Suspension adjustments and how they affect handling

par4bmw

Thanks so much for the post. I have never had a chance to track yet and look forward to it with my Z. Useful stuff to start diving in with.

ZAtLeast

Great post!

JoeyD

In a typical turn/vehicle if you release the wheel it begins to re-center its self. If I remember correctly the rate at which the wheel returns to center is a result of caster. (correct me if I'm wrong). I have noticed at low speed and high degrees of turn the wheel actually fights me to turn further in to the turn. Any thoughts?

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M.Bonanni

Yes, you are correct. Positive caster will help the wheel re-center itself.

As far as the turning thing, this could also be a result of caster or maybe even a little toe out. The more negative caster you have, the more the wheels will want to turn around on themselves when turning. Again think of a shopping cart wheel. If you were to turn one backwards then start pushing the cart forwards, the wheel will instantly flip back around to normal position. When you have negative caster, this is what your wheels want to do, but obviously they can't.

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Black kNight

thanks DD
very useful thread
i learned alot of things

Supergoji

figured i'd post this because everyone with a performance suspension and anyone who does spirited driving should know about this.

To Increase Understeer (reduce oversteer)

Stiffen: front springs, front compression damping, rear rebound damping
Soften: rear springs, rear compression damping, front rebound damping

to increase oversteer (redunce understeer)

Soften: front springs, front compression damping, rear rebound damping
Stiffen: rear springs, rear compression damping, front rebound damping



adjustment points
Bump: This controls the stiffness of a shock relating to compression. Sounds just like a spring, and it pretty much is. The difference being that while a spring's stiffness always has the job of holding up your car, the shock's bump setting only acts on temporary forces likes bumps and roll. Adding more bump will act very much like stiffening the spring on the same corner.

Rebound: This controls how quickly the spring descends after compression. This is a VERY important setting when tracking a car. Without enough rebound a spring will hop and skip along the ground, making it hard to put down power, braking or cornering force. If you have too much rebound, the spring will not be allowed to expand quickly enough to return to its proper ride height before the next input. Too much of this will lead to "jacking down", which is a term for when a vehicle lowers itself until it is riding on it's bump stops (hard rubber, used as a last-ditch safety feature to keep tires from rubbing on very hard bumps). You can use rebound to control roll. By increasing rebound you decrease the velocity of the spring's expansion. If the spring cannot expand, it cannot push that side of the vehicle up. So the vehicle must either not roll as much, or lift its inside tire. Obviously you don't want to set so much rebound as to end up with the latter.

Sway bar settings: Increasing a sway bar's stiffness will reduce roll, but also increases the sprung tension on that axle. Granted, most of the increase in tension is apparent only when there is body roll - but even statically there is an increase. This means you must modify your rebound settings when you change your sway bar settings (just as you must whenever you add spring tension).

Camber: This is a tire's difference from vertical when looked at from head-on. + means the bottom of the tire is in more than the top. - means the bottom is out more than the top. Remember, this setting is only accurate when the car is NOT moving. As the wheel moves with the suspension, the camber will change depending on the geometry of the suspension. What is important is observing how the tire wears, and by taking tire temperature readings on the outside, center and inside to make sure that all of the tire is being used when it is at full load.

Castor: This is the difference between a wheel's centerline and the axis of suspension travel on that corner when viewed from the side. This is rarely adjusted on a street car. The more forward the wheel's centerline relative to the suspension's axis, the better the car will soak up bumps. And the more it will nosedive when you hit the brakes. The reverse is also true.

Toe: This is the difference between the direction a tire is pointing and straight ahead, when looking down from above. + means the tire points in. - means the tire points out. Positive toe makes a car more stable. This is useful at higher speeds and for general steering comfort. Negative toe makes a car more darty. This is useful to initiate quick directional changes, but can also reduce your total level of grip with excessive tire scrub (more on that later).




Options
Reduce understeer:
-Enter turns slower! Then power out.
-Reduce front tire pressure, and/or increase rear tire pressure.
-Reduce front spring tension, and/or increase rear spring tension. This can be done by swapping springs, or by changing sway bar settings/diameters.
-Reduce front bump, and/or increase rear bump.
-Reduce rear camber, and/or increase front camber.

Reduce oversteer:
-Do the opposite of the above "reduce understeer" options.

Reduce roll:
-Increase tire pressure all around.
-Increase bump settings.
-Increase rebound settings.
-Swap springs for stiffer ones.
-Increase sway bar settings/diameters.

Increasing traction for applying power:
-Reduce rear tire pressure.
-Reduce rear spring tension.
-Reduce rear bump.
-Increase rear rebound.
-Reduce rear sway bar settings/diameters.



Increase braking traction
-Reduce tire pressures.
-Increase front spring tension.
-Increase front bump.
-Reduce rear rebound.
-Reduce all sway bar settings/diameters.

Bluemeanie

Don't forget that the type of tire you are running will influence your adjustments such as street tires vs. slicks

jeffreyfranz

Yes. Super effort. Thank you.

Jquad

+rep

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Endgame

O.K. I am still not grasping the effect of sways on my driving experience.

I currently only have coilovers (Stance GR+) on my Z. What type of effect could sways add?

I would be all for better turn in and even less body roll, but would be adverse to upsetting the balance of the car which could cause the rear end to kick out more easily.

What are the pros and cons to adding sways. And, does anyone know if my Amuse single exhaust would interfere with installation?

BGTV8

I have had a useful guide I have carried around for many years .. it is a little handbook authored by Carroll Smith called "Engineer in your pocket" which has the ISBN 978-0965160018 and is available via Amazon.

I also have a cheat-sheet which I have attached which is a short-hand helper - which I have attached ....

RB

Attached Files

THE370 SetUp Tips.pdf (94.5 KB, 265 views)

Endgame

Thx! I just glanced over it, but it looks to be a great guide! I think I want to go with Sways, but I am looking for impressions from members to see if they felt it caused the Z to increase oversteer to the point where it was scary in the twisties or difficult to drive.

Per this guide, with the more noseheavy Zs, and my even wider than stock rear tires, I would think I should be o.k. (came up with that really quickly using your guide; in fact rep points for you).

thispecialk

hey if u get coilovers r u required to buy camber kit and for springs which springs can go without camberkit

djpathfinder

Camber kits are only required if you are not able to bring the camber settings back to recommended range as specified by the manufacturer or a custom race setting (personal preference) with the OEM components. The 370Z does not have any adjustment capabilities up front in the upper control arm for camber. When you lower a vehicle on springs or coilovers it will add negative camber. With an alignment you are trying to bring the camber back to spec, or reduce the amount of negative camber created.

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Mt Tam I am

I went with sways first, then coil overs. Sways took 3-4 days to get used to responsiveness. Reduced roll like you can't believe. The roads have been wet since I put on coil overs. Today was the first chance to get on it and I did notice the rear wanting to go but just letting go, of the gas for a split second corrected it. I may need to adjust things. It was a fast and confident ride home. I noticed a better ride with the KW's. Especially on the rougher sections of road.

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