The men's Santos Tour Down Under will start on Tuesday with a 5.5km prologue time trial.

The UCI, teams, and race organizers have agreed that for race logistical reasons, the time trial will be contested on standard road bikes, a decision that highlights a lack of clarity in the UCI rulebook.

Disc wheels and aero helmets are allowed, but time trial bikes and aero bars are not allowed at all. However, after questions and discussions at pre-race meetings between teams and UCI race officials, Cycling News understands that riders will be allowed to race with their forearms resting on the handlebars in some sort of aero tuck or "puppy paw" position.

Rohan Dennis (Jumbo Visma), Ethan Hayter (Ineos Grenadiers), and Michael Matthews (Jayco Alura) are among the leading competitors in the prologue time trial. This time trial will determine the first race leaders and the battle for the overall win will begin.

An explanation of the UCI rules for the prologue of the Tour Down Under was sent overnight by Michael Rogers, Head of Road and Innovation at the UCI.

In his message to Cycling News, Rogers cited rule 2.2.025 (Athlete Conduct - Position on Bike).

"It states: riders must observe the standard posture defined in article 1.3.008. Sitting on the top tube of the bicycle is prohibited. Furthermore, the use of the forearms as fulcrums for the handlebars is prohibited, except in time trials."

"The rider must not use his or her forearms as fulcrums for the handlebars.

The only condition regarding the aero-tach position is that the rider must at least touch the brake lever or hood with his fingertips to respect UCI regulations.

It is unclear how the UCI monitors all riders during time trials and whether it sanctions riders who enter aerotack without touching the brake hood.

Teams interviewed by Cycling News are well aware of the aerodynamic advantages of the aero tuck position, but are disappointed that the UCI rulebook for time trials contested on road race bikes is largely unclear.

It is also unknown whether riders will take the risk of entering the aero tuck position on the winding course; there are straight sections of the 5.5 km course where the aero tuck is effective, but riders race at 50 km/h and have little time to try this position in training or on the course There is little time to try this position in training or on the course.

The full benefits and risks of the aero tuck position will only become apparent during the time trial and will probably be measured in the final stage results.

Teams will also be looking for marginal gains in other areas, with some riders using tri-spoke front wheels along with disc brake rear wheels. However, not all teams seem to have disc brake disc wheels.

Weather conditions could also have a significant impact on rider performance, with wind expected at the start of the early stages and the risk of a shower later in the race.

Some teams opted to place their team leaders in the middle of the start list to avoid weather extremes.

No rider wants to crash in the prologue time trial before five days of intense racing. Another concern is whether the surface of the long bridge from the start ramp to the course will be smooth.

Cycling News will provide detailed live coverage of the time trial, stage reports, photo galleries, interviews, and race analysis.