Granpa

The standard M05 is notorious for this. There are a # of things that will help. Use a rear roll bar. Add a 1mm spacer to widen the rear track. Use softer springs. the standard Tamiya Mini springs are much too stiff. Try the #53333 spring set and use the yellow in front and the blues in back. If you insist on using the standard Tamiya Mini springs, nothing will help.

Also, play with the amount of rear camber and the ride height. Sometimes just adding or subtracting can make a huge difference. Setting the front and rear at different ride heights can be helpful at times. The amount of toe out can affect the driving qualities of the car also. My usual routine on hitting the track is to work with ride height, toe, and rear camber.

There are other things, but you didn't mention them. The tires are the biggest things for setting a car up. Also, for the shocks, There is a difference in the shock oils from various companies. The 35 weight from one company might be the 50 weight from another. How you built the shocks will have an influence. The amount of rebound and the overall shock length is important. I'll often use different length shocks front and rear, but hardly ever use shocks with any rebound.

One of best things I ever did for my M05 was to purchase the option front and rear shock towers, especially the rear. Of course that required some changes in shock length when fitting the rear one. It requires a bit of experimentation to get it right.

Yeah, most people want the answer to be, just change the XXXX and your problem will disappear like magic. Sorry, but it just doesn't work that way. It takes a bit of work which explains why you see so many bad handling M05's out there. The M05, out of the box, is pure garbage. With a few option parts and a lot of hard work, it can be made into a really good car, albeit with a nasty disposition, most of the time.