Suspension adjustments and how they affect handling
 

Double Down Motorsports has a lot of track experience, especially in production based cars, and even more specifically in Nissan's 350Z. I thought it would be good to pass some general suspension tuning knowledge along to my fellow Z enthusiasts.

Lets start by going over the different adjustable parts of suspension systems and their function.

Ride Height: Lowering a car's ride height, lowers its center of gravity resulting in less body roll and better handling. Beware though, because lowering your car also changes its alignment specs. Lowering your car will affect the amount of camber on your tires. Lowering your car can also affect toe, which can be very dangerous if not set properly.

Dampening: Most aftermarket coilovers are dampening adjustable. There are two basic types of dampening adjustments, compression and rebound. Then further into that is high and low speed compression/rebound. Compression adjusts the rate that your dampers (aka shocks) compress themselves, or basically the rate they soak up bumps in the road. Rebound is the opposite. It adjusts the rate your dampers rebound from being compressed. The best example I can think of off the top of my head is a memory foam matress. You put your hand in it and when you remove it, it slowly goes back to its original state. That would be a much exagerated version of a really slow suspension rebound.

Spring Rates: Spring rates can either be linear or progressive. Linear spring rates remain the same as they are compressed. Progressive spring rates get progressively stiffer as it compresses. Linear springs are better for performance, while progressive springs offer a better ride quality.

Camber: Camber is defined as the angle of the tire in relation to the road surface. When looking at the front of the car, if the top of the wheel is inward more than the bottom of the wheel, that is negative camber. If the top of the wheel sticks out farther than the bottom, that is positive camber. Camber adjustments are dialed in to achieve even tire wear for the type of driving you are doing.

http://z.about.com/d/autorepair/1/5/l/6/-/-/camber.jpg

Caster: Caster is like a shopping cart wheel. The wheel is forward or behind the lower ball joint. Positive caster is when the wheel sits behind the lower ball joint point (like when you are pushing a shopping cart normal). Negative caster is the opposite (like if you were to turn a shopping cart wheel backwards). Caster affects stability at speed and steering response.

http://z.about.com/d/autorepair/1/5/m/6/-/-/caster.jpg

Toe: Toe is how the wheels are pointed in relation to eachother and are measured sepearate front and rear. Zero toe means that the two front or rear wheels are perfectly parallel to each other and are facing perfectly forward. Toe in, is like someone who is pidgeon toed. The front of both wheels point in towards each other instead of pointing directly ahead. Toe out, is the opposite. Toe can affect tire wear, how the car rotates in a turn, and on the front wheels, it can affect how the car turns into a corner.

http://www.dunlop.ca/img/care/toe_in.gif

Sway Bars (or anti-roll bars): Sway bars are desingned to combat body roll by transferring force to either side of the car in a turn. It is basically a device that helps with weight transfer while turning.

Tire Pressure: Tire pressure can have an effect on the handling of your car by adjusting the tire's contact patch.

Now lets get into some handling dynamics and how these parts can cause or cure them.

The handling of a vehicle is all about weight transfer. Controlling the amount of weight transfer to specific tires is essentially what suspension tuning is all about.

Ride Height: Ride height can affect many other handling dynamics. If your car is too low, it can result in too much camber gain. The camber changes as your coilovers compress. Remember the lower your car the more negative camber. This theory, depending on the suspension geometry of your car can multiply on itself the lower your car is. For example, a car with stock ride height might gain -1 degree negative camber in a turn. A car which is lowered already might gain -2.5 degrees in a turn. So there is a point where you can be too low. Rake can also play havoc on your aerodynamics. If your car is higher in the front than in the rear, your car essentially becomes a wind catcher at speed causing lift and ultimately dramatically less grip.

Dampening: Compression and rebound are a main staple in handling and is constantly being adjusted on race cars. The ideal setup is a coilover system that can move along with the undulations in the road without upsetting the weight balance of the chassis. You can also use it to dial in or out understeer/oversteer. For example, if you are experiencing understeer softening the front dampening and/or stiffening the rear dampening can help dial that out. The opposite is true for oversteer. There is a trade off though. The softer you go, the more body roll is experienced, but the better your car absorbs undulations and bumps in the track.

Spring Rates: Spring rates are not something that is easily changed at the track for most. Spring rates can also change the handling dynamic of your car. The front to rear split of your springs can also aide in how a car rotates through turns. If you have too much spring in the rear, it will result in oversteer. Too much spring in the front and it will result in understeer. It is also very important that your dampers are valved correctly for your spring rates.

Camber: Camber is adjusted to help keep maximum contact patch on the ground resulting in maximum grip. Drag racers should run 0 camber in the rear to maximize contact patch in a straight line resulting in the most forward grip. Road racers on the other hand have to adjust for lateral as well as forward grip. This is when negative camber comes into play. Negative camber helps maximize contact patch when turning yeilding in higher corner speeds. The trade off is less contact patch for forward acceleration when driving in a straight line. The most accurate way to tell if you have the right camber settings is by taking tire temperatures on the outside, middle, and inside of each tire while they are still hot from a lap around the track. Taking tire temperatures can also help you determine weather or not you are running the correct tire pressure.

Caster: It is rare to find caster adjustment in a car or even aftermarket setups. The problem you don't want to run into is having too much negative caster. Negative caster is very unstable at high speeds. It also amplifies steering wheel input to a point where it is not helping your turn in. Think of a shopping wheel cart again. If you were to turn the wheel backwards, then start pushing the cart, that wheel will immediately flip back to the regular position of positive caster. That is essentially what your car wheel will do in a negative caster situation, except without the ability to be able to actually flip around into positive camber. You can also have issues if you are running too much positive caster. Caster also affects camber gain when turning the wheels. Although you won't have any stability issues at speed, too much positive caster will result in too much camber gain and less overall grip.

Toe: Toe is one of those things that minute adjustments can completely change the characteristics of the car. Toe out in the front can help the car turn in crisper. Toe out in the rear can help the car rotate through the turns better. Toe in, can help keep stabilize a car that may have worn out bushings. There is a fine line though before toe settings can become dangerous. Too much toe out and your car can become virtually un-controllable. Generally speaking, you want to keep your toe at 0. Sometimes front or all wheel drive cars can benefit from a tad toe out to get the car to rotate. If you are drag racing, you will want nothing other than 0 toe.

Sway Bars: Sway bars are sometimes adjustable and can be used to help dial in or out understeer/oversteer without affecting dampening or alignment settings. Stiffening the bar in the rear will help dial in oversteer, while softening it will help dial it out. The same goes for dialing in/out understeer in the front. The sway bars are probably the simplest part of suspension adjustment.

Tire Pressure: Tire pressure can be used for fine tuning a car's handling characteristics. Again though, there is a fine line. If you are suffering from mild oversteer, lowering the rear tire pressure can help. The same goes from understeer and front tire pressure. The opposite is also true that if you are suffering from oversteer, adding tire pressure to the front can help, and if you are suffering from understeer, adding pressure to the rear can help. There is a catch though. If you are running too much or too little tire pressure, your tire's contact patch will shrink. Too much tire pressure and the middle of the tire starts ballooning, too little and the middle of the tire starts caving in.

http://www.myautocafe.com/uploads/pi...rinflation.jpghttp://www.myautocafe.com/uploads/pi...y_Inflated.jpghttp://www.myautocafe.com/uploads/pi...rinflation.jpg

Now I will give some sample suspension and alignment settings for different types of driving. Bear in mind these are only examples or starting points. Every car and driver is different and when it comes to fine tuning suspension, it is a never ending battle as so many things can affect it.

Ride Height:
Road Racing - As low as you can go while still running ideal alignment settings and avoiding too much camber gain and/or not enough ground clearance.
Drag Racing - Same as Road Racing, although probably won't be able to go quite as low.
Street Driving - Same as above, with ground clearance being the main concern.

Dampening:
Road Racing - Depends on the track and handling characteristics of the car.
Drag Racing - Generally softer in the back and stiffer up front to help the car squat. (RWD Cars)
Street Driving - Most will want full soft for comfort reasons.

Spring Rates:
Road Racing - Linear springs, depending on weight of vehicle and handling characteristics.
Drag Racing - Like dampening, probably softer in the rear, stiffer in the front (RWD Cars)
Street Driving - Progressive springs, rates depend on vehicle and user preferences of stiffness.

Camber:
Road Racing - Negative Camber.
Drag Racing - 0 Camber (Maybe some negative camber in the front to lessen the contact patch and rolling resistance on RWD cars.)
Street Driving - 0 or very mild negative camber front and rear to maximize tire life.

Caster:
Positive for any type of driving.

Toe:
Ideally 0 for all types of driving.

Sway Bars:
Road Racing - Stiff.
Drag Racing - Remove them to save weight :).
Street Driving - Medium or Stiff

Tire Pressure:
Road Racing - Changes for every vehicle, day, track, weather conditions, you name it.
Drag Racing - Same as road racing, but generally less in the rear, more in the front. (RWD Cars)
Street Driving - Manufacturer recommended tire pressures.

Hopefully this helps someone out there. If you have any more specific questions, need help diagnosing handling issues, or need help choosing suspension components for your specific car, please don't hesitate to ask.!

DoubleDownMotorsports.com
702.834.5254 M-F 9am-5pm PST
mike@doubledownmotorsports.com
AIM: DDM Time Attack
or of course you can always just PM me or reply to this thread.

Sticky this somebody.

I was going to do this one of these days, but I opted for the weight reduction thread first. Good job. I would go a little bit further into how changing each setting affects the way the car behaves. This is a good intro though, people will appreciate the simplicity I'm sure.

Yeah I plan on going alot further into it, thats why I reserved the third post as well. I just got tired of typing lol. I will finish it soon.

There finished it, although I will probably add more as it comes to mind and questions start getting asked.

I am more satisfied now haha thank you.

sticky

This thread should be transferred to the track section.

Call me crazy but I thought if the top of the wheel tucks in more than the bottom it's negative camber...

That sentence uses negative twice. The sentence you highlighted describes positive camber. The preceding sentence is correct :)

Fixed.

This is brilliant - Thank you DD.

awesome post...

Thanks guys!

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.

Great post!

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?

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.

thanks DD
very useful thread
i learned alot of things

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.

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

Yes. Super effort. Thank you. :tiphat:

:iagree: +rep:tup:

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?

Quick Reference Guide to handling
 

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

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).

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

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.

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.

Great primer!

thanks for the numbers and tips. just posting to verify #s for my 370Z that's lowered about an inch on Espelir springs. i had installed SPC rear camber arms to adjust my rear camber to maximize rear tire life (285/35/19).

i had a shop align the car and adjust the camber. they told me that they adjusted the rear camber to -1.7 because it was in factory specs. i asked if they could adjust the camber to 0.0 because i drive the car on a regular basis. they told me that this would not be safe.

so my question, can i run 0.0 rear camber? the car is mainly for cruising the streets, and i doubt i'll be seeing any track time soon.

toe is fine. i'm just looking to see what's best and safe to get the most tire life.

Rear camber factory spec is between -1.18 and -2.17 degrees, with nominal being -1.67 degrees, according to the service manual. So, the shop aligned it properly. This should give you the best wear and safety, as recommended by Nissan. I would keep it like that.

Does anyone have any Recommendations on how to have the softest ride possible, I have the 2011 nismo

Did you check out this thread?
http://www.the370z.com/nismo-370z/12...ere-first.html

I did that but it still seems rough. Do you know if it is possible to soften up the dampers and would that have any negative effects?

We have a relatively firmer ride due to the performance nature of our cars. The Nismos come with slightly lowered and stiffer springs than the base and touring models. That's the nature of the beast.

So there is no adjustment dial or anything like that to soften the dampers? I figured if I did that and got progressive springs then the ride would be smoother

Does anyone have and recommendation on progressive springs?

I only have 400 miles on it. Does it get smoother after you break it in ?

if you get swift springs, it'll feel smoother

Great post, taught me a lot.