Making tire friction scale editable in blueprints

What I would like to do is to be able to make a specific value eg. friction scale able to be changed in the blueprints.

In detail what I want to achieve is to have the tire friction scale set to 2 at the start of play. then I want to have that value multiplied by the amount of time the player holds down W, and have the new friction scale that has been multiplied by the time set as the new friction scale number until the player finishes.

How can I achieve this, or is there a better way of doing this?

I would greatly appreciate any help!!