Suspension adjustments and how they affect handling

M.Bonanni

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.



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.



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.



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.

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M.Bonanni

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.

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Fishey

Here is my little guide for track setup.

let me say this guide will help you with a 350z or 370z but there are some differences you need to be aware of between the cars.

The 370Z was built to be more nimble then the 350Z and the way they went about doing this was they decreased the wheelbase by 4 inches. Then on the front suspension Nissan used a few other tricks to change the feel of the car like decreasing the amount of caster from 7.6 to 8.9 degrees to 4.4 to 5.9 degrees for the 370z. This change in Caster reduces steering effort along with the reduced wheelbase makes for a car that feels far more nimble and is likely is a bit more nimble. However, to do this they had to increase the SAI from 4.3 to 5.8 degrees on the 350z to 6.9 to 8.4 degrees since caster will help promote camber gain during cornering. The 370Zs increase in SAI is a more mechanical change to how fast the suspension increases camber as it really is the measurement between the long arm and short arm in the suspension. In a 350Z the top arm is longer so it has less SAI vs the shorter top arm of the 370Z that allows for faster camber gain during compression.

Some of you might know but I do alot of track setup work at my shop and I am also involved in a few professional racing efforts. Let me say that I have done track setup on everything from Grass Roots to Professional racing and unless its a time-attack car setup or AutoX it always has a general profile that will benefit 95% of you but certainly changes on venue/conditions/etc but I want to give a few general guidelines and things I see all the time that keep people from getting that extra edge. This is the way I think about it in my own head when I get a new car to setup.

First, I want to tell you that everything is a compromise and I am talking about generalities here. I could counter my own way of thinking very easily. So to talk about tires and a few general guidelines. The very first being that the grip level of the tires you are using is going to effect setup. So if your running a very sticky compound (Short life) generally speaking your going to be more on a harder setup and if your running on street tires your going to be running a softer setup. I generally error on the side of soft vs hard as when you get to hard in your setup mechanical grip suffers and things like curbs can really start unsettling a car.

Second, I want to talk about Camber and how it is going to change depending on situation. I can tell you right now that an acceptable range is from -3.5 to -2.2 front and -2.5 to -1.5 rear. Your spring rate and your tire compound will be primary factors in your camber levels. I have yet to come across a situation yet that has required a higher rear camber then front camber.

Third, Caster because it goes hand in hand with camber.

Since camber changes to negative on the loaded wheel and positive on the unloaded wheel. I tend to keep Caster consistent until I can get good tire data. Also, if your one of those guys running crazy amounts of camber because that is what your seeing right now from data. It might be time to think about making a drastic caster change to reduce the need for crazy camber numbers. I have also noticed if you are seeing increased front grip with larger front sway bars its highly likely its time to increase front caster.

This is one area I think the 370Z can really be improved. I have not done alot of testing and being late to the setup party I don't really know what B.J. and the guys have tried. However, there could simply a limitation where it no longer helps as camber gain gets to dramatic on the outside/loaded tire and reduces grip. In that case take B.J.'s advice and add more front bar! I do not think the 350z suffers the same problems as a result of different geometry.

Fourth, lets talk about toe as its one of the best ways to make changes to your car. Rear toe is going to depend some on parts you have in your car. Front toe on a race car generally going to keep it pretty close to zero but some drivers prefer a toe out for more turn in. The rear toe we always leave some toe in to keep the rear stable under braking and under acceleration off the corner. A zero toe with soft bushings can turn into toe out on acceleration and make for some very interesting dynamics.

Fifth, Shocks! If you are running a full remote res setup with the ability to adjust pressures do me a favor and please buy yourself a nitrogen bottle/reg and a dry-break or whatever it is called tool. Keeping shock pressures at a constant pressure from weekend to weekend will help you. I can't tell you how many times I have seen very nice aftermarket shocks that were way uneven or way low on pressure. I always keep an eye on the pressure inside the shocks before the start of a weekend.

Sixth, Corner weighting your car. I always suggest this be the very last thing you worry about in your setup and I would only start to mess with it after you get a general handle on your car. If you do decide to get a corner balance then remember that you need to have at a minimum. adjustable ride height with coilovers and adjustable swaybar endlinks. When I do corner weighting the individual numbers are not important. The important numbers to me are the cross weights so what is the split from RF/LR or LF/RR

I hope that helps.
Also, remember if you have any questions about your setup feel free to E-mail me at shop@metricgarage.net. You also can always reply to this thread and like us on our facebook page www.facebook.com/metricgarage.net

M.Bonanni

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
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mike@doubledownmotorsports.com
AIM: DDM Time Attack
or of course you can always just PM me or reply to this thread.

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LiquidZ

Sticky this somebody.

RCZ

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.

M.Bonanni

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.

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RCZ

I am more satisfied now haha thank you.

onethreefive

sticky

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RCZ

This thread should be transferred to the track section.

zman1910

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

chubbs

This is brilliant - Thank you DD.

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Ryan@IP

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

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Slidefox

Fixed.

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TerribleONE

awesome post...