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When to Stiffen, When to Soften?

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kind of a broad question but something that RaceCraft said in one of their videos really stuck with me........

"It doesn’t matter what level you’re racing at, the contact patch between your wheels and the race track are going to determine how fast you can go"

So my question is. If everything we do is to optimize the contact patch on all 4 tires then what is a great explanation of when to stiffen a suspension or anti roll bars and when to soften them? If heard the misconception that your average person thinks a stiff racer is fast but not always and sometimes it can hurt grip.

My understanding was that if the track is rubbered up and warm and you have a grippy set of tires that are not worn you should go as stiff as possible since the there is plenty of grip in the track in tires.

On the flip side if the track is green, wet, cold or tires are weak you should soften the suspension and anti roll bars or even raise the ride height to promote body roll and weight place on the tires.

I know that this might be a broad question with many different scenarios and answers but the more feed back the better

As you pointed out this is a very broad question.

Before the question can be answered you need to consider what the various parts of the suspension do, both on their own and in conjunction with other parts.

Springs provide the means of enabling the vehicle frame to withstand bumps and shocks from traveling over an uneven surface. They also enable the suspension to hold a certain amount of weight and control the effect that weight has on vehicle dynamics. In general the softer the springs the better and this is because NVH is a huge cause of driver fatigue but also because the vehicle structure isn't subject to harsh conditions compared to harder springs. As long as the springs are doing their job of keeping the tyres on the road the softer the spring the better.

The purpose of shocks is to slow and prevent the springs from continuously cycling and causing the vehicle to undulate while moving. In my experience the softest settings that allow the springs to do their job while stopping unreasonable cycling of the suspension is the best setting.

The sway bar is where, in my not so humble opinion, the magic of handling is. Not all sway bars are created equal but if they were the stiffer the bar system that keeps the vehicle flat and does not enduce under or over steer the better. Having said that remember they are not all created equally.

All of these things work in conjunction with bushes that depending on the material used and their hardness have a certain amount of deflection which enables the suspension to move smoothly and without undue binding. Together with a wheel alignment that is the end result of alot of testing and data gathering you should be able to get the best contact patch possible.

Thanks for the reply. nice read

I guess what I trying to get at is.......if you were to go to a track that was freshly resurface(so obviously little grip) would you presume to lean towards setting the car up softer? On the flip side, you go to a track that gets frequent motorsport use and stays well rubbered in, would you presume to be ale to run your car stiffer(lets say its not a bumpy track either)

Just looking for a few baselines to go on to give me somewhere to start then tune from there

To many variables (e.g vehicle weight, track design, air temp, etc etc etc) to give a definitive answer to that. As a baseline I personally, and this is just from setting up street cars, would start with a soft suspension and see how the vehicle feels with regards to suspension movement (spring rates, absorber valving, etc etc etc) and then set up the sway bars for best cornering.

Hey Blair, as Michael has mentioned, there's not a lot of absolutes when it comes to spring rates. The optimal range will depend on the car, the tyre, the track, and to a large degree driver preference. A car that's softly sprung will tend to ride bumps and track irregularities better which can maintain better contact between the tyre and the track. Of course the downside is that the car will body roll more and this can affect the handling and control, particularly as the car is transitioning from one direction to another. Added body roll and suspension movement in turn affects the tyre footprint on the ground and may require more static camber. If the spring rate is too soft you'll also find that you're going to run onto the bump stops which will adversely affect handling since the wheel rate at that corner will basically climb to infinity. On top of the basics, altering the spring rate at just one end of the car can affect the handling balance between understeer and oversteer. Everything is compromise.