rat with understeer
 

i've been thrashing my newly built mad rat round the garden,on the grass and when i really power it round a corner there is a lot of understeer do i need to weight the front down?or do buggies do this and i need to get used to it!

Buggy do this, but you can set up to have less understeer.
You can try to set up the wing, with less angle, or you can put the front shock in the inside hole (not sure it will be good on the grass)

Try about 80g of lead aound the front end. That's what it took on mine to get the front end under control.

Don't forget though that fullspeed cornering will never work very well...

if you are running lipo then a bit of weight would be good if running nimh then i would just soffen the front up and make the rear harder also run the longer camber link on the front and a shorter wheelbase