diff --git a/physics-2D-Verlet/MMBalloon.h b/physics-2D-Verlet/MMBalloon.h
index faeafa7..75bf125 100644
--- a/physics-2D-Verlet/MMBalloon.h
+++ b/physics-2D-Verlet/MMBalloon.h
@@ -25,6 +25,8 @@
 
 -(CGFloat) distanceFromPoint:(CGPoint)point;
 
+-(void) constrainCollisionsWith:(NSArray*)objs;
+
 -(void) constrain;
 
 -(MMBalloon*) cloneObject;
diff --git a/physics-2D-Verlet/MMBalloon.m b/physics-2D-Verlet/MMBalloon.m
index 6b4f6a7..a3b81c0 100644
--- a/physics-2D-Verlet/MMBalloon.m
+++ b/physics-2D-Verlet/MMBalloon.m
@@ -124,6 +124,32 @@ -(CGFloat) distanceFromPoint:(CGPoint)point{
     return dst;
 }
 
+-(void) constrainCollisionsWith:(NSArray*)balloons{
+    // make sure the balloon isn't hitting other balloons
+    for(MMBalloon* otherB in balloons) {
+        if(otherB != self){
+            CGFloat dist = [otherB.center distanceFromPoint:self.center.asCGPoint];
+            CGFloat movement = (otherB.radius + self.radius) - dist;
+            if(movement > 0){
+                // collision!
+                
+                // fix their offset to be outside their
+                // combined radius
+                CGPoint distToMove = [otherB.center differenceFrom:self.center];
+                distToMove.x = (dist != 0) ? distToMove.x / dist : dist;
+                distToMove.y = (dist != 0) ? distToMove.y / dist : dist;
+                distToMove.x *= movement;
+                distToMove.y *= movement;
+                
+                self.center.x -= distToMove.x / 2;
+                self.center.y -= distToMove.y / 2;
+                otherB.center.x += distToMove.x / 2;
+                otherB.center.y += distToMove.y / 2;
+            }
+        }
+    }
+}
+
 -(void) constrain{
     [stick constrain];
 }
diff --git a/physics-2D-Verlet/MMPhysicsView.m b/physics-2D-Verlet/MMPhysicsView.m
index 0f181c6..95bf44c 100644
--- a/physics-2D-Verlet/MMPhysicsView.m
+++ b/physics-2D-Verlet/MMPhysicsView.m
@@ -388,6 +388,7 @@ -(void) constrainWheels{
         MMStick* stick = [sticks objectAtIndex:i];
         if([stick isKindOfClass:[MMWheel class]]){
             MMWheel* wheel = (MMWheel*) stick;
+            [wheel constrainCollisionsWith:sticks];
             [wheel constrain];
             
             // constrain the wheel
@@ -427,7 +428,6 @@ -(void) constrainWheels{
                     wheel.center.oldy = wheel.center.y + deltaVY;
                 }
                 
-                
                 if(moveX || moveY){
                     // update other 4 points
                     for(MMPoint* p in @[wheel.p0, wheel.p1, wheel.p2, wheel.p3]){
@@ -479,29 +479,7 @@ -(void) constrainBalloons{
                 }
             }
             [b constrain];
-            // make sure the balloon isn't hitting other balloons
-            for(MMBalloon* otherB in balloons) {
-                if(otherB != b){
-                    CGFloat dist = [otherB.center distanceFromPoint:b.center.asCGPoint];
-                    CGFloat movement = (otherB.radius + b.radius) - dist;
-                    if(movement > 0){
-                        // collision!
-                        
-                        // fix their offset to be outside their
-                        // combined radius
-                        CGPoint distToMove = [otherB.center differenceFrom:b.center];
-                        distToMove.x = (dist != 0) ? distToMove.x / dist : dist;
-                        distToMove.y = (dist != 0) ? distToMove.y / dist : dist;
-                        distToMove.x *= movement;
-                        distToMove.y *= movement;
-                        
-                        b.center.x -= distToMove.x / 2;
-                        b.center.y -= distToMove.y / 2;
-                        otherB.center.x += distToMove.x / 2;
-                        otherB.center.y += distToMove.y / 2;
-                    }
-                }
-            }
+            [b constrainCollisionsWith:balloons];
             [b constrain];
         }
     }
diff --git a/physics-2D-Verlet/MMWheel.h b/physics-2D-Verlet/MMWheel.h
index fa84839..e7fef23 100644
--- a/physics-2D-Verlet/MMWheel.h
+++ b/physics-2D-Verlet/MMWheel.h
@@ -17,4 +17,8 @@
 
 +(MMWheel*) wheelWithCenter:(MMPoint*)center andRadius:(CGFloat)radius;
 
+-(void) constrainCollisionsWith:(NSArray*)objs;
+
+
+
 @end
diff --git a/physics-2D-Verlet/MMWheel.m b/physics-2D-Verlet/MMWheel.m
index 44e1517..f3e12a4 100644
--- a/physics-2D-Verlet/MMWheel.m
+++ b/physics-2D-Verlet/MMWheel.m
@@ -98,6 +98,36 @@ -(void) tick{
     [crossBar5 tick];
 }
 
+-(void) constrainCollisionsWith:(NSArray*)sticks{
+    // make sure the balloon isn't hitting other balloons
+    for(MMStick* stick in sticks) {
+        if(stick != self){
+            if([stick isKindOfClass:[MMWheel class]]){
+                MMWheel* otherW = (MMWheel*)stick;
+                CGFloat dist = [otherW.center distanceFromPoint:self.center.asCGPoint];
+                CGFloat movement = (otherW.radius + self.radius) - dist;
+                if(movement > 0){
+                    // collision!
+                    
+                    // fix their offset to be outside their
+                    // combined radius
+                    CGPoint distToMove = [otherW.center differenceFrom:self.center];
+                    distToMove.x = (dist != 0) ? distToMove.x / dist : dist;
+                    distToMove.y = (dist != 0) ? distToMove.y / dist : dist;
+                    distToMove.x *= movement;
+                    distToMove.y *= movement;
+                    
+                    self.center.x -= distToMove.x / 2;
+                    self.center.y -= distToMove.y / 2;
+                    otherW.center.x += distToMove.x / 2;
+                    otherW.center.y += distToMove.y / 2;
+                }
+            }
+        }
+    }
+}
+
+
 -(void) constrain{
     [super constrain];
     [spoke1 constrain];