gain" as the vehicle rolls onto the outer wheels and compresses the suspension, to help offset the body roll and keep the tire sitting a flat as possible.

if the LCA on a mac strut car is angled down when static, (like it is on our Foci) as the car turns, rolls and compresses the suspension, the LCA swings through an arc that moves the Lower Ball joint a small distance in the outwards direction. This changes the angle of the strut/spindle/wheel increasing Negative Camber. (I.E. Negative Camber Gain)

If you drop the suspension so the LCA sits horizontal when static, as the car turns, rolls and compresses the suspension the LCA will continue to swing through it's arc. But it is now moving the ball joint inwards as the arc is curving up and inwards away from its static horizontal position. As the ball joint is moving towards the center, so is the lower portion of the tire. This causes the top of the tire to angle away from the car producing "positive camber gain" making it more difficult to keep the tire flat on the track.

as wrc_fan suggests, most drivers will never worry about the little differences with these dynamic angles etc, but on the track or autocross its as important as having a few points more of horsepower.

While you can just crank up the static camber to an extreme negative number to keep the tires flat on turns, this dramatically reduces your braking abilities, and can make it difficult to keep tire temps where you want them. It also affects your ability to put power down mid corner becuse the inside tire is just touching on a small area on the inside edges of the tread.

Our simple single LCA and strut design of the front suspension does not offer any "tricks" of geometry provided by more advanced multi-link front suspension like seen on honda, acura, BMW, and countless other cars that have moved on from a simple strut design. So the best you can do (when allowed by the racing class) is raise the inner pivot points to set the LCA in a slight "droop" condition when sitting at static ride height. This helps recover that little camber gain effect as the suspension rolls and compresses the suspension so the LCA is horizontal when the turn/roll/compression is at it's peak, and you get the most camber gain possible.

This allows a milder static camber adjustment, producing better braking effectiveness/stability, and a bit more rubber in contact with the track on the inboad wheels to help power out of a turn.

And all of these benefits help keep tire temps more uniform etc.
 

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slow
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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.
 

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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.
 

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

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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!
 

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

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

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

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.
 

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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?
 

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Discussion Starter #14
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)
 

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Discussion Starter #15
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.
 

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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.
thanks tb. Yeah, i just bought the car for my son and don't know alot about it yet. we just replaced the tires and the inside of one was pretty worn. then i noticed the back wheel alignment.

How can i know if it's been lowered? Its sitting on 18" rims so im guessing no but how can i tell? sorry for all the dumb questions, but i'm totally new to this![???:)]
 

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Discussion Starter #17
thanks tb. Yeah, i just bought the car for my son and don't know alot about it yet. we just replaced the tires and the inside of one was pretty worn. then i noticed the back wheel alignment.

How can i know if it's been lowered? Its sitting on 18" rims so im guessing no but how can i tell? sorry for all the dumb questions, but i'm totally new to this![???:)]
If you can measure the distance from the center of the rim, to the fender lip that will provide an estimate of the drop on your car.

You'll need to compare it to a stock vehicle that has not started sagging to get an idea of how far your suspension has been dropped.

You can also measure from the pinch weld below the rocker to the ground.

Maybe someone here on the forum with access to a car at stock ride height can provide some baseline numbers for you.

Just keep in mind that when you go for an alignment, you still want to have the stock alignment angles to get the best wear even with different size rims and the lower ride height.

Unless you are going racing, or want to run autocross etc, keep the alignment stock. You will problably need camber bolts in the rear, and some sort of camber plates on the front struts to make this happen after the car was lowered. A good repair shop will work with you on that, there is no reason why you can't get decent tire wear on a vehicle with a lowered suspension if you get the alignment done correctly.

I'm not sure where you live, but IMHO if you have bad roads/potholes, the 18 inch rims are going to be a constant source of grief, and prone to rim/tire damage, and possibly knocking you alignment out more frequenlty.
 

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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
 

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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!
 

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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.
 
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