Tall Driver Too Much Grip. Seat Stiffness?

Seeking some wisdom guys! I have red the forums here for wisdom and am striking out a little it seems and maybe want to dive a little deeper on my situation to maybe get some help.

6 foot 4 with 2020 otk in ka100. Just ran local event here at gopro motorplex and scraped by with a top 10 just 2-3 tenths off the pace. Struggling with the kart being bound up in the center…I just get a pretty bad hop in the middle if I dont drive it super smooth or if I go in with any kind of aggression to the apex. I feel like I need to wait for the kart to settle before committing to power. Track had loads of grip so that maybe why it felt like it did, as the night before track had less grip and my kart felt hooked up, no hop. But trying to make it better on higher grip scenarios. Its easy for me to add grip, not visa versa. Im not saying its only the kart either, I certainly can drive better for sure, but just sharing my thoughts and maybe this can help me find time!

Ive tried many things… neutral caster (not negative), softer front bar (too soft and it just doesnt turn), no seat struts (this was the biggest change that helped the most), stiffer axle (N to H, minor change for the positive. Also tried a cut N, this is worse), no third, axle up chassis down (makes it worse almost, left in the middle), one big spacer up front (will try two small ones next), might try bringing front and rear down together next. But essentially anything I do, I seam to have the same problem… there’s something bigger (my stature lol) in play that these smaller changes just aren’t fixing.
One thing that I feel may be a contributor is my seat…Maybe my seat is too stiff or too far back, Its an NEK standard seat. I was thinking of going to a tillet t9.5t and was wondering if anyone has any words of wisdom?

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I would try throwing a softer seat like the T11VG seat.

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If removing seat struts and harder axle had the most positive changes, then it sounds like weight transfer is the issue. Could try slight negative caster and/or lowering your center of mass (i.e. lower the seat or tilting it to lower your shoulders).

Hopping is because the OP overloading the chassis torsionally (twist). The rear hikes too easy, overloads…then releases dropping the inside rear…then it repeats. You need to make it harder for kart to twist at the waist. I would not go softer on the seat

I would actually suggest the following to the OP:

  • On the money with a T9.5. It is reclined 10 deg more than a T11. Big difference. It is literally made for this situation. (Tillett Racing Seats - Quality Comes 1st - T9.5 Kart Seat). You may have to special order.
    -T9.5 will make getting weight % right some work. Luckily you have a new gen OTK with the new seat mount system You can custom make a seat bracket that will work. Get 42% on the front.
    -Your legs may be seriously scrunched up…
    -Low position on rear axle. This will give the track/grip loads less leverage to twist the waist of the kart.
    -Mount seat as low as possible. How often can you afford to replace? Can you fiberglass work. It is not that hard to repair seats if you do it before it gets really bad.
    -Less castor as fine tuning
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If N to H was directionally better, you could also try HH. Did you try cutting the H?

I’m not sure soft seat is the answer, I tend to agree with @Thomas_Williams here.
We want less flex in the center of the frame, and a soft seat will flex the center more.

I basically echo his ideas on this one.

Don’t be afraid to go negative caster. It might not turn-in great, but if it reduces center-out hopping you know that’s the right direction.

Removing seat struts helps, not because you are softening the center of the kart, but because you are taking load off the outside tire and not planting it as hard in the center of the corner. Less direct weight-jacking from the seat.

Cut N would definitely make it worse, that makes sense. Shorter axle will dig harder in the center of the corner. I wouldn’t hesitate throwing the third bearing in to keep it from flexing a bit more as well.

What happens when you lower rear ride height? Shouldn’t make it worse, that would definitely be something I would explore. I use rear ride height a lot, though I’m usually going up because I have the opposite problem as you.

Of course, max rear width is a necessity, as is lowering the seat as much as possible and laying it back if you can. The T9.5 will help with that.

Are you on MXC wheels or stock?

I worked on OTK stuff for a few years with a 6’4" driver. It can be tough getting it to settle down with all that upper body weight, but it’s possible.

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I’m 6’2" and run into the same problems you do. I would be going towards seat struts off, H or HH able with full track width, leave the third bearing out to start, axle up/frame down, a standard OTK seat versus the NEK, mounted at least flush with the bottom of the frame if not a little lower, narrowing the front track to standard (I can’t remember what that is on an OTK), less caster, and standard bar. Basically:

  • Seat struts are basically just what TJ said, I don’t particularly understand seat struts super well, but I usually like running with them off versus on.
  • A stiffer axle will also keep the kart from jacking too much as well and keep the rear end free, as will the full track width.
  • The third bearing isn’t something usually done, but if the problem persists you can try it.
  • I’m surprised you said that raising the axle made it worse, I found that raising the axle would keep the kart more free on exit, and not be bound up especially on longer corners.
  • I don’t believe that the NEK seats work particularly well with the OTK stuff, so if you can go to an OTK standard seat that’ll probably help the chassis work better.
  • A narrower front track will reduce the front end turn in, and should keep the kart from over jacking as well.
  • Less caster will keep the kart from over jacking, as being 6’4" will do more jacking than a normal driver.
  • If you wanted to change the front bar, you could go stiffer to lock down the rear a little more, but it’s more of a front end change that I don’t think is necessary.

Most of that work is to keep the kart free at the apex and reduce the jacking on turn in. It’s a struggle sometimes, but it can be made to work.

Edit because I forgot things: I would also definitely be on MXC’s like TJ said as well. I think a Tillett would work in replacement of a factory OTK seat if you want to try the laid back version, or you can tilt the standard seat back. Any weights should also be mounted as low as possible on the seat.

Hey thanks guys!!

Yeah, more or less when I changed the axle height it didn’t make a noticeable change at all. I just lost braking grip and I still had the same problem…

Yes I’m on mxcs, that helped quite a bit as well. Found 3 tenths in that just with how it freed the kart up compared to the mxj.

I did go softer on the front bar, but just lost the front end completely and lap time suffered. I’ve been neutral on caster but haven’t gone more negative than that. Maybe center pill on top and stiff front bar may help response that I’d lose with the caster change? Thinking out loud.

From what I’m hearing locally here, the nek is definitely not a popular one… I do wonder if the properties of it just arent meshing.

I’ll say if the other thing that helped me initially was just pushing on the outside heal stop at the apex and that was one thing that helped a ton to stop hop from continuing off the corner. It was the only way I was able to drive around the problem…but it’s really hard to have a smooth brake and throttle input pushing on the outside heel stop on entry…which is kinda where things start. With that being said I’d be curious if this seat is just acting like stiff spring on an open damper and the chassis starts lose control and gets into an oscillation.

But, from what it sounds like a tillet t11 tilted or a t9.5 (which seems impossible to find btw) is something I should try in combo with hh, less caster and stiffer bar. Not discounting throwing a third in there or axle height once seat is changed.

I’ll report back with my findings in the future.

You mention pushing on the heel stop. Are you planting your outside hip into the seat? Using the core to keep your larger than average upper body from inducing the hop? I am also a bigger guy and find that in feature races (end of a long, tiring day at the track), I have to remind myself to keep my core engaged and keep my body from leaning over on that outside rear. If you need a mid race adjustment you can even exaggerate it by leaning forward and in a little during the corner to keep the weight from transferring as much (or as harshly). I know this is not the tuning advice you are looking for, but a tip that helps me deal with the “bound up” you are experiencing.

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I’ll pretty fit, so I don’t don’t really have a fatigue issue. I should’ve mentioned that this is my fore back into karting after 6 years out of the sport. I raced karts before that from when I was 8 for 8 years. I ran otk stuff before. So I know at least a little.

I’ve never ran this type of seat before and since day 1 I’ve had this hopping/ bound up problem. I feel like I’ve tried a lot of things with not much difference. Hence why I feel there is maybe a bigger problem at play.

When I was karting before, a seat was a seat. Lol So my knowledge of how it influences the kart is non existent

Being a tuner for my son for 8 years now and him growing about 1 foot in the last couple years. We gave been having the same problem with hopping middle corner out. We have been trying alot of things as well.

First issue for us is his height is mostly from his legs. We run into the issue of having seat back as far to the rear as possible so his legs aren’t up into his steering wheel. We have adjusted and adjusted. What worked for us is a combination of things. Seat lowered as far as possible, widening the rear to max width, and increasing air pressures by 2lb, and raising the axle so frame is lower in the rear. Hop is now gone put you can see that the inside rear tire depending on which way your turning is scrubbing the inside of the rear tire.

Next time we are out this will be adjusted for with jacking, either more caster or widen the front just a bit. When those adjustments are made I see us possibly having to go with a softer axle as the increased jacking may require a softer axle to keep the outside rear flatter to the track surface without starting to roll the tire onto the outside edge of the tire and causing another hopping condition. All the things you can do are; lower ride height or seat position, seat forward, seat struts removed, widen rear track, shorter rear hubs, higher air pressure’s in the rear, third bearing removed, softer axle, softer seat. Then move to the front.

If you have plenty of steering control already try Less caster, narrower front track. One adjustment at a time so you know what works and what doesn’t. It can only take one adjustment or a combination of adjustments. Seat being to hard would be the last thing i would try to correct. Loosen seat just a bit maybe. Might be overly tightened. Hope this helps!!

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Thanks for the recommendations!

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Try to reduce the time between braking and going on the throttle again to a minimum,try to keep chassis under load,this will help.

Reporting back on T11vg vs Nek…

The difference was very large… kart just freed up through the center and off, not bound up like before.

Physically the two seats feel similar in stiffness, when you put them in your hands to flex. But the carbon in the nek makes laterally stiff in a different way than the tillet.

In the chassis itself the nek feels like it builds potential energy much quicker and has to expand that energy once loaded…which causes my oscillation and therefor hopping in the middle. It wants to keep the tire on the ground and when the tire comes up, it slaps it back down and then causes it it bounce. Maybe for someone with less height might build the energy slower with less leverage? But for me my moment of intertia sets something off with that seat it doesn’t like.

The T11vg had a similar flex and definitely didn’t noodle out at all even with my height. The damping effects of the seat is what I feel made the biggest difference in the transition to the apex in making the kart more predictable on how lift occurred. The tire lifted to the same degree, and landed softer and just made the whole middle phase calm (no hop) and predictable.

Only thing…seat is a little low on my ribs. So I’m gonna try getting those tillet rib cage add ons and mounting them just a little above the top of the seat to help support me a bit.

I mounted the seat with a tilt. Front of the seat flush with the rails and rear of the seat 5mm under the rail. Might need to bring it up so I don’t destroy it…

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I am running a T11 on my Tony as well. After much research, I went with the T11t. Slightly stiffer than the VG, but supposedly comparable to the the factory seat in stiffness. Overall, I am quite satisfied, but I think the T9 would allow me to drop my center of mass a little more. Keep in mind, I am 6’9 and carry a lot of weight in my shoulders.

Love the t11VG… in my Tony kart I originally had the T11T… had issues with the kart binding and literally bicycling on two wheels. I swapped in the VG and everything literally calmed down

Interesting, I thought the VG would allow more flex in the chassis not less. After the sealing of NTK, I find myself bicycling in T7. Its a 180 left hander after a long straight. Before going to the H axle, I would just get a bad hop. Now its hooked up so hard, I am on two wheels! :rofl:

The VG compared to a T would certainly let it flex a little more.

Like I said in the post, the softer seat felt like it allowed the chassis to lift and set down smoother and not hop through the center and exit. The stiffer seat acts like spring, as you compress (aka twist the seat) it has more potential energy…so as the chassis flexes it wants to slam the inside tire down and cause that hop. The higher the grip the higher that wheel will want to lift. So softer seat, narrow the front up (two little spacers), go nuetral on the caster, stiffer axle, take the seat struts off. This allows the kart to not hike a wheel as much with geometry changes and combined with the seat having better damping properties, the kart stays flatter and more predictable. At least my kart feels pretty darn hooked up and easy to get in a window now with little changes depending on grip levels.

Hope it helps! Get the VG!!

I appreciate the explanation, but my issue seemed a little different. I was lifting the inside rear so much, that the outside rear tire was losing contact patch with the road surface, the tire would break loose and drop the inside rear, rinse and repeat (aka hop). My thought was by tensioning the spring effect at the waist (stiffer seat, stiffer axle and removing caster, I could lessen the twist at the waist and keep the rear of the kart flatter under high grip conditions. Sort of slow the whole lift and drop thing down or at least make it more controlled. It seams to work for me, but that is not to say the opposite would not work too.

The feeling is the same, description may vary. But it’s the same problem I was having.

Were you in the VG and experienced the problem then went to standard seat? Or have you not tried a softer seat based on your thought that it actually will make it worse?