Wheeeeeeeels! (Friction vs Traction Control)

[Juno_Atlas_Saturn]

I had a "oh now I get it" moment after doing a bunch of research and testing on wheel settings in career mode, and here's my attempt at the post that would've saved me some time:

Friction Control: Varies the amount of friction between the wheels and the ground. You can think of this as changing out different sets of tires with varying amounts of grip.

• Higher Friction Control: The wheel is less prone to sliding, slipping, and spinning out, at a tradeoff of the craft being more likely to flip over during a turn (the wheel becomes more likely to lift off the ground when rapidly changing direction since it doesn't want to skid). Higher friction can help keep a vehicle in place when braked on an incline. It can also help keep wheels from spinning out in low gravity environments (lower gravity = less downward pressure on the wheel, for which higher FC can help compensate). 
• Lower Friction Control: The wheel is more likely to slide, both front to back and side to side, and hence a craft with low FC may be more likely to spin out than to flip over. It can also make your steering-enabled wheels less responsive (they slide a little in addition to turning), which helps keep a rover stable at high speeds by preventing overly tight turns. Wheels with lower FC are less responsive to acceleration and braking as well. 
• Tips:
  1. Having a higher friction control on the back wheels (with steering disabled)  can prevent you from spinning out
  2. Having a lower friction control on the front wheels (with steering enabled on the front and not the back) can prevent you from flipping over while trying to steer at high speed (effectively makes your wheels less responsive to steering without enabling advanced tweakables)
  3. You may need higher friction control when driving up and down steep inclines or on low gravity surfaces
  4. UPDATE June 2023: Per the third link below (and my testing), while counterintuitive, you actually want to lower the friction control when driving on low-gravity bodies. While you may want to compensate for the low gravity environment (which imposes less downward force on the wheels) with more friction to make your vehicle more responsive to acceleration and breaking, you also make the vehicle more likely to flip over when turning. First priority in a low gravity environment is generally keeping your wheels on the ground in the first place when driving, and low friction control helps you do that at the cost of lower responsiveness.
  5. Consider combining tweaks to brake percentage with tweaks to friction control when trying to keep your planes from spinning as you land/brake
  6. More of a brakes thing, but remember that KSP doesn't have anti-lock brakes, so if you're spinning out while breaking try pumping the breaks rather than holding them down

Traction Control: Lowers the motor output to a wheel if it is spinning faster than the vehicle is moving. It's like the traction control in cars. The Drive Limiter function lets you lower the amount of power the motor is outputting to the wheels

• Higher Traction Control: The motor will put out less torque as a wheel meets/exceeds the vehicle's speed. This can prevent a wheel from spinning out (no torque for you until you match the rest of the vehicle!), but tends to lower motor output for the wheel overall. This lower output can also use less electricity per wheel on average when traveling.
• Lower Traction Control: The motor will continue to provide higher output as the wheel approaches/exceeds the vehicle's speed. This can make a wheel more prone to spinning out (overcoming its friction with the ground and sending your rover flying out of control). Lower traction control can help a vehicle on steep inclines (as it delivers more power to the wheels) or if a vehicle is stuck. 
• Tips:
  1. Pay attention to electricity resource consumption and the "Motor" status gauges in the wheel right click menu to get a better sense of what Traction Control is doing to your vehicle
  2.  Unlike Friction Control, Traction Control only affects your vehicle if you're using the motor. If you're powering your vehicle with jets, rockets, or rotor blades, Traction Control isn't relevant

Dev Blog References here, here and here

Hope this helps, and if I missed something important/got something wrong, please chime in!

Edited June 19, 2023 by Juno_Atlas_Saturn
I reread one of the Devblogs when tweaking a rover design and realized that one of my points was inaccurate. This update corrects it.

[Robin Patenall]

I wish I could have seen this a week or two ago before I went on my Minmus circumnavigation road trip. I think I got the wheels configured okay, but his would have made me more confident in the settings I used and had some tips that I might have implemented (different friction front and back). With any luck KSP2 will have better documentation.

[fleventeen]

On 9/20/2022 at 5:57 AM, Robin Patenall said:

With any luck KSP2 will have better documentation.

I am all for proper documentation, but with any luck, KSP 2 will have wheels that behave like actual wheels. 

I am still trying to figure out how to make my planes not porpoise down the runway on landing...

[Juno_Atlas_Saturn]

3 hours ago, fleventeen said:

I am all for proper documentation, but with any luck, KSP 2 will have wheels that behave like actual wheels. 

I am still trying to figure out how to make my planes not porpoise down the runway on landing...

Some tips that might help with the porpoise issue:

• Make sure the rear landing gear touches down first
• Decrease the angle of attack on your wings once you land, either using flaps to force the plane downwards or even by arranging the landing gear so the wings are angled down (ie taller landing gear in back - makes more sense on space shuttles that take off vertically)
• Locating the rear gear just behind the center of mass, which also helps with takeoff
• Higher brake percentage in the back and lower in the front (can also do this with friction control)
• Try to get your vertical descent speed to be less than 10 m/s, ideally  even 5 m/s when touching down
• Consider pumping the brakes instead of locking them on
• Make sure your landing gear setup can bear the weight of your aircraft without being bouncy (e.g. sufficient landing gear size/quantity and using struts to reinforce wings and other parts to which the gear is attached)

Took me ages to figure out how to land a plane I recently designed using MK III fuselage and F.A.T. 455 parts and the above worked for me (it even works for landing on uneven surfaces such as Kerbin's Highlands)

Edited September 22, 2022 by Juno_Atlas_Saturn
Clarify the landing gear arrangement

[LHACK4142]

Another thing I've noticed is that turning friction control up really high causes wheels to glitch and bounce around. I guess that's probably why it's adjustable.

[QPC]

This is necessary. Especially on Gilly. I often cause rocket cars to roll over because the tires don't have enough friction, and I expect the KSP2 to have a better system.