(adsbygoogle = window.adsbygoogle || []).push({}); The Gran Turismo suspension.

I'll update the OP as I figure out how to word it better, as is its more thoughts written out. This is a highly important subject for all the tuners out there

There is a big dfference between the suspensios on real cars and the "Gran Turismo" suspension. While many will be upset with some of the differences and its still up for debate on the reasoning behind them, knowing the differences will greatly help tuning. I like to leave it at simplicity. In my opinionion most differences are due to simplicity for the average player to tune and this IMO is partly due to the sheer number of cars in GT. Where cars in real life will have many aspects specific to the vehicle being tuned, GT uses the same "core" suspension design on all cars.

Breaking Down The GT Suspension

Every single car in GT has the same fully independent suspension, there are no live axles or variations of double wishbone or multilink suspensions, they are all fully independent. They all have the exact same amount of camber gain from car to car, basically using the same suspension geometry. No suspension in GT is progressive, cars in real life may use progressive rate springs or have progressiveness in the design (rocker actuated) no progressiveness is simulated in GT, they are all linear.

There is an odity with the GT suspension where raising and lowering the ride height moves the entire body and only the body up or down while the suspension is fixed. The camber gain as you raise or lower ride height on real cars changing the static camber angles is not simulated as raising or lowering ride height basically has no impact on suspension but rather moves only the body simply lowering or raising it. This is important, as its very different to reality. Dropping the suspension does not reduce damper stroke on compression while raising it on extension as it does on real cars. The amount of stroke on both sides remains the same as the height is adjusted, and the camber gain on both sides also remains the same, this is the same on all cars, the difference is the position of the body only. There are no bushings in GT, bushings and flex in links basically is not simulated. We do not need to account for any flexing of the links/bushings in the suspension at all.

When raising or lowering the ride height moves the body up or down, tere is a limit before "botoming out" its determend by how much travel the damper needs (specific to the car being tuned) and how much travel is availible, specific to the body of the car being tuned). If for example the damper needs 40mm travel on the compression stoke and the car is lowered to the point where there is only 30mm of body travel available on the compression stroke before botoming out, then the compression stroke will be short 10mm of travel. This is different from car to car in that each car will use different amounts of stroke and the limits of the body movement will also vary. Steering varies from car to car using different caster angle and amount of Ackerman effect. The Ackerman effect simply increases steering angle vs input progressively.

Spring rate and leverage factor work together to determine the freequincy of the wheel. While in real cars this is also true, in GT the leverage factor is a fixed value, in real cars its determined by the suspension geometry. In GT its solely represented by a fixed leverage factor that varies from car to car even though the suspension geometry from car to car in GT is the same.

The chassis determins how far apart the wheels are spaced, along with the weight and weight distribution. Behind the scenes PD also calculates the sprung weight and this weight is applied to the body. The chassis also varies how much flex there is distorting the wheels positions. The more rigid the chassis is the less the wheels will flex from position. Older chassis have more flex than newer chassis and improving rigidity reduces flex by a fixed amount. The more rigid the chassis is the more true the settings hold.

The body dictates the aerodynamics, more or less drag and downforce created. It also dictates the height of the center of gravity impacting pitch and roll.

PD simplified the suspension however it will throw off people who tune in real life, especially if they are tuning a car in the game that they are familiar with tuning in the real world. Often tuning they do specific to the car will not really apply to the car in the game. While at the core the raw tuning for handling performance will be the same

I'll be able to get more details when the Data dumps arrive, but I fear that's on a back burner due to some technical issues FSX is dealing with loosing so much stuff and having to redo much of his work.

When it arrives I plan to analyze spring rates vs leverage looking at the available adjustment range, and then the frequency. The frequency and sprung weight data will be highly useful.

I am stuck trying to figure a way to measure/calculate/estimate the COG height. This could seriously help calculating weight transfer. I've got all the math worked out but Im estimating the amount of sprung weight and COG height so its rough at best.

A big reason for this thread is to squash all the stupid arguments that mix real life and GT. Debates over GT physics often mix up the 2 and its annoying.

Good post, can't deny the logic.

Thank you, I was one of the guys at the start of GT6 who was applying all the real world tuning techniques I know. Especially damper tuning that after testing the suspension geometry turned out to be useless. I'd stiffen up my comp stroke thinking I had to when dropping ride height, but after much testing finally realized I still have all the stroke I had at stock ride height. Only when I lower to the point the body runs out of travel do I start loosing stroke, it was a wake up call for me to fully break down the suspension so I don't make the same mistake or waist time tuning stuff incorrectly. My damper calculator is a good example as its more suited to IRL tuning and doesn't work on GT6 cars, but now that I've figured out how the suspension works I have the knowledge to fix it (I should get on that lol) its improved my tunes and shortened my tuning time quite a bit.

Sir, thank you for this research and information. At the begining, i was using real world tuning methods too, just to find cars handled like
s h i t, thinking "oh let see how real this game is".

Now, this ends with all discussions, GT6 suspension is not very realistic, as simple as that. Still like the game, but it disappoints me, however, it's good to know.

Was playing with castor today and can confirm a few things. Castor is not the same on every car, at one point I saw a post that assumed it was, can't remember where. Also it is adjustable but there are limits imposed (at least graphically). I am basing this on visual checks only. The lower limit is greater than 0. Zero was not possible, although I need to test more my guess it is around 5 and the upper limit is most likely 25.

I was thinking 6 to 12, 25 seems crazy high but wouldn't be too surprising. I visually confirmed it was different car to car, but I'm measuring how much neg camber it takes to flatten the inside wheel, so its rough at best. Nice more confirmation of good dynamics, it would kinda suck if they were all the same. It would be nice to adjust it