Started running a new kosmic mercury in Rotax senior light. Our driver’s pace is great, but says he hates how the front feels light and darty. Dialed in full caster (which helped some), but not sure if this is the right approach! This is our first OTK, so is there something we should be doing to make the front feel more planted?
When he says “darty”, he means too reactive? If that’s the case, more caster will make the front more reactive so that’s probably not the right route from a mechanical point of view, though it will make the wheel heavier, so it may make it harder to physically steer.
The steering being both “light” and “darty” seems contradictory. The OTK kart is also known to have heavy steering so it’s surprising to hear it’s too light!
If he wants heavier steering, you can buy the “slotted” OTK steering shaft which can make the steering heavier in its bottom setting.
I would like to confirm whether this is a handling issue or a general driver feel issue though. Don’t want to ruin the handling trying these things.
Remember that the OTK kart’s advantage is the strong and reactive front end, so nerfing it too much might take away from the kart’s ability to work properly. It may be up to the driver to adapt and smooth out the inputs a bit.
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How is the rest of the front-end alignment setup? (Camber & toe)
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Yep, let us know the alignment and front-end settings.
I felt a marked difference between the front-end of a 2017 and 2019 OTK (between the S and R models), with the 2019’s being more reactive.
I liked this.
Did you come from an older OTK? As mentioned, your driver might just need to adapt.
According to the snipers, it’s dead in the middle - no toe or camber, just the caster fully poss (standard pills). Standard ride heights, 1396 on the back, 15 spacer on the fronts and he preferred no torsion bar - tried blade and medium bars, but made the darty feeling worse. He drove a KR on the same day and said it felt more planted, so that’s the feel we’re aiming for. Another observation is how much the OTK loves new tyres, and how after 80’ish laps they completely fall away - maxxis sportsman. Not our experience with other chassis.
The kart won’t work properly without the front bar, the OTK is designed around getting big weight jacking on entry so it needs a front bar. Also pretty contradictory to go full caster but no bar. You basically negate most of what the caster is working with by noodling the front end so soft. A bar is a must-have for that kart.
The kart is probably not using the tires properly if you’ve got a bizarre front end setup in there with no bar and full caster.
If the driver thinks the kart is twitchy, we should be slowing down the steering with the slotted steering shaft, removing caster, lowering rear ride height, going out to 1400mm in the rear, and probably making a driving technique adjustment as well. If a kart is reacting too fast, the driver may need to slow their hands down too. Probably some overdriving happening if they aren’t used to the reactivity of the OTK kart.
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Seat too far forward? See the thread on “new” seating position for OTK
OTKs always feel like noodles to me…
Pretty much was going to say exactly what TJ said - flat bar at the minimum is a must. Without it, an OTK just isn’t an OTK.
I’d put a dollar on saying he needs to change inputs. Don’t ever flick an OTK in to the corner. It’s a firm, consistent input with the outside hand and a controlled wheel release.
No toe is going to feel twitchy. I’d toe it out at least 1mm per side, if not 2 to get some balance. I’d also narrow the front to 2 small spacers. The toe change will reduce the front overdriving the rear at entry somewhat and the width will help the front from overdriving the rear at mid corner.
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Thanks everyone for the advice. A few things to try at the upcoming test! Will report back.
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