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I just have a few questions on tire pressure and some other things.

I'm a decent tuner, so a few days ago I decided to try to run some Hot Laps. I know that the best all-around A Class car is the Lotus Elise 135R, so i tuned that up to A850. I have been runing some decent laps, but I'm not quite sure how to get the tune that slight bit faster. Here's a list of the upgrades I installed, if I need to change something please tell me.

• Sport Intake
• Race Cams and Valves
• Sport Intercooler
• Street Positive Displacement Supercharger
• Full Platform and Handling
• Race Tires (Hoosier Compound)
• Full Tire Width
• Forza Front Bumper and Rear Wing

I'm mostly racing on Laguna Seca, Suzuka East, and Tsukuba.

My main question is what a good tire pressure would be for optimal handling with the most speed I can get out of it. Am I correct in saying that higher pressure=more speed, less grip and that lower pressure=lower speed, more grip? Right now the tire pressure is set at 27psi front and 28psi rear for Tsukuba.

Also, what is a good camber/toe setup? Mine is set at -0.6 front camber and -1.0 rear camber, 0.4 front toe and 0.2 rear toe. I'm pretty lost as to how to set these up for racing.

Any help is greatly apreciated. Thank you in advance,

Freaky.

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FrEaKyxXxStYLey
Absinthe Minded Auto Haus-Tuner/Tester
Free Tune/Test Drive Request Thread

tire pressure is pretty easy to set. personally, i've tried running outrageous tire pressures at cicuits like new york, and IMO, you don't get more speed in this game with increased tire pressure. i've run my tire pressure at 35/35, all the way up to 55/55. no difference. you'll get greater straightaway speed dividends by reducing your downforce, and adjusting your transmission gearing. but to optimize your lap times, tire pressure adjustments won't do much.

anyway, use telemetry. the word is tires are at their optimal peformance HOT at 32psi. all you need to do is set them at like 28/28, run some laps, then use telemetry to check your pressures. tweak them, run some more laps until you get them around 32psi. done deal.

okay, camber and toe. this confuses a lot of people.

1- never, ever, ever, run positive camber. again, use telemetry. the object is to get all three zones (inside, middle,outside) of your tires evenly heated. if your overall tire temps are between 180 and 200 degrees, you're pretty good. if your inside tires are hotter - you have too much (negative) camber. if the outside of the tires are hotter (this is bad) you don't have enough (negative) camber.

rear camber should generally be less than the fronts, especially in mid-engine cars like your Elise. Why? firstly, because there's more weight displaced in the rear of the car when the car is standing still. secondly, when you accelerate, the car's weight shifts backward. this is known as 'squat'. whatever camber you're running will increase with the added load on the rear tires. if you have too much camber on the rear tires, when you accelerate, you're tire to surface contact will decrease, in effect, placing too much of the load on the inside of the tires. this hurts acceleration.

2- toe OUT is NEGATIVE toe. toe out helps the car steer in on turn entry. you currently have .4 of POSITIVE TOE IN on the front tires of your Elise. considering you're running it at Tsukuba, with all those tight slow turns, the toe in is most likely hurting your turn entry.

set your FRONT TOE to 0.0, and run some laps. the Elise is notoriuos for having a very tight turning radius, and a ton of oversteer. if you feel you want more turn in on corner entry, add 0.1 NEGATIVE toe (out), and try again. repeat until the car turns in to your liking, but you shouldn't need too much.

you have .2 TOE IN on the rear wheels. this may be good as is. toe in is good for stability, and conidering how much oversteer your dealing with on turn exit. you may want to leave this as is.

one scenario where you'll notice the difference in rear toe is in medium speed sweeping turns (like the last long curve at Tsukuba). in turns like this where you need throttle control, but too much will make your car break traction in the rear, a little TOE IN can help, here.

as an exercise, try running Tsukuba with 0.0 rear toe, and pay close attention to how the rear end responds as you feather the throttle. if you're having trouble keeping the rear end in line, add a little TOE IN, and try it again. this will help you get a feel for your adjustments, and how the car responds to your inputs on the track along with them.

Good post, Brodeur.

I would add the following two points:

1. If your tires don't get warm enough: You can get them to heat up more by increasing the amount of toe (in or out, just further from zero). More downforce should also heat the tires up more. Or, you are just plain running too much tire. Pick tires that are narrower or don't have as much grip, and spend those PI points on more engine.

2. You may have an excellent temperature profile on one front tire, but not on the other. Adjusting your caster may enable you to get a better temperature profile on both front tires. Caster affects the amount of dynamic camber that is added by steering input. One tire will gain camber, and the other lose camber, according to how far you turn the steering wheel. Try watching the camber telemetry of a parked car as you turn the steering back and forth to see what I mean. Again, your tire temperatures will tell the story on whether your changes helped/hurt.

Finally, the real-life temperature profile of a tire that is properly setup would give you 10 to 15F higher on the inside of that tire than on the outside. That's what I shoot for in-game, as I have no personal knowledge of it being different in-game.

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Click image to see the car's sale thread.
GT: EXOR x Bart x
http://www.exodusracing.net/ - Unassisted Racing at its Finest

Lot's of good tips from Brodeur there. Here are a couple of comments that I would add...

BrodeurSux:

anyway, use telemetry. the word is tires are at their optimal peformance HOT at 32psi. all you need to do is set them at like 28/28, run some laps, then use telemetry to check your pressures. tweak them, run some more laps until you get them around 32psi. done deal.

Yes, you'll probably find that since the drive wheels create more friction with the road when driving hard, they will build up heat and pressure more so than non-driven wheels. Keeping that in mind, its very common to start with cold pressures for a front-driver of say, 28 / 29 and a rear-drive at 29 / 28.

Generally speaking having higher tire pressures increase the sidewall stiffness and improve responsiveness in high-speed maneuvering whereas lower pressures result in more sidewall flex and increase slip angles, better for slow-speed corners. Keep in mind that the tires "add" spring rate so, don't be bashful about testing different pressures in conjunction with your other suspension settings as they will affect the overall handling charateristics of the car.

BrodeurSux:

1- never, ever, ever, run positive camber. again, use telemetry. the object is to get all three zones (inside, middle,outside) of your tires evenly heated. if your overall tire temps are between 180 and 200 degrees, you're pretty good. if your inside tires are hotter - you have too much (negative) camber. if the outside of the tires are hotter (this is bad) you don't have enough (negative) camber. 

Ideal tire temps depend on the tire type. Race tires ( slicks ) provide optimal grip at hotter temperatures than street tires. Tire heating due to camber can be a tricky one. Keep in mind that if your tires are negatively cambered, the inside of the tire is doing most of the work, even on a straight and therefor will be generating more heat than the middle or outer edge of the tire. My opinion is that, because of this, the inside of the tire is, for most tracks, going to run hotter than the other two zones. It might be more ideal to try to get the INCREASE in tire temp across the tire during cornering to be even and allow the inner edge to be 5- 10 degrees hotter overall.

BrodeurSux:

2- toe OUT is NEGATIVE toe. toe out helps the car steer in on turn entry. you currently have .4 of POSITIVE TOE IN on the front tires of your Elise. considering you're running it at Tsukuba, with all those tight slow turns, the toe in is most likely hurting your turn entry.

In the rear world this is true, in Forza this not. In the real world negative toe does help to make turning easier and positive toe stabilizes or 'discourages' turning. However in FORZA, this was modelled backwards. Moving your tuning sliders to 0.2 actually adds negative toe and improves turning and a slider at -0.2 adds positive toe and inhibits turning. I don't know why it was done this way but, if you turn up the adjustments and then go to a telemetry replay, you'll clearly see which way the tires are trully pointing.

Generally speaking, I would say that if you are using more than 0.2 or 0.3 of toe to help turning, you might be better served to look at suspension settings or diffs to help the car turn better.

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R.I.P Pale Rider

GT: AMG Moctane

Its time to make the donuts!

Wow, thank you for all the input. This helped me to understand a lot of stuff.

I'll update if I need some more help, which I probably will.

Oh, by the way, I'm a HUGE Martin Brodeur fan...haha

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FrEaKyxXxStYLey
Absinthe Minded Auto Haus-Tuner/Tester
Free Tune/Test Drive Request Thread

I told you I would need help. haha. Anyway, I've done what you've told me, and it helped a whole hell of a lot, but I still cant seem to control the rear end. After running about 50 laps on Tsukuba, I can't get a better time than 56.042. I hitting my apex's, nailing the line, but I either slide on the way out of the corner or have to slow on the throttle to control it. Basically, I'm not getting full acceleration out of most of the corners. Any tips on how to control the rear of this thing?

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FrEaKyxXxStYLey
Absinthe Minded Auto Haus-Tuner/Tester
Free Tune/Test Drive Request Thread

soften the rear suspension just a tad, It will help throw some more weight on the rear when you get on the gas.

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Or loosen front down force and give it more down force on the rear.  You could also adjust the diff, lowering your accel%.

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"Never knock on Death's door: ring the bell and run away! Death really hates that!"

GT: sk15kev

kevinhinnels:

You could also adjust the diff, lowering your accel%.

Incorrect. That's a common misconception, I believe. His problem is not one tire dragging during a turn. That would be cause to lower differential settings.

His problem is during acceleration, so he would want to raise the differential settings so as to get both rear tires in on the action.

The differential settings do not reduce the total amount of power put down. That is simply a function of throttle application. All the power you ask for with the throttle is going to go to the drive wheels (assuming no TCS). The differential setting just controls how much can go to each tire.

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Click image to see the car's sale thread.
GT: EXOR x Bart x
http://www.exodusracing.net/ - Unassisted Racing at its Finest

Barthanatos:

kevinhinnels:

You could also adjust the diff, lowering your accel%.

Incorrect. That's a common misconception, I believe. His problem is not one tire dragging during a turn. That would be cause to lower differential settings.

His problem is during acceleration, so he would want to raise the differential settings so as to get both rear tires in on the action.

The differential settings do not reduce the total amount of power put down. That is simply a function of throttle application. All the power you ask for with the throttle is going to go to the drive wheels (assuming no TCS). The differential setting just controls how much can go to each tire.

Not to try and start trouble but, I'm afraid that I must disagree with you on this Bart. In all cases where I have experienced this symptom and then watched the telemetry, it is the inside wheel that is losing traction.  If the diff accel setting is high, the diff tries to lock the two wheels in at the same rotational speed. The outside wheel has the most weight on it and so has the most traction. It is also travelling in a wider arc and so, is rotating faster than the inside wheel has to. The inside wheel is forced to try and rotate at the same fast speed as the outside wheel and over-rotates, breaking traction and losing grip. With only the outside wheel now gripping, the car will start to slew sideways ( oversteer ).

If the OP checks telemetry on corner exit and the inside rear wheel is showing red on the traction circle screen, reducing the diff accel lock point may help.

Also, if the inside rear wheel appears as a tiny circle, this can be an indication that there is too much anti-roll bar and the inside wheel is trying to lift off the ground. In that instance I would recommend reducing the rear bar and adding to the rear springs in equal percentages to reduce the lift and improve the contact patch while maintaining similar levels of overall spring rate/ roll resistance.

 A rear suspension that is too stiff will also cause exit oversteer so, my recommendation ( without being able to drive and feel the car myself )would be to make note of the settings for rear ARB, spring, damper bump and diff accel, then lower each one individually to see which one improves the oversteer most without negatively affecting the handling of the car otherwise.

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R.I.P Pale Rider

GT: AMG Moctane

Its time to make the donuts!

JG4tr:

Not to try and start trouble but, I'm afraid that I must disagree with you on this Bart.

No, you're spot-on, really. Excellent explanation. I think I had more in mind the scenario in which the car is already straightened out.   

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Click image to see the car's sale thread.
GT: EXOR x Bart x
http://www.exodusracing.net/ - Unassisted Racing at its Finest

JG4tr wrote the following post at 07-17-2008 5:00 PM:

In the rear world this is true, in Forza this not. In the real world negative toe does help to make turning easier and positive toe stabilizes or 'discourages' turning. However in FORZA, this was modelled backwards. Moving your tuning sliders to 0.2 actually adds negative toe and improves turning and a slider at -0.2 adds positive toe and inhibits turning. I don't know why it was done this way but, if you turn up the adjustments and then go to a telemetry replay, you'll clearly see which way the tires are trully pointing.

man, this is mesing me up, now. are you sure about this? i've had tuning discussions with VooDoo from R2P about this and his take on it is that negative toe in-game is toe out. about a month back, before he and I starting chatting about tuning, i used to add positive toe for toe out and he told me i was wrong. so i went back and changed the toe on all my set-ups. ughhh..........

not that the in-game help menu in tuning mode is neccessarily accurate, i suppose, but i'm under the impression that the view of the diagram (the wheel with the shock and spring to the left of it) is from the perspective as if you were in the car, looking at the back of the front, right side wheel.

from this perspective, the (-) sign is to the left (inside), the (+) sign is to the right (outside), which would mean turning the back of the tire inside toward the (-) sign would point the front of the tire OUT, or negative, toe out.

of course, if the developers somehow botched the programming and got this feature bakwards, it just blows my theory out of the water, i guess.

it'd be nice i someone from T10 could reach out to the community and clarify this.

but for my own purposes, i suppose i'll park a car with the toe pointed max (in both directions) and check the telemetry replay as you said.

You can also drive the car with the settings at each end of the spectrum - the uncontrollably wandering settings will be toe out.

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Real racing. Real clean. Real fast. SimRacers.

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JG4tr wrote the following post at 07-18-2008 12:41 PM:

In the rear world this is true, in Forza this not. In the real world negative toe does help to make turning easier and positive toe stabilizes or 'discourages' turning. However in FORZA, this was modelled backwards. Moving your tuning sliders to 0.2 actually adds negative toe and improves turning and a slider at -0.2 adds positive toe and inhibits turning. I don't know why it was done this way but, if you turn up the adjustments and then go to a telemetry replay, you'll clearly see which way the tires are trully pointing.

wow, man...you were 100% right. i just went and set the toe to positive 5.0 on a test drive, parked, and panned the camera around to the front of the car. front wheels were clearly pointing way out.

did the same with the camber, set it to -5.0 and you can clearly see the bottoms of the wheels are out wider than the tops.

thanks a bunch for the info!

You are most welcome. Having done alignments in the real world myself, back in another life, this was confusing to me also until having proved it to myself by watching the force vectors in the traction circles of a telemetry replay.

I am left to make the assumption that T10 did this thinking that for the non-automotive types who would play their game, that it would be easier to associate positive adjustments with making a car turn easier and negative making it harder. With the number of car enthusiasts working on the project, I find it hard to believe that this was just an oversite. However, I have no first hand knowledge of their true intent.

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R.I.P Pale Rider

GT: AMG Moctane

Its time to make the donuts!

JG4tr:

You are most welcome. Having done alignments in the real world myself, back in another life, this was confusing to me also until having proved it to myself by watching the force vectors in the traction circles of a telemetry replay.

I am left to make the assumption that T10 did this thinking that for the non-automotive types who would play their game, that it would be easier to associate positive adjustments with making a car turn easier and negative making it harder. With the number of car enthusiasts working on the project, I fing it hard believe that this was just an oversite. However, I have no first hand knowledge of their true intent.

Noooo I gotta go back and change all my settings?? *sobs*

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Thank you guys for this thread. It's really helped me alot. I'm very impressed by folks' willingness to help.

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Tango Tuners Catalog

TT Seller

Thirig:

Thank you guys for this thread. It's really helped me alot. I'm very impressed by folks' willingness to help.

Ditto to that. Thanks for all the help, I'm running much better now.

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FrEaKyxXxStYLey
Absinthe Minded Auto Haus-Tuner/Tester
Free Tune/Test Drive Request Thread

I have a couple of small questions about the differential. This is a good thread and I don't want to fill it with bumps so this will help keep it on the front page.

Front acceleration 70%: Does this mean if there is a 70% difference in the speeds of the drive wheels, the differential locks? Maybe I'm wrong about the locking part, maybe the differential unlocks.

What is the downside for setting your differential to 0%? Do you lose acceleration noticably or is there something else wicked that will plague your car? Thanks again for all the help!

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Tango Tuners Catalog

TT Seller

 I don't know precisely how this works in Forza. I'm not sure if the diff we get in our race package is mechanical or viscous or, even if they are actuated by speed differential or by torque. In fact, it may be that the "70"  we see in our tuning screen is just some arbitrary numerical number that makes it easy for us to communicate with each other about our diff settings...

The number definitely seems to represent some aspect of locking. The zero value represents no lock and the 100 value represents completely locked. Now, this "lock" might be based on the split of torque between the two axles or it could be a split of the rotational speed of the two axles. I don't believe that this has been established with any certainty as of yet, at least within the greater Forza public. I would assume that the folks who wrote the code could tell us exactly what is going on behind the scenes but, I'm not expecting to get any answers from them, as nice as it would be to actually have that cleared up once and for all.

So, in your example of 70% Front acceleration, you would have a car ( FWD or AWD ? )  that accelerates very well as long as the wheels were pointed in the same direction. With the front wheels being responsible for turning the car, this is probably way too much and will have a tendency to push the front end under cornering-acceleration . High accel settings can be used in RWD vehicles a little more easily since the wheels are at least pointed straight ahead all of the time. When the wheels that do the steering also provide drive power, they must be allowed to spin at different rotational rates so, lower lock settings are needed.

For my tunes, the front accel settings are typically somewhere in the 20 - 35 range. Too low and you're not really getting the maximum power out to your drive wheels and down to the ground. Too high and you start to induce a throttle-on understeer because the inner and out wheel are being forced into rotating at nearly the same speed.

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R.I.P Pale Rider

GT: AMG Moctane

Its time to make the donuts!