Troubleshooting Understeer

Chassis Setup, Tires & Handling Forum
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I’ve been troubleshooting some understeer issues for the last couple of races over a couple sets of tires and hoping someone can point in a direction in things to test…. (both new and used tyres) I started off the year with similar tyre pressures as previous but I found that I was overheating the rears which assuming is overpowering the fronts and which caused a bunch of oversteer (assumption based on the rear visuals). I’ve experimented by dropping the pressures down -3 PSI (Front and rear, tested by .5 increments) and it seemed to resolve the tyre visual and the kart felt “ok”. I find that when I re-use my older tyres I still have a bunch of understeer, somewhat putting this into the category that I’ve overworked the fronts and they are just done and I should move on…. When I use new tires set at lower pressures from the start they seem to be better but still suffer from a touch of understeer into hairpins as they get older.

I feel that I’ve discovered that my “baseline” setting naturally generates allot of rear grip and that when I started with a higher tyre pressure It just heightened it (yet based on the dimples they are “newish”). I feel that the OTK baseline I’m using is fairy generic (big space, -1 toe, neutral camber, flat bar, 1395 N rear with 3rd bearing locked, 1 seat stay per side).

Any thoughts or suggestions on how to change the balance? Usually my go to for understeer in caster but thinking that will just overheat the fronts and I should focus on removing grip from the rear… Maybe adding more seat stays, a harder axle, cut axle, lowering front?

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I would unlock the 3rd bearing. 3rd bearing loose is baseline for OTK.

1 Like
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Class?
Tires?
Class weight?

Lastly, what types of corners are you having understeer and what parts of those corners.

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VLR Senior/345lbs/levanto’s
Primarily into entrances of tight hairpins

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good to know, I thought unlocking the 3rd bearing would increase the grip (simulating a softer axle) which is why I usually have it locked.

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Add caster, widen the front end a small spacer. Leave the bar as it is for now. Half caster should be a good change. The OTK responds well to caster.

Your baseline setup is good but would agree that the third bearing should be loose basically all the time.

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Out of curiosity, what seat are you running, and is it mounted in the factory recommended position?

2 Likes
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Yeah im using a standard OTK 2 seat and it’s mounted to spec. Kart is scaled to 50/50 and 43/57

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+1 on TJ’s recommendation of adding caster. I was having a similar issue with my Compkart and that made a huge difference in getting the front end to bite. I narrowed the rear 10mm as well to get it to increase jacking in the hairpins. We went from MG Reds to Levantos this year and I hate them…but that’s a different rant topic.

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Thanks TJ, I’ll give this a go.

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If you feel like you have too much rear grip and not enough front, try moving the seat forward a 10 mm. That will take some weight off the rear and move it to the front. You can test this by shifting you body weight forward on turn in and see if it bites more. I had a similar issue, I was overcooking the rears and pushing into tight corners. Moved the seat forward and it fixed most of the issue. TJ’s suggestions took care of the rest.