Can anyone explain to me how "better" suspension creates more traction? Or, if that's the wrong question, how do suspension and traction interact? What's the mechanics behind the relationship?

 

If your car is not applying steady force to the wheels

If the weight of the car is not properly distributed

If the wheels are not flat on the ground

If the wheels are not pointing where you want them to go



Traction will be negatively affected.



These all are affected by suspension, and that is off the top of my head and by no means an exhaustive list.

 

You are trying to press all four tires into the road as hard as possible, compared to how much the car weighs. The very important bit is: for every additional lb that you vertically press on to the tire, you get a diminishing amount of additional grip. Otherwise, trucks and cadillacs would be the best handling cars on the road because of all of that tire loading...



So for example:

car A is 2000 lbs and can provide a maximum of 1000 lbs cornering force

car B is 4000 lbs and can provide a maximum of 1500 lbs cornering force

car C is 6000 lbs and can provide a maximum of 1800 lbs cornering force

etc: with more weight, there is more cornering force available, but that force has to shift an even greater amount of weight, so the result is less actual grip



That's an important concept. It also matters within the same vehicle: you get the most grip when all four tires are evenly loaded. In a corner, a softly sprung car with a high center of gravity will transfer more of its weight to its outside tires than a stiffly sprung car with a low center of gravity. As you can see, when you increase the weight over a tire, it can provide less grip. When you transfer weight from the inside tires to the outside tires, there is less overall grip available to rotate the car through the corner. If you have poorly set up springs and dampers, the car is hopping and skipping across the ground instead of pressing all four tires into the tarmac, and you lose grip.



Also it helps if the tires are upright and not all keeled over like this:

 

When it comes to comparing an almost 15 year old Tib with stock suspension, to something with coilovers, low profile rubber and a proper corner balance; the difference is incredible. The science is just as stocker and wheel have described. Its just about keeping the rubber on the ground as often as possible. This does come at the expense of comfort as the stock Tibs had very light suspension that was really more akin to a commuter sedan.



To give you an idea, I did a local downhill run in my stock beta-ed Tib vs. a (low) boosted FD Civic sedan on stock suspension and wheels. He had me in the few straits, but he just couldn't keep speed in the corners. I had him by more than a car length by the end. Suspension makes ALL the difference, but it also helps that I have very nice big breaks and tons more experience.









However the transformation is not cheap. I have found that the chassis is plenty stiff even after all this time, so there isn't a huge need to invest in BS rods and bars, save for a good strut bar; but good luck finding good ones. It took me forever to find one for the front that actually had some (though limited) actual support. For the rear however I had to get one fabbed since everything still available that I could find is cheap, functionless, poorly constructed sh*t. I'll also add that for some of the components I actually wanted I had to come up with with 3rd party solutions. EX: for front swaybar end links I am using products from a Golf GTI. The deeper you go, the better grip gets. And the more poor it makes you, but no one is in the hobby to make money. Also keep in mind, the more you toy with the suspension, the more there is to adjust. So a simple alignment like most cars receive only does a fraction of the job. And the harder you drive the more stuff is likely to shift. If I am going to the track even for a meet or parade lap I still get the basic alignment done the day before and after. Once a year I get a full corner balance done, which is not a cheap operation, especially for a street car that sees regular use.

 

The points above are all good.



The best suspension setups are designed to dynamically maximize the contact patch with the ground throughout range of motion. The components and required geometry vary depending on maximum level of grip for a given surface and amount of suspension travel. An optimized touring car's suspension will be vastly different from a rally car's suspension even if the same make and model is the basis for both cars. The goal will be the same, but the surfaces are different and neither one would be worth a crap if they switched surfaces.



The difference in maximum cornering force between two stock or nearly stock production models with similar weight and weight distribution and the same drivetrain layout mostly comes down to how well the suspension keeps the outside tires perpendicular to the road surface during compression. There are LOTS of other factors, but if you maximize that you're going to make the most difference.



I race the Accent which is not blessed with particularly well designed suspension. My workaround is to run suspension much stiffer than would be ideal to reduce travel during compression and optimize front camber to ensure that at max cornering force my front tires have the max contact patch. I review GoPro footage to ensure this, plus check chalk lines. I let the outside rear roll a bit past perpendicular because then at the limit the car will rotate off-throttle but plant on-throttle.



But what about the inside tires? Even with a stiff sway bar the rear is about 8 inches in the air, so suspension configuration is irrelevant, and there's next to no pressure on the front either.

 

Basically, The suspension has only on purpose... keep the tires in contact with the ground. Everything else (ride, NVH, etc...) is just a bonus.