Can someone explain why almost always spool goes in combination with wider front?
And does it work on ETS carpet with low-medium grip or better to keep standard front width?
No true
Front width is tire dependant. If you running a hard tire, like the "spec" lilacs in the usa, then a narrow front end is best to make the car turn
I've never run ETS rug, but at Worlds the UK team was saying everyone is running spool now no matter the carpet type. Grip eventually rises and spool wins over diff