Birel - Briggs 206 Hopping in Turns on MG Red

My Birel came with a 40mm 1000mm axle.
I am using some Douglas spun Aluminum wheels with more offset and that makes my rear track just 1300mm (1400mm is the limit per the rulebook).
Kart started hopping which made me get long 110mm hubs. The hopping is so bad that I am just a passenger in fast corners.
Arrow (the only owners manual I found) suggests 1370-1380mm with the MG Red tires.

What class are you running? Unless it’s 206 or similar, 1300mm rear track is way narrow for anything with some HP.

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Yes its 206 with MG red. I am trying 1360mm next. The hopping needs to stop otherwise my ribs suffer too much and driving is also not so much fun. I will try it this weekend and report back.

Do you have any video? Hop can be caused by many factors, although track width is certainly a good place to start.

What model Birel is this?

Sorry, no video yet but I will make one if it does not go away.
Its a MY21 Birel AM29, axle is 40x3x1000-B, 75mm hub- all the way in.
Maybe a little background. I was running the original Birel MAG wheels and there was some hopping. Switching to the Aluminum douglas wheels made hopping worse, I noticed that the wheel offset is 7mm less (less rear track). So there seems to be a trend.
All speculation is difficult, I will report back after this weekend.

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@Ben_Stahl @StahlRacing can hopefully give you some pointers but that sounds really wide on the rear track for a 40mm 206 setup.

Seat position (Vertical and longitudinal) might be worth noting as well.
If it had hasnt been mentioned already, inspect the frame and seat brackets very closely for cracks.

I’m on my third AM29 chassis now.

Are you running the front bar and seat struts? I’ve found that a spacer and a half in the front is best with the metal bar and two full spacers with the plastic. Very comparable setup but I use the plastic bar on tracks that have more low speed technical corners. If you’re not running the bar and struts I’d start there.

If you are, my rear track is 5-5.25” rim to frame rail.

I’m on Lecont Reds

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Ok, 2 race weekends with the wider setting. I was running a few different rear width between 1335 to 1375mm and the hopping is pretty much gone. As I mentioned before, there is a fast corner on our track where the hopping was so bad that I had trouble seeing where I was driving. Even on the slower turns my wife mentioned that my kart was the only one hopping, I did not notice it too bad on the slow speed corners.
I am running the kart as it was purchased, front steel bar full round, 30mm spacers front but with douglas spun aluminum tires. These have a slightly different offset than the original Birel Magnesium tires. I need to measure the front track width and report back.
I also need to do an alignment and check what the toe and camber is. I think camber is too much negative since my tires run mostly on the inner side, I am missing probably 10% of the outer tire width.
We run the SH tires MG red and I keep it at the recommended 15.9psi hot.
Regarding the front bar, I tried it once w/o but could not feel any difference in driving. Maybe I am numb to any type of changes except the rear axle width.
BTW the rear axle width was achieved with much longer hubs, they are now 110mm instead of the 75mm hubs which came with the kart. That of course also shortens the working length of the axle a little.
Thanks for all the tips so far, I am getting excited about trying different setups soon.