SVG not working properly

Hi,

I've created this Truck Icon in illustrator.

This is how I save it out below as it's the closest I can get to it working. 

My problem is when I open the SVG to use when I try to resize it it distorts some of the objects like the wheels are out of place or the load on the truck moves it just warps like the shapes are not one.

I just want to scale it so everything is uniform and scales as it does in illustrator.

I've grouped the objects together and still no result when I open the SVG I want to use it looks like this as you can see it's not one shape how do I export the whole thing from illustarator as a one piece SVG?:

The more I try to resize it the more warped it gets!!!  You can see below the more I resize it the more the wheels get our of place and there's movement with the truck load.

When I've used SVGs from other sites that have pieces like this it's contained as one piece or object so am I doing something wrong?

Can anyone help please? I've attached the file if you want to see what I've done