pivot joint too sensitive over bumps

I have a pivot joint, I user a enterFRame to move an object below
and it works fine.

However when I move over a ‘bump’ on a flat surface (smaller then the wheel) the object topples over too easy.

I have a rectangle on 2 circles .

How do I set the object too more smoothly go over objects without
it bouncing off them too easily?
[lua] backwheel = display.newImage(“backwheel.png”)
physics.addBody( backwheel, {friction=1.0, bounce=0, density=1.0, radius=16});
backwheel.myName=“backwheel”
backwheel.x=x;
backwheel.y=y;
frontwheel = display.newImage(“frontwheel.png”)
physics.addBody( frontwheel, {friction=1.0, bounce=0, density=1.0, radius=16});
frontwheel.myName=“frontwheel”
frontwheel.x=x+40;
frontwheel.y=y;
body = display.newImage(“body.png”)
physics.addBody( body, {friction=1.0, bounce=0, density=1.0});
body.myName=“body”
body.x=x+20;
body.y=y-30;

myjoint = physics.newJoint( “pivot”, body, backwheel, x,y )
myjoint2 = physics.newJoint( “pivot”, body, frontwheel, x+40,y )
myjoint.isMotorEnabled=true; – (boolean)
myjoint.motorSpeed =200;
myjoint2.isMotorEnabled=true; – (boolean)
myjoint2.motorSpeed =20;
myjoint.maxMotorTorque=100000;
myjoint2.maxMotorTorque=100000;[/lua] [import]uid: 138547 topic_id: 26048 reply_id: 326048[/import]