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rFactor Ride Height Tutorial

Generating "Ground Effect" by using optimum ride height



When we start talking about ground effect there aren't really any shortcuts. You need to work out;

1. For the car you are driving, what is the relationship between ride height (front and rear) and the downforce generated by the diffuser?
2. What ride height are you actually running.

For the first, unless someone has tested and posted the data (and you trust them!) you need to get the utilities out and check for yourself. For the second...there is no shortcut - you need to get your hands dirty with the MOTEC add-on.


1. Analysing the car model

For this the easiest tool to use is Kangaloosh Car Factory. Load up your car's HDV file (found in the relevant vehicle's directory), and go to the "Analysis, aero" section. There are tick boxes so you can look at overall downforce, only front wing, only rear wing etc - but I generally just untick all of those and leave only the diffuser (the one we are interested). Then you can see the chart on the very left, which shows front ride height on one axis and rear ride height on the other. Then in the chart you can see where the maximum ride height is generated - you can also see at what ride heights the downforce begins to drop or stalls.
NB: The graph data in Kangaloosh (in the legend when you hover your mouse over the chart) is shown in Newtons (N). To convert to kilograms of downforce, divide the figure by 9.81

In some mods there is little difference - those are not "ground effect" cars, or else have no diffuser. In that case don't worry, and set your ride height based upon other things. In other mods (like GP79, CART etc) the ride height is critical. Taking GP79 as an example, you can see the downforce gets better and better (more and more) all the way down to 30mm ride height. Then as the car's height drops below 30mm the downforce starts getting worse again. Note also that running "too low" is worse than "too high" - that appears to be to simulate the effect of "stalling the diffuser", where there is insufficient airflow under the car.

So armed with this knowledge your goal is to get the car's ride height as close to 30mm as possible, particularly in the critical corners where downforce really matters. Also, you need to ensure that your setup is not STALLING the diffuser by being too low in key corners.


2. What's our ride height?

How do we target 30mm ride height? Well, we can't just dial up 30mm ride height in the garage - that value is your "static" ride-height, and doesn't tell you what happens on track. As you build speed the wings and body press the car into the ground, reducing your ride height. Softer springs squash down more. Lower tire pressures also squash down more. Softer springs or bumps in the track "bounce" the car more - all of these things affect the ride height. What matters is your ON-TRACK ("dynamic") ride height. I'm afraid that means MOTEC. You can use rfDynHud which can show ride height, but it's a very rough figure and hard to keep an eye on when you're driving! Really the only way for reliable data is MOTEC.

The very first thing you need to do is identify where you need to be quick. So take Monza as a good (and easy!) example - everyone will be running skinny wings, so apart from the downforce generated by the body etc, basically ALL of the downforce comes from ground effect. If you set up your ground effect properly and others don't it will be a massive advantage over those other drivers - you get more downforce, but no increase in drag. So thinking of Monza, downforce matters in Lesmo 1, Lesmo 2, and to a lesser extent Ascari. Everywhere else is low speed (where downforce will anyway be low from wings and from ground effect) or it's an acceleration zone (e.g. Curva Grande - flat out). So knowing Lesmo 1, Lesmo 2 and perhaps Ascari are the key ones, you need to find what is your ride height at those three corners.

Load your race setup with about 3/4 of the fuel you plan to start the race with - remember too low a ride height is worse than too high, and your car will run lower if you whack in lots of fuel - that would mean less downforce and possibly an unbalanced car, so always test with race fuel and setup.

Below you will find a link to a GP79 MOTEC analyser, which you can load into the MOTEC program. From there load the data files generated from your testing and select the suspension section in the MOTEC analyser. You will see a graph which shows your ride height, and also a small circuit map. Your fastest lap should be auto-selected, so move your mouse along the chart until the circuit map shows you are at the Lesmos. Now check what's your ride height. Say you are at 24mm front and 26mm rear, you would go back to the garage and try raising 6mm front and 4mm rear. Then test again.

(Note: As a tip you can right click on the chart "legend" and "filter" that data. So tell it to average the data across 5 or 10 samples. As you see the chart "bounces" a lot, and that is quite literally the squashing of your tires. As you hit bumps there's a huge amount of movement comes from tire squash, and "filtering" the chart can eliminate that movement (from the chart - it will still happen on track!) and allow you to see the average ride height).

Remember optimising ground effect by changing ride height has other consequences - your car's centre of gravity will be slightly higher or lower, and by raising the front and rear by different amounts you can affect the balance (e.g. the car might oversteer, as you could be adding more grip to the front than the rear). However it's almost always better to get the ride heights correct, as that will give you maximum downforce for no drag, which is GOOD!. After that adjust other things to fix the balance - so you might stiffen up the front suspension to rebalance the handling, or play with the dampers, depending when/where you get the oversteer.



That's an example for GP79, however it works the same in any mod. Find what the design optimum is, then tune your setup to suit.



Related links: rfdynhud - Motec - GP79 Motec Analyser - Kangaloosh Car Factory

Article written by John Wallace

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