hey all, the title says it. I’ve got a weird handling problem that we were not able to solve entirely, we tried most of the things in the kart aside from axles which we only have the M20.
the kart sort of mini-hops/rebounds at the traction zones of the corners ie the exit. Going softer at the rear worsens this effect (short hubs, cut axle) BUT because money is limited I want to make sure which axle hardness to try out.
I also know it should be free-er. the class we’re running is really low hp (in a different country than ours) so any bogging just destroys lap times, we’re a few tenths off the top, but this isn’t a straight up change.
rear is 1400mm, front has caster on the middle, camber is 1 degree positive, toe is 0 degrees, front heigh is low but not on the lowest position, front bar is out, so it’s not like the front is overpowering the rear too much (although I was thinkig this could also be a cause)
anyways, there’s a video I made for you to see, listen closely and notice the engine revs going up and down like a spring effect, these ‘oscillations’ can be felt too, as if the kart was jumping.
The balance looks good. Wheel inputs seem smooth and no big corrections. I agree with Clayton that it looks like the track is just rough. A stiffer or softer frame will react differently to bumps on the track. The OTK may absorb some of the bumps better than the CRG. I have driven 30/32mm karts vs 30mm karts back-to-back and noticed they handled bumps quite a bit differently.
Hard to make a definitive suggestion because as I said, the balance doesn’t look too bad and you are only a couple tenths off the pace. To me, an axle change is a big swing, and mainly used when you need to drastically change the balance of the kart.
no struts, they make it dig too much and the engine bogs down, I recall some guys using a harder axle on grippy conditions just as that day of the video, so that’s why it came to my mind. Although that was 7 years ago on a street track in summer.
edit: the problem with their set of regulations is that there is a very fine line between a fast kart and a slow one. everyone is using OTK for that reason that they’re very ‘light’ and fast from the get go. CRG on the other hand needs a lot of tweaking and we are still struggling somewhat, but well at least we’re closer lol
I know it’s a mental game, but don’t get in that state that brand X is better than brand Y. You will already put yourself behind mentally. Experiment, make your changes, observe the results, go faster! Go beat the guys on the OTKs.
the seat is the next thing im gonna test, maybe move it just a little bit forward. It’s a IPK silver, not the softest really, but it has so many repairs already that at this point it might be bulletproof already
The results of this year’s races show that the only manufacturers capable of building a fast kart are SodiKart, OTK, Birel, CRG, IPK, Parolin, Kart Republic, Emme, TBKart, Arrow, Haase, Intrepid, Margay, and Factory Karts.
I wonder if a hard axle would actually be the wrong way to go. It doesn’t look like those oscillations are from binding the kart up, so I’d think that a softer axle and maybe taking a touch of caster out would actually be the way to go.
I think your suggestion of moving the seat slightly forward or as TJ said loosening the lower bolts of the seat could help too.
I have raced CRG chassis for many years and found positive camber did not work for me. It made the front too reactive and the kart wouldn’t jack which would sometimes cause a hop/crab walk at the apex or a bind that would sound like the rear tires vibrating as I went through the corner. I would try 1 box of negative camber on each side and one box of toe-out. The box I am referring to is on the Sniper gauges.
I had a Praga Dragon that was bad for this mid-corner crabwalk too. Besides this camber and toe set-up, I had to use shorter front hubs and the kart finally felt balanced and didn;t do that mid-corner crabwalk.
I’ve used both hard and soft but my circumstances are kinda unique. Hard increases grip level (bite) on a dusty track which I’m almost always running on. Shortening the axle has the same effect.
First thing I’d try is widening your rear track to help flatten the outer tire somewhat. It’s the edge of your tire biting (digging in you may say) that causes it to hop. You need to flatten it so the edge isn’t at such an oblique angle on the contact patch. Not sure if that makes sense dm me if not I’ll explain in easier terms
Hi guys, Hope my two cents is worth something in this thread
I have been running a KT5 all year in nationals and club-level events in my country. I had this issue in preseason testing and made a couple of changes and all was well. Firstly, keeping the rear track width between 1395 and 1398 is essential, on top of that, with a hard axle I was still having the jacking issue on a mildly gripped up track, so we cut the axle 20mm (so the key still fits in its slot), and that solved it. Later in the year, we went back to that same track with even more grip, the issue came back, however, we tilted my seat back a little bit, and it fixed itself. I’ve used all 3 axles this year and a cut hard, and the cut hard is pretty much the default for me. The only outlier for this has been a high grip high geforce speedbowl style corner which changing to a soft axle fixed the problem. However mostly the cut hard works best. The order I would be trying things is: (no middle bearing, no seat stays, all neutral front end)
Drive harder into the corners keep the kart bound up, and drive as smooth (but fast) as possible
Tilt the seat back a little to give more weight at the rear (make sure it’s not bottoming out)
If all else fails, cut the hard axle
I’ve run recent OTK, Birel/Compkart, and CRG, and with a default setup, otk is solid, but if you are able to work on the setup and perfect that, the CRG is my favorite and quite fast.
Thank you for pointing out the lack of detail Richard, I don’t think I need to answer that as you seem to have figured it out, but yes.
I’m not necessarily a physicist however hubs tend to be able to move when loosened, and from that, you can either add a spacer (or a couple) to make up for the 20mm. (which on a cut axle, is still possible)
Pretty new to this, and not too sure about the level of detail I need to go into