Tall driver, very high grip, bind and hop

Chassis Setup, Tires & Handling Forum
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New to karting, have about 13 months experience. Mechanical engineering background with strong mechanical skill. I am working with my 16 year old, very tall son. He is 6-4”. We are lost!!!

Our home track is North Texas Karters in Denton TX. We are experiencing a significant loss of pace during the summer months when the rhino lined track surface picks up ridiculous grip. Have witnessed more than a few grip flips in our 13 months. Turn 1, 2, 3 are all banked, turns 4 thru 9 are all flat. In winter or wet, my son is competitive, in hot conditions anywhere from 0.4 to 0.9 off the leaders that he was in front of at times this winter.

Kart is a 2022 OTK LN running a Briggs LO206. Motor is mounted on a 15 degree mount with the sprocket in-board and set as close to the seat as possible (we bent the posts over slightly to accommodate chain. New frame, no cracks or bends. Running a size 2 Tony seat set as far back as we can and seat bottom flush to just below frame rail.

Baseline setup is
3 mm camber
1mm toe out
caster with neutral bottom pill and sniper top pill at 1 stop forward
Front spacers at 1 full and 1 small
Front bar horizontal
Rear width at 54.75 to 55.125 (max)
Std med rear tony hubs
Douglas magnesium wheels (he doesn’t like the feel of the different offsets in the OTKs)
Ride heights at medium all around
Steering links on upper holes of steering shaft
1030 mm HH axle
I don’t have the current front/rear weight but can get that tomorrow evening.

Right now we are forced to gear to compensate for the lack of corner exit speed and are running out of gear on the end of the straight. So typical 1-2 tooth bigger on rear than competitors.

We have experimented with lower rear ride height, narrowing the rear, adding caster, going vertical on the bar, adding spacers. All have either made no measurable difference in the lap time or made the hopping severe enough that he can’t push an entire run.

He has convinced himself the kart is down on power, I see the rapid gap that forms from middle to exit and am convinced we have a chassis tuning issue or the driver turning in a bit late and asking too much of the kart. The latter is going to take some feedback from an experienced driver for my son to accept, as I have no driving experience.

I believe we should be exploring narrower front with 1 full, or a half spacer, running the bar out, and standing the kingpin up even more to take even more jacking out of the kart, but at this point am not confident.

Any suggestions much appreciated.

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To me it seems like he is not able to hold the lift, in this case I would narrow the front and remove caster with a zero pill to rely on the grip to make the thing jack.

Remove caster would slow down the lift and take it to the end of the corner. Also use 2mm total toe out instead of 1mm

Any seat stays? In my experience they are good at holding the lift for longer if you can take the corners at a smoother rate to hold the lift.

A shorter rear hub would give you more bite at mid/exit corner hence holding the lift for longer😁

On a otk do not remove the front bar at all, it’s a sin! I would use the chrome round bar. It is pretty much the only one you need, a stiffer bar would give you better turn in but it will push at the exits.

Ever tried a different seat? The Tillett T9.5 is a more inliced seat that will take his gravity down a bit.

Which Douglas wheels are you running? Standard?

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What has worked on my crg road rebel and KT5 - These all are needed to take away the hop. Just one mod doesnt help in my case. I bet its the same with other brands. Taking the caster out was the most effective, after that narrowing the front.

Rear to max width. If any hopping issues - this is the first step. Widening the rear alone doesnt remove hopping but cuts some of it. If you lack rear grip - start narrowing the rear only after the hopping has gone away. Any narrowing while having hopping issues makes the hop severe

All caster out, from top and bottom

If taking the caster out isnt enough - Narrow the front until hopping goes away. For example yesterday my hubs were as far in as they would go. I guess in otk that would mean taking all the spacers out. Stock width in my case caused severe hop. The more I narrowed the front the faster I went. The hop got less and less

Put more negative camber. You already have quite a bit of negative camber so you might be maxed out. Neutral or positive camber in my case made the hop severe

Add rear tyre pressure

Add seat struts

I would commit the ultimate sin and try without the front bar :smile: But only if taking away the caster and narrowing the front didnt help. Put the front bar back when cooler weather arrives

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Tough situation. That track is brutal and with your son’s height it will be tough.

You’re doing a lot of the correct steps and the above suggestions are great.

For sure you need max rear width, lower rear ride height, and I would start taking caster out until it goes away. You probably need to go negative caster to solve it. Can also narrow the front width.

And even if your son doesn’t like it, I highly suggest switching to MXC wheels. They’re a must in conditions like you’re driving in.

Something I’ve also done with similar height drivers is raise rear tire pressure a bit. It isn’t ideal from a tire performance standpoint but it can stiffen the tire up a bit and keep it from digging in so hard.

Agree that running no bar on an OTK is a sin. But given you are in 206 you can try it and see what it does. The front will feel like a noodle and the kart won’t work like it’s supposed to but you are in an extreme situation. It hurts me to suggest that :sweat_smile:

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TJ, what about a different seat to get the center of gravity down? Comet Beasley is what I would recommend, but there’s others out there.

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Also a possibility. As Lucas noted the T9.5 is for tall drivers and in 206 a Beasley seat could be good too. The only experience I have with the Beasley seat is staring at the back of one for laps at a time back when Sam was racing…

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Thank you. I totally missed Lucas’ recommendation. Yes, I would be looking for a seat other than an OTK to get my CoG down a bit just as he said. That may get you into a window where you don’t have to get so extreme on the tuning.

FWIW, @Matt_Geist won quite a few races on an OTK with a 206 and a Beasley seat. Couldn’t get it freed up enough with an OTK seat. Eventually, though, he just ran out of options and had to pick a chassis that was more favorable to the lower hp, high grip, large driver scenario we are all in now.

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@tjkoyen- what is the typical outcome when changing seat rigidity with the OTK chassis? Will a softer seat free up the kart (I’ve found it does with other chassis)? The OTK seat is quite stiff, so he could try a T9.5 VG.

@Chuck_Goodson- I have experience tuning for a taller driver, as my younger brother is 6’3". We would always recline his seat to get the CoG lower, and that allows you to do so without having to switch to a different seat if that’s something you’re trying to avoid. Usually we’d try to get to around 18cm from the axle to the top of the back of the seat.

In my experience the OTK does not work well with Douglas wheels.

Do you have exact seat dimensions you can share? In low HP classes you can definitely have the seat too far back.

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I am 100% on different seat will lower CoG significantly

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Softer seat will free it up generally, but you’ve gotta be careful not to introduce too much flex to the rear of the kart.

I run the T11VG as my baseline.

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One note regarding seat stiffnesses

Some seats might be labeled as hard or soft but what matters quite a lot too is how stiff the seat is at the mounting points. Some seats give in a lot at these points although they might otherwise be labeled as “stiff” or “hard”

A seat that has more material (thicker) at the mounting points gives more side pressure to the tyres. Its easy to notice if you ever race with a seat that has somewhat broken mounting points. Theres a lot of delay in side pressure. Theres a lot less pressure that you can apply if the seat gives in

I laminated few extra layers carbon to the mounting points. Laminate covered about 150x150mm area. Noticed immediately at the track that the seat could deliver more side pressure. It felt like proper racing seat instead of lazyboy chair. Felt like I had fitted extra seat struts

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I can second this. kart feels quite different with DWT rim vs MXJ. I think only AMV 3F and 9F has the same offset as OTK rims.

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I’ve put a lot of time in on the AMV 3F now on the OTK and I’d place it between MXJ and MXC in terms of tire temp management and overall feel.

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We are using the DWT wheels. It is what came on his used 2017 OTK when we started and when we got the new LN Kart in November he preferred the feel. Now it is warmer and he is being a touch stubborn about trying the stock OTK wheels that came with the LN.

The seat is set leaned back quite a bit. But even at that it isn’t enough to meet OTK specs for his height? The rear of the seat bottom is approx 3-3.5 cm below the frame. Right front of seat is at 660mm, left front is a 656mm, Back of the seat us 206 mm above the axle. The front of the seat bottom is just below flush with the frame.

Should be at 670, 665, and 185…well then. I need to figure out how to post some pics.

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This is what I should be aiming for, correct? I just don’t know how I can get it there???

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If you can find a set of MXC’s to use, I would get them. Those are essentially the gold standard for wheels in everything but a CRG or KR. The stock OTK wheels are pretty high grip, but the MXC will free up the kart a good bit. At a place like NTK I would imagine those should be getting used year-round. If you can’t find those, the AMV 9F is a good wheel to free up the kart that we’ve used on the Kart Republics pretty much year-round that they have in the OTK bolt pattern as well.

As a taller driver, you may benefit from lowering the rear ride height, that worked well last time I worked on am OTK although that was in Yamaha and not 206.

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I know you said you dropped the rear ride height, but is the seat as low as it can go? Sometimes you can go as much a 8mm below the rails with the seat. Depends on the track of course.

This gets the driver lower down without messing too much with the rake of the chassis.

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@tjkoyen Any thoughts on seat? I thought we were closer to OTK recommended, but looks to me like we are forward by about 10 mm and high by about 20. The rear mounts are stuffed in the lip of the seat now, how can we get further back and lower? The seat front is flush, but the rear is slightly below the frame, but I think we could squeeze more out of it.

@Muskabeatz @tjkoyen @MinionSpeed Definitely going to force him on to the stock OTK rims in the heat. Have been looking at a set of MXCs to add to our meager set of rims.

@KartingIsLife Yes we have experimented with lowering the rear. It made the kart a touch to unstable in the flat out banked corners 1 and 2 and would force him to chase the kart some. So we went back to mid.

Headed to Amarillo with TSRS this weekend. Never been there, but excited to run somewhere with a little less grip than NTK. :rofl:

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As a way to quickly get an idea of what is going on, try having your son “lean outward “ on a troublesome corner. Especially the exit of the corner. If things get better then the kart is not holding the inside rear up long enough. It’s not a fix but it might point you in the right direction.

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