Question about seat stays

I was testing today and found interesting thing. My kart was sliding bit more and tried some things. The best result was when i removed the both seat stays. On turning in until apex the kart was more stable and less sliding and going out of corners it was alot better much faster. The tyres looked also alot better. What could you suggest to reproduce it but with seat stays? I have a medium axle (yellow freeline) width was 1395mm and mojo d5

Thx

Removing seat stays will reduce the amount of weight transfer you are getting from the seat. If the rear is sliding and you take the stays off and it improves, it’s likely you were transferring too much weight.

If you want to keep the stays on but solve that handling issue, you could try:
Widening rear track width - reduces kart “tipping” from weight transfer, softens up rear
Lower rear ride height - reduces weight transfer
Softer seat - absorbs weight transfer
Reduce caster - less jacking effect
Narrow front track width - less jacking effect

If the kart works without stays and it’s fast, don’t hesitate to leave it like that and see how it goes for different conditions. I almost never run without stays, but in certain conditions or grip levels, it can be useful.

Thx for the hints but i tried some things already but it wasnt better.
-I could try go a bit wider in the back didnt try it max. That would be next step.
-lowering in my dd2 is not possible, standard position is already the lowest.
-reduce caster was a bit better but not so good. Due to lower jacking effect i had to turn more and very ofter the back overloaded and had snap oversteer, but the exit was pretty good.
-as seat i have already a t11 Vg

  • i could narrow the front a little bit more but the steering forces increase

What about a shorter hubs or softer axle? I also got a hint to put a shorter axle inside? What about this?

TJ,

You say “Removing seat stays will reduce the amount of weight transfer you are getting from the seat”

The physics do not support this statement. If the rear tire is off the pavement, weight transfer = 100%. 100% = 100%. What is really going on is the LOAD PATH is different. If you add struts, the chassis is loaded differently. With no struts, driver mass is reacting to the frame seat posts. Because of their location, they tend to flex up the rear cross member more.

When you add struts, now more load is going direct to the tire contact patch. The chassis, especially the rear cross member, is not loaded as much. But weight transfer is the same. 100%.

Now, if you change the rear track width, or raise/lower the driver, then weight transfer IS DIFFERENT, so you are correct there. Think of the driver as a lever arm, and the axle as a lever arm resisting the driver forces due to cornering. The ratio of CG height above the contact patch to the rear track width determines weight transfer. Say you were at 1390mm on a gripped up track. You went full wide at 1400mm and the kart was noticeably better. What do you do? You mount the seat lower.

Right, that’s what I meant. I’m not an engineer so I guess my wording was incorrect.

This is an interesting question to me as I am experiencing a similar problem of, what I think is, too much sliding in a particular corner at our track. Now this is with MG reds on my kart so I guess the first question is…how much sliding is too much? Now in Dimitri’s case I am guessing it was enough to slow his lap times and making changes improved his lap times, but I have always understood some degree of “loose” is fast.

If running without struts is faster is there a problem with leaving them out? Will the seat crack or fatigue from the extra movement? I have been reluctant to try this for fear of what does this do to the seat as I have a lot of upper body mass.

90% of the time, loose is NOT fast in a kart. Unless you are on very hard tires and the only way to get the kart to rotate without scrubbing is to induce slide. The inside rear wheel needs to unload to some degree to get the kart to rotate. If you are sliding excessively, you will need countersteer which will obviously keep the inside rear loaded.

You can run without seat struts, for sure. For me, tuning with the amount of seat struts is a pretty atypical adjustment though. There are many other adjustments I would try first. Having at least one strut per side is a fairly baseline setting, so I prefer to leave things like that and tune with the chassis adjustments first to make sure we aren’t introducing unusual side effects from having something other than baseline setup.

If you have a lot of upper body mass and you’re struggling with oversteer, it’s likely you are transferring too much weight too quickly. Have you tried:

  • Wider rear track
  • Narrower front track
  • Softer front end
  • Lower rear tire pressure
  • Reducing front caster

Also it’s worth nothing that if the kart is struggling in just one specific corner, it’s a pretty good chance there’s something going on with the driving there. The kart will remain constant throughout the lap, so the variable is the driver if something is happening in only one corner. Is there a different approach you can take for that corner to fix the handling issue?

Here is a small update. When i expirienced my behavior, it was on older (older not worn had around 70 laps on) tyres. I put before the race a new set of tyres and it was the opposite. The back was planted to much and the kart was too sticky in the back. I tightened the stays again and it was alot better. Grip was still there and coming out of corners was much faster.

To add to this thread. I purchased a lightly used kart, a very popular brand and one that I’m very familiar with. The kart was very loose on high speed turn in and didn’t brake like it should have. I tried all of the of the mechanical seat/chassis adjustments to no avail. By chance, when I had the the seat out, I discovered a crack at the base of the weld that joins the right seat stay to the rear cross member. The crack was about 180 degrees around on the front side of the seat strut weld and it appeared as if the paint had a crack in it. So it was not easily visible. Looks like poor weld penetration. I had it TIG welded and took it out last Saturday for practice and it cured the problem.

One would think that with the stiffness of the array of seat struts, a broken seat stay wouldn’t make that much difference but it does. It’s all there for a reason.