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Tires and Tuning

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Tires and Tuning

Post by Guest on 10/17/2011, 4:40 pm

Got this off of the Forza site. (Good Tuning Help)

Tires.

You can't transmit your car's power and handling potential to the road without the right tire setup, because tire pressure affects a tire's peak grip, responsiveness and wear. Adjust the front tire pressure when the tires are cold so they reach peak grip after they heat up to race temperatures.

Peak Grip Temperature is between 180 and 210 degrees.

You will need to use the telemetry for this.

Start by picking any track and test run 3 laps in test drive mode, now bring up the heat and tires misc. telemetry and observe the temperature & pressure.

As long as you're running a race psi of 30-34 degrees, you're still in good grip range. Race psi and race temperature is measured after a few laps when your tires have heated up and reached their performance levels.

Tire Temp - Cause - Recommended Adjustment

Center hotter than edges - Tire pressure too high - Reduce 1 psi for each 5 deg F difference

*****
* ** *
* ** *
* ** *
*****


Edges hotter than center - Tire pressure too low - Add 1 psi for each 5 deg F difference

*****
* ** *
* ** *
* ** *
*****



Inner edge hotter than outer edge - Too much negative camber - Decrease negative camber

*****
* ** *
* ** *
* ** *
*****



Outer edge hotter than inner edge - Not enough negative camber or too much toe-in - Increase negative camber or decrease toe-in

*****
* ** *
* ** *
* ** *
*****



Tire below peak temperature range - Tire pressure too high, tire too wide or springs/sway bars too soft at that axle - Decrease tire pressure. reduce tire width or stiffen up springs and sway bars on that axle

Tires above peak temperature range - Tire pressure too low, tire too narrow, or springs/sway bars too stiff at that axle - Increase tire pressure, increase tire width or soften up springs and sway bars on that axle

Front tires hotter than rear - Car is under steering. Too much front spring/sway bar, not enough rear spring/sway bar, front pressure too high, front tires too narrow, rear tires too wide - Soften up front spring and sway bar, stiffen up rear spring and sway bar, decrease front pressure or increase rear pressure

Rear tires hotter than front - Car is over steering. Too much rear spring/sway bar, not enough front spring/sway bar, front pressure too high, rear pressure too low, rear tires too narrow, front tires too wide - Soften up rear spring and sway bar, stiffen up front spring and sway bar, decrease rear pressure or increase front pressure

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Alignment.

Handling characteristics are usually defined by over steering and under steering.

Over steering is fish tailing, when the back end comes out. good for drift bad for race pace.
Under steering is when the car experiences little or no steering when you’re trying to turn left or right.


Camber, Toe and Caster

The three major alignment parameters on a car are toe, camber, and caster. Most enthusiasts have a good understanding of what these settings are and what they involve, but many may not know why a particular setting is called for, or how it affects performance. Let's take a quick look at this basic aspect of suspension tuning.

Once you understand the terminology you can move into the adjustment stage.


What is Toe?

My simplest analogy is made to pigeons and ducks. Most people's feet point straight ahead. Compared that to a pigeon or duck there is a significant difference. In some people, however, the feet point inward. This is called in toeing (say "in-toe-ing"), or "pigeon feet." If you’re Charlie Chaplin then I'm sure you've seen his duck walk with his toes pointing outward.

Top down view of a tire in pairs

Toe - Straight (0 degrees)

/ \ **** ****
| **** ****
| **** ****
| **** ****
| **** ****

Toe - In (Positive Degrees)

/ **** ****
/ **** ****
/ **** ****
/ **** ****
/ **** ****

Toe - Out (Negative Degrees]

\ **** ****
\ **** ****
\ **** ****
\ **** ****
\ **** ****

The amount of toe can be expressed in degrees as the angle to which the wheels are out of parallel

Toe settings affect three major areas of performance:

Tire Wear
For minimum tire wear and power loss, the wheels on a given axle of a car should point directly ahead when the car is running in a straight line. Excessive toe-in or toe-out causes the tires to scrub, since they are always rotating relative to the direction of travel.

Too much toe-in causes accelerated wear at the outboard edges of the tires
Too much toe-out causes wear at the inboard edges.

Straight-line Stability
So if minimum tire wear and power loss are achieved with zero toe, why have any toe angles at all?
Is that toe settings have a major impact on directional stability. With the steering wheel centered, toe-in causes the wheels to tend to roll along paths that intersect each other. Under this condition, the wheels are at odds with each other, and no turn results. Even with slight steering input the rolling paths of the wheels still don't make a turn. In this way, toe-in enhances straight-line stability.

Corner Entry Only
If the car is set up with toe-out on the front tires any minute steering angle beyond the perfectly centered position will cause the inner wheel to steer in a tighter turn radius than the outer wheel. Thus, the car will always be trying to enter a turn, rather than maintaining a straight line of travel. So it's clear that toe-out encourages the initiation of a turn, while toe-in discourages it





what is Camber?


Have you seen the stance of a skier, usually their knees are closer than the feet. This stance is said to be a camber effect. Imagine running on a 200m oval track. When on the corner, you feel to get better track traction you need to make your outer feet is touch the inner side of your feet. Camber is the inward or outward tilt of the wheel when viewing from the front or rear of the car. Camber is probably the most useful and popular alignment adjustment that can be made to a streetcar.

Maximum cornering force is achieved when the camber of the outside wheels relative to the ground is about -0.5 degrees. A slight negative camber in a turn maximizes the tire contact patch due to the way the tire deforms under lateral load. Hence, it is good to have some negative camber to increase cornering force.



View from the front of a car

Camber - Straight (0 degrees)

**** ****
**** ****
**** ****
**** ****
**** ****

Camber - (Negative Degrees)

/ **** ****
/ **** ****
/ **** ****
/ **** ****
/ **** ****

Camber - Out (Positive Degrees]

\ **** ****
\ **** ****
\ **** ****
\ **** ****
\ **** ****

The best way to determine the proper camber for competition is to measure the temperature profile across the tire tread immediately after completing some hot laps. In general, it's desirable to have the inboard edge of the tire slightly hotter than the outboard edge.



What is Caster?
This is probably the hardest to explain. The technical description is the angle to which the steering pivot axis is tilted forward or rearward from vertical, as viewed from the side. Lost? Don't worry I bring it back with some diagrams. Picture a Harley with a long nose or fork. A positive caster setting that is very high. Makes it good to go straight mostly, but the mini will beat it at turning radius.

I na car you have ball joints connected to your wheels. These keep the wheels attached to the car. Also you have a steering column attached to the ball joint. The angle between the joint and the steering is the caster angle.

Say you driving down the straight on the hwy and you need to get your hands of the wheel. Notice how easily the car continues to go straight when you let your hands off. This is because of caster in the wheel. Anything attached to a wheel has caster. With caster you have a positive and negative setting. In Forza it’s represented by low and high. Forza doesn't have a negative caster because cars are not designed the same way the casters are in shopping carts.


Positive Caster which provides good directional control but harder top speed cornering.
Negative Caster does not provide good directional control stability but easier low speed cornering.

Top Down View of a car


******
****** () <- Lower Ball Joint
******
****** () <- Upper Ball Joint
******

Side View of a car

********
*******(*)* () <- Lower Ball Joint
***********
****(*)**** () <- Upper Ball Joint
********

Low Caster (Positive) of a Car

********
*******(*)* () <- Lower Ball Joint
***********
******(*)* () <- Upper Ball Joint
*******



High Caster (Positive) of a Car


********
*******(*)* () <- Lower Ball Joint
***********
*(*)******* () <- Upper Ball Joint
********

Low Caster (Negative) of a shopping cart

********
**(*)****** () <- Upper Ball Joint
***********
*****(*)** () <- Upper Ball Joint
********


Notice the shopping cart. See how easy it becomes to turn at a low speed. Imagine 60 mph with that caster setup turning left of right would be dangerous.

So high caster is good but makes it hard to turn, low caster is bad make it hard to keep straight.

Now the fun part.

Tuning

Questions? What are you experiencing when you drive the car through turns? Over steer or under steer?


Camber
Patience is the key because alignment tuning is the hardest in Forza.

Again you will need telemetry for this. Stop the car completely on a flat track with no elevation. Launch Telemetry and go to Tires. Note the camber angle of the car makes with the road. If it matches the setting you have tuned then you are on flat surface.

Restart tuning and race for a couple of hot laps. Usually 3 is good enough. Don't worry about red penalty. Stop after 3 and watch the replay. During your video launch the telemetry and jump to the "Tires Misc".

You need to watch the replay at least 2 times to get this down.

Start by looking at the camber angle on the front wheels.
Note how many times you see a positive number.
Repeat for the rear tires on the 2nd replay.

Now go back to tuning and change the following if applicable

Positive camber on straights - Decrease camber by .1
Positive camber on turns - Decrease camber by .1

No Positive camber on straights - Increase camber by .1
No Positive camber on turns - Increase camber by .1

What’s the point? Positive camber is the enemy and reduces traction and stability.

Tuning for Cornering.

For Left Turn
The right Tire must be less than or equal to 0.0 degrees.

For Right Turn
The left Tire must be less than or equal to 0.0 degrees.

Closer to 0 better the handling. Anything above 0 means that the tire is not helping you.

(You must have negative camber on your car. Don’t tune your car to have 0 on the straights only in the corners. But if you are tuning for drag racing. Always put camber and toe at 0.0)



Toe

General Rule of Thumb is to improve the car for corner entry.

Combination's include


Front Toe + Rear Toe 0 <- Better Corner Entry Any Car
Front Toe - Rear Toe 0 <- Reduce Steer Sensitivity Bad Corner Entry

Front Toe 0 Rear Toe + <- Under steer tendencies but Better Corner Exit in any Car and stability under braking.
Front Toe 0 Rear Toe - <- Slow Corner Exit

Front Toe + Rear Toe + <- Provides stability under braking and creates over steer tendencies in cornering.
Front Toe + Rear Toe - <- Amazing Handling on any car but can cause under steer

Front Toe - Rear Toe + <- Amazing Handling on any car but can cause over steer
Front Toe - Rear Toe - <- Oval track


Examples
Any Car for Better Turn In Response
Front Toe Out : .1 (duck feet ready for turning left or right)

\ **** ****
\ **** ****
\ **** ****
\ **** ****
\ **** ****

/ \ **** ****
| **** ****
| **** ****
| **** ****
| **** ****




Cars with massive power and no handling.
Front: 0
Rear Toe In: -.1 (pigeon feet, ready to face the direction of turn on acceleration)


/ \ **** ****
| **** ****
| **** ****
| **** ****
| **** ****


/ **** ****
/ **** ****
/ **** ****
/ **** ****
/ **** ****

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Brakes.

What is Brake Bias?

Brake bias is the balance of braking power between the front and rear brakes.It is usually represented as a percentage. For example, a brake bias of65/35 means that the front brakes get 65% of the braking power, and the rear brakes get 35% of the braking power.

Why do I need to know?
Brake bias controls the way that the car handles when the brakes are applied.Therefore, it is useful in changing the corner entry handling characteristics of a car if braking is necessary going into a corner.

What happens on adjustment?
Moving the brake bias toward the front brakes makes the car tighter and more stable while braking and entering a turn. Moving the brake bias toward the rear makes the car looser while braking and entering a turn.Excessive front braking power can lock up the front tires and decrease the overall effectiveness of your brakes since you are not using the rear tires to slow down the car.

Rule of Thumb
The front brakes should always have more braking power than the rear because the weight transfer during braking loads the front tires an dun loads the rear tires. If you have too much rear brake, the rear tires will lock as weight transfers forward and makes the rear of the car lighter. However, make sure you do not have too much front brake either.

How To Tune Brakes?
As a starting point "TURN ABS OFF", try setting your brake bias between70/30 and 80/20. Fine-tune the car from there. I found that the Optimal Setting is 47% Front. I will get into the pressure later. ( I disagree with this. When you brake most of the weight is transferred to the front of your car so you need to have a little more to the front. I would say start at 51% front. However you can use brake bias to tune your turn in. If you have more rear brake bias your car will tend to oversteer under braking into corners and less brake bias will give you a more stable braking but you could get a bit of push. Play with it and see what works for you)

As Usual Replay Your Runs and Bring up Telemetry and go to Friction.
Reading the Telemetry for Friction is as follows.

Red Circles is a visual of the grip available at each tire, and the blue lines inside them are the amount of grip you are actually asking the tire to produce. This displays a more detailed brake down of the "Friction Circle" type telemetry from the "Body Acceleration" telemetry screen. If you watch the red circles off the start line, the front ones will get slightly smaller and the back ones will grow. That is because a tire's grip is related to the amount of weight on that tire... more weight = more grip, to an extent. So as you jump on the gas, weight shifts backward, and the rear circles grow because your rear tires have more grip. When you go into a corner, you will also see the circles change size as weight shifts side-to-side. jump over a curb, and the circles disappear if the tire leaves the ground! The blue line shows how much you are asking of the tire - if it is outside the red circle, it means you are pushing that tire too hard and it has lost grip, so it is sliding. If you look at the telemetry during a spin, the blue lines will be well outside the red circles. If the blue line is inside the circle, it means that there is more grip available, since the circle is the limit. You are using your tires most effectively when the blue line is touching the red circle.

Notice while Braking which circles are getting bigger, usually the front will get bigger than the rear with the bias > that 50% Front. Keep moving 1% Front till you have lost grip completely skidded out as a result of understeer when braking. Move back 1% to be in the safe zone.

Tuning Brake Pressure
Also look at the brake indicator (vertical red line on the left of the telemetry) notice if you are completely at 100% or just 70%. This will simply your braking input sensitivity on the controller. Once you have found the optimal setting for your brake bias. Brake pressure will improve your stopping.

Based On Braking Style You Maybe Doing 1 of the following:

1. On Demand (Pull the trigger all the way back)

2. On Power (Pull the trigger all the way back with acceleration)

3. Off Throttle Down Shift Half Brake (Pull the trigger half way)


With ABS OFF (ABS ON counters your braking, meaning more the light is on the more your travelling forward)

1.On Demand: Try going for a less brake pressure, you want all the tires to skid only when the trigger is completely back. Try tuning so that you have a little play to create a skid and a good brake. Start at100% and keep going down 5% till you have that perfect brake. Using the Telemetry make sure you have 4 big red circles when skidding to indicate good brake bias.

2. On Power: Same as above but make sure you don't get into a race-brake situation where your locking the front and burning the rears tires..looks cool but can be costly.

3.Off Throttle: Brake sensitivity is the key. You use only 10~40% on sensitivity (i.e depressing the brake 1/2 to 1/4, you never completely hold the entire brake down during a race (unless you want to show off your ABS skills lol). You know how to lock brakes to your advantage.You use the gear down to your advantage ONLY AFTER you started braking.Typically you keep going up in pressure settings because feel you can stop at a dime.


I'm personally at 130~160% in most cars without ABS. Since the game came out I've been doing without ABS so now it comes a bit natural. Bottom line is if you can drive with TCS off you can do the same with ABS off. If you can gently squeezing the throttle coming out of a corner, you can gently squeeze the brakes.

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Thanks to CerebralColton

Differential.



Differential: Your differential controls how well your car is able to put down its power and torque to the road. A differential will send the power the wheels with the least amount grip, in normal, everyday driving condition the power is sent to the wheels on the left aka outside wheels, when turning right, or the wheel which are not crossed out

/ /

I I

However in aggressive, racing condition, power is often sent to inside wheels, or the wheels on the right aka the inside wheels, when turning right, or the wheels which are not crossed out. It does this because due to weight transfer to the left side of the car, the inside wheels have the least amount of grip

/ /

I I

This causes the car to lose traction and waste power, which is why high performance cars usually have limited slip diffs. If the differential sends to much of the torque to the inside, or outside wheel or wheels, the limited slip kicks in, and locks the wheels together, although keep in mind that a limited slip diff evenly lock your wheels together, one wheel is still receiving more torque, but only slightly.

Acceleration (accl)=The acceleration setting controls at what point the differential locks while on the gas. Having a higher % will prevent individual wheels from slipping, allowing you to use more of the power when exiting a corner, but in a rwd car, will make the car easier to spin out and drift. Having a lower % will make it easier for individual wheels to slip, causing you to waste more of the power when exiting a corner, but in a rwd car it will make the car hard to spin out and drift and if its too low then you will see a black patch coming from the inside wheel. Lower power cars usually can withstand a high rate.

I recommend using a higher slip rate, even in the front wheels, it usually creates a less sloppy feeling when you exist a corner and I find that it allows you to leave the corner with higher speeds. But if your back end slides out more then what you want it to, then it may be a good idea to lower the rate.

Deceleration (decel)= The deceleration setting controls at what point the differential locks when you let off the gas, usually when entering a corner. The high the rate the more stable your car will be, reducing over steer and create a "on rails" feeling, but it will make your car less agile and can cause under steer. Also if you do over steer, while accelerating, having a higher rating can make it harder to correct the skid.

I recommend using a lower slip, which will make will make your car more agile, but if your car tends to over steer, or feels unstable, it may be a good idea to increase the slip rate.

Center (Only with AWD cars): The center differential controls the how the torque is divided between the front and back wheels in an AWD car. Like any other differential it sends more power to wherever there is the least amount of grip. By setting a rear biased rate your making it easier for the power to be sent to the rear wheels. But the rate still changes biased where the most amount of grip is and will still try to send more power to the front wheels if they have less grip.

I recommend a slightly rear bias, of around 60-75%,to get the most performance out of your AWD system

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Thanks to KTLR

-Damping:

Controls the suspension's stiffness and compression between wheel and the wheel-well. Both Rebound and Bump work in "reverse-way", for example having the Front Rebound higher than rear increases grip on the rear, because more weight is concentrated in the front tires under spring compression, so rear wheels can work more freely.



Rebound Stiffness:

Increasing Front Rebound - More grip in the rear (weight shift blah blah etc.)
Decreasing Front Rebound - Reduces transitional under steer

Increasing Rear Rebound - More grip in the front
Decreasing Rear Rebound - Reduces transitional over steer

Front biased Rebound - Increases under steer & increases grip in RWD cars, sacrificing turn-in slightly
Rear biased Rebound - Increases over steer & highly recommended for FWD & AWD cars.
(The bigger the balance difference, the bigger the effect - bigger than 3.0 differences not encouraged)

You cant really have excessively high Rebound setups, it all depends what the Bump stiffness are set to. If you are using high Rebound (9.0+) with low Bump (<4.0) your car may become upset by curbs and such, this is also modified by ride height and suspension stiffness. Higher Rebound than Bump is a must. The Bump stiffness should be 75% of the Rebound's stiffness at maximum. Although the in-game Damping description says ~50% of the Rebound's stiffness should be minimum, it really doesn’t have to be. Low bump stiffness works great.



Bump Stiffness:

Increasing Front Bump - Increases under steer and slightly increases rear grip + modifies the effectiveness of Damping and Spring setups
Increasing Rear Bump - Increases over steer and slightly increases front grip + modifies the effectiveness of Damping and Spring setups

Decreasing Front Bump - Improves bump absorption + modifies the effectiveness of Damping & Springs
Decreasing Rear Bump - Improves bump absorption + modifies the effectiveness of Damping & Springs

Front biased Bump - Increases under steer + slightly increases grip in RWD cars
Rear biased Bump - Increases over steer & highly recommended for FWD & AWD cars.
(The bigger the balance difference, the bigger the effect - bigger than 2.0 differences not encouraged)



You will know when your Bump stiffness is excessively high. The chassis feels like it floats on the tires and you feel unconnected to the road. A good, practical way to test out your bump stiffness if you don’t want understand all the mumbo gumbo, is to take a mild curb aggressively and then seeing if the car rolls. (Don’t try Sebring or Maple curbs, they'll roll you no matter what). If it rolls, your setup is too stiff, if you already had your bump at <3.5 then the problem is in your ride height or rebound. Bump stiffness can always be kept relatively low. (I personally never use 5.0+ bump stiffness). Bump stiffness in general fine-tunes the Damping & Suspension.



Tune the springs & ride height before going over to damping.



Also; Rear-biased Damping works for RWD cars well too, front-biased is just one of the several ways to increase grip on some RWD cars, not necessarily on all of them.

Guest
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Re: Tires and Tuning

Post by Timpegoose on 10/17/2011, 7:11 pm

That's good stuff man. Definitely a huge help to me at least.

Timpegoose
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Re: Tires and Tuning

Post by Guest on 10/17/2011, 7:29 pm

Not mine. I haven't even had time to go through it all. It does lay it all out in a way that even I can understand!

Guest
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Re: Tires and Tuning

Post by Timpegoose on 10/17/2011, 8:05 pm

Yeah, it was a good find though for sure. I need some of this tuning stuff dumbed down as much as possible lol.

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Re: Tires and Tuning

Post by sjokkomoes on 10/19/2011, 10:36 am

What does this mean:
2. On Power: Same as above but make sure you don't get into a race-brake situation where your locking the front and burning the rears tires..looks cool but can be costly.

sjokkomoes
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Re: Tires and Tuning

Post by Guest on 10/19/2011, 10:51 am

Could be referring to trail braking into a drift?

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Re: Tires and Tuning

Post by sjokkomoes on 10/19/2011, 11:47 am

Ok ty. Im having trouble getting my tires up to optimal temps on some cars.

Ive tried lowering the pressure but it didn't do much.
Could it be because Im fitting the"best tires on a car that doesn't have the HP to get any heat in?

sjokkomoes
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Re: Tires and Tuning

Post by Guest on 10/19/2011, 12:06 pm

I was having similar issues (though I didn't know it because I wasn't looking as critically at the telemetry). A couple of options above are to increase the sway bar strength and/or spring rate. I had an issue with an R3 car, with the front sway on 40, where the front tires wouldn't reach optimal temperature for 3-4 laps. I bumped up the front spring rate and now they get to temp within the first lap.

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Re: Tires and Tuning

Post by sjokkomoes on 10/19/2011, 4:08 pm

Tnx, ill give it a try.

sjokkomoes
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Re: Tires and Tuning

Post by luongo27 on 10/19/2011, 4:45 pm

Got a pretty nice setup now on the jag thanks to this, but would still like to try some other tunes. Ones that people who what what they are doing have done.



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Re: Tires and Tuning

Post by Guest on 10/19/2011, 5:01 pm

I'll detune my PI and shoot my setup over to you. Oh wait. You want something from someone that knows what they are doing!

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Re: Tires and Tuning

Post by luongo27 on 10/19/2011, 5:16 pm

will give it a shot, will most likely be better than mine



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Re: Tires and Tuning

Post by Guest on 10/24/2011, 10:05 am

Another guide I found on FM.net.


This is the tuning guide I wrote a bit ago. If you have anything to add to it let me know and I'll be glad to do so.

Thanks

--VVV Worm



First Rule: Fix the end of the car that has the problem. If it's the rear sliding around don't go adjusting the front. Start with adjusting the back end to stabilize it first. You can then go up or down in unison to stiffen or soften the car.



Tires and Temperature

Getting the correct temperature/pressure combination is like fitting together a big puzzle. Stiffer spring = more temperature and stiffer roll bars = higher temperature and on and on. It all fits together and the tires are the only thing we have direct control of. It's often the most overlooked part of tuning yet it is the most important.

I'll use the recommendations that I have gathered from Pirelli for temperature as some manufacturers differ +/- 10° F. The optimal grip for a tire will differ by what compound you put onto the vehicle. The softer the tire the lower the temperature needed for optimal grip.

GT cars 27.5 to 31.9 psi hot.

Touring cars 29 to 36.2 psi hot.

Temperature range can be from 180° to 210° F. A softer tire will lose grip more rapidly once it gets past 210° than a harder compound.

How does tire temperature relate to pressures?

Higer pressure = Lower temperature
Lower pressure = Higher temperature


This works in small amounts. On FWD cars in the game you can have a really high PSI in the rear and it will slide all over the place.

Adjustments Decrease Understeer Decrease Oversteer
Front Tire Pressure Higher Lower
Rear Tire Pressure Lower Higher


Uniform rules no matter what

Give the tires 3 laps to warm up before looking at telemetry.

You should never have more than 20° between the inner portion of the tire and the outer with the inside always being hotter.

You should never have more than 25° between the front and rear of the car

Alingment

Keep in mind you want no more than 20° difference between the inside and outside of the tire with the inner 1/3 always being hotter (10°-15° are good numbers). Make sure you look when actual load is on the tires going through a corner and the tires have had proper time to heat up (3 laps minimum).

Camber
You always want negative camber

Negative = More inside
Positive = More outside

There is a sweet spot in this setting that usually doesn't change unless you move the Caster around too much once everything is set. You also always want more camber in the front than the rear. Rear camber isn't as necessary as those tires don't turn and I want them with a touch of negative camber when throttle is applied on exit.

Toe
Front toe favors a positive number (more responsive and better turn in) between 1° and 5°. Anything above 3° will cause excessive drag in the straights and gets really bad above 160mph.
Rear toe favors a negative number and becomes more responsive through turns at 1°. However anything over 2° and the back end loses a lot of stability in acceleration and braking. On bumpy tracks any amount of rear toe will cause the car to lose stability and the driver will have to make corrections even in a straight line costing you time.

Caster
Allows the tires to roll with the chassis giving a larger contact patch through a turn. It also helps to balance the temperature of the tires on tracks with predominant left/right turns.

A larger number here will also help absorb bumps on the track while decreasing stability as too much caster causes the tires to wander a bit.

I personally like a really high Caster (5.5-7.0) in the lower classes but on tracks with longer sweeping turns less caster is better.. Most cars aren't sensitive to caster changes.

Adjustments Decrease Understeer Decrease Oversteer
Front Wheel Camber More Negative More Positive
Rear Wheel Camber More Positive More Negative
Front Wheel Toe TowardToe-Out Toward Toe-In
Rear Wheel Toe TowardToe-In Toward Toe-Out
Front Wheel Caster More Positive More Negative

Anti Roll Bars

Anti roll bars control how much side to side roll a car has. In theory you would want to minimize body roll as much as possible. This is especially true in the higher classes but on occasion in FM3 some body roll helped things. I guess we will see in FM4. The end of this one is long winded but helps to understand it all.

Rear ARB soften = decrease oversteer or increase understeer
Rear ARB stiffen = decrease understeer or increase oversteer


Understanding what the ARB's do

"Limiting the lean of the body is good because it means that when you take a quick set into a turn, that the body isn't still moving sideways after the tires are at their limits. Otherwise you turn in quickly, the tires grip, then the body finally finishes leaning, when it stops, the tires lose grip."

"It limits camber changes. The camber directly impacts the angle at which the tire cross section meets the road and thus controls lateral grip. As the suspension compresses the camber angle generally changes relative to the chassis. With a normal McPherson strut that hasn't been lowered, the camber goes from positive to more negative as the lower A arm swings out straight, and then back to positive as it swings up. That swing up into positive camber is BAD. At that point the chassis is already leaned over so the tire may be starting to roll onto its sidewall. Changing the camber even more positive is just nasty. A big sway bar will prevent the body roll in the first place, and prevent the suspension compression on the outside which causes the positive camber change relative to the chassis."

"Here's where it gets really tricky: If decreasing the size of the rear bar doesn't help enough, the next thing you do is increase the size of the front bar. When the outside front compresses in a corner, it causes the inside front to compress and may actually lift that tire completely off the ground. The car is now sitting on 3 tires and guess where the weight that was on the inside front goes? Outside front? Some of it. The rest goes to the inside rear where we need more grip. The total weight of the car hasn't changed. It's just been redistributed, and a sway bar at one end, actually transferred weight to the other end of the car. Increasing the front bar then translates into more motive grip at the rear, and thus more acceleration"

Springs & Ride Height

From speaking with Dan the spring tuning and adjustments have changed drastically from FM3 to FM4. Every car is now different based upon what it is in reality as opposed to just one generic suspension being stuck under every vehicle like Forza titles in the past. (his direct words were not all suspensions are the same and the same springs weights don't do the same thing on every single car)

Any change in the spring rate will change the ride height due to the rate of spring deflection. They also change the compression(bump) and deflection(rebound) ratings of the shocks.

I personally like to balance the weight of my vehicle with my shocks and leaving it set to the weight % of the vehicle. Aero also affects the weight on the car and needs to be figured in. Some tracks require a softer spring while others require stiffer.
If you use Xtreme Skills formula it figures everything in for you to actually balance the springs. You can then multiply things by 1.1 to increase or .9 to decrease the spring rate and still keep the % correct and balanced. In most cases I like to soften the springs until the telemetry starts to blink red on the spring screen and multiplying it by 5% or 1.05.

Xtreme Skills formula is: (do this for the front and rear) (I think this may be a bit too soft for FM4 and have been multiplying by 1.5-2.0)
Simplified (Car weight+ downforce at front-rear) / 100 x weight % at front-rear / ride height at front-rear x G-force = YOUR SPRING RATE

Also keep in mind that a softer suspension will create more load so if one side of the car is under more stress it MAY benefit from a stiffer setup.

Ride Height
Keep this as low as possible without the car bottoming out



Damping (shocks)

The extension when the tire is unloaded (force back out) = REBOUND
The compression of a shock (making it smaller) = BUMP

Braking
Under braking the front axle will compress while the rear will rebound. As the weight shifts the front axle will have a higher velocity than the rear which is good because the front should settle before the rear. If the front does settle too quickly the tires in the front will lock a little premature and vice versa for the rear. Brake bias only maskes the problem and moves it to a different portion of the track.

Acceleration
Under acceleration the rear axle will compress while the front will rebound (think of a see-saw). On a RWD for example if the rear squats before the torque reaches peak it reduces the time the driver has to feather the throttle as the tires begin to break loose. Try to balance the compression againstthe required grip of the torque. FRONT REBOUND SHOULD BE FASTER THAN REAR COMPRESSION.

FWD is different in a sense. For acceleration increasing the front rebound will give more grip initially while increasing rear rebound increases a sustained level of grip.




Downforce and Braking

Downforce
More at rear = more understeer and a stable back end
More at front = more oversteer and increased turn in.

More downforce = less speed in straights, more speed through cornering.

Don't forget that any downforce adjustment = a spring adjustment to compensate for the added weight. Especially at higher speeds.

Braking

Braking pressure is a preference of the driver in my experience.
Your brake bias controls understeer and oversteer while braking.

More front bias = more understeer and can bind the front tires up to where you can't trail brake if you prefer to.
More rear bias = more oversteer and can cause the rear tires to lock up faster than the front which is really bad. Will cause the car to spin. This can also be a preference as some like to go early in fast out and some find it easier to brake later and trail brake through the corner. Those two can create a full scale argument.



Differential Settings

Differential settings increase the amount of lock your inside wheel has while turning. At 100% both the tires turn at the same speed which on a rear differential creates oversteer (on FWD it eliminates torque steer). A higher differential will allow you to use the throttle to help turn around a corner but can cause mid-exit oversteer.

On deceleration when you lift off of the throttle one tire locks faster than the other. This can cause the back end to want to kick out over the locked tire in extreme settings (under 15%). A lower setting does help things and the further apart the accel and decel are on the same differential the more unstable the car seems to get in my experience.

There isn't a ton I can find on differential settings so sorry for being so brief here and it is pretty simple. A higher number creates oversteer and a lower number prevents it.







EFFECT ON

VEHICLE – POSSIBLE CAUSES

Straight Line Instability

* Too much rear wheel toe-out.
* Not enough rear downforce.
* Too much front downforce.
* Not enough rear toe-in (under hard acceleration) –presumably for RWD.
* Too much front toe (either in or out) – car darts over bumps.
* Front ARB is way too stiff – car darts over bumps.


Instability Under Brakes

* Front end darts or wanders – too much front brake bias.
* Car wants to spin – too much rear brake bias.


Response

* Car feels heavy and unresponsive.
o Too much downforce.
* Car feels sloppy and is slow to take a set in corners.
o Too little shock.
o Too much body roll (not enough spring and/or ARB).
* Car responds too quickly, is twitchy, and slides easily.
o Too little downforce.
o Too much shock, too much spring, and/or too much ARB.
o Too much tire pressure.


Understeer

* Corner entry understeer – car won’t turn in at all.
o Front
tires not wide enough.
o Too much front roll stiffness – ARBs and/or springs.
o Not enough front bump – shocks.
o Not enough front downforce.
o Too much dynamic camber on front wheels (not enough static negative camber).
* Corner entry understeer – car turns in initially then starts to push.
o Too much front toe-in.
o Rebound too stiff – shocks (not enough droop travel).
o Not enough front downforce.
o Bump not stiff enough – shocks.
* Corner entry understeer – car turns in and then darts.
o Insufficient front suspension travel in either or both directions – shocks.


Oversteer

* Corner exit oversteer – gets progressively worse from the time throttle is applied.
o Too much rear roll stiffness.
o Too much rear camber.
o Too little rear downforce.
o Too little rear toe-in.
o Not enough rear spring, shock, or ARB – allows car to roll over on outside rear wheel.
* Corner exit oversteer (sudden) - car takes its set then breaks loose.
o Not enough rear suspension travel (too much shock in either bump, rebound, or both).


CAUSES – EFFECT ON VEHICLE

Springs

* Too much spring – overall
o Harsh and choppy ride, lack of tire compliance.
o Can’t put power down on corner exit - excessive wheelspin.
o Car slides too much.
* Too much spring – front
o Initial understeer.
o Front end breaks loose in corners.
o Front end breaks loose over bumps.
* Too much spring – rear
o Oversteer when power is applied on corner exit.
o Excessive wheelspin.
* Too little spring – overall
o Car bottoms out.
o Car feels like it’s floating.
o Sloppy response.
o Car is slow to take its set.
* Too little spring – front
o Front end hits ground under brakes.
o Too much body roll on corner entry.
o Initial understeer – car won’t point in.
* Too little spring – rear
o Too much squat under acceleration, and the resultant increase in negative camber.
o Car falls over on outside rear wheel causing power-on oversteer.


Anti-Roll Bars

* Too much ARB – overall
o Very sudden turning response and little feel.
o Car slides or skates instead of taking its set.
o May dart over one wheel bumps or diagonal bumps.
* Too much ARB – front
o Corner entry understeer that gets progressively worse.
o Steady state understeer in the middle of sweeping turns.
* Too much ARB – rear
o Corner exit oversteer when throttle is applied.
o Excessive sliding coming out of corners.
* Too little ARB – overall
o Car is sloppy and lacks response.
o Car is slow to transition, especially in chicanes and esses.
o Car rolls too much resulting in too much dynamic, positive camber and the resultant loss of cornering power due to decrease in tire traction.
* Too little ARB – front
o Car rolls over onto outside tire on corner entry then ‘washes out’ (understeers).
o Car lacks steering response and is slow to change direction.
* Too little ARB – rear
o Back end doesn’t want to rotate on corner exit under power (difficult to throttle steer).


Shock Absorbers

* Too much shock – overall
o Very sudden car with harsh ride, sliding, and wheel patter.
o Car crashes over road surface irregularities.
* Too much rebound adjustment
o Wheels do not return to road surface quickly after displacement.
o Inside wheel pulls off the road surface in a corner.
o Lack of tire compliance over bumps and surface undulations.
o Car may be jacked down in long corners.
* Too much bump adjustment
o Initial reaction to bumps and curbs is harsh.
o Initial chassis roll slow to develop.
o Car slides rather than sticks.
o Driven wheels hop when the power is put down.
* Too little shock – overall
o Car floats a lot in ride and oscillates after bumps (underdamped).
o Slow and sloppy response.
o Chassis rolls too quickly.
* Too little rebound adjustment
o Oscillates after bumps.
o Doesn’t put the power down well.
* Too little bump adjustment
o Initial bump reaction soft.
o Car dives and squats a lot under brakes and under power.
o Car rolls quickly and falls over outside tires – front tire on corner entry and rear tire on exit.


Wheel Alignment

* Front toe-in – too much
o Car darts over bumps, under the brakes, and during corner entry.
o Car won’t point into corners.
* Front toe-out – too much
o Car wanders under the brakes.
o Straight line instability especially over one wheel and diagonal bumps.
o Car may point into corners then refuse to take a set
o Understeer as a result of tire scrub in long corners.
* Rear toe-in – too much
o Rear feels light and unstable on corner entry.
o Car slides a bit in corners rather than rolling freely.
* Rear toe-in – too little
o Power on oversteer during corner exit.
* Rear toe-out – any
o Power oversteer during corner exit.
o Straight line instability.
* Front wheel caster – too much
o Excessive physical steering effort (probably non-applicable with the XBOX controller)
* Front wheel caster – too little
o Too little steering feel and feedback (also probably non-applicable with the XBOX controller)
* Camber – too much negative
o Inside of tire will be hotter than the rest and wear faster.
o Front tires – reduced braking capacity (dive)
o Rear tires – reduced acceleration capacity (squat)
* Camber – too much positive
o Outside of tire will be hotter than the rest and wear faster.
o Rear tires – corner exit oversteer and reduced tire traction.
o Rear tires - If extreme may cause corner entrance instability.
o Front tires – too much body roll and understeer after car turns in.


Tires

* Too much tire pressure
o Harsh ride.
o Excessive wheel patter, sliding and wheelspin.
o High temperature at center of tire.
* Too little tire pressure
o Soft and mushy response.
o High tire temperatures at inner and outer edges.
o Reduced contact patch

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Re: Tires and Tuning

Post by Guest on 10/24/2011, 10:16 am

I've been struggling with my FSCS car at Sebring. Over the weekend, luongo27 and I tested several cars to see if we could find something that would work well for the team. One thing we both noticed was how fast some of the cars were straight out of the manufacturer's garage. With no tunes we were running within a few seconds of our upgraded and tuned cars.

Out of frustration, I reset my Jag to the default tuning settings (with the exception of gearing, brakes, and the diff). I then ran some laps to get the tires warmed up and checked my telemetry. Using the first guide I posted above, I started with tire temps and adjusted the front and rear camber over several multi-lap sessions. I also used the tire heat telemetry to adjust front and rear sway bar settings, referencing both of the above guides. Once I got the tire temps relatively even, the car was definitely not fun to drive. I then relied on the second guide to fine tune the damper settings. By identifying what the car was doing into and exiting the corners, I was able to fine tune the car. Also note - at no time did I adjust the aero setting and the springs were only adjusted a few clicks up or down to get the tire temps squared away.

After all was said and done, I went from consistent 2:14s with occasional dips to 2:10 to consistent 2:08-2:09's with occasional dips into the 2:07's while leaving quite a bit on the table.

I am by no means a master tuner, but the results speak for themselves.

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Re: Tires and Tuning

Post by Guest on 10/25/2011, 11:25 am

Yeah, I've started using that second guide and its been nice so far, slow going still getting used to what I want out of the car for my style (if I really even have one) but I'll get there with time.

Its frustrating as hell at times but rewarding when you get it right or close to right.

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Re: Tires and Tuning

Post by LethalHoudini on 10/25/2011, 11:34 am

Tuning can be very frustrating even after years of it mate lol. 1 point that is often missed is to make sure you have the best build you can get first running the stock tune ie:

best HP-TORQUE-HANDLING for your pi

Also its tough but you have be honest with yourself I meen when im test driving and say get a slide I am always thinking now was that the cars fault or mine etc. This is why I always tune on the tracks I know the best and am most consistent on. After a while youl work out your driving style and how you like your cars to feel. Another thing is I always see tuning as bringing the car to me so to speak so all my cars feel similar that way when I go from car to car I don't have to think to much about the car I can concentrate on the racing etc. Obviously some are different due to speed/handling cars and drive types but at the apex and body roll etc etc they are pretty much the same.






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Re: Tires and Tuning

Post by Guest on 10/25/2011, 6:06 pm

DelZaster wrote:Also its tough but you have be honest with yourself I meen when im test driving and say get a slide I am always thinking now was that the cars fault or mine etc. This is why I always tune on the tracks I know the best and am most consistent on. After a while youl work out your driving style and how you like your cars to feel. Another thing is I always see tuning as bringing the car to me so to speak so all my cars feel similar that way when I go from car to car I don't have to think to much about the car I can concentrate on the racing etc. Obviously some are different due to speed/handling cars and drive types but at the apex and body roll etc etc they are pretty much the same.

+1 to this, Del

I have to agree with this completely. I've found a major help to dropping times at a track is running laps consistently (within 0.5 seconds of each other for multiple laps). Once I can do that, then its time to tune the car to start dropping those 0.1's and eventually 0.01's.

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Re: Tires and Tuning

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