wow, those are some baloons! Which GRP's are those? If those are 35mm rims, then true rears no larger than 43mm depending on traction (bigger traction-smaller tire) and 45-46mm if those are 38mm rims. If you have high traction you might want to go much lower than that. For fronts start at 42mm and see how it goes. If you have problems only on second part of the run I would recommend to reconsider your tire treatment, try putting the traction additive a bit earlier.