This is what I did for more mechanical grip, works good and also has the effect of taking some steering away without limiting the throw in any way. Take some stick on weight, clean off the double sided tape, drill a 3mm hole through the weights and rear hub, put a 28mm through the lot and secure with an m3 locknut. Had 10g on there could have easily gone 15.

Get the car handling as good as it possibly could with other adjustments first and then leave this for last as an extra tuning aid.