What class and what tire? In my experience on the KR and also working with the factory WPK team here in the US we rarely if ever ran that much negative. The chassis has tons of front grip pretty much no matter how you set it up, but even small front end changes affect how then kart releases off the corner.
Basically what Lucas said for the baseline. @Muskabeatz and I ran the KR2 last year in Masters X30 at 400lbs with MG Yellows. I did 1 FWT race with RoK GP at 390 with LeVantos. You will probably end up going full rake – lower the front max and raise the rear. I thought the kart was better on the LeVantos than the MGs.
FYI – 390-400 lbs is a lot of weight for the soft KR2. @Muskabeatz tried a lot of stuff. I am sure he will chip in shortly with useful info.
Rok masters 390 lbs levanto tires. Apex to exit to straight rides like a raped ape. Im putting fresh rubber on today and testing this week. Problem i have tuning wise is i dont have a jecko seat. Im running a crg standard sear cause its the only extra one i had that fits. Typically i run a large tillet seat which is a bit loose now, but medium large is too small still
Ill try that. Its only 55 degrees here still so front grip helps seems to stick pretty good in the rear but with this softer seat i feel like some seat struts maybe necessary as rear wheel have excessive inner wear
We have a similar issue even in the heat of Australia. Running Rotax senior light on maxxis sportsman. Loads of front-end grip, but our driver’s tall and has issues keeping the KR2’s rear from sliding - it’s not a problem for his smaller teammates though! Has anyone tried the other axle compounds on offer - soft / hard?