Originally Posted by Conrad

Mechanical grip is a term i would use to describe the car generating alot of natural grip (not from the tyres), generally the more chassis flex a car has the more natural/mechanical grip it will generate. Having more chassis flex will make the car easier to drive but it wont be as responsive or as nimble as a stiffer car that doesnt have any chassis flex. The car with more chassis flex wont work the tires as hard either and you can often run a higher temp rating of tires because of this natural grip. Where the stiffer car needs the softer/lower temp rating of tyre to work. For example when you race on carpet you run your car really stiff with no chassis flex as there is so much grip but if you raced on slippy floor where there is very little grip you would want a car that has more chassis flex to get some mechanical grip back. Hope that helps, if not i'm sure someone else could explain it better in less that 50 words