I've made some tests for an automotive constructor in the past with usual cable with 3 wires (CAN_H, CAN_L and Ground) and twisted pair with 30 turns/meter without ground on a 250 kbits/s CAN bus.
The twisted pair was better for EMC immunity than the usual cable on a 40 meter lenght bus.

After several tests on differents topology (backbone, star and mixed), I've wrote some recommendations. This was the conditions where we had the best results (no errorframes whatever the topology used) :


- The maximal lenght without turn is 1 turn (3,33cm at 30 turns/meter)
- Maximal stub lenght : 0,3m
- Minimal stub lenght : 0m
- All stubs should have differents lenghts
- Minimal distance between stubs : 0,1m
- The nodes shouldn't be at the same distance between them

The cable was a twisted pair with 0,5mm² Resistor : 37 ohms/km
Capacitor : 45pF/m
Inductance : 0,6mH/m
propagation time : 5,0ns/m
Turns : 30 spires/m tolérance à confirmer


Hope it may help you

Stephane