# Body roll and tire load

Discussion in 'Assetto Corsa' started by BhZ, Mar 24, 2017.

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I just finished reading "Tune to win" by Carroll Smith and while it helped me to understand better the dynamics of a racing car, it left me with some questions about some topics. From what i understood, each tire has its graph with grip/tire load. The grip on the outside tire should increase thanks to the weight transfer during a turn, but too much weight will have the opposite effect, reducing grip due to the slip angle getting too big. Based on this, i suppose that reducing the weight transfer should help, since the inside tire will have more load, being able to get more grip and the outside tire less, developing less slip angle at the same speed as before. Am i correct?
If so, my thought was to play with springs and ARB. Is there a way to know approssimatively the correct value to get more grip?

2. ### AndrewOut of my mind! Back in five minutes.StaffPremium

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Look, no offense, but that guide is extremely simple and lack of details. As i said, i read the entire "tune to win", so my question goes a bit more into detail. Your guide also state "Minimises roll under weight transfer allowing a lower ride height to be used" but it doesn't specify if changing springs/arb change the actual weight transfer. It may seem a stupid question, but i wanted to understand better if and how weight transfer is controllable (and obviously the relation with the traction circle). Thanks for the answer anyway.

4. ### Stereo

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Tweaking roll with springs will have minimal effects on weight transfer. Basically you're talking about the entire ride height vs. the distance the weight moves during roll. So if the car's CoG is at 60cm up and when it rolls it moves 1cm, then making it roll 0.5cm (which would be significantly stiffer) is still less than 2% change in weight transfer. Whereas you could drop the car 0.5cm and get that same change in weight transfer without making the car super stiff.

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Thanks for the answer. So i guess that's not a viable option. So if that's not usefull, the only thing i can do is to tune the springs a bit stiffer in order to avoid extreme camber change during roll and tweak the ARBs to mantain agility and grip, am i correct?

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mod-edit: can we please give each other some respect?

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Well, sorry if english isn't my first language and i may have misunderstood some things. I guess next time i will just accept my ignorance and inability to understand by myself and i'll stop asking questions. Afterall in this forum people just talk about issues with the game, not about cars, setups, driving...i think i may know why at this point. Thanks for the answer...

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mod-edit: removed

Last edited by a moderator: Mar 31, 2017
9. ### Ross GarlandR3E & AMS Club ManagerStaffPremium

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Asking questions is one of the many ways we learn, and should never be discouraged. Just because you may know something and consider it easy to understand doesn't mean it's the same for everyone. He also clearly states that English is not his first language and, surprise, that guide is written in English.

I don't really see what's wrong with asking a sim racing community about car setup either. It's not like he's asking the questions on Mumsnet, is it? If you can't be bothered to answer helpfully, perhaps you should save the effort of posting at all?

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10. ### RacingManiacGT1

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Amount of overall roll in and of itself does not affect overall weight transfer, only thing that affect total weight transfer is CofG height(higher = more), track width(wider = less), and grip(more = more). Sway bar balance(ratio between front and rear) affects the amount of roll and weight transfer at that axle. Stiffer increases the weight transfer at that axle, and also shifts some weight to the cross car corner. It could also affect kinematic grip based on tire characteristics(rolling amount vs tire camber)

The grip(lateral load of the tire) increases with vertical load(what the weight transfer is doing to the tires), but not at the same rate, at some point you won't get more grip increase with more vertical load(it'll increase, but at a reduced rate), and you will at the same time lose grip on the inside tire of the same axle. So adding more roll stiffness at a given axle always reduces overall grip at that axle, caused by weight transfer. Which is why sway bar tuning usually has the biggest effect on the oversteer/understeer characteristic.

Spring can do the same thing. All swaybar does is adding wheel rate in roll, you can add wheel rate with spring too. But spring has effect on other suspension characteristics too. So choosing which one to use is often situation dependent, and probably car dependent too. Since most cars in AC don't have ability to really tune ride rate and roll rate as independent variables, you are often compromising one when chasing another. In theory on a billiard smooth track, and if the car and tires work best to be like a stiff kart, both will probably get you there, whether you are running a lot of spring rate to get the car to not roll or really stiff sway bars to do the same thing. In reality you might want softer spring to give you more ride compliance to handle bumps and just use the sway bar to control the roll, or when you do run on smooth tracks you may want stiffly sprung car, run as low as you dare before bottoming.

In real life all these variables can in theory be simulated to out put the best combination based on track, tire data, and any of the environmental variables. In sim racing part of the fun I think is to figure out what the car needs after you drive it and play with the variables and see if it gets to the effect you want.

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I have a question on my mind for a while. How many seconds can be won with a really good setup comparing using the default one? I know that it varies from track to track, but let us pick monza for example. Does anymore have experience with that? I've tried tuning my 488 GT3 and found 2.2 sec. Not too much I think...

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I'd say 3 seconds on average.

13. ### Brandon WrightI may not be fast, but I'm wide!Premium

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Really? In my experience it's about a half second, maybe a second at the most. I usually go drive the car stock first, get to know it really well and how it handles around the specific track. Once I feel I'm getting the most out of it I'll find a tune to throw on and maybe shave another few tenths off but nothing major. But just by driving the stock setup around for 15-20 laps I will shave several seconds off from my first laps and I really get to know the behavior of the car.

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Take Monza...just working on wings and gear can give you one second. Spa is usually the most setup dependant. Speaking of gts cars, i usually run 2.20-22 with the default setup and the car can go down to 2.16 with a good setup. Last race at Mugello with the ferrari i used to run high 1.49 with the default setup, i went down to 1.46.9 with my setup. Btw, i also drive the car for a while before changing anything.
I may be extremely setup dependant, who knows...

15. ### Brandon WrightI may not be fast, but I'm wide!Premium

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Probably doesn't help that I'm fairly useless at driving and even more useless at tuning.

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I don't know how on Earth someone can run 1:49 on Mugello with a GT3 car. I don't say it is impossible, just dunno how to. I did over 300!!! laps and unable to go under 1:51. My average is 1:52 middle. I saw dozens of videos how to turn...starting outside, then touching the inside, then the outside again in the end. I saw others running 1:47 from the cockpit over and over again, at least 25 times, and didn't see the difference. Not one. Touching the kerbs at the same spot with the same speed. Tried several setups, trieu everything and to be honest, I start to lose my interest. My one and only problem, that since I play on a 4 years old laptop, I only get 15-19 fps with the lowest settings...

17. ### RacingManiacGT1

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I think that depends. how well the default setup suits a given track to start with. One that works well at Zandvoort would be very different at Monza or Spa. So that isn't really an easy question to answer. And some tracks would demand a more specific setup vs others. Monza you would need to eek out top speed, Imola would need a car that can handle curbs. Balance on a tight chicaney course may not be the same for a sweeper heavy course like Mugello.

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With 15 fps i wouldn't be able to leave the pits. Those are definitely part of the problem. Speaking of driving style, we'd need to see you driving to be able to understand if you can improve there.

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I will record some laps and upload that video somewhere. But where?

20. ### Rupe WilsonrFactor Senior Club ManagerStaffPremium

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Learning the track is so, so important. I always drive to RD rules ( two wheels inside the white lines on corners ect) so find it hard to talk about lap times in general.

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