Purchase the standard EU rubber version. This will work fine on asphalt and carpet with rubber tyres. The only item you would need to purchase separately is a spool # 79156, especialy when running hotter modified motors.
Thanks.
I'm asuming the 79655 (mentioned in manual) is similar to the 79156
The RDX PHI manual states the following:
Spool (#79655) is like a fully locked diff but has no moving parts. It's super-solid with no adjustments. Because there's no differential action at all, a lot of speed is scrubbed off in corners. A spool at the front will make the car very hard to turn in. But gives stability under acceleration and deceleration. A spool at the rear will give a lot of steering.
So, the intent (especially for modified) is to wash off the high speed entering the corner