Hey guys. I will have a test day this weekend and I’m trying to learn the basics of chassis setup. I was wondering if my inside rear tire litteraly have to lift of the ground or if just have to go up a little bit without get off the ground completely. I drive KZ and the tire don’t get off the ground conpletely. What I can do to lift more or less? Thanks
The tire just has to unload enough to not scrub on the track surface. So it may not come fully off the ground or it may come 6" off the ground, it depends.
Lift comes from weight-jacking. So to increase lift, you need to twist the frame more. To do so, you need to do things like increase caster, widen front track, stiffen the front torsion bar, narrow the rear track, raise the seat or rear ride height.
I wonder if messing with setup to adjust rate of lift is a good use of testing time if you are a newish driver? (Language suggest yes but KZ says no). Are you feeling like the kart is really skatey or overly planted? Can you play with adjusting wheel lift via driving approach successfully? (I have no idea, really, just seems like an extreme thing to chase, initially).
Is there a rule of thumb on how much lift per type of turn? As an example - a hairpin might require a lot of lift quickly whereas a less sharp turn may require a small amount of lift for longer?
Yeah but that’s very general. Different karts, different driving style, different setup configurations will all give a different amount of lift, so can’t really say hard and fast one way or the either. Two drivers on the same kart might find two different setups that work and one might have 6" of lift and one might have 1" of lift.
I might be wrong, but don’t you also need to consider the ‘rate’ of lift (how quickly the tire goes from no lift to max lift), and the ‘duration’ of lift (the amount of time between when when the tire becomes unloaded to when it gets loaded again).
So, for example, in a low HP kart where momentum conservation and scrub minimization are priorities, you might want a relatively slow rate of lift (so you don’t impact braking capability and/or induce too much oversteer with a quick lift), but also a relatively long lift duration (so you don’t set the tire back down too early in the turn), which can scrub speed because the engine doesn’t have the power to overcome the drag.
In a kart like a KZ, which is quite good at both decelerating and accelerating, and has the power/gearing to overcome a reasonable amount of corner-exit scrub, you might want a quicker rate & duration of lift (starting & finishing the whole lifting process closer to the apex), which might allow you to use the kart’s natural advantages. That is, for a hairpin, maybe you want to drive it in deep, so you have lots of energy at the apex (rotation point), and then have it setup so the rear lifts quickly and briefly so the kart can rotate efficiently. The shorter lift duration should set the back end quickly after rotation to stabilize the kart (with the kart now oriented to exit the turn in a relatively straight line) so you can take advantage of the KZ’s ability to accelerate aggressively out of the turn.
Sorry for the delay. Last month with medium grip conditions felt like I was planted in the ground, and last week I reduced caster and looked like the rear tires were pushing the front tires and inducing a HEAVY understeer.
If the tires do not lift at all, you will get under steer. If the lift too much you can slip the outside tire, set the inside back down, and then still fight under steer on exit.
There is a balance between track conditions, driver behavior, kart weight balance, and caster. More grip, more aggressive steering inputs, higher CG, more rear weight bias will all produce more jacking.
So things like a wet track or rubbered up high grip track can matter. How you are attacking the corners and managing steering, braking, throttle can affect lift as well.
So a smoother driver can get away with more jacking (caster, and front end width), a smaller driver usually requires more, wet conditions usually require more.
Work on smooth inputs, make adjustments, and follow the stopwatch.
Like TJ said, it just has to lift up enough to not scrub. Widening the front track width is a good start. If that still doesn’t work, stiffen the front bar up and hopefully that will make the difference you need.
Just note that any time you stiffen the front bar, you are effectively stiffening the whole chassis, so it will indeed turn-in better because it will jack weight faster, but since everything is now stiffer, it will also set the inside rear wheel down sooner in the corner too.
Not always bad, especially in KZ where you need exit traction.