So, I’ve had a hard time wrapping my head around how seat struts work. In Yamaha, I was told OTK won’t typically need a seat strut because of the lack of power, so I never really worried about it and focused on other things.
Now, I’m moving to KA100, and on an entirely different brand of kart. I want to do some testing to confirm what changes do what to the kart, but I’d like an explanation of how seat struts change a kart’s handling.
As far as I can figure/visualize in my head, a seat strut should stiffen up the rear of a kart, and keep the back end from lifting off the ground as much, however I’ve read other stuff that says otherwise and it really just confused me a lot more. I don’t know much in this area and may be completely wrong, so a better description of what can happen would be really appreciated.
Great question Aaron. I maybe wrong with some or all of this but I’m going for it. If you notice most people ran the ka with 1 and 1 or 2 on brake side and 1 on the engine side and even 2 and 2. I have been running Kochan for two years and we have always run 2-1. Granted we were on the 4 pipe which kills the bottom end and isn’t right for my track as the two pipe is actually faster and that pipe is restricted. Seat struts actually add rear end bite and make the rear end dig and lift even higher. Seat struts add grip to the rear end. They also stabilize the kart more than with no seat struts. The kart is more springy in the rear end with seat struts. Without seat struts the kart is more likely to flat slide because the kart can’t hold rear end up or understeer because the inside rear won’t unload because their is no rear grip. It also depends on your seat and axle that you have in. I might be wrong. @tjkoyen could tell you more. Being that the KA100 has low end grunt you will need some seat struts, and how many is up to you. But I think 2 and 1 is the way to go with the tires we have. I could be totally wrong thou:joy:
The most basic answer is that typically seat struts give you more rear end grip. There are caveats to this, and TJ likely can dig more into the nuances than I can at the present moment.
One downside to seat struts is that they will resist a kart’s tendency to ‘hike’ in slower corners. Overall, however, seat struts are a very powerful tool in your tuner’s toolbox to influence the behavior of the kart. They are a common tool or option in high and low powered classes, and while it certainly is true they can bind the kart up, if you don’t have rear end grip, adding seat struts often helps.
The seat strut will stiffen the relationship between the driver’s upper body movement and the rear wheels, so less of the forces are absorbed by the flex of the seat/chassis. We’ve done some testing with it, and with the struts completely off, the kart lifts much higher, but it doesn’t have the sidebite to hold that load on the outside tire, so it tends to wash out or set down early.
It’s a bit give-and-take… On one hand, they will help the outside tire dig into the track better, but they also limit the flex of the whole kart, so they limit the lift you get. I always run 1 or 2 per side.
If you have enough sidebite, but need more lift, I would take struts off. If you don’t have enough sidebite but have more than enough lift, I would add struts.
We’ve found that seat struts pull up on the inside of the kart more than they push down on the outside. For us they seemed to help the inside tire lift off the pavement in turns sooner and kept the tire elevated longer. This was on Birel and Tony karts with World Formula and hard tires, and Shifter engines with sticky tires. How stiff the top of the seat is and your drivers style can make a difference. Do you stay back in the seat or do you lean in or forward?
If seat struts tend to add more grip to the rear of the kart by generating more sidebite and lifting the inside rear more, wouldn’t it actually free up the rear of the by lifting the inside rear? I would think it would bite more corner entry but then essentially free up the kart from the apex through corner exit?
Good note Rick. This is where the “grip” vs. “lift” nomenclature gets confusing.
My experience is that seat struts add GRIP to the outside rear, BECAUSE they create more LIFT of the inside rear. You’re tipping the kart harder and pushing more force into the outside tire.
So yes, they can free up a kart that isn’t getting enough side bite, because they push the tire into the track harder. So in this sense, you could say you’re freeing the kart up by adding grip, which seems completely backwards, but that’s why I try not to use the word “grip” so much. The tire has a finite amount of traction, this is your grip. You can’t really alter that apart from tire pressures. You CAN alter how you use that grip to achieve lift, and control how the kart rotates through the corner.
