Is my chassis straight enough?

Chassis Setup, Tires & Handling Forum
1

I had a chassis straightened, but it still a seems little tweaked. I’d like to get someone’s opinion on the following:

  • I did a front end alignment, but tightening the RH kingpin moved the camber. Bent king pin?

  • After the alignment, I put a 6-foot level on top of the Snipers to check the frame relative to the axle. The RR end was slightly higher than the level, but not by much. Not sure how to measure.

  • Measuring from the axle to the top center RH king pin is 3/32” less than the LH.

Are these side-to-side differences within tolerance? I imagine no frame is perfect, and mine seems close. Is it close enough?

For the RH king pin, I could get the alignment I wanted, but it took a few tries. I’m going to get a new king pin regardless.

Anything else that I should check?

Thanks!

2

Make sure when doing this that your axle is same height setting both sides and spindles are same place in their C support…

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3

A good way to tell would be to sit in it on the scales and see how it looks weighted up on the ground. That can change a lot of the geometry.

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4

I’ve done a lot of frame straightening. Usually we go for 0.5mm deviation in the right and left side yokes. Depending on how tweaked it can take a couple times to get it to stay decent as the metal has a lot of memory. Usually we’ll go a little past where we want it expecting it to spring back some.

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5

Corner weights with half a tank of fuel:

  • LF: 74.3
  • RF: 82.9
  • LR: 104.2
  • RR: 105.9
  • Total: 367.3
  • X: 49.1%
  • F/R: 42.8 / 57.2
  • LF-RF delta: 8.6

I have to add 25-30# to hit the 360 minimum, mostly on the front of the seat to get a decent distribution.

It all looks pretty good except for the difference between the fronts: 8.6#. Too much? (This was always a large difference even before I had the frame straightened.)

6

This looks fantastic. 49% cross is great especially if you’re running CCW. Add your weight and let her rip

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7

I like to use a laser level in a darkened garage. Set the trolley up so that the rear axle is dead level. Then use a tape measure to check the distance between the laser beam and your kingpin tops. Before doing this, you have to remember to loosen torsion bars and maybe even the seat to let the chassis relax. I do all of this while the kart is on a trolley where it’s suspended by two points at the rear end and one point in the middle of the front. Then I decide whether or not I take it to the shop and have it straightened.

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8

Beginner observations when scaling:

  1. Don’t forget components: I forgot to put my front bumper on, and that skewed my original numbers;
  2. Follow the same process each time;
  3. Baseline set up is the biggest thing to get right. Adding ballast helps, but doesn’t change things significantly. Ditto for different seat positions;
  4. Let ChatGPT do the math: I entered LF, RF, LR, RR and asked, “What’s my X and F/R?” Boom. Answer in seconds with comparisons (better/worse) to the last set of numbers.
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9

If the L/R weight difference can’t be narrowed with ballast, does it ever make sense to bend both seat stays away from the motor (to put more weight on the LR wheel)?

Question inspired by: Chassis Too Narrow For Seat?