Handling Question


(Dom Callan) #1

After I put on new tires this Sunday I was experiencing a strange handling issue. The primary thing was that the kart would be giving me a ton of grip and all of a sudden the rear traction would sort of “pop”. I’d briefly lose traction (not a slide but rather a momentary loss of grip that would then return). This didn’t really feel like a “hop” but had the same effect of briefly unsettling the kart mid turn.
I felt like I was driving OK and I ran good laptimes but the kart felt like it couldn’t hold the loading.
Jerry widened the rear a bit to compensate but I felt like I was struggling to manage the grip while the kart felt pretty “darty”. Widening helped but didn’t get totally rid of this.
If I had to try to put it into words it felt like I had huge grip, tire would deform, it springs back (loss of traction for split second) then normal grip resumes.
Any thoughts?


(Davin Roberts Sturdivant) #2

Do you have any onboard or pictures of the track conditions?


(Dom Callan) #3

Yes. I haven’t edited yet but will tonight.
Track was green. No race in past 2 months and a lot of rain in between. I’ll do quali for you as tires were at there grippiest then.


(TJ Koyen) #4

What tires and pressures?

New rubber obviously is going to be much grippier, so the transition from grip to slide is going to be more dramatic. It’s harder to go over the limit, but it snaps much quicker.


(Dom Callan) #5

Le cont whites. 11psi cold. Never felt this before.


(Marin Vujcich) #6

This sounds like you are have to turn the wheel too far to unload the grip from the rear tires. Then once it unloads all of a sudden you get a snap (think of a spring) . I see a lot of people trying add rear grip, when in fact you need more front end to mechanical jack the kart earlier. I see this often with people that don’t run grip very often. Check your video if you have it and pay attention to how much steering lock you have on.
Could be not the issue at all but I see this a lot.


(Dom Callan) #7

Marin,
Come to think of it, I did notice that I was having to do bigger moves with the steering wheel than usual. At times I really had to jam it.


(Marin Vujcich) #8

Ok, what has happen in this case is as you enter the corner with lots of grip in the rear you need to put a little more lock on than normal (slight push), as the centripetal (g force) forces increases due corner radius, at some point you get dynamic jacking from your body in the seat. Then all of a sudden the rear wheel clears the ground (or unloads enough) and you now have too much steering lock on and the kart snaps as you overload the rear tyre. You may notice if you look at other karts in these conditions they will have the front end stiff, bar in, a little wider in the front etc. Some drivers do drive around this issue by trail braking very deep to get the kart to “fall over the front”, but your timing has to be on point with this. Hope this gives you a visual of what is going on. Just remember a kart unloads the inside rear tyre 2 ways, mechanically with front end geometry and dynamically with your body and the transition between one and the other is the key………that I’m still working on. I can see it in other peoples driving, just cant always do it…*sigh


(Dom Callan) #9

Ok well I just reviewed the footage and it’s even wierder than I thought. As I first get started it almost looks like I’m drunk for about 2-3 laps. It looks like the kart is bouncing around and clearly I am having to muscle it. It felt as if the kart was too grippy and somehow binding up the chassis in a bad way that would sort of explosively release. It was also darty on turn in.
As the tires progress it noticeably gets better. By the end it’s not a disaster and I qualified 3rd with about .4s on either side of me.
I went on to gain a couple tenths in the prefinal as they wore in further.


(Marin Vujcich) #10

Are you allowed to mount your camera somewhere else? If you cant see wheel and pedals pretty hard to see whats going on


(Dom Callan) #11

Sadly that’s all the footage I got. The problem went away as the tires came in


(Marin Vujcich) #12

curious as to why your camera was wiggling, the frame was moving. Is it the new gopro hero 7?


(Dom Callan) #13

I don’t see any excessive shaking or at least anything out of the ordinary. What part are you referring to? Time stamp?


(TJ Koyen) #14

I think you probably just had a little too much grip. I would try narrowing the front a little bit and going wider on the rear if you can. Also just try and be as smooth as possible on the wheel.

It got better as the run went on because the tires fell off a little. Also why you got faster in the next session.


(Dom Callan) #15

Ok thanks guys. Hopefully slight tweak will settle it.


(Lee Swindell) #16

Marin:

Awesome explanation.
:sunglasses: