The bikes have a weight regulation that was set in the 90s, 6.8kg.
Ultra light bikes can be as light weight as 2.7kg. That gives 4kg to hide a battery and motor and still hit weight. A really good lithium battery offers 350 Wh/kg. 1kWh can grant 100 miles of range by itself.
That weight comes obvious in components. All teams are required to use widely available components and it's quite easy to spot one that's not normal. For the bike builds that are 4kg or even less, it's quite obvious that all components are non-standard.
You can save at max a bidon before rousing suspicion, and the whole operation is just not feasible in terms of cost vs. benefit.
> the whole operation is just not feasible in terms of cost vs. benefit.
Batteries and a motor are a huge benefit. Even if you can't squeeze in a full blown motor or 1kwh of battery, just getting an additional 200 or 300 kwh of assist in can make a huge difference.
As for cost, these guys are already doing crazy things like blood doping just to get a tiny edge.
By contrast, blood doping is much easier to get away with. Claim you had an altitude camp, inhaled CO or whatever, but you carry your blood with you.
A small motor had to fit in the tubes, somehow connect to a control, have to be integrated into the gearing which are constantly under about 300 W of torque and can be easily discovered via X-ray or maybe heat gun. That's a lot more risk vs. a much smaller reward since your laptop sized battery is likely less juice than a single energy gel.