Lack Of Rear Grip Through Long, Fast Sweeper

Hi all current setup as follows:

Haase Zenit
TM KZ10C
4mm negative camber each side
2mm toe out each side
Neutral caster
Standard front bar in
2 left seat stays
1 right seat stay
3rd bearing tight
1400mm wide rear
115mm double knuckle magnesium hubs
1020mm hard axle (Spec for series I run)

At my new home track (Hamilton, New Zealand) I am struggling for rear grip even on brand new Vega XM (white) tires. Following other karts I am faster than most in class through the rest of the lap but then lose 2-3 kart lengths through this left sweeper. I can’t maintain the same speed as the other drivers without sliding toward the center of the track and starting to overheat tires

I took the caster out to minimum and didn’t really like how the kart felt and added a few tenths to my lap time. I also tried bringing the rear in to 1396mm and this made the rear feel even more unpredictable and snappy through this section. Could some changes be recommended to me to trial next time I hit the track.

Cheers

Sweeper in question:

KS%20HAM

Spec axle in a KZ, that’s interesting. At what point on that pic does the rear start to slide. For sure I’d keep the rear at Max track width in a shifter. Bringing it in will increase the load transfer which is probably not what you want in that turn.

Go back to Max track width on the rear axle and tune the rest of the kart around it.

Yea agreed that’s what I did. Only ran 1396 for 1 session then went back to 1400.

Sliding starts at apex really. So where the rubber meets the curb in the above image

1 Like

How do your tire pressures look when you come off a run? Is right higher than left?

My local has two fast right handers, same kind of deal. I fixed it by running a lower tyre pressure (cold) on the left tyres since they work more than the rights. Up to temperature they’re nicely even instead of the lefts over heating

1 Like

Have you tried moving the seat back?

1 Like

Seat is set up to factory recommendations and is as far back as it can go without moving the orientation of my water pump

On suggestion of a multiple series winner I was running cold psi:

FL: 10.0
FR: 10.2
RL: 9.0
RR: 9.5

The tires looked good after the run and feel good throughout the race

Depending on where it is right now, I’d try moving it back 10-15mm. The water pump shouldn’t decide how your kart handles!

Treat the factory recommendation on seat position as a baseline. It’s likely based around a setup with a different axle (ie not the hard one), different driver weight and different tire compound.

You can use a shorter water pump belt, or turn the pump around, press off the pulley, and press on a rubber wheel as a “gear” to turn against the axle.

For sure look to get that seat back so your weight is over the axle / wheels more.

Interesting - CRG chief mechanic told me last year never have unbalanced seat struts. 1-1,2-2,3-3

Depends on the kart. We never offset seat struts on the DR when I ran it, but I remember doing 2 on the left and one on the right with an OTK before. Now with the KR we don’t even use seat struts so it’s really chassis dependent.

One question I have; if you’re really fast through the tighter sections of the track, do you possibly have too much grip in the kart? Last weekend at Ocala I was really solid through the tighter section but was losing out through the last turn which is a long sweeping 180 where the back end would step out on me at the apex. As we took grip out of the rear, or set the kart up to jack less, the kart was more stable through the high speed corners since it wasn’t overloading the rear tire through there. This is also in KA100 vs. KZ so I could be totally off with this possibility.

1 Like

It sounds like you have to raise the chassis in the back,or/and reduce Ackermann.

I would start by taking camber out 4 neg is to much will make kart turn in an then get loose mid to out on turn. some karts do best at near zero an if a bumpy track try softer axle

Add a 2nd seat strut to the right side.