Help with OTK setup and handling issue - oversteer after turn-in

Chassis Setup, Tires & Handling Forum
1

Sorry ahead of time for the wall of text, but trying to give as much info as I can. I’ve been struggling this year with my kart wanting to oversteer after turn in and during the entry to middle phase of the corner. I seem to get into this cycle where I try to make adjustments and think I have a path to success, but ultimately still end up with the issue. Then I think it’s just my driving and I try to focus on that instead, but ultimately come back to thinking the kart should behave differently. So I could use your expert advice.

I’ve tried to capture some instances of the behavior in these clips. Earlier in the season (gopro in the clips) I was waiting for the oversteer to settle before getting back to the gas which then always made me late to the throttle compared to my competition it seemed. More recently I’ve tried to get to the throttle earlier thinking it would set down the inside rear and settle the kart, but sometimes I think I’m causing the rear to set down too fast and causing the slide that way.

I am 5’11" and 188lbs which I guess is on the bigger side for a karter, but not as tall as many I see at the track. I’m running a 2021 Redspeed with an OTK seat set at 630/635mm (in-between the 180/190 recommended setup) height is even or a hair below the frame rails because if I try to run it lower at the tracks I normally run it’ll rip the bottom out.

I’ve tried adjusting with different front torsion bars, rear width, rear axle length (cut N vs standard N), front width, caster, and seat stays in various configurations. I find the problem typically more noticeable on colder tires or lower grip. It was harder for me to control with stiffer front bars so I went back to the flat bar in the front to slow down the transitions. Taking the rear width from 1395mm to 1385mm helped, but also seemed to bind the kart up a bit.

I’ve found myself trying to add grip via jacking (caster, stiffer front bar), but it seems that when the tires are up to temp and/or the track is gripped up that I then get an issue that I’d call oscillation from mid-corner to exit that you can hear here which I take to be the kart too bound up and on the verge of hopping. Am I correct there?

My most recent race I ran 3 setup changes between qualifying, pre-final, and final:
-Qualifying: Flat front bar, 2 small spacers up front, extra seat stay on the non-engine side, stiffer adjustable seat stay on the motor side, 1300 N axle at 1385mm width. The kart felt good, but a good amount of the oscillation noted above almost on the verge of hopping.
-Pre-final: changed to rear width of 1395mm. Kart felt like it had the oversteer on entry issue again, but I only got 2.5 laps in before throwing a chain.
-Final: took off the extra seat stay on non-engine side, went back to non-adjustable standard stay on engine side. Went back to 1385mm rear width. This felt the best to me, but again was oscillating (2 of the clips above from that race) and felt pretty tight.

I have 3 theories as to the issue but could use some guidance:
1: I’m overloading the outside rear on turn in when transferring weight which causes it to slide. I could potentially remedy this by reducing the transfer to the outside tire by removing seat stays, going with a softer seat, or going more narrow in the front although that may leave the kart without enough jacking.

2: The outside rear tire doesn’t have enough grip to handle the load no matter how slow it’s delivered. I could try to add more “side bite” by raising the rear height without trying to change the other dynamics of the chassis stiffness.

3: I’m a spaz and I’m too abrupt with my turning and throttle inputs and I’m causing it all myself. Here I could put a stiff spring on the throttle to help me not engage it so fast. I’ve tried going to the lesser ackerman holes on the steering shaft for this, but I didn’t like it, and it felt like i had to comparatively saw at the wheel to get the kart to turn. I also think I could go more narrow in the front to calm down the inputs of the wheel as a compromise.

1 Like
2

So, that’s a lot of informations. Given the chassis isn’t bent, an OTK is supposed to run great out of the box. That is the main point of racing an OTK. And I think they are still prone to oversteer.
On both the videos, it doesn’t feel like the chassis is doing anything strange. I am pretty sure it is down to your driving, especially the throttle application and maybe you are a bit slow to catch the rotation

1 Like
3

Chris - Long shot and doubt its the problem since your chassis is brand new. I bought a lightly used 2020 OTK and it oversteered very easily and on more than few occasion, the kart would spin out on the out lap. Also the braking was very nervous and it drove like a bucking bronco in some turns. I found that the right seat stay had a partially cracked weld at the crossbar. The crack was on the “inside” portion of the weld, so I couldn’t see it until the seat was out and if I weren’t suspicious wouldn’t even noticed the cracked paint at the base of the weld. To confirm there was a crack, I was able to slide a corner of a piece of paper into the crack. I got it TIG welded and that fixed the problem.

3 Likes
4

I didn’t see any mention of going faster/slower after certain changes. What did the stop watch say throughout all of this?

How old are your tires, and what sort of PSI?

What wheels? 3rd bearing loose or tight?

2 Likes
5

Its interesting to see someone else had the same problem. We have had 3 OTKs (1x 2020 and 2x 2021) and cracked the left seat post on all 3 of them.

In another interesting fact, we never felt the issue as oversteer. Always found it as bind/hop in the chassis in places where it normally would act fine.

Definitely worth checking for the OP.

1 Like
6

Hey Evan, hard to generalize those answers over the course of many races, but I’ll use this weekend as an example

Tires were MG reds on MXCs. Tires were new for qualifying.
Qualifying: 16psi cold - fast time was 46.02 on lap 6. Had some traffic
Pre-final: 14psi cold - 46.72 on lap 2 then threw chain
Final: 12.5 psi cold - 46.04 on lap 14

So times very similar for outright pace I think that the setup for the final likely just gave me more consistency and comfort. I’m still a good 0.30-0.5 seconds off of the pace though and it seems when I’m having these mini slides I’m losing time there.

To the others, thanks for the suggestions on the welds I’ll look them over closely.

2 Likes
7

So first off, good work compiling a lot of detailed information. It’s a lot to sift through here so I’ll try to address everything I see.

Video 1 - It definitely looks like the kart is too twitchy on initial turn-in and at apex. I don’t think your hand inputs look that aggressive, so I don’t think that’s the main problem. And your size shouldn’t really be an issue either. Plenty of similarly built drivers having success on the same kart.

In general, whatever balance the kart has will be exacerbated in cold/low grip situations. So if it’s oversteering more in the cold (not that uncommon for the OTK anyway, I’m always terrible in morning warm-up sessions) that’s probably to be expected. I’m assuming you are keeping the MXCs on for morning sessions? I know that will make the kart come in much later if it’s cold out.

So your method seems to be adding grip by way of jacking more weight up to this point. You’ve narrowed the rear and added caster or stiffened the front bar. As you’ve noticed, this is going to make the kart good in the morning, but start to get too stiff/transfer too much by the afternoon when the track has come in.

Video 2 - Looks a little like it’s on the verge, but not too bad. Some of it could just be the roughness of the track or minute steering inputs.

Looking at your theories:

  1. Yes, I think this is probably the case that you’re jacking too much weight, especially with caster in. Removing the seat stays altogether is something I don’t like doing, but recently @kentonkoch noted he had tried this and liked it. Might be worth an experiment at least.

  2. I think this is the wrong path. Your theory might be right that you need the kart to have more sidebite, but I think the issue is already that you’re asking too much of the tire and it has nothing left to give. Adding sidebite by raising ride height would just be pushing the tire over its limit sooner. A good example of why we need to think in terms of “rate of lift” and not “grip”. The kart lacks rear “grip” in this case, but this is down to us pushing the tire too hard. Any attempt to add more “grip” by pushing the tire even harder will cause it to slide even more, producing the opposite result of what we want. I think if anything we want to be reducing the amount of jacking/sidebite we are producing.

  3. I don’t think you’re that much of a spaz on the wheel, but the throttle pedal might be a partial source of your problem. I didn’t hear a lot of throttle modulation in the above videos. It can be hard to pick that out, but I mostly heard the kart revving and bouncing like you were on the cushion at Knoxville when you were sliding. A lot of drivers have a hard time treating the throttle pedal progressively and not using it like an on-and-off switch. I would experiment with testing a spring on there or trying to attune yourself to modulate the throttle a little more smoothly. Some of what I hear sounds like you’re preoccupied with getting to the throttle as early as possible, but not having consideration for how quickly you roll into the throttle. It’s very subtle, but something like that can really change the dynamics of the kart.

I hate reducing the steering rate as well, I feel like it gives the kart such a light and understeery sensation.

So just to recap, you went 1385mm in the rear and 1395mm in the rear (albeit with other adjustments thrown in there too), and narrow was too twitchy and almost on the verge of hopping but we didn’t really get a good read on how 1395mm felt. At your height would be guessing 1395 would be closer to where you want to be. Have you simply tried splitting the difference and going 1390? It’s important to remember that the OTK kart responds to really small changes. When the kart is on the verge of hopping, it’s aaaaaalmost at the limit of what it can provide in terms of sidebite before it hops. So at 1385mm, if it’s close to hopping, I would say 1390mm would provide just that tiny bit of extra comfort to make it less twitchy. I would try isolating some of the things you’re doing as well, as a rule of mine is to try not to make too many adjustments on one end of the kart at once. If you’re moving struts around and changing width in 10mm increments, there’s no way to isolate that and you might be contradicting one adjustment with another. One adjustment for each end of the kart per session is kinda how I do it.

Do you have any data to look at or study on these sessions?

Oh, also have you tried going neutral or half-caster out at all? I mean, we can get this thing to not slide at all, but will it turn?

8

Thanks TJ that helps a lot. Where my mind was going is that I’m transferring load to the outside tire too quickly after turn-in which overloads the tire. I wasn’t sure if the answer is make that transition more progressive to build the load slowly or more aggressive to give more pressure at an attempt to have more grip. Sounds like attempts at more aggressive won’t likely work which is what I believe I experienced when it was harder to control with the stiffer front bars.

I’ve only recently played with changing the rear width as previously I always left it near max. The 10mm changes were mostly due to ease of switching out hub spacers that were 5mm different each side. I think I have 3 mm spacers so I can likely get around 1392 each side to try that. In my recent experience I felt like the full width had less “grip” and was more prone to sliding.

To clarify in the times when I’ve added caster, it was only to half caster with the centering pills in the bottom and never tried full caster. You’re correct that I’m guilty of sometimes changing more than one variable at a time mostly due to not having time for practice days and having to make these changes during the limited runs on race day.

In lieu of removing seat struts completely, would a softer seat help slow the weight transition to the outside tire? I have a used Tillett T11VG I used on my old OTK chassis I could try out.

1 Like
9

Softer seat might help, it seems to be a good choice for taller drivers. I have a VG in my new kart. I was never a fan when I tested it but it seems to be the standard right now for OTK stuff so I’m going to give it another shot.

Yeah, I think given your size, we can rule out that lack of transfer/sidebite is your issue. I think it’s too much. Your path of thinking isn’t totally wrong; wanting to push the tire into the track, but in context I think it’s the opposite of what you need.

The other thing I was going to note was, have you tried staggering tire pressures front to rear? It sounds almost like you’re bouncing back and forth between balances a little bit with your adjustments, and sometimes I find that if you make some tire pressure adjustments front to rear, you can fine tune the balance a little. For example, if I feel like the kart is a little too free at max load (similar to what I think you’re experiencing), I might drop rear pressures 1-1.5psi compared to front. That’ll help the rear tire squat and flex a bit more, giving it a little more play before it breaks traction and snaps.

1 Like
10

I hadn’t considered the tire pressure change I’ll look into it. I was typically staggering pressures to aim for near even hot pressures after a session. For instance on this counter-clockwise track I’d start with my base pressure on the RR then add 0.5 psi to that for the RF and LR, then +1.0 PSI for the LF. that would typically give me hot pressures within a few tenths of a pound of each other after a session.

11

The other part of this story that isn’t helping is that Chris and I are racing together, sharing notes with each other, comparing data to each other but our karts are reacting differently…probably because of driver size / style differences. We probably need to quit assuming that what works for me is going to work for him because it’s only adding to the confusion.

I’m a few inches shorter 10lbs fatter and I’ve found a setup that works for me and my driving style but doesn’t seem to work for him…so I’m constantly suggesting stuff that worked on mine and it’s just not applicable.

12

OTK seat
OTK seat1360×1906 122 KB

OTK have “new” recommendations for the seat position.
If i have understood it right these are intended for chassis from 2019 and onwards.

13

Wow, that’s quite different from what I had. Since I’m 180cm I never know which measurement to follow but even if I went with the lesser of the measurements that’d have me moving my seat back 30mm which seems like a big difference. Any ideas how that’s affect the kart and the issues I’m having?

Side-note, I can never seem to get to the listed “c” measurement OTK gives without noticeably tipping the seat back at a further angle meaning the bottom isn’t flat and/or dropping it further below the rails than I’m comfortable with. Anyone does have that issue?

14

Assuming seat is moved back off baseline… I recently moved seat back 3cm. One of the effects that was odd is how it makes the braking very sensitive. The kart wants to unload much quicker so I found that braking had to get pretty surgical. Almost as if the kart wanted to hop in a straight line under braking and lock was a thinner margin of error. I widened front to make more stable/less hoppy under braking.

15

Chris for what it’s worth the OTK guy at GoPro recommended I mount my seat in the further back position. That’s the only place I’ve had it mounted and FYI I’m at a 41/59 weight split. Like you I was struggling for rear grip at the last club race. I went back a couple days later with similar weather/grip and switched to the concentric pill on top to remove caster and tended to like it. It settled down the rear for me in Turn 4 and the double rights. It brought down the LR tire temp as I believe I was overworking/overheating it. Next time you’re there give it a try.

16

Wow that’s a crazy amount of set back. That would almost make the steering wheel unreachable for me.
Maybe it’s to accommodate the taller drivers.

17

I was going to recommend moving the seat back based on the video, so it’s interesting to see the “new” OTK seat measurements. Try going back 1-1.5cm…that will certainly be enough to make a difference.

I’d also advise against copying other people’s setups. You can use that as information to help get you close, but often times there may be differences in driving style or feel preference that could cause a setup to work for one driver but not another.

18

@tjkoyen is this what you guys are using for seat position on the newer OTK chassis? Mine’s also in the wrong place if this is correct for the new chassis’

1 Like
19

I believe so, I haven’t put my seat in yet but I will be using the new chart. I’ll ask some of the guys if they are using the new specs.

20

so looking at the video it looks like your holding the brake while turning the wheel and then once you release the brake you slide so i think the issue would be solved if you let go of the brake before you tun the stering wheel