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Old 02-11-2011, 09:24 AM   #21
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Originally Posted by felixthecat View Post
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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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.
I agree with both, it just depends on the overall dynamics of the vehicle. Chassis tuning / design is always a compromise, there is no perfect set-up and driving style is an important part of the set-up considerations.

Chassis set-up is definitely a black art, and for most amatuer racers, the most significant points to focus on are......

Does the car remain stable under heavy braking?

Can you trail brake with confidence to improve weight transfer and induce vehicle rotation?

Can you use the entire track effectively, IE, turn in, hit apex, track out without making constant corrections?
You should be able to turn in to a set sterring angle, and hit your apex and track out with minimal steering correction if any at all.
IS the car balanced under steady state cornering? IE no bobbing, pitching, rolling etc

Is the car stable on corner exit/under acceleration?

Unless you are running with the pros' looking for a 10th of a second per lap, having an overall balanced set up is all that's needed to have a competitive vehicle, the rest is just driver skills and consistency. (brass balls help too!)

When trying to resolve handling issues and troubleshoot what needs to be corrected, ( sometimes it's just the driver, not the car) Carroll Smith's "Engineer In Your Pocket" is going to get you sorted out 95% of the time.

If you are serious about getting your car set up for track events, this will be a big help. If you need more in depth technical reference for chassis dynamics I recommend his book, "Tune To Win".

Remember there is no PERFECT set-up, however driving style and set-up must match.

My sway bars are somewhat stiff, (the largest made for the focus) but springs are a touch on the soft side since I like to tag the curbing alot. You always have to be looking far ahead of where you are, focusing on where you are going to be 5 seconds from now. Tagging the curbs is my way of knowing where the edge of the track is, without drawing my visual focus to the front of my car. When i'm really dialed in and driving my best, I can run curb to curb with confidence on all but the most difficult corners.
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Last edited by tb1999; 02-11-2011 at 10:57 AM. Reason: sp
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Old 02-11-2011, 11:08 AM   #22
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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.
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Old 02-11-2011, 12:28 PM   #23
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I second picking up "Tune to Win" excellent guide to every thing racing, even for FWD guys like ourselfs.
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Old 02-11-2011, 12:53 PM   #24
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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.
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Old 07-28-2012, 03:10 PM   #25
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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.
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Old 10-01-2015, 10:27 AM   #26
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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!!
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Old 10-01-2015, 10:40 AM   #27
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Fresh "Stickie" status to get more looks.

Lots of good info. to think on here!
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Old 08-20-2016, 04:53 PM   #28
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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...
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Old 08-20-2016, 08:11 PM   #29
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Quote:
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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^^^^
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Old 08-22-2016, 06:56 PM   #30
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felix. if i searched "this^^" what would come up?
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